wdrag

I'm pretty sure GEFS and GEPS mean is 10 to 1 and converts sleet as well to 10 to 1. That can easily inflate numbers-mean. NWS please correct me if necessary on GEFS ensemble being 10 to 1. Thanks. Walt

I want to make sure this gets noticed: by all who have interest in GFS model snow fall in the United States. The model update on 11/30/22 I think is resulting in improved snowfall prediction. It certainly was a cyclically very good performer here in the NYC subforum coverage for 12/15-16. It's picking up on warm ground and elevations better. Attached are some notes from a recent presentation: I only snapped the primary conclusions. Note: Using 10 to 1 is not going to be a consistently good approach, especially warm thickness (1000-500MB 540DM or higher) snows and/or temps 32-34F. This presentation also references Tropical Tidbits Positive Snow Depth Change (SNOD in NCEP language).

Just in case no one knows: and this can be shared with all other forums. Below from an NCEP representative. The GFSv16.3 upgrade that occurred on 11/30 DID contain a correction to how snow depth is computed. We are confident that this is a very positive change to the model. I noticed this for the Dec 15 event... Positive snow depth change. Walt

Uncertainty this far in advance but by 11AM Tuesday, we'll know what the NAM and RDPS models say (72-84 hour). Let's see if global models lose this prior to tomorrow morning. I don't think they will. Globals since the EC switched inland cutter with the 12z/16 (last Friday) cycle have been onto this sort of wind/back end scenario for the Appalachians. Gone for the rest of the day.

Looks like everyone is reading the models. My primary concerns for membership. Poconos: A little ice or snow to start Thursday afternoon-evening, shouldn't last too long and probably minimal impact. A potentially far more dangerous situation is possible Friday when a 1-2 hour period of brief intense snowfall may occur as temperatures plummet through the 20s. If this occurs, it will be difficult to manage if traveling in this 2 hour window. Snowfall generally under an inch or 2, but if it occurs, would result in slippery travel everywhere. Timing and confidence of occurrence is below average but sometime between Noon and 6PM. Worthy of monitoring. Otherwise the main story is damaging wind that will make headlines from the Great Lakes and Ohio Valley, throughout the northeast USA. Looks like a period or two of scattered 55-65 MPH wind gusts is likely from VA northward to Canada. If you don't have a generator, be aware that if power goes out, you'll need to depend on other SAFE sources for heat and communication. This is because the coldest air of the season so far, should be in place by Saturday morning with subzero nightitme wind chills in the I-84 corridor northward and near zero wind chill in the cities from Atlanta to Boston. Due to the expected heavy rain: post cold frontal icing of any remaining runoff (road shoulders etc) is possible by Saturday morning.

RDPS 18z available on the Meteocentre web site. Ice far nw NC and far w VA at 84 hours.

Anyway: I hope we don't get shut out interior. Seems like we should get some ice or snow. I noticed the 12z/18 UKMET has a little slug of snow for the I84 corridor later Thursday. That could be ptype problem and not converting partly to ice? A decent band of FGEN shows on the Pivotal website at about 102-108 hours both 850 MB and 700MB and its subzero at those levels so we may have a chance small accumulative snow inland nw-n-ne of NYC?? That's me--- still holding onto hope. 18Z RDPS did not post anywhere as far as I know as of 435PM... definitely late.

Just a note here: I hear OUTLIER lingo on coming events, especially beyond a few days. Here is a case where the outliers (a distinct minority as Don noted) are correct. That's why stats are part of the solution (whiskers of possibilities) but can't be a sole determinant without some sort of thoughtful consideration.

I'm sorry, I don't really know. I think a secondary is going to occur along our Delmarva-NJ coast but not much factor, in comparison to the deepening of the vertically deep cyclonic circulation over the eastern Great Lakes.

I haven't given up on the two hazards (front and back end) but had to give it up for the coastal cities. Complex and the colder solutions are not yet kaput. Already 12z/18 NAM has positive snow depth into central VA. Could it be wrong??? yes, but I do think ice and or snow will develop in w NC and nw 1/2 VA at the very start. Can I hope for the 12Z/18 GFS to give me a little more to grasp onto?

