ApacheTrout Posted January 16, 2019 Share Posted January 16, 2019 (edited for grammar and formatting). For comparison of how each of the NWS offices covering New England is viewing this weekend's event. Highlights from each shift discussion over the next few days will be included within each forecast office. Full discussions for the 1/16/19 PM Shift can be found here. Burlington 1/16/19: AM Shift Synoptically not much has changed from yesterday’s NWP with potent southern stream energy ejecting out of the four corners region Friday and surface low pressure developing downstream near the Ozarks Saturday. While the surface low tracks east-northeast through the Tennessee Valley Saturday night to the New England coast by late- day Sunday, a positively tilted upper trough digs southeastward from southern Ontario into the Great Lakes, and this is when the forecast diverges a bit from yesterday. While southern stream energy does phase with the northern stream trough, latest guidance indicates this does not happen until later Sunday afternoon when the surface low is already tracking off the eastern seaboard. The result is a shift of the axis of heaviest QPF south of the forecast area from the Poconos northeast through Massachusetts to the Maine coast. Good news is that there`s less potential for any mixed precipitation across the BTV CWA with all snow expected instead. While early in the game to nail down all the finer details, a first guess at accumulations based on a blend of model QPF would yield warning criteria for the entire CWA with a general 6-12" of high ratio snow Saturday night through Sunday Night. PM shift, 1/16/19 Highlights Snowfall gradient sharp, 4-6 inches SLV to 10-16 toward southern VT 1000 mb low pressure will develop in the Mississippi Valley and head toward southern New England, deepening to 992 mb or so by 18z Sunday. Northern and southern jet streams try to phase Sunday, but probably too late to significant impact area Very cold temps Sunday, single digits north to teens south, falling in the afternoon. Dangerous wind chills Sunday, low temps -10F to -25F. Albany 1/16/19: AM Shift A significant winter storm will impact the region this weekend with potentially heavy snowfall from the Capital Region north and west and snow transitioning to a wintry mix south and east. As the low pressure system deepens and intensifies northeast of Northern New England Sunday night into Monday, a surge of arctic air, gusty winds and potentially dangerous wind chills will likely impact the region. Saturday...the calm before the impending storm, as high pressure will initially be building in from south-central Quebec. This anticyclone will funnel southward some very cold air with 925 hPa temps starting the day 1 to 2 standard deviations below normal based on the 00Z GEFS. Meanwhile, low pressure will be organizing over the southern Plains and the lower MS River Valley. A dry start to the day is expected, but mid and high clouds should quickly increase from the south and west in the late morning into the afternoon in advance of a warm front to the system. We gradually increased the POPS in the late morning into the afternoon with over running snowfall beginning based on the latest EC/GFS/GEFS/CMC. The trends are a little slower this cycle and we kept POPS in the high chance/low likely range mainly from the Hudson River Valley westward prior to 00Z/SUN. High temps are only expected to be in the mid teens to mid 20s over most of the forecast area with single digits to lower teens over the southern Dacks, and a few upper 20s in the mid-Hudson Valley. Saturday Night-Sunday...Low pressure continues to organize as it moves northeast from near the TN Valley. Strong isentropic lift on the 285/290K sfcs increases across the forecast area. Lots of Gulf of Mexico moisture over runs the area with the southern stream wave. The 00Z GEFS has PWATS increase to +1 to +2 STD DEVS above normal from Albany southward, as a strong low- level jet will focus the moisture transport into the region. In fact, an 850 hPa low-level +v component wind anomaly /southerlies/ of 1-2+ STD DEVS above normal will advect in the moisture. The QG lift looks very strong with this system, as several inches of snowfall are possible Saturday night into Sunday. The consensus from the medium range guidance and ensembles is a more southern track to the wave to ern VA or near the Delmarva Region by 12Z/SUN, and then moving northeast towards southeast NJ and Long Island by the afternoon, as the mid and upper level trough shifts from positive to neutral tilted. The Gulf of Mexico to Atlantic fetch of moisture looks impressive, and we could be looking at 1-1.5+ inches of liquid equivalent. The sfc low tracking close to Long Island and southern New England may allow for some mixing just south of the Capital Region into the Berkshires, NW CT, the