wdrag

January 2, 2021 605AM Update: Am probably not commenting for our NYC forum on anything beyond 9AM January 4, which is about the still possible extension for eastern New England. That part of our oncoming light to moderate Nor'Easter snow event for the entire I84 corridor, will not happen for us. The remainder of the NY Day comments below seem reasonable. My anticipation is a widespread plowable 2-6" elevation dependent snow event from I95 northward through the I84 corridor and probably I90 eastern NYS and northern NJ/ne PA eastward through southern New England. I-84 valleys will manage this better because of marginal melting temps (32-34F) and the southeast edge near I95 will also be manageable, in part because a little rain/freezing rain/sleet is possible there. as well as the daytime temps near 33F. So, it's a mixed bag but the I84 corridor should enjoy this, with the primary event mainly Noon Sunday-6AM Monday. This storm will probably affect some of the return home holiday travel and also may force some Monday morning 2 hr cleanup delays, especially CT-MA portion where it still may be snowing a bit. NYC-LI should see a touch of snow/sleet but whether it measures or not and where, i don't know. My guess is eastern LI may do a little better and thats where there will probably be some wind gusts to 35 MPH but NYC might also see less than an inch?? There will be 1 or 2 brief periods of moderate snow with this event, but I'm not thinking of more than 10 to 1 snow ratios, possibly only 7 or 8 to 1 near I95. Will begin the OBS/NOWcast thread later tonight. Earliest part of snow/sleet/very brief ice arrival is around 8A-10AM Sunday for our NJ eastern PA membership. I don't anticipate adding any further potentially helpful information until maybe this evening. Noting the WPC ensembles for more than 2" are not very enthusiastic for this event, so we need to keep in mind failure. They also weren't as enthusiastic as they should have been for glaze this past night and the SPc SREF did much better. It already has 2-4" in ne PA by 7PM tomorrow night. Keep an eye on the SPC HREF MEAN snowfall after the 12z/2 cycle completes around 1030AM. The HRRRX was all over the place for this freezing rain/sleet/snow event that is wrapping up now and am not referencing it today. I as others here , like consistency in the modeling. One event at a time. NY Day 2021 558AM quick update: Extended the date to Jan 4. Ensembles suggesting a pretty good chance of 3+ inches for some the I84 corridor high terrain in possibly two long duration episodes. A short wave diving into the back side of the initial short wave trough may prolong the event considerably for the New England portion of the forum by forming a a very slow moving upper low along the New England coast. So it's complex but potent, especially if the 850-500 MB lows form in a favorable position for banding on the northwest side of this storm near I84. Just too early to overcommit but this could be a nice snow event for the I84 corridor and as previously proposed (modeled), can't rule out a touch of wet snow on the back side for NYC and especially eastern LI on the 4th. Just too early, especially with marginal thermal profiles and absolutely do not want to buy into any 8" amounts seen on some of the single member operational models for New England, at least not this early with so many differing solutions. If it's progressive and mainly afternoon of the 3rd into early 4th, then the 8" amounts won't happen and this would be an interior I84 standard climo modest event. Graphics is the 00z/1 GEFS prob of 2+ inches for this coming storm-- 10 to 1 ratio. Just an idea of primary risk area. --- Uncertainties exist including how much deepening and track for NYC subforum qpf, timing thermal profiles for phase change to wet snow. Looks like it will happen despite GFSV16 dropping it in recent cycles. EC has been on it for 3 successive cycles (prior to the 00z/30 cycle) and EPS now throwing out decent qpf (still does with the 00z/30 cycle) and a bit of snowfall all the way down to LI (questionable but could occur late in the storm and not be much...but??). 12z/29 NAEFS has it a little and the fact that the 12z/29 GGEM lit into it, also the 12z/29 UK, should be enough for us to give it a good chance to produce snow down to at least the I84 corridor. Others have been wanting a topic to track the models etc for this increasingly likely Sunday January 3 potential nor'easter. The initial precipitation (rain) from this initially weak Virginias low pressure system could begin after sundown Saturday Jan 2, as rain. As it intensifies and 500 MB heights lower, the combined lift, cooling thicknesses plus north-northeast wind advection of somewhat colder boundary layer temps southward, should change precipitation to snow along the I84 corridor by early Sunday, and possibly down to I95 west and north of NYC by nightfall Sunday? Rain over NYC and LI possibly ends as a bit of snow later Sunday or Monday morning? Probably too early for all this scenario detail but it's based on the 12z/29 NAEFS, EPS, GGEM, UKMET. No snow amount forecast though it appears that elevations should have highest accumulations, presuming it does snow. Snow looks to be slushy during the daytime and generally controllable for road crews, especially valleys, since daytime melting of any snowfall would occur during periods of lighter precipitation rates with marginal temps of 31-34F. LOW chance paragraph but reserve the option to increase IMPACTs of wet snow, add a small chance of gust 50MPH LI and minor flooding for a couple of NJ/PA rivers based upon the already anomalously wet December, plus future unknown qpf's from Jan 1 and 3...IF qpf up to I84 increases to 3/4" and mostly snow along I84? This is unlikely for now, but could happen, especially in the deformation zone if a closed low to 700MB develops near LI in this positive tilt trough. After review of the 00z/30 and 00z/31 cycle-no changes. Best to keep options open and look to the I84 corridor as most likely area to see some snow. Marginal thermal profiles the continuing concern. 00z/31 ensembles are growing qpf... but surface and upper lows may be too close to LI/se MA for much snow in the NYC subforum. This looks to me to be mainly an elevation I84 corridor wet snow concern. Definitely cannot commit any further details - just too uncertain and that uncertainty may continue another day or 2. Far from an ideal snow event, but also the typical winter uncertainties for our area.

