wdrag

Some finals, past 24 hr CoCoRaHs snowfall, and the entire mid Atlantic 2 totals totals from NOHRSC. If interested click for clarity.

CoCoRaHs data this morning had a bunch of T's snowfall southwest of NYC. Sometimes I think observers got to it late, wind impacted measuring, or that less than 1/2" was commented as a T-the latter I hope I'm wrong. Imperfect... but the main thing, many had a little snow to brighten spirits last evening. I see nothing confidently more than 0.1" CP snowfall for at least a week.

Snowfall axis past 48 hours ending 12z/21. The main one was a 250-300 mi miss to the south on the D6.5 ensemble outlook issued around 4A/14. Our general snowfall in the area was roughly near 1/2", with the primary scooting out to sea well ahead of the ULL that crossed NJ-LI near 00z/21. These cool season max axis departures on D6 multiple model agreement ensembling is troubling-something that I think will be reduced considerably over the next 5-10 years, provided our science will be permitted the tools. For now, my winter time threads based on cyclic ensembling agreement will be limited to at most D5. Less lead time, an attempt to detect the sudden departures from the glide slope of the D6-7 cyclic expectation. This will reduce thread disappointment, but mean that American Weather comments cannot imply need for thread till we are more assured of snowfall-those comments depositing in the monthly thread, if needed.

Thanks for this post Don. I want to add... The LGA snowfall was on an ASOS T... doesn't work that way in temps 20s. That needs NWS fixing as does NYC and EWR meager or nonexistent w.e. Common sense tells you from the web cams that this is too low for W.E... I'd use 13 to 1 NYC metro, as per modeled snowratios prior to the event. Guess that doesn't mean much in the big scheme of things except when someone goes back to verify model qpf, or check on days with measurable w.e.

CPC issued 2/20 is attached, however it reliability and implications are uncertain beyond March 10 since we should start the first week of March, normal or colder than normal with events of sorts around March 2, March 5-6. The wintry risk on those seems to be mainly north of I80 (especially the I84 corridor). Just hoping March can produce 4" of rain which is bit below normal for CP (4.29") and even with below normal snowfall (norm = 5"), receive enough snow in CP to raise our seasonal total to 15" (a hopeful 2.1"). Even with these values, drought might persist. Reservoirs for NYC per DEP on 2/20 are about 15% below normal and it would be nice if Match could become actively wetter than normal. The CPC outlook is attached.

A hand for PHI... just published their snow reports... click for clarity.

Not CP but glad it happened fairly close to CP.

Not true IVT but certainly a nearly closed low at 500MB, with weakness west across LI at 7/8h and satellite IR suggesting seeing aiding snowfall at 7P. Also added the MODELED IR to check how good the HRRR can be at 1 hr prediction via the IR link below. https://www.tropicaltidbits.com/sat/satlooper.php?region=goes16-meso1&product=ir

https://nyctmc.org/map I didnt see the CP amount at 7P but imo it has to be 1/2" or so... roads are soaked and shoulder snow covered-slushy per web cams above. Take a look.

Also want to point out that measuring snow out this way is problematic with the wind blowing. AND I dont believe this ASOS Trace 6 hourlies... ASOS has trouble melting snow into a reasonable liquid equivalent when temps are below freezing, especially where we were today. The ASOS experts can add info, but my seeing those vsbys in the KNYC obs (occasionally below 2MI), a trace W.E doesn't reflect what is going on, ESPECIALLY with fairly well modeled measurable. One further comment: In winter... when T-TD spreads are 20F, its difficult to get snow to reach the ground. In summer... a T/TD spread of 30F is sometimes possible 100/70 or 95/65 and severe's occur due to somewhat drier sub cloud layer and evaporational downdraft development due to the cooling in the rain column. So a rule of thumb in cool season doesn't not necessarily work in warm season.