mid-Hudson Valley, and the eastern Catskills. The 00Z ECMWF brings the 0C line at H850 to northern Dutchess and southern Berkshire Counties by 1800 UTC on Sunday, but then the colder air rushes back in, as the sfc low deepens quickly moving over Cape Cod and into the Gulf of Maine by nightfall. The question remains what time frame the northern and southern streams phase. Right now, it looks like late Saturday night into Sunday morning. This could be the biggest snow event of the Winter for the majority of the forecast area, and we will continue to mention it in the HWO with the major impact time frame of late Saturday afternoon into Sunday evening. A heavy snow accumulations look possible for a large portion of the region, especially from the Capital Region and the northern Berkshires north and west. The mixed pcpn zone, and any transition to maybe a brief period of rain is tricky and uncertain, but any mixture to sleet/freezing rain could cut down on potential accums. Temps will likely rise Saturday night, after lows in the teens to lower 20s for most of the region (single numbers of the southern Greens and southern Dacks), and highs in the 20s to lower 30s from the Capital Region south and east, with teens to lower 20s to the north and west. Sunday night into Monday, the 2nd phase of the storm kicks in, as mid and upper level deformations snow, and snow showers continues into the early evening. The winds will increase in the wake of the system with strong northwest winds. They could be quite gusty in the 25-35 mph range especially over the higher terrain. A surge of arctic air occurs in the wake of the system with H850 temps potentially falling to -18C to -30C across the region by 12Z MON according to the latest ECMWF. The 00Z GEFS have 850 hPa temps 1-2 STD DEVS below normal. The gusty winds and frigid temps will produce wind chills at dangerous levels Sunday night into Monday morning. They could range from 15 to 40 degrees below zero. Lows temps will be zero to 10 below in most areas, except 10 to 20 below over the southern Dacks, and southern Greens. A few zero to 5 above readings are possible in the mid Hudson Valley. Wind chill advisories and warnings may be needed. We will keep mention in the HWO. Some lake effect and W/NW upslope snow showers/flurries are possible with the H500 closed circulation near eastern NY and New England. High temps will struggle to get out of the single digits for most of the region with below zero readings over the southern Dacks, and southern Greens, and lower teems in the mid Hudson Valley. 1/16/19 PM shift, Highlights Main hazards include heavy snowfall amounts and rates, possible period of sleet/freezing rain leading to ice accumulations for some(mainly Catskills, mid-Hudson Valley, NW CT) followed by strong winds/blowing snow potential and an arctic air mass that may lead to dangerous wind chills Sunday night into Monday. Delayed phasing of jet streams suppresses snow/wintry mix line to the Hudson Valley/Berkshires, NW Connecticut, keeping areas north and west all snow. Warm nose may inch into area Saturday night, introducing brief wintry mix on Sunday morning. 1.0 to 1.75 inches of liquid precip, warnining criteria in most areas north and west of Capital area Possible icing in southern and eastern areas, details to be ironed out Very cold with dangerous wind chills Sunday evening New York 1/16/19: AM Shift A more significant precipitation event is taking shape for the weekend as elongated low pressure moves into the lower Tennessee Valley by Saturday afternoon. Due to the strung out nature of the upper level energy in the southern branch and its positive tilt, low pressure will not consolidate initially. The models agree that an inverted trough is progged to run SSW to NNE. Along and to the east of this boundary is where most of the liquid precipitation will set up for late Saturday through early Sunday. Northwest of this is where a heavy stripe of frozen precipitation will fall. We will have to keep an eye out for far NW part of the CWA at least for this potential. Precip types will be tricky with the front almost taking on a anafront type nature with the nose of warm air from the initial warm surge during Saturday night getting into the mid levels just above the boundary layer. As the colder air rushes in as the surface reflection begins to get better organized over the region look for a period of freezing rain in a stripe across inland zones to the northwest. During Sunday into Sunday evening as the wave amplifies and gets further northeast the leading edge of arctic air dives in and any precipitation should transition quickly to all snow. Difficult at this time to tell if there will still be any precipitation along the coast by the time the colder air moves in. Regardless if there is a period of wintry precipitation at coast into Sunday evening, there will likely be a hard freeze of any standing water that is left from the rain that fell earlier. Places that are mainly all rain will get about 2 inches of rain, before the colder air plows in. Therefore a quick freeze of all surfaces could make for hazardous travel during Sunday night. 