wdrag

Good Tuesday morning everyone, Jan 21. No change from yesterdays originating post with new support graphics added. Still need to root for southeast of current 500-850MB and sfc low tracks, for NYC-LI and south of I80 to get some little amounts. However, right now I dont have much hope for that. For our nw fringe of the NYC forum... I think this is a Saturday event, with focus especially afternoon-evening when some banding may occur. Snow impact is also I think elevation dependent, where it's potentially a 6+" wet snowstorm. There could be some backside banding-wraparound snow down to LI Sunday morning but above freezing temps there probably preclude any accumulation in the city. The images: NWS ensemble graphic produced I think prior to 00z/21 ensemble incorporation. Probs for 3" have increased 20% into far nw NJ since yesterday. Then the EPS probs for 3" and 6+" are included from 00z/21 courtesy the ECMWF and Weather.US ( no major changes there). The fourth image is from Bob Hart's MOE FSU weather page, which allows a vertical profile of temps and upward motion for Sparta NJ. You can see potential for a period of heavy wet snow there and temps cool during the first shot in the afternoon, IF this lift in the snow growth zone occurs. You also get a good sense of the boundary layer temp there and the likelihood for elevation dependent accumulation. I've also checked 00z/21 GFS MOS for MPO/MSV/FWN/BDL (consistent with previous cycles) and all suggest elevations will be near freezing during the precip. Finally the downer. LGA snow plumes... at least a few have biased the bold black line mean higher but the preponderance of this 00z/21 snowfall plume diagram is less than 1". I added the Scranton snow plume which shows the potency in the plumes but with most clusters in the 4 and 6" range there which I think is reasonable start for higher elevations of there I84 corridor. POU snow plumes have ~3" mean with those outlier foot plus also probably related to excessive QPF which is unlikely as this storm for us looks transitory. I may not post tomorrow if there isn't a significant change in the model ensembles, or if I do post, could be delayed til 8AM. 616A/21

For what it's worth... am part of the NYC Forum so I won't split my allegiance. My graphics occasionally include references to I84 which is my briefing group at home. You've got excellent forecasters up there! Regards to all and hopefully winter makes some sort of comeback. Walt

Definitely uneasy this far in advance. What I do like is the tracking of both models ensembles of the 500 low and a shot at se flow at 850 for 6-12 hours down here. Wish somehow we could leave a little more cold air in here in advance. Boundary layer warmth is a potential big problem. Did look at snow growth stuff and while modeled snow growth changes radically from run-run, there is potential, where the BL doesn't change to rain. For now, i have to think northwest of NYC. I wont post again til ~7A Tuesday but everyone here will know prior tk that whether these is still a little hope for close to NYC. The GEFS plumes for LGA--I'd like to see those increase a bit by the time Thursday rolls around. I do remember Don's post from 2 day ago about the statistical snow chance for NYC being pretty low so... am not too hopeful for NYC, certainly not now. I think it's best to think of all the downsides this far in advance.

Good Monday morning (Jan 20) everyone, Am a little uneasy starting this event specific topic since uncertainty exists regarding thermal profile and latitude of the primary-secondary development but I thought it best to get this going since it's a potential national news story from the Ohio Valley-Great Lakes to the interior northeast. Upfront: NYC-LI doesn't look promising at this time for more than 3" of snow , if any snow at all, due to the marginal thermal profile in advance of this system. The GEFS through 00z/20 was north of the EPS. There is still plenty of time-room for adjustment but at face value (00z/20 ensembles), this looks to me to be a primarily a northeast PA, northwest NJ northeastward into nw CT (I84 corridor) wet snowstorm with lots of potential (for a bust=no significant snow). My take is it will snow there for a time and that this event could be substantial impact upon higher terrain. I'm adding some graphics - these should not amp up NYC or points south.... but for me serve as a starter for a winter event. These include the 05z/20 NWS ensemble chance of 3+ inches of snow which is less than 10% for NYC. Then I've added..courtesy of the ECMWF and Weather.US, the 00z/20 EPS probs for 3 and 6" for this event (6 days in advance). I've also added the 00z/20 GEFS snowfall plume for LGA which is very low... most plumes under 2". This all adjusts as we move forward in time. If you want to root for snow, root development south of both ensemble systems 00z/20 positions. Am still concerned this will end up north and warmer (rain) up to I84. 625A/20