Starting a topic by 3P for late Jan 2-early Jan 4. Just need a little time. Looks like it will happen despite GFSV16 dropping it in recent cycles. EC has been on it for 3 successive cycles and EPS now throwing out decent qpf and a bit of snowfall all the way down to LI (questionable but could occur late in the storm and not be much...but??). NAEFS has it a little and the fact that the 12z/29 GGEM lit into it, also the 12z/29 UK, should be enough for us to give it a good chance to produce snow down to at least the I84 corridor. Walt 220P/29

fwiw: This is probably sleet or ice mistakenly 10 to 1 snow ratio, but UK seemingly coming on board for Fri afternoon-night.

Yes... just hope it's consistent. will recheck everything at 4P and finally set up Jan 3 at that time GGEM and UKMET are now on abord. Hope the 12z GV16 comes back, and Euro stays on it. Thanks for all the posts. Suspect will favor I84 for primary now event but may allow for closer to I95 option. Need more thinking time.

It could. I’m just worrying about the fact that primary jets split us. North and south so that WAA QPF is less than 1 inch in that ice period. I see 12z GFS still on track and the for some reason furnace RGEM this year does have some ice but less than USA models. For now I’m playing the lower end of icing but it is coming from what I can tell remotely

Wantage NJ: 0.1" snów shower 805-825A. Vsby briefly 1/2SW. 31.8F. wind blown. driveways and where covered elsewhere, slippery. Treated roads wet. 828A/29

Agreed: Maybe Pike too, and High Point SR 23 extreme northern Sussex County. Just difficult for me to see above freezing prior 9P Friday night at High Point, points n and w, at least based on modeling through the 06z/29 cycle. Enclosed map shows the defined subforum coverage area. Sometimes, I'll mention interior MA for those who might be interested in New England.

I edited the 1/1 event about 20 minutes after posting. The change: I'll begin a new topic for 1/3 late today if its still modeled by the GFS para and EC but prefer GGEM on board.That one would be very low confidence for what could be a grazing fast developing nor'easter w snow somewhere close to NYC??? Again low confidence but on recent GFS parallel and EC OP. My energy is focused on 1/1 since ensembles are not very enthusiastic for land impact on 1/3.

Good Tuesday morning everyone, Dec 29. Have concentrated the event to primarily 1/1. It may bleed into 1/2 morning, but for now trying to simplify. From the topic update; Decreased model qpf has dropped the impact level to what i think is a relatively routine 3/4" to 1.5" qpf event with sleet and glaze expected I84 corridor. I dropped the front end concern on the 31st since it's minor, maybe a bit of snow or ice mix in the higher Poconos with the CFP. I'll begin a new topic for 1/3 late today if it's still on the EC and GFS para but prefer GGEM on board That one is very low confidence for what could be a grazing fast developing nor'easter w snow somewhere close to NYC??? Again low confidence but on recent GFS parallel and EC OP. Timing for renewed precipitation seems to have delayed about 6 hours from prior modeling with 6-10 hours of ice anticipated for the I84 high terrain, beginning midday the first in the Poconos-far nw NJ-se NYS and late day CT/MA portion. Treated surfaces may be just wet during the daylight hours, but if it's several hours of sleet, then a bit of a different story. Glaze, probably 1/4" or less even if .75" freezing rain occurs. This will need much more refinement as we move into mesoscale-fram analysis. So I see this as an advisory hazard NY afternoon/evening for at least parts of I84. Unsure if temps can remain at or below freezing long enough to have glaze approach 1/2" in our I84 corridor high terrain. As of this time, would not favor that higher end impact but worthy of monitoring. Flooding rain is probably no longer a risk,due to less qpf. However, those who had sump pumps running for the 12/24 event, may see a resumption-not that this is a big deal, provided they are operational, but in our area of nw NJ, it's unusual for this to occur in December. No new graphics today. 537A/29