1/16/19 PM shift, Highlights Precipitation type greatly dependent upon final track of system. A track to the south and east would mean colder air and more snow. Temps upper 20s to mid 30s on Saturday, supporting snow initially before warm air arrives Temps into the 40s on Sunday, most areas should see rain before changing back to snow Sunday afternoon. Wind chills 5-10 below zero Sunday night and Monday morning. Boston 1/16/19: AM Shift Ensemble data indicated an injection of deeper moisture within the phased mid level flow. Still a rather large variance in storm track. Consensus track suggests a path NW of the 40N/70W benchmark. In addition, downstream high pressure should be more of the North Atlantic, rather than SE Canada. Both of these suggest a wintry mix, rather than an all snow event. Still too early to pin down the details. Have high confidence it will precipitate, but only low confidence on the timing of transitions between various precipitation types. In general, still thinking snow to start some time Saturday night, then transitioning to a wintry mix during the day. 1/16/19 PM shift, Highlights GSF has moved toward Euro, indicating colder solution Moisture rich system starts all snow, then switch to rain south coast Saturday night, up to Boston and North Shore on Sunday Potential band of sleet/freezing rain in the interior, whereas western areas should stay all snow. Strong winds (35-50 mph) along coasts on Sunday Wind chills below zero Sunday night Portland 1/16/19: AM Shift The cold air comes flooding back into the area tonight on a gusty post-frontal northwest wind. By morning we`re 5 to 10 below zero across the mountains and foothills with single numbers above zero elsewhere. Across the mountains and along the international border we should be close to wind chill advisory criteria for a few hours late tonight and early Thursday morning. Mostly clear and cold with diminishing wind on Thursday as arctic high pressure builds overhead. It`ll be much colder than today with highs of 5 to 10 above in the mountains...with teens and lower 20s elsewhere. LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Extended forecast focused mainly on two windows for winter wx. The first Fri is the appetizer for the meatier main course late Sat into Sun. Split flow across the Wrn CONUS will have a S/WV trof slip under the upper ridge and cross the center of the country. But fast and/or confluent flow in the Nrn stream will not provide much room to amplify...and it generally remains progressive. For the forecast area that means we are relying on the Nrn stream to provide both the lift and moisture...which it lacks. Ensemble guidance is not bullish on QPF over 0.25 inches...and likewise WPC probabilistic QPF suggests that we would need to hit the 75th or 90th percentile to approach QPF that could lead to advisory level snowfall. Snowfall forecast is generally 1 to 3 inches...with the near 3 inch amounts mainly Midcoast ME where low pressure strengthens a little as it departs E. The most notable thing about this light snowfall will be the timing. It looks to occur over the first half of Fri...so the morning commute will be on the messy side. Still the more significant impacts are likely to come with the follow up storm late Sat into Sun. A stronger S/WV trof will slip the ridge again and is forecast to have more room to amplify with a stronger Nrn stream wave helping create more meridional flow. NAEFS guidance suggests that a plume of strong integrate vapor transport...atmospheric river...will develop along the East Coast...terminating at the warm front somewhere in the vicinity of New England. At this time model forecasts are of a magnitude that occurs roughly once every year...so nothing extraordinary but heavy precip is a possibility. Most notably was that the 00z suite of models trended sharply colder...surface and aloft. That complicates the forecast somewhat...because we are still over 100 hours until the event and there is plenty of time for additional changes. Ensemble sensitivity for 16.00z features a spread of greater than 10 mb N of the mean surface low on day 5. The uncertainty derives from the central Pacific between Hawaii and the Aleutians...and additionally from the trof dropping out of the Arctic...especially after 36 to 48 hours. So the next two days could see modeling shift based mainly on satellite estimates. Positioning of surface high seems more certain...and favors colder than guidance 2 m temps. Aloft is a different story...and given that 15.12z models were quite warm