No further post from myself yet... would like to see GEFS snow plumes a touch higher for LGA before getting NYC group amped a bit. Lack of cold air in advance is a big concern so that this is a marginal thermal situation. Seems like EPS and GEFS stayed the same or trended down slightly (model noise and insignificant?) on snowfall but this is still a consistent signal for the I84 corridor itself to continue monitoring. Just having doubts south of I80 in NJ. There will be much much better scenarios in future winters, maybe later this winter, but will take what we can eek out from this winter. Will not post again til tomorrow morning 7AM. Later, Walt

Good Sunday evening everyone, The NOHRSC snowfall map for yesterdays 7 hour south-southwest surface flow event is appended. It suggests ensembles are useful... with what I think are the usual mesoscale enhancements-suppressions that for me are impossible to be sure about more than a couple of hours in advance. You can compare this to the ensemble predictions for 3 and 4" as posted on prior days.

I think this far in advance there are several questions... thermal profile cold enough? will the qpf diminish considerably at 5 days? Right now i see a nice RRQ of the high level jet in se Canada and the LF quad of the Great Lakes sw. I see see flow at 850 (as opposed to ydy), And for now I sense an option of reintensiifcation of the Great Lakes sw to a closed 500 LOW somewhere near the New England coast late Sunday. Til the option of a negative tilt 500 trough with energy pouring across the mid-Atlantic states goes away, my hopes continue. Obviously this is a terrible winter pattern so far and not a lot of teleconnection support for a snowstorm. However, I am a 'timing' favored forecaster as events pass through. Sometimes, it is all about timing. The GEFS plumes for 06z/19 are appended as well and that is what I am monitoring to trigger. I'd like LGA to increase to a 2" snowfall mean with fewer near zero plumes to trigger the topic. By the way, I am keeping in mind Don Sutherlands message from this morning. While far from a statistician, I do like stats as limiters on expressing extremes. So, at this day7-8 stage, not at all optimistic for NYC but definitely potential for I84. One other note... from my perspective, it's always a good idea to check GGEM track. Have a very good day and I do not expect to post anything more prior to 5PM.

Curious what prompted the EURO comment? Thanks, Walt

Holding off on starting this as a topic (25th-26th) till i see a little better chance for an inch or 2 of snow LI... i do think this is something to watch. Great Lakes low with a possible secondary L to the mid Atlantic coast. Marginal temps for snow-ice in an above normal temp regime during the coldest time of the year. Maps posted are several LR tools... stats. Only rather low chance of ensembles 3+ I84 corridor at this time. Nicely modeled (GFS version) confluence zone se Canada giving us a chance of a sfc high to the north and definite good 500 mb jet structure for an event...but is it all rain. Lets see what happens. AT 654AM I added the GEFS plumes for LGA. Right now its at 1" of snow. There 00z/13 GEFS LGA plumes had 4" of snow with over 1" qpf. 00z/14 onward, LGA was in the 1.5-2.5 mean for Yesterdays event, which I think is excellent consistency. I expect the GEFS/EPS is going to continue with near 1" qpf for this coming event and its a matter of trends on snowfall. I still want to see 12z/19 EPS/GEFS probs for 3+ inches next weekend before comitting. It's still possible for all rain LI, especially with our winter in progress. No rush here... savoring yesterdays south-southwest wind bonus. 659A/19

Wantage NJ 8 s High Point final 2.2 with only a touch of sleet the last hour or so. Season 16.5. Below normal like all of us in the northeast.

Wantage NJ (this part of Wantage Which is 8s High Point) Mixed ice pellets and snow...both small sizes. 2.2" at 7P... probably last report til morning. 24F.

Might not make it...may still all snow then end as freezing drizzle or freezing rain showers around 01-03z./19?? seems like northward push of IP is slackening.

CC and obs has IP up to I80 in NJ with a southward swing to somewhere near JFK at 628P. NAM slightly too aggressive northward but I think better than all the other models for 23z/18.

Wantage NJ 2.0 at 6P, still snowing at 619PM. 23F . Dingmans PA 1.8" (CoCoRAHS observer reported 1.75") freezing drizzle there at this time.

Wantage...this part...8 s High Point 1.2" at 355P no ice pellets yet but expecting sometime around 5 or 530P. 20.8F posted 403P/18

Wantage NJ 245P 0.8" 20F

Agreed w your science. Also more painful when wind driven and moderate. Save that info for future posts... What now must occur is better science translating the sleet into proper accumulative amounts in these algorithms that bias very high in mixed precip. Gotta walk the dog before the ice pellets or heavier snow arrives.

