NYC/PHL January 7-9 Potential Part Deux

[winterwx21]

To be honest this has the look to it where most areas (outside the best band) get 2-5", 6-8" inside the band, and the jackpot amounts it the favored Catskill areas get 15"+. I really would not be suprised come Saturday morning if a few reports of 15-20" came out of the Catskills region.

Some areas get only .10 to .25 of precip on quite a few of the models. I think 2 to 5 outside the band is too high. More like 1 to 3, with some areas maybe near 4.

[jdt]

Mt Holly just updated the to its moring AFD.Seem to be backing off the higher amounts with the reduced qpf in the overnight models. No advisory or warnings at this point. Door still open as to what later guidance may show regarding qpf. Seems reasonable and cautious. I think Upton has the tougher call as it seems this heavier axis of snow (however heavy it will be) will potientally effect a much greater portion of there forecast area. With the exception of Sussex, Warren, & Morris and perhaps Carbon, Monroe and Northampton counties in Mt Holly's area this will probably be a 1-3 or 2-4" event at most. Could possilbe only be that in the mentioned counties too depending on how it works out. Still think areas in NNJ within ~10-20 miles of the NJ/NY state line will be a solid advisory to near or low end warning event when all is said and done.

[jdt]

Some areas get only .10 to .25 of precip on quite a few of the models. I think 2 to 5 outside the band is too high. More like 1 to 3, with some areas maybe near 4.

Could very well be correct. If the drier models are right then the 2" covers it and if the event goes a bit wild then the 5" amount covers it. We can get more detailed and specific hopefully after 12Z. Also I am mainly thinking of NNJ mainly north of I78. South of there 1-3" and maybe only a t-2 SNJ

[snywx]

Strongly agree...there's a steep snowfall gradient between the Wallkill Valley and the Shawangunk Ridge. I remember driving up there numerous times in 07-08 and being amazed at the snowpack despite the meager amounts falling in the Hudson Valley that year, especially down towards my house. I think Ellenville and into the Gunks could see up to 12" in this set-up although I wouldn't count on any widespread amounts over 8". The possibly long duration of the event should allow for upslope to be a factor if we get many hours of lighter precipitation from the arctic front on either side of the more intense Norlun banding.

Yeah the elevation jumps pretty good when your on Rt. 52.. From Pine Bush to Walker Valley it jumps from 300' to 1500' in about 2 miles or so. From Rt. 52 you can take a quick right onto Cragsmoor rd and jump another 700' or so in about a mile. That area gets smoked when it comes to these orographic lift/enhancement scenarios..

[Ababa]

Upton's new AFD:

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE NEW YORK NY

355 AM EST THU JAN 6 2011

.SYNOPSIS...

WEAK HIGH PRESSURE OVER THE REGION MOVES OFFSHORE TODAY INTO

TONIGHT. AN UPPER LEVEL TROUGH WILL MOVE ACROSS THE GREAT LAKES

AND INTO NEW ENGLAND FRIDAY...WITH A SECOND LOW DEVELOPING OFF THE

MID ATLANTIC COAST. THIS COMPLEX SYSTEM WILL BRING SNOW TO THE

REGION INTO SATURDAY. HIGH PRESSURE WILL BUILD EAST FROM THE

CENTRAL US EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

WEAK HIGH PRESSURE OVER THE AREA THIS MORNING...WITH LIGHT WINDS

AND COLD TEMPERATURES. TEMPERATURES GENERALLY TEENS AND LOW

20S...WITH A FEW UPPER 20S IN THE 5 BOROUGHS OF NYC. WARM AIR

ADVECTION CLOUDS ARE MOVING IN AND ITS EXPECTED THAT EARLY MORNING

SUNNY SKIES WILL BECOME MOSTLY CLOUDY BY MID MORNING.

LIGHT WINDS AND CLOUD COVER WILL KEEP TEMPERATURES NEAR OR

SLIGHTLY BELOW SEASONAL NORMALS. MOS GUIDANCE HIGHS WERE GENERALLY

CONSISTENT WITH A POORLY MIXED CLOUDY AFTERNOON.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...