Saw the comments on GFSV16. I'm the outlier and you may be correct but I see it lagging on big events except on two occasions the past 6 weeks. I'll monitor temps etc the next 3 days vs GFS. On GEFS 2-3" snow still on the 18z/28 run, you probably already knew (old news?)... but from my perspective, that's probably the GEFS trying to treat sleet as 10 to 1 snow ratio. Therefore the GEFS implication that a bunch of sleet is coming Jan 1 to I84. I won't say what will be right, but noticed the 18z EC op has 27F in PHL 12z Friday..not precipitating yet. That's 7F colder than the 12z/28 GFS MOS. So, i know cold air can erode, especially since 850 flow is southwest, not aiding CAD, but yet, the max 850 jet cores are split... one to the Adirondacks and the other s of LI...leaving not quite so much scouring potential into I84. If models warm from here on out, then I'm wrong. However, if RGEM is not furnace and starts showing 9-12 hours sleet/freezing rain into parts of the I84 corridor, I won't be surprised. GGEM should start tipping us off soon, one way or the other. One other note: I saw the note on Jan 3 being included in a topic. On our NYC forum I did that so we can keep all the discussion of multiple coming events in one place. They know that this original topic was 1 day either side of 12/29 and 1/1, as originated 1/21. I'm letting the models vacillate for another 24 hours. By Wednesday morning it should be more defined whether there is a significant I84 ice event. Added the 00z/21 NAEFS averaged trough for 00z/2. Have to go...probably won't see the forum til 6A Tuesday.

Think I figured out the GEFS snow accumulations on the first. I think it's taking sleet and converting it as a 10 to 1 ratio. Therefore, I think the GEFS is offering quite bit of sleet to I84 on the first as the 18z/28 version continues with its 2-3"snowfall there. I kind of think that is correct (sleet, but total sleet less than 0.3"). Noticed the 18z EC op has 27F in PHL 12z Friday..not precipitating yet. That's 7F colder than the GFS MOS.

Patience on this coming event: I could be wrong and I see lots of folks are on the EC warm, very little ice. That could be right. However, the NAEFS is arguing considerably colder than the op cycle of the GGEM. The BL temp has dropped about 4-5C near I90 for 00z/2 and now sitting nr 0C with at least 1/4 qpf by that time. I'll add these NAEFS images and let this be, til tomorrow morning... maybe consensus by then will convince me that I'm wrong. I sure like the RRQ of the Maritimes Jet and LF quad of the Ohio Valley, and while thicknesses are warm, in the top of the ridge it can snow down to a 543-546 thickness. That will need individual checks of soundings. 12Z GEFS continues the 06z several inches I84. 12z NAEFS qpf by 00z/2, BL temp 00z/2, 500MB pattern 00z/2. Use with caution as I know many like the north, stronger and warmer. Until the NAEFS caves, it's just time to wait on outcomes with I think the 12z Wednesday cycle the potentially more reliable guidance and closing in on whatever. As far as GFS V16: seems like I'm an outlier on it's lack of reliably improving here in the northeast, but i only look at the big events. Coin flip for me. Go with your colleagues on it's improvement over V15 (hopefully improved BL temps).

It's D4 but here are the 06z/28 GEFS probs for more than a T of freezing rain and more than 0.2" The snow probs for more than 3" (10 to 1 ratio) look good just north of I90 (NNE and N NYS). Offline til 1 or 2 P. Hopefully Global models are not depressingly warm for I84.

