Roger Smith

I feel somewhat more optimistic given that the cold high in Iowa is fading while the parent high, a monster 1062 mb center up in the NWT, is slowly pushing south. That should stop the southward push on the wave train and when I look at the RGEM output the precip shield looks realistic but the thickness and thermal profiles look unrealistic (too far north) which would argue for more of the depicted precip to fall as snow. Hence an early call of 4-7" for the I-95, max could be a bit south of the DC-BWI-ILG corridor at 5-9" but I don't think it would be pushed as far south as RIC.

It was really though because President Dewey resigned over that fiasco.

Will join the party at 4-6" -- snow modelling does not seem to fit the pressure evolution very well, and then northward displacement of max snow axis has worked in past two storms, why not this one? ... 6-8" would be the upper end of possible outcomes given the speed. Good luck anyway. Great looks later in the 18z run for additional significant snowfalls.

All we need down in that part of the table is two decent storms, nothing massive, 6-8" type events x 2 or 4-6" x 3 would suit our requirements, and I already see one good candidate around day 8-10 on guidance. And you're closer to mappy than me and the Jebman, seems like solid company to me.

Half the field would benefit from a nice juicy coastal at this point. Cold air incoming, but models can't find much energy. We live in hope.

Would be a shame to waste all that cold air coming along without much snow but the CMC does show a bit of potential around days 8-9, nothing very exciting yet. And I get excited fairly easily.

I am controlling the weather right now in Allentown PA. So far they haven't paid the ransom.

Table of forecasts for February 2021 FORECASTER _______________ DCA _ NYC _ BOS __ ORD _ ATL _ IAH ___ DEN _ PHX _ SEA ___ bias RJay _______________________+2.0 _+2.0 _+2.5 ___ +1.0 __ 0.0 __ 0.0 ___ +1.0 _+1.0 _+0.5 ____+0.71 BKViking ___________________ +1.7 _+1.2 _+0.8 ___ +0.5 _+0.8 _+0.5 ___ +0.9 _+1.0 _--0.5 ____+0.37 so_whats_happening _______ +1.6 _+1.2 _+1.0 ___ --1.0 _+1.4 _+1.8 ___ +1.4 _+1.2 _+1.8 ____+0.76 wxallannj __________________ +1.2 _+1.2 _+1.4 ___ --1.0 _--1.3 _+0.3 ___ --0.5 _+2.7 _+0.6 ____+0.11 Scotty Lightning ___________ +1.0 _+1.0 _+1.0 _____ 0.0 _+1.0 _+1.0 ____ 0.0 _+1.0 _+0.5 ____+0.32 hudsonvalley21 _____________+0.3 _+1.1 _+0.1 ___ --0.3 _--0.2 _--0.2 ___ +1.3 _+1.7 _+0.9 ____+0.12 ____ Consensus ____________ +0.3 _+1.0 _+0.8 ___ --1.0 _--0.2 _+0.5 ___ +0.5 _+1.2 _+0.5 ____ DonSutherland1 _____________+0.2 _+0.3 _+0.8 ___ --0.9 _--0.5 _+0.2 ____ 0.0 _+0.4 _--1.0 ____--0.46 ____ Normal _________________ 0.0 __ 0.0 __ 0.0 ____ 0.0 __0.0 __ 0.0 ____ 0.0 __ 0.0 __ 0.0 ____--0.40 RodneyS ____________________ --0.4 _--0.3 _--0.1 ___ --1.9 _+0.8 _+1.6 ___ --0.3 _+1.1 _--0.4 ____--0.39 Tom ________________________ --1.5 _--1.4 _--1.0 ___ --2.5 _--0.9 _+0.9 ___ +0.5 _+1.2 _+1.2 ____--0.79 wxdude64 ___________________--3.1 _--3.1 _--1.9 ___ --3.2 _--1.1 _+0.6 ___ --1.1 _+1.3 _--0.8 ____--1.78 Roger Smith _________________--4.5 _--4.7 _--5.2 ___ --6.0 _--7.5 _--3.0 ___ +1.5 _+2.5 _+2.3 ____--3.13 (-5 e/c) _____________________________________________________________ highest and lowest forecasts are color coded. Normal is the coldest forecast for PHX (all forecasts +ve). Bias measures your average departure from consensus. This may not be regionally the same, in my case my bias was a rather unusual -5 for east and central regions, and around +1.5 west. Bias may help you and especially me analyze our forecast tendencies for later correction (or self-congratulation, probably correction though).

My "north of PHL" comment was probably fairly general, jackpots are most likely to be Pottstown to Easton but let's say something like 24" PHL, 27" Warminster, 30" Doylestown-Buckingham area, trending to max north of there 33-36 inches. And that would be a median of ranges about 50% to 150% if the coastal long-duration looping takes place. Even so, could see how 10-20 inches would actually verify, if some other scenario actually takes place. No crystal ball here, would say though the RGEM has remained pretty consistent run to run while slowly shifting max north. GFS seems to be changing its tune faster.