aloft vs 16.00z I tried to avoid a whiplash forecast. I blended the latest model consensus forecast with the previous forecast and the 18z GFS to produce a colder forecast but a more gradual step towards colder than blending the previous with 16.00z alone. With model forecast frontogenesis and deformation in good agreement on banding parallel to low track...heaviest QPF is just inland from the coast. This is also were highest snowfall totals are. With how cold 16.00z models were...much of the forecast sounding is within the snow growth zone...so ratios could be quite high...which may act to spread the wealth more evenly so to speak. There is certainly a growing likelihood for snowfall greater than 6 inches...and possibly much higher. While near surface cold looks to be quiet cold/deep...there is a risk for a stripe of freezing rain just W of surface low track. Right now that looks to be near the coast...but forecasts are quite a narrow stripe and little shifts will mean big things for sensible impacts. Right now I am leaning towards more sleet...but ice accumulations in the quarter inch range are possible. Behind that system much colder air will pour into the CONUS as the real winter looks to settle in. 1/16/19 PM shift, Highlights Sunday morning the low will move offshore of Delmarva with significant snowfall in the northwest quadrant As of 12Z a super majority of ensemble members would keep the low center east of the Maine coast over the Gulf of Maine keeping our region in snow. Northern stream short wave will provide the forcing to keep the warmer air offshore Potential for very heavy snow accumulation /widespread double digit snowfall/ continues to increase Caribou 1/16/19: AM Shift Clds will thicken and lower ovrngt Sat with snow ovrsprdg the FA from the SW by erly Sun morn. Ovrngt lows will likely occur prior to mdngt, but despite this, it is likely that this sn event begin with sfc temps sig less than zero, with NW and far NE ptns of the FA likely not getting abv the single digits for hi temps late Fri aftn. Latest trends from the longer range models by the 00z model run suite indicate a little more Erly track of the sfc low compared to recent prior model runs, possibly remaining just S of the Downeast coast. If this happens, precip type will be msly if not entirely sn for Nrn and Cntrl ptns of the FA, with a mix still possible Fri aftn/erly eve for interior and spcly Downeast areas aft a sig amt of all sn there as well. Total QPF potential with this event looks to be in the 0.50 to 1.00 inch range across the NW hlf and 1 inch + for the SE hlf, which will be enough to justify wntr stm watches if we were closer to this event. Attm, we do not know whether this slightly ewrd track of the low by the 00z models is the beginning of a trend or just a singular solution, but for now, the consensus model solution would have colder air rapidly returning to the SE hlf of the FA ovrngt Sun, resulting in transition back to all sn before steady sn tapers to sct sn shwrs by Mon morn and ends by Mon ngt. Another shot of high residence arctic air will arrive into the FA for Mon with brisk winds and msly fair skies with some moderation in temps for Tue as winds become lgt after a cold ngt Mon ngt. 1/16/19 PM shift, Highlights Link to comment Share on other sites More sharing options...
mreaves Posted January 16, 2019 Share Posted January 16, 2019 Good idea for a thread. Thanks for putting it together Link to comment Share on other sites More sharing options...
HoarfrostHubb Posted January 16, 2019 Share Posted January 16, 2019 BOX not really going into much detail/depth. Maybe later installments will be deeper. Link to comment Share on other sites More sharing options...
Bostonseminole Posted January 16, 2019 Share Posted January 16, 2019 Nice.. like .. let's keep it to NWS stuff here Link to comment Share on other sites More sharing options...
Typhoon Tip Posted January 16, 2019 Share Posted January 16, 2019 28 minutes ago, HoarfrostHubb said: BOX not really going into much detail/depth. Maybe later installments will be deeper. I also disagree with some of their synoptic points - ...this high pressure is not North Atlantic ... not sure where that interpretation is coming from, but it fixes into their reasoning on p-type which to me is a glaring error. Link to comment Share on other sites More sharing options...
NorEastermass128 Posted January 16, 2019 Share Posted January 16, 2019 I wonder if these discussions get shorter and shorter as the gov't shutdown continues along with no end in sight. Link to comment Share on other sites More sharing options...
dryslot Posted January 16, 2019 Share Posted January 16, 2019 Pretty clear who was banging the long term desk at GYX, I was trying to find the use of tourbillon in there.................. Link to comment Share on other sites More sharing options...