Maybe we favor indices too much and not enough timing-track? I'm real glad we're not focusing on MJO in Dec. Long ways to go before we really know what is best fit for each storm scenario.

So far, I'M probably going to be WRONG about my scenarios for possible snow to the coastal cities Thu-Fri (other than flurries-ice pellets). 00z/18 operational models just too warm. Interior I-84 corridor still might have some wintry advisory hazards Thu afternoon-eve and Friday afternoon. Wind might be the greater concern (short period of 45-60 MPH gusts). Still looks like the coldest well mixed airmass of the season to the coast by Saturday morning lasting into the 26th. I see nighttime wind chill modeled to near zero in the coastal cities and subzero I84 corridor??? So a decent early winter storm. All the 00z/18 ensembles (EPS and CMC-GEPS have increased considerably) have a little more snow than I expect I84 corridor... and only advisory potential. While there can be changes near the snowfall gradient boundary, I think I'm now convinced that the coastal cities won't see much more than flurries or ice pellets.

Not going to post the graphics and may be meaningless??? but the 18z EC is 2C colder at 850MB IN NC at 90hrs than the prior 12z at 96 hrs. More cold air aloft to get rid of. I'd love to extrapolate but this can be a rabbit hole and useless. I do like that 12-18z EC trend, especially since it's 12z was implying a decent amount 850 MB se flow WAA Thursday. I won't see new model guidance til 6A..hopefully sleeping in. I

Hi! I just saw the D10 comparison. Both 240's look similar to me... all you have to do is raise height a little on the GEFS to show the positive anomaly but 500 pattern looks similar to me. Regarding the upcoming: I am hoping my scenario below works out. Thinking we are going to see two upper lows come Friday the 23rd...one Great Lakes and one crossing PA/NJ before they merge north of us in Canada on the 24th. Some of the modeling may be putting too much stock on the lead short wave developing the midwest low. Expecting just like this last one... an upper low developing on the eastern flank of the 500 trough. Added this mornings analysis as an example of evolution except this one further south by 1-3 degxrees latitude. Suspect, the upcoming system is going to dig more than that of the 15th-16th. That doesn't mean Long Island will see much if any snow but it does allow for further east wintry weather just inland. I will be looking for future 12/18-19 cycles of the EPS and GEPS to start losing the intensity of the upper low attempting to bodily develop in the Ohio Valley--instead permit an eastward extension. IF all the marbles have been properly placed on big UA low in the Upper Ohio Valley Great Lakes, then I'll have to admit being wrong. All I know is we're still 5-6 days away and something will probably change in the lat-lon of the developing upper lows. I'll check back tomorrow. Raw verification for the elevation based wet snow of 12/16-17 is in the 12/16-17 thread. added the 12z/17 analysis at 658P that helped support secondary development

Well when I remotely read we were in trouble with snow, I am modestly encouraged coming home seeing both 12z EC and 18z/17 GFS both front and back end snow west of I95. Think we need to give this more time before we call it quits on the coast. Complex... I am pretty sure we're going to need advisories I84 corridor for either the front or back end. The front for your normal WAA transition snow. Thursday. Plenty of time to get this to a front end thump???? Back end for sharply falling temps causing transitioning rain to snow to freeze... never really sure what flash freeze is... don't think that is defined clearly but if we get a 30-35 degree 6 hour temp drop with precip changing to snow and lasting into the time it drops below freezing... I'd say road management would be difficult, at least in the elevations. It's not easy to attain this latter back end occurrence. I'd say if we dig this trough a little further se of the current 00z/24 position, it will get interesting for a a couple of hours on the back end---quite the 500MB vort max associated with the developing upper low. Could it cross NJ? And the wind driving it??? scattered gusts 45-55 MPH in NJ expected late Friday..cyclically consistently by the EC 00z/16 cycle-12z/17 cycle. I'll check back tomorrow.

