wdrag

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!

Good Sunday morning everyone, Dec 27. I won't repeat it here, but if you're interested..I've posted a topic in Met 101: My own concern about the overuse of the term Arctic Air. Have a good holiday season. Walt

Good morning this 2020 holiday season. Weather tends to highlight dramatic events. I find the term - use of ARCTIC air far too often here in the northeast USA. I have provided the American Meteorological Society definition of arctic air, and the NWS lesson source regions. I think it would be good for us to review the source region of many of these air masses (and if we know how, use trajectories to locate the source). In essence, I am concerned about the overuse of this term. I myself would probably reserve the use of the term to something like wind driven 20 degrees below normal (and only in winter in the USA). Here in the I84 corridor, i don't think of arctic air til we get wind driven near zero airmass in DJF or maybe the NWS definition of Wind Chill WARNING as it is applied in the USA.. There is no specific definition as I've written in this paragraph but I'd like to see the use of ARCTIC reduced, to where it can be of more value (VERY cold). Your approach and counter concern with this topic- let em rip. arctic air A type of air mass with characteristics developed mostly in winter over arctic surfaces of ice and snow. Arctic air is cold aloft and extends to great heights, but the surface temperatures are often higher than those of polar air. For two or three months in summer arctic air masses are shallow and rapidly lose their characteristics as they move southward.

On the 27th, at 703A..have added the tail end CoCoRAHS snowfall for the I84 area on Christmas evening. , also the CoCoRAHS two day totals for the rainfall of 12/24-25 and the radar - platform analyzed rainfall for this event. This should close it for me.

Just a note: Unsure if anyone noticed the river stage forecasts for the snowmelt-rainfall combo on 12.24-25 appeared to be too high- less impact.

12/27 620AM Topic Update. Evolution of this topic continues as 12/29 is gone (except a few I-84 snow showers) . This includes dropping graphics for 12/29 as 12/21ish modeling completely missed this non-event for our area. New graphics will be added Monday morning as modeling consensus grows for 12/31-1/2. This system for 12/31 and especially Jan 1-2 is trending toward broad high impacts, ranging from at least a period of advisory or warning ice and possibly advisory snow for the I84 corridor (high terrain above 1000 feet especially), to a multiple slow response river flood response (minor to moderate flood stages in our NYC forum), depending on new qpf (not including any remaining snowmelt) and how much of that qpf is ice and remains ice through Jan 2. In my mind this is complex. Scenario is a weak northern stream short wave passage on the 31st dragging a cold front through the NYC forum accompanied by rain, (possibly a little snow or ice I84 high terrain). It's possible NY eve celebrations will be precip free for a few hours? Meanwhile the southern stream short wave may split into two pieces, leaving something behind for the 3rd, but of little or no impact here. It's the preceding newd lift out of the Gulf States short wave that is going to be a potential high impact player here on the first and second of January. How this plays out is uncertain but clearly the 00z/27 GFS and EC op have trended colder while the run to run inconsistency of the UK and ICON continues. In essence though...it appears to me that a warm front to our south will provide the necessary lift with a southerly jet of 50kt (PWAT 1") impinging on it, to dump heavy qpf on a large part of the NYC forum, on the order of 1-3". I am tending to lean widespread heavier than 1.5". That front may eventually lift north of LI/I80 but I think there is a chance of an occlusion and waves of low pressure moving out to the s of LI. That leaves potential for heavy icing parts of I84. So, tbd, if this read is generally reasonable but worthy of comment-updates. Wind: 50+MPH gusts...still possible for LI/NJ but less likely. Have left the Topic TAGS as is, but updated the topic headline. Basically done w this for 24 hours. Thank you for your updates-impressions of the modeling. I know this differs from the GFS parallel (not necessarily a desired model upgrade yet, in my mind, especially if it misses this qpf event down here-remains to be seen but I'm concerned about consistently better GFS V16 performance vs the operational V 15). Ice, snow and wind support for my expectations above are derived from 00z/27 GEFS probs and operational model trends.

Good Sunday morning everyone, While there is still opportunity for a short period warm-wet windy scenario for the NYC forum Jan 1, this large scale long duration complex event is trending colder icier for I84 and definitely heavy qpf-exacerbated flood potential, as the southern stream separation and northern stream deamplification short waves continues. Topic updates ~ 7AM.

Could be windy warm rain... don't think we'll all have a firm handle on this til Monday morning. Just too many solutions. EC is still warm, not as wet as GFS ,and quite windy, but less northern stream amplitude.