ApacheTrout Posted January 16, 2019 Author Share Posted January 16, 2019 1/16/19, PM Shift Burlington A winter storm is still expected to produce a widespread snowfall Sat night thru Sunday across the North Country, followed by the coldest airmass of the winter season. Our forecast area continues to be on a sharp northwest to southeast qpf/snowfall gradient and a 15 to 25 mile shift either north or south will have significant impacts on anticipated snowfall and precip type. As the system continues to become better sampled over the next couple of days, the details and especially snowfall forecast will become clearer. I agree with the previous forecast of a general widespread 6 to 16 inches with localized less amounts toward SLV (4 to 8 inches) and higher amounts possible toward VT (10 to 16). Another challenge besides sharp qpf gradient is snow ratio`s given the very cold low level airmass and expected moisture and mid level temps profiles. Water vapor outlines our upcoming system nicely over the eastern Pacific, while deep sub tropical moisture is advecting already of deepening western Conus trof. Interesting our short wave of interest is located near 150 W and will quickly eject around closed circulation near 140W and 40N into the western Conus, before lee side cyclogenesis occurs on Saturday. GFS/ECMWF/GEM and FV3 all track this potent southern stream energy into the MS River Valley by 12z Saturday, while 1000mb low pres is located over western TN. Meanwhile, strong 1038mb high pres near Hudson Bay will be driving a very cold and dry low level airmass into northern NY and VT on Saturday, per falling 925mb temps btwn -20c to -24c range, setting up the low level moisture/temp battlefield across the ne CONUS. 1000mb low pres will ride along this low level thermal gradient toward southern New England, while deepening to 992mb or so by 18z Sunday. 12z guidances continues to show open 7h/5h circulations, while 925mb and 850mb have several closed contours progged. As in previous years open waves at 7h/5h tend to produce sharp nw/se qpf/snowfall gradients with models typically overdoing the northern extent of heaviest qpf. In addition, models progged pw values range btwn 0.25 to 0.50 across our cwa, which is only a std or two above normal, while values approach 1.0 over southern New England. These factors support qpf ranging from 0.25 to 0.50 slv/western dacks to 0.50 to 0.85 central sections to 0.75 to 1.25 southern zones. As far as snow ratios given good deep layer moisture in favorable snow growth/omega couplet I would think 18/20 to 1 for a 6 to 8 hour window, with slightly lower on the beginning and end due to limited moisture/lift. This results in snowfall amounts of 4 to 8 slv/western dacks, 8 to 16 inches eastern dacks into VT, with local variability and subject to change. Soundings show all snow profiles for majority of our cwa, however latest 12z gfs at VSF shows warm layer btwn 890mb to 770mb of 1 to 2c, supporting some sleet potential. Once again the thermal gradient is very sharp and a slight change in track will impact ptype. Will continue to mention all snow in grids, as threat for sleet is still minimal attm in our cwa. Jet structure still looks favorable with anticyclonic curved 170 knot lifting over southern Canada, while developing 850mb southerly jet of 45 to 55 knots is moving across the mid Atlantic States and nosing toward our southern cwa. This jet couplet structure, along with strong 850 to 700mb fgen forcing btwn 06-12z Sunday will aid in deep layer lift across our most of our cwa. By 18z Sunday, developing northern stream energy tries to phase with southern energy and advect additional moisture back toward our region, but feel this occurs to late to have significant impacts. This energy will help to deepen sfc low pres over eastern Maine, while brisk northwest winds and strong low level caa develops. For temps, 1038mb high pres advects 925mb temps btwn -20c to -24c by 12z Sat with some northern gradient. Lows generally in the 0 to -20f range, with coldest across northern NY. Depending upon gradient flow, some wind chill highlights maybe needed. On Saturday, 925mb temps warm only 2 to 4 degrees with developing clouds, support highs 0f to 10f. Temps with clouds/precip developing on Sat Night hold in the single digits to near 10 above. Very cold and developing northerly winds occur on backside of sfc low pres for Sunday with highs ranging from single digits slv/northern CPV to upper teens/lower 20s vsf, but falling. The core of the coldest temps arrive on gusty northwest 850mb winds of 40 to 50 knots on Monday aftn/night as progged 925mb temps plunge btwn -25c to -28c, before modifying on Tues/Weds. Looks like an advection cold on Monday night, with wind chill highlights expected. Lows mainly in the -10f to -25f range with much colder wind chills. Temps rebound quickly as southerly flow develops Tues/Weds ahead of our next system. Trends are your friends if you like a colder and more wintry precip system. Albany Confidence continues to increase for a significant multi-hazard winter storm impacting eastern NY and western New England Saturday into Sunday. Main hazards include heavy snowfall amounts and rates, possible period of sleet/freezing rain leading to ice accumulations for some(mainly Catskills, mid-Hudson Valley, NW CT) followed by strong winds/blowing snow potential and an arctic