Some rather extreme looking solutions on RGEM and GFS 18z, makes me think this storm may join the elite memorable storm category but probably more for what it does in PA than any other state, however NJ, MD and NY could have some of the historical mentions. Each run seems to drop the central pressures (at comparable times) a couple of mbs. Very interesting to watch this unfold (and let's face it almost 0% of this storm has actually happened yet).

GFS apparently just caved to the RGEM but then said, listen since you rented the room, I'll pay for an extra night. Danger is more with mixing than total QPF if these coastal long-duration scenarios work out. Severe mixing may intrude into se NJ but what about PHL? Thinking maybe 20% loss to sleet? If these scenarios actually happen, if more like NAM/Euro then total QPF a lot lower anyway. Seriously, a little north of metro PHL could get buried 1888 style if these maps pan out. I live in a high snow area myself so you might catch up to me by Tuesday (snow on ground 32" here).

8-50" would be a good call at this point.

Some monster snow potential in e PA and quite a bit of NJ also if the North American models are correct, in particular the RGEM, very tight frontal boundaries will be shoved up against the cold trapped over e PA, with a coastal making a bit of a retrograde motion later Monday. Euro solution more like 15-25" max. I suppose that makes it the more likely to verify just on probability alone, but if there's more of a curl to the circulation, look out, some place in e PA could top 40" like BGM did in the December storm. If I had to guess where the jackpot will be, would say Pottstown to Easton. Would not expect much today, all unfolds with the coastal rapid deepening phase.

Based on 18z obs the primary low has deflated to 1003 mb in n KY but the circulation is very flabby within 100 miles of the center, indicating that the coastal transfer is starting to develop. The wave formation near the coast is most evident near SAV, when an impulse now forming near the AL-GA border catches up to this coastal wave that should initiate the coastal as a separate circulation around 00-02z. Models seemed to be struggling with multiple coastal vortices that suddenly jump forward towards NJ, in reality there would probably be something more organized by 12z east of Hatteras. What this looks like is analogous to the blizzard of 1888 only aimed more at NJ/PA than LI/CT. There will quite likely be some enormous snowfalls in eastern PA and the contours around those maxima would be quite impressive even into MD, DE and NJ. Local amounts of 40" or even higher would not be surprising given the curved moisture feed aimed at one region for 24h.

Not as pessimistic as some here after looking at 12z guidance and current analysis. The GEM and GFS both show quite a strong curved trajectory towards ACY for the coastal and still hint at a stall if not a loop. While this would obviously jackpot e PA, last time I looked there are no states between PA and MD and that jackpot is only 30-50 miles into PA so would expect at least the northern tier of MD counties to approach 20" snowfalls -- the higher this jackpot goes, the better MD does, there would be no physical rule to say that the more snow falls in PA then less would fall in MD. Also the dynamics of this are quite unusual, especially if the CMC is right and they do after all have as good a set of the data input over the current complex upper pattern as any rival model would have. Looking at 12z analysis, the low in the Midwest is not stacked but has an unusual C-shaped vertical profile from 500 mb in nw IN to surface in se IN (at that time) with 700 and 850 back in IL. That will distort over 24h into the coastal setup and the hook will then be rotated about 90 deg (counter-clockwise) anchored by a 500 mb low over VA, to a surface low bombing east of Delaware. I think with these unusual dynamics there could be more wrap around effect than you might expect with a more standard Miller B. As to bust calls at this early stage, most of the potential of this storm is Monday-Tuesday, I would not write it off anywhere in the mid-Atlantic and especially not in ne MD or n DE. It could be a 60h storm with an interruption later today, so even if 40 of those hours only produced 0.2" inch snowfalls that's still 8.0" and some of these hours tomorrow into Tuesday will produce considerably more, would expect at least moderate snow in some of the bands extending into MD (S+ obviously possible and will be widely reported in PA and NJ, NYC). Another consideration is that if a lot of very mild air dams up against a wall of cold south of Long Island while the low is stalling or looping, then some of that will be entrained west across NJ and PA and around the circulation which may create a warm seclusion, which is probably that feature on some models that rotates back across MD in latter stages of the storm. Anyway, bottom line is this will turn into an intense coastal almost without a direct parallel and do its own thing with memorable results, and you have a front row seat, enjoy.

The 06z RGEM begins to hint at explosive development off the coast by late Monday, looks like bad news for LI and se MA snow potential but possibly returning a stronger potential for MD-DC-VA as a lot of Atlantic moisture is going to be forced aloft and uppers are still marginally favorable (more than a few miles from the shore at least). Some place in PA will probably top four feet at this rate. If that's not too far from the PA-MD line then some place in MD could top three feet. This could get very interesting.

A little to the west of Columbia MO, center is 997 mb and went over Whiteman AFB around 0030z. Rain-snow dividing line roughly DSM to LAF. Should be near STL by 03-04z.

