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NYC/PHL: January 25-27 Potential Bomb Part 4


earthlight

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You've pretty much made it clear what you think.

Well no worries on the flow with this per the NAM.

Winds across the region out of the NNE or N. Thusly this may be why interior sections are dry on this run. But with surface temps at or below freezing from 95 NW and a strong N/NNE flow and a low bombing SE of the coast, would expect a nice solution if it were extrapolated...

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Well no worries on the flow with this per the NAM.

Winds across the region out of the NNE or N. Thusly this may be why interior sections are dry on this run. But with surface temps at or below freezing from 95 NW and a strong N/NNE flow and a low bombing SE of the coast, would expect a nice solution if it were extrapolated...

The NAM always does not throw enough precip back into the cold sector late in its range...all models sort of have that bias to an extent from my experience but the NAM is very guilty of doing it and also not having very smoothed out edges to its QPF either late.

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The 12z NAM forecast sounding for PHL (via Bufkit) has the low-level thermal profile going pretty much isothermal from about 6,000 feet down. This leads to a little rain to start then the column cools and then snow occurs. The depth of the isothermal layer then makes the precipitation type go back and forth several times between rain and snow. If this thermal profile happens, it would probably be a dump of heavy wet snow with perhaps a period of mixing. Lots can go wrong with this thermal profile as a slight change in a layer would impact the precipitation type.

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Per Coolwx rain/snow line close to I95 in philly area. (and generally from DC to NY)

Given the event has an increased chance of occurring at night and with as deep of a low as would be out there I'd be surprised if it was not all snow if the exact scenario the NAM and Euro want to show occurs.

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Given the event has an increased chance of occurring at night and with as deep of a low as would be out there I'd be surprised if it was not all snow if the exact scenario the NAM and Euro want to show occurs.

Yeah and would probably trend to snow as low develops offshore. 850 low is in a favorable position.

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Consistent with that observation, Bufkit through the end of the NAM's run shows LGA as all snow.

Pretty easy call at the end of january with cold air and snow cover all over NE. As long as the wind profile stays like that with the low bombing to the south and east its snow. But this is really close and it really will be a day of call I fear.

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Made a post last night in regards to the closest analogue I see to this storm and the 12Z NAM comes even closer to that analogue playing out...

January 25, 2000

Really similar surface and h5 depictions.

The upper air pattern is close to it...the actual type of scenario that might play out is closer to 3/15/99

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SG, I agree...just checked that out on the NARR.

I guess this is the closest we've been to a Jan 2000 scenario in a long time. Could see this continue to move closer to coast and possibly wind up and occlude like 2000 once that piece of energy dives into the system that the NAM seems to be picking up on.

No solution off the table. Touch and go until 12Z tuesday or later probably.

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MT. Holly updated AFD ! :scooter:

THE WINTER STORM...

TUESDAY NIGHT AND WEDNESDAY PORTION....

AT THIS POINT...THE 0000 UTC MODEL CONSENSUS IS SHOWING A MARKED

SLOWING FOR THE POTENTIAL SIGNIFICANT STORM DURING THE MIDWEEK.

RIGHT NOW...THE 0000 UTC GFS AND ECMWF ARE COMING INTO CLOSER

AGREEMENT WITH THE POSITION OF THE SURFACE LOW AS WELL AS THE

TIMING. THE 12Z NAM IS SLOW BUT AT LEAST ITS RETURNED TO A COASTAL

STORM SOLUTION. STILL THINK ITS AT LEAST 6 HOURS TOO SLOW BUT WILL

DEFER TO 12Z OP MODEL GEFS/HPC CONSENSUS IN THE AFTN FCST.

AS HAS BEEN THE CASE FOR THE LAST COUPLE OF DAYS...FORECAST

CONFIDENCE IN THE PLACEMENT OF THE LOW...AS WELL AS PRECIPITATION

AMOUNTS AND TYPES. WHILE THERE APPEARS TO BE A TREND TO A COLDER AND

SLOWER SOLUTION...NOT MUCH CAN BE MADE OF THIS YET. WE WILL CONTINUE

TO WATCH TRENDS.

THIS EVENT...WHATEVER IT IS...HAS HAD A CONSTANT SIGNAL /NAEFS SINCE

THE 20TH/ FOR LARGEST QPF ALONG THE COAST. UNFORTUNATELY...PRESUMING

THIS IS CORRECT... IT MAY NOT MATTER SINCE THE SFC LOW AND

ASSOCIATEDN SHORT WAVE SCOOPING GULF OF MEXICO MOISTURE IS SEEMINGLY

MAKING THIS A HEAVY QPF PRODUCER ALONG THE COAST. 00Z/23 PROBS FOR

2 INCHES ARE 10 PCT ALONG THE COAST WITH PROB FOR AN INCH 30-50

PCT ACROSS OUR ENTIRE CWA. THATS NOT SAYING AN INCH WILL OCCUR

ALONG AND W OF INTERSTATE 95 ..IN FACT YOU COULD LOOK AT IT AS A

50 TO 70 PCT CHANCE OF LESS THAN 1 INCH.

THE POINT...THE STAKES ARE SUBSTANTIAL FOR BOTH THE WEDNESDAY

MORNING AND EVENING COMMUTES AS IT DOES APPEAR IT WILL BE COLD

ENOUGH FOR MAINLY SNOW OR ICE I95 WEST...PRESUMING THE OUT TO SEA

VERSIONS OF THE 06Z NCEP ENSEMBLES ARE INCORRECT...AND THAT THE

EC/UK TANDEM OF RECENT CYCLES ARE CORRECTLY SUPPORTING AN EVENT.

ONE THING I DONT LIKE ABOUT THIS POTENTIAL EVENT... THE APPARENT LACK

OF MODELED PHASING... IE A SMALLER SEPARATE SRN STREAM SHORT WAVE.

THAT PLUS A WARMER PRE-EVENT BOUNDARY LAYER ENVIRONMENT MAKES THIS

A DIFFERENT POTENTIAL EVENT THAN THAT OF 12/26/10.

WE`LL REREVIEW SEVERAL TIMES BETWEEN 1130AM AND 230PM.

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SG, I agree...just checked that out on the NARR.

I guess this is the closest we've been to a Jan 2000 scenario in a long time. Could see this continue to move closer to coast and possibly wind up and occlude like 2000 once that piece of energy dives into the system that the NAM seems to be picking up on.

No solution off the table. Touch and go until 12Z tuesday or later probably.

I agree but the ecm/ukmet have been farily consistent with a more robust storm. Lets see if they hold or trend in anyway later today

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While we wait for the GFS, snow growth layer is pretty high up as one would imagine but for LGA is does show some decent vv through the snow growth layer with good saturation, so that is a positive. Again, its an eternity when using the NAM, but just throwing that out there.

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For Jersey Shore folks, checked soundings at Sandy Hook (K56N) and clearly looks like snowstorm getting going on NAM. Surface briefly goes from freezing to around 35 in the hours before event and as the precip moves in it cools quickly to 33. All other layers below freezing and wind is WNW at around 280s in hours before storm moves up, goes to 55 degrees at worst and by the time the good precip is moving in and pressures are dropping it goes to 37 degrees and heading more northerly. With snowpack, coldest part of year, looks like pseudo banana high (not the most favorable but it will do) and water temps very, very cold, looks like a snowstorm to me. Belmar is similar but a degree or two warmer at surface. Other layers are also borderline but could be overcome by dynamics. ACY has favorable wind flow and heavy precip but BL a few degrees too warm to be overcome, and other layers are above freezing. Looks like rain there for now.

So I would put a rain/snow line somewhere around Asbury Park.

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