air mass that may lead to dangerous wind chills Sunday night into Monday. Strong 1035hPa high pressure in Quebec noses builds southward into the Northeast during the day on Saturday with northwesterly flow advecting in a chilly air mass across eastern NY and western New England. High temperatures are expected to remain well below freezing through the region with most staying in the teens and 20s. As upper flow backs to the southwest, clouds continue thickening through the day. The 12z/16 global guidance has come into better agreement that for a stronger moisture rich southern stream wave originating from the Pacific Ocean will dig into the Gulf States and pick up additional moisture from the Gulf during the day Saturday. As it travels northeastward towards the Ohio Valley and warm air overruns the cold air wedge over the Northeast, snow will begin from southwest to northeast. Exact start time for snow is still uncertain but guidance continues to suggest some light snow is possible Saturday morning from weak isentropic lift before the more appreciable snowfall associated with our winter storm overspreads the region Saturday afternoon and especially after sunset. Overnight Saturday, our southern stream wave moves into Ohio Valley as a potent northern stream wave associated with a strong upper level low and a very cold air mass over the Hudson Bay drops into the Great Lakes. Global guidance has come into better agreement that the two do not phase until during the day Sunday and this delay would mean our intensifying storm tracks across the I-95 corridor with the associated 850hPa low tracking from eastern PA across the mid-Hudson Valley into eastern New England Saturday night into Sunday. This has implications on the northern extent of our wintry mix/snow line would keep it suppressed further snow to the mid- Hudson Valley/NW CT/Berkshires with areas north and west likely remaining all snow (perhaps brief period of snow/sleet). While the first half of Saturday night likely remains all snow across eastern NY and western New England with high snow ratios (dry/fluffy snow) and possibly high snowfall rates given strong lift extending through a deep column intercepting the dendritic snow growth zone, we could then see the warm nose inch northward towards our area. The second half of Saturday night looks to experience the strongest warm air advection as our 850hPa jet intensifies to 50-60kts which would warm the column and increase the fetch of Gulf/Atlantic moisture reaching the Northeast. This would then shrink our dendritic snow growth zone and even shift the "sweet spot" experiencing the best lift through the -12C to -18C zone to the Upper Hudson Valley and Adirondacks. While this would decrease snow ratios for areas from the Greater Capital District south and eastward, there is strong agreement amongst the global guidance that a copious amount of moisture advects into our area with potentially 0.50 - 0.75 inches of liquid from 06z - 12z Sunday. In fact, the snowfall band overnight Saturday resembles that of a quasi- stationary snowfall band as described in previous CSTAR research. Thus, even lower snowfall ratio closer to climatology (10 to 12:1) would not limit significant snowfall accumulations and high snowfall rates. Thus, our confidence for areas reaching warning criteria snowfall continues to increase from the Capital District north and west. For areas in the mid-Hudson Valley, NW CT, the Catskills and perhaps the Berkshires, the warm nose could inch close enough the mid levels warm close enough to or even higher than 0C that these areas mix with sleet and even freezing rain. This could lead to ice accumulations as the sfc-925 layer remains cold. Exact icing potential is still uncertain but should be ironed out this event draws closer. The ECMWF is the coldest solution limiting the wintry mix to the far southern mid-Hudson Valley and NW CT with the CMC-NH a bit farther north with the mixing potential while the GFS is the warm outlier. For this update, again went with a ECMWF and CMC-NH blend for precipitation type. By Sunday, our northern stream and southern stream wave phase over the Northeast allowing our positively tilted trough to become neutrally titled. Snowfall continues into Sunday morning with cold air quickly wrapping in behind our system with our warm nose quickly shifting into New England. Any wintry mix Sunday morning should then transition back to all snow during the day with snow ratios increasing again. Winds during the day Sunday look to also increase as the storm matures over New England with gusts up to 25-30 mph possible potentially leading to blowing snow. Snowfall should linger through most of the day Sunday before exiting from west to east late in the day into Sunday night. Total liquid equivalent for this event remains impressive with very good model agreement with 1 - 1.75 inches of liquid across the region which is why we continue to believe this event will lead to significant snowfall amounts. Very cold air continues advecting into eastern NY/western New England Sunday night with 850hPa isotherms dropping to -19C to -28C and surface lows falling into the single digits and even below zero from the Capital District north/west. Strong winds continue overnight as well with gusts 25 - 35mph possible which could lead to dangerous wind chills and necessitate wind chill headlines. New