WARM AIR ADVECTION AHEAD OF A WAVE MOVING ACROSS THE GREAT LAKES

STRENGTHENS A BIT THIS EVENING...SO CLOUDS SHOULD CONTINUE TO

THICKEN AND LOWER. FLURRIES ARE POSSIBLE...WITH A STEADIER LIGHT

SNOW POSSIBLE WEST OF THE HUDSON RIVER. THIS SYSTEM IS MOISTURE

STARVED...THUS LITTLE TO NO ACCUMULATION IS EXPECTED.

HIGHER IMPACT AND MORE CHALLENGING SETUP ON FRIDAY...WITH AN

ACCUMULATING SNOW EVENT EXPECTED. THE UPPER LOW DIGS INTO THE

CENTRAL APPALACHIANS...WITH A SECONDARY SURFACE LOW DEVELOPING

OVER THE DELMARVA. MODELS CONSISTENT WITH THE OCEANIC LOW GOING

TOO FAR EAST FOR A DIRECT HIT. THEY ALSO REMAIN CONSISTENT IN

DEVELOPING A NORLUN INSTABILITY TROUGH...WHERE MOISTURE OFF THE

OCEAN IS DRAWN BACK OVER A SLOW MOVING CONVERGENCE BAND.

THE HEAVIEST SNOW WILL OCCUR NEAR AND JUST DOWNSTREAM FROM WHERE

THIS CONVERGENCE SETS UP...AND UNFORTUNATELY THAT PLACEMENT IS THE

MOST DIFFICULT ELEMENT TO PREDICT.

AT THIS TIME...THE HIGHEST CONFIDENCE IS IN WIDESPREAD, LIGHT SNOW

DEVELOPING FROM WEST TO EAST OVERNIGHT THURSDAY NOT FRIDAY

MORNING. HEAVIER SNOWBANDS ARE EXPECTED MID TO LATE AFTERNOON

FRIDAY AS LOW LEVEL CONVERGENCE BETWEEN THE TWO TROUGHS BECOMES

STRONGER. ACCUMULATIONS FROM THE LIGHT SNOW IS EXPECTED TO BE 2 TO

5 INCHES...WHICH WOULD CONSTITUTE A WINTER WEATHER ADVISORY.

ADDITIONAL...POTENTIALLY HEAVY SNOW WOULD BRING THOSE AREAS INTO

WARNING CRITERIA (7 INCHES OR MORE IN 12 HOURS).

DUE TO THE UNCERTAINTY IN PLACEMENT AND SNOW AMOUNT, BUT ENOUGH

CONFIDENCE THAT HEAVIER SNOW WILL OCCUR WITHIN THE CWA...A WINTER

STORM WATCH HAS BEEN ISSUED. THIS COULD EITHER BE UPGRADED TO A

WARNING ONCE IT IS EVIDENT WHERE HEAVIER SNOW WILL FALL...OR

CONVERTED INTO AN ADVISORY WHERE LESSER AMOUNTS ARE EXPECTED. IT

IS ALSO POSSIBLE THAT THE HEAVIEST SNOW COULD BEGIN MID TO LATE

AFTERNOON...AND SIGNIFICANTLY IMPACT THE FRIDAY AFTERNOON RUSH.

FOR NY/NJ/CT MEDIA...IT MUST BE REITERATED THAT CONFIDENCE IS VERY LOW ON

PREDICTING WHERE THE HEAVIEST SNOW WILL OCCUR. PLEASE HIGHLIGHT

THIS UNCERTAINTY AND THAT A WATCH MEANS FAVORABLE CONDITIONS EXIST

FOR WARNING LEVEL SNOW WITHIN THE WATCH AREA. A SUBTLE SHIFT IN

THIS CONVERGENCE ZONE WILL MEAN LARGE DIFFERENCE IN SNOWFALL.