Thanks for all the reports, Wantage NJ a wind blown slippery 0.1" and 19F. Thanks for all the road reports. Our T/T spread is still 5F so we may get a little more dusting this evening. The road reports are important for me since I saw a met saying no big deal on travel this evening. Rush hour.. temps mid 20s NYC and colder NW subs.. 511 traffic report seems to have a lot of incidents and slower travel. If I'm correct, we cant be dismissive about 1/4-1" of snow on mid 20s roads, in rush hour. Thanks for your reports. Snowfall up this way in nw SC NJ less than expected the past two days. Enjoy whatever it is... better than a complete shuit out. I'll post a summary sometime late tomorrow morning.Maybe we wont have to have any more threads for NYC this winter. For now, the Max snow axis was a nearly 300 mile southward bust on a D6.5 issuance that held serve for only a day before going south. I'll hold off on a good looking thread til D5 or 4.5 led time ---modeling picked out a good event but still has trouble D6. Like it or not, the thread covered for an event but I'd never have issued a D6 thread for 1" or less... that was not my intent. Also... you will eventually see the day when a D6 thread and its ensemble support can nail an event axis within 100 miles, if we can keep our science going.

I'll post a summary snowfall map tomorrow morning at 10AM... to close this thread at that time.

Good mornin all:: OBS will probably start here sometime midday or early afternoon. Should see a nice refreshing powder per the mapping added below. or as you see it differently but snow is coming and you'll see it rapidly expand on radar during midday as the short wave approaches through Philly northeastward. Wont surprise me that there is a short period of 3/4S- near 6 or 7PM CP and a 1/2-1" snowfall there though uncertainty exists. Let us know if sticks to the streets this evening... I kind of think in the area described below that will be slippery on untreated surfaces sometime during the evening rusk hour, especially after sunset. Winter driving habits advised, for sure side streets. Dendrites might increase from the typically cold thickness small flakes, briefly to moderate sized flakes this evening per modeled lift in the deeply saturated dendrite growth zone aided by cirrus seeding. Graphics hopefully are self explanatory including the 09z/20 NWS ensemble chance of 1" (very low a you can see) the 00z/20 SPC HREF which is optimistic for near 1" in parts of our area, 00z/20 European ensemble snowfall output and the 4AM NWS snowfall forecast.

My expectation for NYC-Long Island-northeast PA, northwest NJ and se NYS Thursday: A period or two of powdery light snow or flurries between Noon and midnight that may slow the Thursday evening commute. Amounts generally under 1 inch but isolated 2" amounts possible in the Poconos and also eastern Long Island. If it does snow steady for 2-6 hours, then road treatments will be necessary. Uncertainty on amounts as most modeling is a slight dusting but the unusual recent and unfolding winter situation may produce somewhat more than a dusting. I've provided my explanations yesterday. If the NAM and RGEM fade on the 500MB low, then I'm wrong on placing so much value on the developing closed low aloft and weak IVT. So while the big storm is far to the southeast....as others have noted, worth monitoring the mesoscale developments for tomorrow.

What I think of as a 2-6 hour snow event between 3PM and 11P in much of the NYCsubofrum, which is gradually becoming accepted in bits and pieces by Global ops (not specialized in smaller scale), but not yet accepted by the Ensembles; should be related to considerable 850 MB vorticity in the inverted trough back from the ocean low, pretty deep FGEN 850-700MB between I80 and I84 with the saturated layer interestingly enough south of the FGEN region. There will be seeding from cirrus aloft, and a deep layer of moisture with the DGZ almost down 875MB. I can even see minor ocean effect on northerly flow off LI sound on the east end. So if there is sunshine, it's only Thursday morning. This is a deepening 500MB low now starting in the northern Plains and modeled to have a nearly 200M 12 HR 5H HFC crossing the Delmarva Thu aft. Closed lows aloft spell trouble... its not yet connecting directly to the ocean, probably cant capture it because its too progressive but there is some westward room for development at 850MB. We'll see what happens, if anything.