York High pressure builds into the region Friday night into the first half of the day on Saturday, resulting in a brief period of quiet weather ahead of the next system. Lows Friday night will range from the upper teens across outlying areas to the upper 20s in the New York City metro. By Saturday morning, a southern stream trough and its associated surface low will begin to eject out of the southern plains, while at the same time a northern stream shortwave begins to dive south out of Canada. Given the time frame, there is reasonably good agreement between the various model solutions with the low tracking through the Tennessee Valley, then passing near or just southeast of New York City during the day on Sunday. However, given the position of the low as it emerges off the coast, small changes in track will have significant implications for the type of precipitation observed across the region. In terms of sensible weather, clouds will increase through the day on Saturday ahead of the system, with overrunning precipitation reaching the area by late Saturday afternoon/early Saturday evening. With daytime highs ranging from the upper 20s to mid 30s, temperatures will initially be cold enough for precipitation to start as snow. As southerly flow ushers in increasingly warm air Saturday night, precipitation will transition from snow to rain from south to north beginning around midnight and continuing through daybreak Sunday. While much of the area will see rain during the day on Sunday as temperatures rise into the 40s, far northern portions of the Lower Hudson Valley could remain cold enough for some mix of snow, sleet, and freezing rain to continue through the day. The type of precipitation that falls during the event will be strongly dependent on the exact track of the surface low. A low position slightly farther south and east, like that of the operational 12Z ECMWF, would bring significantly more snow to the region. As the low moves off to the northeast on Sunday, cold air will rapidly rush into the region, changing any lingering precipitation back to snow Sunday afternoon. As temperatures rapidly drop back below freezing, any lingering standing water could quickly freeze, creating hazardous travel conditions. Temperatures will continue to plummet through the overnight hours, with lows Monday morning ranging from the single digits to lower teens. Gusty northwest winds will result in wind chills 5 to 10 degrees below zero. Thereafter, arctic high pressure builds into the region through the first half of the work week before drifting offshore Tuesday night into Wednesday ahead of the next system approaching the area. Boston Saturday night and Sunday... Phased-stream flow brings higher moisture amounts to this system. Cross sections again show deep moisture. Precip water values have diminished a little, but still show values around 1 inch feeding into southern and eastern parts of our area. These PW values are well above normal in mid January. Still uncertainty in this forecast as the models continue to shift. Most confidence is in the ECMWF and allied models which have been the most consistent in showing a center track along or near the South Coast. The GFS solution has shifted toward the ECMWF. This is a colder solution, and supports more snow and ice in the forecast than previously. Based on this, the forecast starts with snow everywhere Saturday night, then brings rain into the South Coast by morning. Rain spreads up to Boston and the North Shore Sunday, also across RI and much of Nrn CT. North of that zone will be a band of sleet/freezing rain in the interior...and snow in parts of northwest Mass. Shifts in the forecast storm path north and south will of course shift these precipitation bands north and south. Strong east winds will reach 35-50 mph speeds along the coast, especially over Cape Cod and Islands. Inland speeds will be more like 25-35 mph. Sunday night-Monday The storm passes our area between 1 PM and 7 PM Sunday. Winds will quickly shift out of the north and northwest. Strong pressure gradient at the surface will generate strong sustained winds, and cold advection will draw strong winds aloft down to the surface with gusts of 25-40 mph possible. The combination of wind and cold air will bring wind chills to single digits and below zero Sunday night and Monday. Portland High Impact Weather: Significant winter storm will impact the region from Saturday night into Sunday. Overview: Confidence is increasing for a significant winter storm to impact the region over the weekend. Saturday will start off clear and cold over northern New England as high pressure exits to the east. Meanwhile our storm will develop over the four corners and rapidly intensify as it moves across the southern Plains. By 00Z Sunday we`ll see the first flakes moving into southern New Hampshire as the low moves up the Ohio River valley. By Sunday morning the low will move offshore of Delmarva with significant snowfall in the northwest quadrant. Heavy snow will continue through the day on Sunday before coming to an end late Sunday night. Trends: Over the past day or so we`ve seen a consistent colder trend in the guidance as the low center shifts further offshore. As of 12Z a super majority of ensemble members would keep the low center east of the Maine coast over the Gulf of Maine keeping our region in snow. Upper level