Has this been mentioned? ... the 1922 Knickerbocker storm looks very similar on historical weather maps at closest approach to DC, although it was entirely coastal in origin ... upper panels on wetterzentrale are obviously back-cast but look rather similar also. Timing (Jan 28-29) and the sort of otherwise bland winter season are also similar. Just a factoid among many. One other detail that caught my eye in assessing model scenarios is that offshore the warmer Gulf stream water has pooled out around 70W with a fairly cool coastal layer, there's no instant torching of lower levels available from contact with these relatively cold seas. This is why I tend towards accepting the RGEM solution, if I saw a sharper gradient out around the Texas Tower then perhaps more of a Long Ilsland bomb outcome. The 24 hours of east winds will probably advect some warmer surface layers briefly but that may just assist in the loop process and strand a cutoff secondary near the coast.

--4.5 __ --4.7 __ --5.2 ___ --6.0 __ --7.5 __ --3.0 ___ +1.5 __ +2.5 __ +2.3

Clearly a high variance situation in the model suite, but somebody's bound to get 24-36 inch amounts, can't see how se PA is not the most likely place given the factors in play. But sure it could be somewhere else. Looks like a sure 12-18 inch outcome at a minimum, if I were more of a stakeholder I might back down to 18-24 from what I actually think will happen. Good luck -- it all depends on that coastal stall retrograde loop aspect, best location for PHL to max is probably central DE, a bit further south may shift the heaviest snow to n DE and ne MD (which are still going to do very well). Weak or absent coastal loop still makes 12-18 plausible.

No need, check official forecast, they did it for me. Can somebody tell me how Temiskaming Shores (pop 50) gets onto a map and Chicago doesn't? Seriously, I can certainly see how actual amounts will be in the 6-12 inch range but my forecast is based on GEM being best available modelling, have been tracking events in Europe for forecasting that I do, and GEM has been quite reliable all winter when GFS and ECM are not in agreement, when they are in agreement I tend to take that blend and just check GEM for possible deviations -- what's interesting, and this may answer a question asked in the thread by Stormtracker IIRC, what the Canadian model may be picking up is the setting up of blocking from the fairly strong trailing wave that formed in the wake of the Tuesday s.e. VA developing low that then exploded to 952 mbs south of Newfoundland, then was followed by developing low -- also developments over Greenland and Europe are slowly building towards a major blocking episode, GEM seems to have done better with this and I noticed today's ECM 12z run has backed off a very progressive 00z solution in Europe towards at least 50% of the cold advection for Britain and Ireland suggested on GFS and GEM. My forecast scenario could also go wrong if the retrograde loop is further north than GEM shows. This would shift the 24-30 inch outcomes into east central PA entirely, and would probably result in 50-60 per cent validation rates on my amounts for BWI and DCA, IAD. Anyway all my forecast really says is that I feel the RGEM has the best call on development. We'll find out on Monday.

RGEM and to a lesser extent GFS have retrograde loop of coastal, which would explain apparently huge snowfall predictions. Not quite buying that totally but factoring it into second call which follows first call (which was 17-23 widespread, 25-30 local). DCA 16.5 IAD 20.5 BWI 24.5 nMD/sePA local 30-35 15" snow line n/c DE to near Annapolis to Quantico mixing zone mainly from that contour to Ocaen City-Richmond (5" snowfalls). Blizzard-like storm for many areas of c, ne MD and e PA, s/c NJ Winds not being discussed much but with the retrograde loop, gusts to 70 mph quite possible in a zone from n/c DE to central Chesapeake, probably 35-45 cities along I-95. Just a relatively brief interval of those winds, associated with retrograde phase mid-day Monday. Further afield, predicting 30" PHL, 20" NYC, 12" BDR, 14" BOS, only a medium sized snowfall for much of inland New England as they get a weaker phase of the evolution. Max snowfall from storm somewhere like Pottstown PA 36"

You know things are going well when (a) you wonder if the 4 inch QPF would be all snow or just mostly snow (b) you wonder why that guy in BC always underpredicts snowfalls

GGEM has an exceptional look for this region, 15-25 inch potential with about 24h of continuous moderate to heavy snow potential as the coastal slowly develops in an ideal location, while the primary slumps southeast to eliminate dry slot and transient warmth. GFS is almost as good. ECM appears to be drifting into the same outlook. Based on that, first call from me: widespread 17-23 inch totals, local 25-30. mixing issues confined to central, southern DE, southeast MD, VA s/e of RIC.

This seems like a good set of model signals with GFS very good, GEM perhaps a bit warmer solution than ideal, ECM now trending a bit suppressed, my guess is that a very large storm is likely and this divergence represents those developing signals coming into the mix -- in fact this could turn out to be a monster storm with the long interval of coastal development and signs that the center wants to set up very close to the Delaware coast. My hunch is we're looking at 20-30 inch amounts with this one.