Ice? we'll see have to ride it out for 36 more hours of model cycles, i think.

Something is up for 1/1. 12z/26 UK op w snow to PHL and southern stream is out in piece and weak(let's keep in mind the UK is a wildly shifting model imo). 12z/26 GEFS ensembles showing southward signs including snow to I84. ICON op is south with temps mid to upper 30s n of the warm front NNJ-CT northward. Not yet a done deal and options seem to be opening up a little more, beyond the windy warm wet scenario. Have to ride it out and I probably won't be back on til this eve.

Here's some more review material: Wind power outages leftover more than a day after the fact. NO snowmelt qpf analysis (general by radar-platforms) which has resulted in many minor small stream flood events. Impact is mainly local detours and flood plain basements/yards. Probably my last on this. Top Areas by Outages Tennessee 22,208 New York 14,596 New Jersey 6,612 Pennsylvania 5,521 Florida 5,411 Last Updated 12/26/2020, 07:32:29 AM

Good day after Christmas everyone! I have adjusted the previous 12/29, 1/1 topic and caved in on 12/29 being a non-event for us. But 1/1 is coming and still one for me with modest winter weather interest for 1/84. Here is from the topic edit. 12/26 612 AM edit. Ensembles (GEFS, EPS, NAEFS) favor a primarily warm wet windy solution for early Friday-NY Day, but thereafter there is some uncertainty. UKMET and to some extent the 06z/26 GFS are suggesting a separation of short waves across the eastern USA with a trailing southern stream significant short wave rotating northeastward as the NY eve cold front is draped somewhere across our forum, possibly even down to the Mason-Dixon line. The UKMET op is an erratic model swinging wildly at times and at 120 hours, am a little reluctant to put much stock in its suggestion. Still, other models are suggesting a more sw wind at 850MB into early NY Day which tells me that the northern stream short wave is not initially digging into the Ohio Valley this time, as per this most recent damage/flood event. However!!! this is a low probability chance but one that I do not want to discard, yet, till I see all models wet-warm-windy with little or no snow behind it, across I-84. That leaves us with a 1-2" qpf event mainly 6PM NY eve to 3PM NY Day, most of it probably in a 6-9 hour period. This would exacerbate-extend the already projected minor-moderate flooding on some of the NYC sub forum rivers, and probably result in even higher stages and a few more streams-rivers into flood. Regarding wind- recent model cycles are offering a short period of 50-55 MPH southerly gusts NY eve night or thereabouts. GEFS and EPS 850MB winds after already over 50 knots. Operational models suggest 850MB winds 80 knots. This event may end up 5-10 MPH less than that of early 12/25, but it could be a bit warmer (more sw wind at 850MB than due south) in some areas, so that downward momentum transfer is slightly better (less of an isothermal boundary layer). With ground already softened by recent rains and snowmelt, and largely unfrozen by the time of the coming Thursday-Friday event, this could yet again result in power outages from limbs and trees down. So, some things to ponder, at least for me. I'll adjust this topic by sunrise Monday, once the event evolution becomes solidly wet windy.

Good Saturday morning Matt and Don, and I hope a continued good holiday season for you and your family-friends-- saw the GFS (00z/06z 26 version). Right now, GGEM/NAEFS not much sign this far northwest but it could adjust and become significant. I am a bit more interested in 1/1 for I84 as GFS is sagging and UKMET a bit more separation and will adjust topic accordingly (still warm but UKMET, the erratic supposedly #2 model in the world) is separating streams and offering a weaker solution 12/31 and a southern streamer late Jan 1. For now will go with the preodondernace of warm 1/1 and await GGEM coming on board with the GFS, ditto EC for 1/4ish. Myself I am quiet and not chatting beyond 6AM Jan 2. fwiw... exit 8 I84 (Mt Cobb at 2000 ft) had a least an inch last evening. will check cocorahs at 10AM.

Hi everyone, FFG will be down quite a bit for the 12/31-1/2/21 event. Wind guidance currently favors 5 MPH less than what we experienced this morning. Want to see 00z/26 model cycle, in particular if any separation between the northern and possibly dragging southern stream short wave, which then would make things considerably more interesting for wintry precip. As of now, continue the warmer wetter windy idea with no model support for my wintry concern. So, tomorrow morning, if it looks solidly wet, I'll work on changing this thread (preserving the original poor 12/29, 1/1 wintry impressions). Happy Holidays! Walt