pattern: This nor`easter will form in a pretty classic pattern along the eastern edge of a deepening 500mb trough. To our west the west CONUS remains under strong high pressure with the result being blocked flow. This allows our storm to source from two regions. A short wave in the northern stream will dive south through the Canadian prairies. As it does the southern stream low over the southern plains will also phase with the two systems combining to for a very elongated low pressure along the coast. Whenever there are two systems trying to act in phase there is room for error, and with neither of them onshore yet that is certainly the case here however the presence of an upper block over Alaska along with weakly blocked flow over Europe supports the strengthening east coast trough. Ptype: Over the past few days ptype has been a concern with this system but it gradually becoming less so as the colder trend appears to be winning. The key here is really that northern stream short wave will provide the forcing to keep the warmer air offshore. Trying not to flip flop too hard have opted to leave some mixed sleet and freezing rain in place along the coast but feel that an all snow solution is becoming more and more likely. A bit of freezing drizzle is also possible on the backside in the dry slot but overall we are looking at a snowstorm with a chance for some mix along the coast not a widespread icing event. Snow Amounts: If you`ve been waiting for winter, here it is. Potential for very heavy snow accumulation /widespread double digit snowfall/ continues to increase. With 1-1.5" of liquid precipitation, even a modest 10:1 snow ratio easily achieves that objective. In fact higher snow ratios are quite possible, particularly in the interior. Forecast soundings show strong upward motion in the snow growth zone on Sunday morning across southern Maine and expect a region of snowfall rates over 1"/hr through Sunday. It`s far too early to pin down any mesoscale effects other than to mention that strong snow bands are likely with this kind of strong dynamic storm and any areas that remain under snowbands may see closer to 2"/hr rates. Wind: A look at the pressure gradient and rapid strengthening of the system says that strong winds are likely with this system. The trick will be getting them down to the surface as a more stable cold layer over land may limit the mixing somewhat. However along the coast line and certainly over the coastal waters stronger gusts are likely. Caribou Lighter winds and high pressure will allow temperatures to drop well below zero Saturday evening before clouds thicken later in the night. A massive area of low pressure will track out of the southern Appalachians towards the New England coast by Sunday morning. This developing Nor`easter will bring an impressive swath of southern stream moisture northward, overrunning the bitterly cold Arctic air mass. Initially, snow ratios will be very high...before winds pick up and the warm nose arrives. Used a multi-model ensemble mean for temps Saturday night into Sunday night. The very cold low level wedge of air will remain in place with unusually cold temperatures to go with moderate to heavy snow. Current forecast wind chills on Sunday meet advisory criteria in northern zones...something that is difficult to recall in the past decade. Our current storm track takes the low across the Gulf of Maine towards Saint John, New Brunswick and keeps the entire area in snow until late afternoon when sleet arrives into the Down East region. Intense banding with 2 inch an hour snowfall rates are a good possibility and overall totals could reach 15 to 20 inches towards Bangor...tapering towards a foot in northern Aroostook County. The warmer GFS solution remains a concern...reducing snowfall for Bangor and southern zones and potentially creating a corridor of significant ice and sleet. Winds increase during the afternoon and blowing snow will be a big concern. Between snowfall rates and blowing snow, travel could be quite dangerous at times on Sunday. The dry slot arrives towards the southern zones Sunday evening, but the trowal will likely keep the snow going in northern zones through Sunday night. Blowing snow will continue into Sunday. Lighter snow will continue into Monday until the upper trough passage. Temperatures will actually moderate after the storm on Tuesday and a warm advection event may generate some snow Tuesday night into Wednesday. One other detail regarding the Nor`easter could be coastal flooding. Right now, the Sunday high tide looks like it`ll occur before the waves really ramp up later Sunday afternoon...and winds will be offshore by the next day`s high tide. For now, it looks like it`s a near miss, but will have to watch whether the storm accelerates and aligns better with the Sunday high tide. Link to comment Share on other sites More sharing options...
OceanStWx Posted January 17, 2019 Share Posted January 17, 2019 12 hours ago, NorEastermass128 said: I wonder if these discussions get shorter and shorter as the gov't shutdown continues along with no end in sight. There might be some disgruntled people who mail it in, but honestly they aren't the AFD writers you want to be reading anyway. The care too much to mail it in. Link to comment Share on other sites More sharing options...
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