New 15z/ WPC D4-5 qpf. As you see, slipping south on max axis. Usually I don't like to be in max axis of qpf for winter weather, UNLESS deep layer cold. The reason: MAX axis suggests warmer higher PWAT closer to the warm front 850MBJET and rain involvement. I like this portrayal for I84 north wintry. This is going to be interesting ... tho to me its front end snow-ice end as drizzle then see what late 2/3 brings, IF anything. 12z NAM looks good to me to at least give us ice and possibly snow on the front side - mid lvl FGEN WELL ahead of the primary low heading into the OH Valley.

Yep: Would be a bit odd for the EPS to miss this 1/1-3 event so I temper myself. Still, what the GEFS and multiple models are telling us... lookout for at a minimum, a significant ice event 1/1-2.

Wantage NJ ..snow pellets... well times 30-60 minute was band moving east. Trace at 845A/28 33.8F Ending as RW- at 9A. Trace and slippery underfoot. Cant tell if its icing but air temp 33.8, dew point 32.2.

Looking pretty good to me for a long duration wintry wx event on I84... starting time on 1/1 uncertain and if you look at the trend, biggest part of the event could be late 1/2-3. For now going with 1/1 solid afternoon in CT but this is not yet completely resolved. What seems to be well resolved now, is no big low into the eastern Great Lakes. Possible yes, but not likely, due to the closed low initially into the Ohio Valley is too far west of us to negate wintry weather, and it weakens out across the top of the ridge awaiting what might be a better positive tilt short wave late 1/2-early 1/3. Interesting for sure.

06z/28 GEFS trends continue ever more wintry with several inches accumulation of snow I84 region on the first-second... even early 3rd looking interesting. EC 06z run through 90 hours looks interesting. Strongly suggests at a minimum, a 12 hr winter weather event is coming for I84 on 1/1... even sleet to NYC possible early on. Start time uncertain but should be going in earnest during the afternoon. Probably going good in the morning Poconos. Ever more looking more like a snow to ice situation, 12+ hours duration at the top of the 500MB ridge with primary upper low too far west to inflict major early on warmup to our area, provided we get the subfreezing temps here by 12z/1.

12/28 535 AM copied from topic update: 5 days in advance so I may be too detailed and too cold in my thinking-therefore uncertainty. Also the overnight WPC guidance does not support my concern. So caution on the following: Don't bet on it, but if you wish, keep it in mind. As everyone can see via the modeling the big warm windy event days ago modeled for 1/1 is gone and snow/sleet/freezing rain has increasingly been added to the mix near I80 northward ,with what I think is a likely hazardous advisory situation for the I84 corridor, especially Poconos-se NYS NY Day morning-midday. For now I left HIGH impact in the headline because I've seen these situations with sw 850MB WAA flow-not scour out whatever 32F airmass creeps into the interior, and the supposed change to non freezing rain does not occur or is delayed 6-12 hours. This whole event may become a routine 1-3" qpf event with an advisory event for the interior and if it becomes completely evident, I'll withdraw HIGH impact. This situation doesn't mean the temp cannot burst into the 40s /low 50s early on January 2, but I'm cautioning on literally believing an above freezing forecast, especially from MOS guidance, IF and only IF, the subfreezing airmass does sift back down into our area NY eve. QPF as per WPC--still outlooking 1-2" and I think there is potential for 3", wherever the max qpf axis, which seems to have slipped south to PA/NJ/LI. Whether this causes any flooding of rivers is unknown, but it does not look major and it's possible that the icing will lock up or delay-spread out runoff a bit in the interior, so the river response is contained within the river banks. It is good to know that that qpf in DEC has been 150% of normal with about 2" in 24 hours, threatening to cause some river flooding, and renew sump pump action in homes where sump pumps were still active yesterday. Big wind is no longer a threat. So the questions: how much sleet and freezing rain for the interior, inclusive of nw NJ, ne PA, on up the I84 corridor to Worcester, MA. The precip comes in waves, with the primary event NY Day. I am expecting a slippery-hazardous morning across ne PA/nw NJ developing northeastward into interior CT/MA but particularly ne PA/nw NJ on all untreated surfaces. Roads during the daylight hours, after initial treatment probably just wet but this ever changing situation should be monitored. Glaze amounts of 1 tench inch foreseen for parts of the interior high terrain, maybe ~1/4" if my concern is correct about temps not warming above freezing until the primary burst of heavier qpf has passed out to sea late on the first or early Jan 2. I didn't speak of snow amounts but there could be some coatings of snow included on NY Day morning at the beginning of the primary event, if an even colder scenario evolves. Again, remember, WPC has no outlook for 1/4" of frozen water equivalent here (but which I dont think includes glaze). 00z/28 GEFS has an over 50% chance of glaze in the interior n of I80. Then there's the trailer short wave for later the 2nd into the 3rd....I think it needs to be monitored for an eventual colder wintry impact here...probably light, IF ANYTHING at all this far north. Finally: for NY eve celebrants and pandemic considerations do not recommend , but if you're outside on the lawn for some reason, there could be an interlude of no precipitation near midnight (between the earlier in the afternoon cold frontal passage and onset of the NY morning qpf). Please be aware that I saw the 00z/28 GFS para which finally has 1+ qpf here (delayed a few cycles from the GFS) but it's temps are warm with no ice threat here in our area- It's a warm option but I think highly unlikely. Graphics are the NAEFS 52 member sfc pattern (NO EPS in this mix, just GGEM ens and GEFS), the GEFS prob of icing, the FFG for 6 hour amounts and our Dec 2020 % above normal qpf.