FROM A GUIDANCE PERSPECTIVE...THE NAM IS BY FAR THE MOST ROBUST

WITH 15-20 INCH SNOWFALL FOR CENTRAL LONG ISLAND...NORTHERN NYC AND

LOWER HUDSON VALLEY. ADDING TO THE FORECAST CHALLENGE...THIS MODEL

ALSO HAS A SHARP SNOWFALL GRADIENT...WITH 18 INCHES IN THE

BRONX...AND 3 ON STATEN ISLAND!! THE GFS AND EC...AND MOST

ENSEMBLE MEMBERS POINT TO LESSER AMOUNTS OF SNOW...AND WIDELY

VARYING DISTRIBUTIONS.

TO ADD YET ANOTHER PIECE...SURFACE LOW PRESSURE MOVES VERY CLOSE

TO EASTERN LONG ISLAND...SO IT WOULD NOT BE SURPRISING FOR ENOUGH

ABOVE-FREEZING AIR TO FORCE A CHANGEOVER TO RAIN FOR A BIT FRIDAY

NIGHT.

BETTER AGREEMENT ON SNOW TAPERING OFF FROM SOUTHWEST TO NORTHEAST

LATE FRIDAY NIGHT...WITH JUST A FEW FLURRIES INTO SATURDAY.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...

BLUSTERY...COLD AND DRY CONDITIONS EXPECTED SAT NIGHT THROUGH

MONDAY NIGHT WITH A DEEP LOW OVER EASTERN CANADA AND HIGH PRESSURE

OVER THE OHIO VALLEY. WILL HAVE TO WATCH ANOTHER POTENTIAL COASTAL

STORM AROUND MIDWEEK. LATEST GFS/ECMWF HAVE TRENDED OFFSHORE WITH

THIS STORM BUT THERE IS CONSIDERABLE SPREAD AMONG GEFS MEMBERS AND

MODELS WILL LIKELY UNDERGO SEVERAL CHANGES BETWEEN NOW AND THEN.

STAY TUNED.

I didn't realize 0z NAM was calling for so much snow on LI and Bronx - didn't look at the soundings.

[snywx]

Watches are up for the entire CWA

http://forecast.weat...ter+Storm+Watch

[tmagan]

In fairness to NWSFO Upton, this is an absolute no-win situation.

[nzucker]

In fairness to NWSFO Upton, this is an absolute no-win situation.

They are doing a good job although I thought the snowfall map of 6-8" for here in Westchester was a bit exaggerated. They needed to get a watch out though because heavier banding could deliver 6"+ to small areas with the ocean inflow and good ratios. I'm pretty convinced we're all going to see advisory conditions with a warning probably verifying here or there.

[tmagan]

They are doing a good job although I thought the snowfall map of 6-8" for here in Westchester was a bit exaggerated. They needed to get a watch out though because heavier banding could deliver 6"+ to small areas with the ocean inflow and good ratios. I'm pretty convinced we're all going to see advisory conditions with a warning probably verifying here or there.

That is why I was mildly surprised by the winter storm watch.

[jdt]

Wow Mt Holly really backed off. Latest map only shows 2-3" even into to far NW NJ with 1-1.5" rest of area. Definitely a tough call for both Mt Holly and Upton. Upton area has much better chance of being in a heavy band just a matter of where and how heavy. While most of Mt Holly area out side of Far NNJ and northern eastern PA is an advisory event at most but may be a warning even far north. Best they an do is make a call and explain the situation as subject to change and perhaps big change. I think they are both doing so this morning each in their own fashion.

[patrick05]

wow that was quick... and 7.4" for my area...

http://www.erh.noaa.gov/okx/stormtotalprecip.php

[earthlight]

They had no choice but to blend some of the NAM into their forecast...this close in, with such an extreme solution. But I think the 06z NAM is much more reasonable..this will probably be an advisory event.

[Ababa]

Maybe they should have waited for the latest NAM. Looking at some of this sounding data is amazing (which I didn't bother to do until reading the UPTON AFD). White Plains went from 28" of snow on the 0z NAM to 5" on the 6z NAM. Incredible in this timeframe.

[A-L-E-X]

That is why I was mildly surprised by the winter storm watch.