Fwiw...checked 18z OBS and NAM, EC, RGEM. On precip type... I think the NAM is a clear winner. My guess it eh RGEM and EC are too far south with the warm ice pellet causing 32+F layer intrusion late today. Hope the 18zNAM cools down but.... Soldi 3/4-1MI S- now 8 S high Point.

Anyone with a Central Park report from NWS? Wantage NJ...after a 45 min lull... snowflakes increasing in size and density. Still only 19F here... think we may not be above 22F at 7P here in nw Nj high terrain, if that. IPT is the next clue on change to IP.

Wantage NJ SB ~Noon, as of 1P 0.5" Was mostly small flake snow w some snow pellets. snow let up around 1P Temp 18F, dew point still only 11F. I see an SPS out of CTP for 1-2"/hr band crossing PA.

Quibble accepted... Thanks. All i think about is IMPACT... So i definitely define paved vs grass-trees-boards when I can/have time. In this case... shovel the walk or plow the road, it reaccumulates on untreated at these very cold air temp. Should that air temp during the day get close to 30...paved roads (darker surfaces) melt barring as you say the snowfall rates during the day.. After dark... then we lose that energy and easier to accumulate. In any case up here at 18F... roads all covered, but treated roads mixed wet-slight slush. 0.5" set 1P.

For what it's worth.... I've added the thermal profile for LGA from there 12z NAM. Some forecasters get concerned about Ice Pellets (IP) once the temp aloft nudges zero. In this case at about 22z, there is a modeled hint of IP before upward motion and wet bulbing may cool the sounding enough to permit snow til about 0030z. The sfc temp may not be cold enough to support much if any additional accumulation after 00z. Also RGEM from the 12z run is slightly warmer aloft and seems like less qpf in NJ. Hope am wrong about the warming aloft trends. I've added the Sparta NJ hourly type for any forum members in nw NJ. Hope it's right about only 1 hr IP. Walt 1530z/18

Good Saturday morning everyone (Jan 18). This is an mPING day. Should produce some accumulation for our entire forum area. I've added some ensemble products as self checks against big amounts... the questions I have...ultimate water equivalent QPF and does it sleet in a marginally thermal column late today, or does upward motion, compensate to produce 1/2S at 5-6PM. I've opted for the snow-sleet=trim amounts scenario for my own area of interest (I84 corridor of ne PA/nw NJ). The EC Kuchera is rather robust in the Poconos/nw NJ and as is the Experimental HRRR. I am definitely concerned about sleet...already sleeting (mPING) where one might have thought it be snowing in w MD. It will be hazardous at times this afternoon-evening on all surfaces up here nw NJ and se NYS. Ground too cold and air temps I do not think can rise as fast as modeled away from LI. So the first 3 graphics are NWS ensemble chances of 1+, 2+ and 4+ inches. Then the EPS prob courtesy Weather.US, for 3+ inches which continues uncertainty nw NJ but favors 3+ with its ~80% probs. Finally the 06z HRRRX variable density product and these amounts look a little too high to me.... I could see this would be possible if ALL snow. So my confidence in an all snow situation til 02z is below average for nw NJ and ne PA. Hope I'm wrong. 658A/18 at 502P/19 added the NOHRSC snowfall analysis to compare against NWS and EPS probabilities for various thresholds 2,3,4" This illustrates value of considering ensembles as limiters on extremes. One thing we know' HRRRX was terrible in northern PA where the sleet I think impacted this variable density product. Rest of the HRRX product looked decent. Later, Walt

Just trying too work with everyone... for good conversation but also a little learning about ensemble value (or lack of), as a self check. Thanks for your reply. There may be others...I'll check back. Later, Walt 1138z/18

Hello to all and the Moderators especially, I need a little guidance. Have checked forum coverage areas. Don't see a map (or I missed a link). In any case, can someone define the western and northern fringe counties of our coverage area. Can I presume north of I78 out to the Delaware River... do we extend into Pike, Monroe and Northampton Counties in PA? Also the north fringe...is that bounded by I84 or is that too far north? I presume no CT coverage but all of LI is covered. A little more clarity will help guide me on any topics. I also noticed some participants might not want to know of any NYC snow amount topics under 1". Is there any guideline for topic starter? Have started topics, when confident that there will be a wintry type hazard, even if I80 south including LI is out of it. Maybe thats too liberal and I should limit to when I think even NYC might get 1+"? Thank you kindly for American Weather Forum consensus advice. Walt Drag 351PM/17