Thank you very much - many times just a little lucky to get close and I learn from our posters. Helps me incorporate multiple thinking. In any case Happy New Year all! Let's hope it is as good or better than the soon to be exiting 2020. Walt

At 120 hours... I think we have time to see a weaker low in the eastern Great Lakes, more of a development on wfront near or s of I80 for ice I-84. I will say this, it appears to me the GGEM is slightly colder...ever so, and it and the GFS are on board with 1-3" of rain. Additionally, the GFS is a bit colder. Does not take much to keep colder air in for ice, high terrain I84. Right now, I'll go with the preponderance of guidance-forum sentiment but I think, unless the EC reverts to it's previous days of 12/24-25 scenario, that the more wintry options have opened up for I84, certainly more than we had yesterday and prior. I am not discounting the northern stream weakening eastward out of the Ohio Valley forcing the occlusion s of LI. It is winter and not every storm is going to be wet. You'll have more info prior to me as I've got to go offline for a while. From my perspective, the fact that the GFS has some ice along I84 is significant since the GFS BL is not very good as compared to the eventual NAM and RGEM incorporations tomorrow and beyond. Noting WPC is waiting on on it's D4-6 winter weather, which means they too are a little more concerned than previously for the interior ne. Here is their updated D4-6 QPF from 14z, with no input from the 12z cycle. So not gospel but I think a decent idea.

On Polar Vortex: wikipedia and then some government definitions. Myself, I prefer not to use Polar Vortex in winter til we get down to a 500MB 498 or 504 DM (corrected 540 to 504 at 419P) height-something more common n of the arctic circle (60N). Use as appropriate with respect to NOAA etc definitions. A strong polar vortex configuration in November 2013 A more typical weak polar vortex on January 5, 2014 A polar vortex is a persistent, large-scale, upper-level low-pressure area, less than 1,000 kilometers (620 miles) in diameter, that rotates counter-clockwise at the North Pole and clockwise at the South Pole (called a cyclone in both cases), i.e., both polar vortices rotate eastward around the poles. The vortices weaken and strengthen from year to year. As with other cyclones, their rotation is driven by the Coriolis effect. The polar vortex was first described as early as 1853.[1] The phenomenon's sudden stratospheric warming (SSW) develops during the winter in the Northern Hemisphere and was discovered in 1952 with radiosonde observations at altitudes higher than 20 km.[2] The phenomenon was mentioned frequently in the news and weather media in the cold North American winter of 2013–2014, popularizing the term as an explanation of very cold temperatures.[3] Ozone depletion occurs within the polar vortices – particularly over the Southern Hemisphere – reaching a maximum depletion in the spring. Polar vortices are weakest during summer and strong

Will try to remember for 1030A... basically it's always been around but along with much of the drama of weather life (I definitely am apprehensive about overuse of extremes, especially if the issuers do not consistently verify). Later... ping me this eve, if I forget to comment with documentation (unless others do so).

Now that we have a day or two of relative downtime, I've started a new topic in MET 101- a concern of mine is bleeding/muting the appropriate use of weather terminology. We have by and large, my guess, is at least 80% routine weather days. Then there are the High Impact events. One of these are arctic outbreaks. It is my opinion, that we tend to apply the term arctic too frequently, reducing it's valued application in truly very cold, wind chill warning (not advisory) criteria situations. If you're interested, it's all in MET 101. Have a day!