They are trying to make sure the city gets an early warning lol-- Bloomberg and Doherty were criticizing the fact that they didnt have enough lead time with the last storm-- they said they still thought it would only be a light event going into xmas day. Of course, they are lying through their teeth....

[baroclinic_instability]

Timing of this event is awful from a public perspective. Even a quick hitting event that it is, highest rates look to be over NYC around early rush hour. NAM soundings are unstable to around 500 hpa early in the event and some pretty hefty rates are likely. The early watch is good in my opinion, and it will get the public ready for what will be a high impact event even though the snow totals won't be anything to write home about. 2"+ snowfall rates per hour at rush hour on Long Island = high impact in my book.

[Ababa]

They are trying to make sure the city gets an early warning lol-- Bloomberg and Doherty were criticizing the fact that they didnt have enough lead time with the last storm-- they said they still thought it would only be a light event going into xmas day. Of course, they are lying through their teeth....

Maybe I'll see a salt truck....still havent seen one this winter here in Queens.....

[A-L-E-X]

They had no choice but to blend some of the NAM into their forecast...this close in, with such an extreme solution. But I think the 06z NAM is much more reasonable..this will probably be an advisory event.

Yeah, a general 3-6 inch event still seems reasonable.

[A-L-E-X]

Maybe I'll see a salt truck....still havent seen one this winter here in Queens.....

Yeah, I mean at this rate-- what kind of lead time did they need? A month?

[jdt]

They had no choice but to blend some of the NAM into their forecast...this close in, with such an extreme solution. But I think the 06z NAM is much more reasonable..this will probably be an advisory event.

Yes for just about all of NJ this probably will be an advisory event and for SNJ maybe not even that. But for a small sliver of NNJ (I like the area along ~10 to perhaps 20 miles south of the NJ/NY line) as possibly reaching warning levels. Not saying it is a sure thing but a decent chance. I will be very interested in what the 12z NAM shows qpf wise. Will it remain drier like 6z or go a little wetter like 0z. This will end up being a nice little snowstorm for a long narrow corridor.

[A-L-E-X]

Timing of this event is awful from a public perspective. Even a quick hitting event that it is, highest rates look to be over NYC around early rush hour. NAM soundings are unstable to around 500 hpa early in the event and some pretty hefty rates are likely. The early watch is good in my opinion, and it will get the public ready for what will be a high impact event even though the snow totals won't be anything to write home about. 2"+ snowfall rates per hour at rush hour on Long Island = high impact in my book.

Weve had colossal rush hour problems with just a few inches that were poorly timed lol

[baroclinic_instability]

Weve had colossal rush hour problems with just a few inches that were poorly timed lol

Exactly. I like the idea of a watch early to get peoples attention. If they need to trim back to an advisory for certain areas, then so be it. NWS is trying to push into "impact based" forecasting in the short range. They are already testing more impact based warnings, etc. to account for non-weather related factors such as high traffic volume, for instance. 3" snow at rush hour is far worse than 3" snow at 3 AM--that kind of thing.

I didn't check BUFKIT soundings, does anyone know what the instability values have been for this?

[Rtd208]

While it currently seems like the heaviest snow band and highest accumulation will fall north and east of Mt.Holly's CWA I think they may have backed off on snow accumulations a little to much, obviously this is subject to further adjustment.

[A-L-E-X]

Exactly. I like the idea of a watch early to get peoples attention. If they need to trim back to an advisory for certain areas, then so be it. NWS is trying to push into "impact based" forecasting in the short range. They are already testing more impact based warnings, etc. to account for non-weather related factors such as high traffic volume, for instance. 3" snow at rush hour is far worse than 3" snow at 3 AM--that kind of thing.

I didn't check BUFKIT soundings, does anyone know what the instability values have been for this?

Yep, there are practical issues to consider here also-- 3 inches falling during a morning rush hour will have a much higher impact than 6 inches falling on a weekend will.

[ORH_wxman]

Exactly. I like the idea of a watch early to get peoples attention. If they need to trim back to an advisory for certain areas, then so be it. NWS is trying to push into "impact based" forecasting in the short range. They are already testing more impact based warnings, etc. to account for non-weather related factors such as high traffic volume, for instance. 3" snow at rush hour is far worse than 3" snow at 3 AM--that kind of thing.