Two day storm totals...CoCoRaHS offers rough idea of elevation based snowfall. Also added the NWS received LSR to supplement.

and now the guidance: Click the maps and note the further east trend in the last 12 hours and also greater consensus in the GEFS at 06z/17. Sunday morning call me wrong if the EPS warm wind south flow is still valid. I am definitely thinking GEFS/GFS are going to be more accurate with EC and CMC to follow: That doesn't mean I'm reading this correctly. I get leery of dismissing the GEFS.

I saw the huge change in the EC yesterday 12z cycle and associated EPS. EPS may start drifting closer to a GEFS solution. Below the 18z/16 and 06z/17 12z/23 GEFS 500MB. I am thinking that the EPS will eventually dig further east, reverting to its guidance prior to 12z/16. Just seems too far west. IF the GEFS is close, the ridge will build north, and the primary storm will redevelop to Delmarva and move NNE. There seems to be too much deference to the EPS. My guess is the very strong block to our north is going to result in a very intense low crossing the northeast late this week, with a following pair of accumulative snow opportunities between 12/26-1/3. 00z/17 GEFS and GEPS not nearly as warm at 360 hours.

Good Saturday morning everyone, Dec 17. I'll add on the two day snow event verification at about 4PM, for those that might be interested. What's next? Thursday afternoon-Friday Dec 22-23. Quite a range of solutions. Looks complex with the likelihood that the bulk of the snow and ice will occur west (inland) of the I-95 corridor from northwestern sections of NC and Virginia up to NYS-New England. The coastal cities from Washington to NYC and Boston could have a little snow at the start and end of the storm (an inch or 3?), with the better chance for higher impact wintry weather along and north of the I-84 corridor. Flurries or a slight covering of snow might even make it down to Atlanta Asheville and Raleigh? There is likely to be at least one short period of 50-60 MPH wind gusts with this rapidly intensifying strong storm. And, it still looks like the coldest air of the season so far, will arrive by Christmas Eve and linger Christmas Day. Two maps for this event were added this morning. Both of these are the NWS Blend of Models for snowfall by Friday night the 23rd... it's not gospel but does show that there might be a first little snowfall of the season for Washington-Baltimore-Philly-NYC? but the bulk of this wintry weather event should be from Pennsylvania NYS and interior New England northward. The last map is the Blend of Models low temperature for Christmas morning. I also saw the GEFS ens snowfall... MUCH closer to the coast and heavier than EPS/GEPS. I am not yet mourning and think it best to keep eyes wide open... til the GFS says, give it up Walt. To get there... the Great Lakes trough rolls through late this weekend...I could see flurries even down here in NYC. Then the colder air follows for the rest of the period Mon-Thu. Added blend of models from 00z/17 for snowfall and 7A Christmas temp.

WOW! I need to see if the EPS 500 looks like the 12z/16 op for 12/23?? offline for a day

If we get ourselves a persistent 24 hours onshore flow of 20-35KT, I see more flooding at high tide the 22nd or 23rd, than what occurred with todays high tides. New Moon coming on the 23rd I think. Worthy of monitoring for potential moderate or greater IF we can muster ne flow for about 24 hours prior to the high tides. I know there is potential for a period of much stronger wind but this storm for us is not a done deal, at least not yet.

Thanks... I hope folks noticed how good the GFS was on positive snow amount, at least in the gradient. Cyclically was VERY good. To me: this is winter as it should be ...we'll have some snow cover here in the elevations daily for awhile. Those who said Dec would be a colder snowier start (at least interior), looks like they will be correct. Overall: I think NWS snow amount numbers will work out well I81 N-S corridor eastward. Onto the next:

Finals will post tomorrow for this mainly elevation 3+" snow event.

Modeling (non 10-1) snowfall was constantly trying to highlight valleys throughout. Very difficult to get good snow in AVP, ditto also extensive big snow through Central Pa.

Snowfall analysis and amounts without LSR's in the 15-16 storm-ops thread.