I didn't check BUFKIT soundings, does anyone know what the instability values have been for this?

I would never issue a watch in this setup if it were me...but I might be off my rocker...it wouldn't be the first time.

Its much easier to ramp up public expectations than issue a watch and then try to downgrade. This is just from personal experience.

[baroclinic_instability]

I would never issue a watch in this setup if it were me...but I might be off my rocker...it wouldn't be the first time.

Its much easier to ramp up public expectations than issue a watch and then try to downgrade. This is just from personal experience.

Well I certainly don't have an EC perspective forecasting these events so I respect your opinions more than my own. Perhaps an advisory alone would have been better then. Would you even bother with that at this point? I could see an advisory sufficing at this point instead of a storm watch.

As for public expectations, I always thought it was better to inform the public early for events such as this where probability is low but impact may be high. It seems the public reacts much worse to an event where they felt like they were "surprised".

[A-L-E-X]

I would never issue a watch in this setup if it were me...but I might be off my rocker...it wouldn't be the first time.

Its much easier to ramp up public expectations than issue a watch and then try to downgrade. This is just from personal experience.

It depends on how much the public even understands what a watch is lol. They might not see it as a downgrade if they dont really understand what it means. From their perspective, they might be thinking of it as a watch being issued to make commuters wary of possible issues, not specific snowfall amounts.

I remember an event here that dumped 4 inches in the middle of a rush hour, it closed everything down, was the worst commute I ever had (6 hours in traffic-- ugh!) being a much higher impact than that faux blizzard in Feb 06. It all comes down to timing I guess

[Voyager]

0z nam qpf totals for pa

abe .33

ptw .25

ukt .29

rdg .25

phl .21

pne .22

dyl .26

lom .24

nxx .24

mpo .47

lns .19

You forgot one....ptb.

Anyway, on a serious note State College has 2-4 for Schuylkill County for what it's worth.

[Voyager]

I would never issue a watch in this setup if it were me...but I might be off my rocker...it wouldn't be the first time.

Its much easier to ramp up public weather message board weenies expectations than issue a watch and then try to downgrade. This is just from personal experience.

Fixed it for ya!!!

Again, on a serious note, you are probably right. I think the public is more critical of "blown forecasts" when we get LESS than called for rather than MORE.

[ORH_wxman]

Well I certainly don't have an EC perspective forecasting these events so I respect your opinions more than my own. Perhaps an advisory alone would have been better then. Would you even bother with that at this point? I could see an advisory sufficing at this point instead of a storm watch.

As for public expectations, I always thought it was better to inform the public early for events such as this where probability is low but impact may be high. It seems the public reacts much worse to an event where they were "surprised".

I don't think the probability of a warning event is high enough to issue a watch IMHO....though I could be totally wrong. There's pretty much only one model that shows it, and that was the 00z NAM. The 06z run trended away from it...and most other guidance wants to shift the inverted trough northeast into CT pretty quickly. I think they get accumulating snow, but not warning snows...advisory maybe, but its not time to issue an advisory yet.

Again, I could be off my rocker here...and I will be the first to admit a bust as I have had my share...but my experience with inverted troughs and norlun type events (I usually deal with at least 1 per winter) is to always hedge low and northeast for amounts.

[A-L-E-X]

I don't think the probability of a warning event is high enough to issue a watch IMHO....though I could be totally wrong. There's pretty much only one model that shows it, and that was the 00z NAM. The 06z run trended away from it...and most other guidance wants to shift the inverted trough northeast into CT pretty quickly. I think they get accumulating snow, but not warning snows...advisory maybe, but its not time to issue an advisory yet.

Again, I could be off my rocker here...and I will be the first to admit a bust as I have had my share...but my experience with inverted troughs and lorlun type events (I usually deal with at least 1 per winter) is to always hedge low and northeast for amounts.

Will, I wonder how much of a role timing and politics played in this; OKX is usually conversative.