April 1st-2nd Nor'Easter Potential

[eduggs]

Okay, but you can't say that because this happened in the past x times, this setup is any less than what is being shown. We have thoroughly analyzed the guidance.

It could have been 90 degrees on April 1st for 100 years straight. But the best guidance is showing a snowstorm right now. That can't just be ignored.

The eventual outcome remains uncertain.

We shouldn't ignore the statistical guidance either. Which still says rain for the metro. I know it's less reliable further out and in anomalous environments, but it verifies way better than individual numerical model runs.

[IsentropicLift]

SREF's came in wetter, but are still very warm (at the surface)

[tornadojay]

EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD

327 PM EDT TUE MAR 29 2011

VALID 12Z FRI APR 01 2011 - 12Z TUE APR 05 2011

THE MEDIUM RANGE PATTERN CONTINUES TO SHOW AN AMPLIFIED BUT

PROGRESSIVE THEME. IN THE MEAN THERE SHOULD BE THREE PRIMARY

FEATURES OF INTEREST DURING THE PERIOD... NAMELY A DEEP TROF

CROSSING THE EAST FRI INTO THE WEEKEND... AN ERN PAC TROF THAT

SHOULD ENTER THE WEST BY SAT AND REACH THE ERN STATES BY NEXT

TUE... AND FINALLY AN UPSTREAM TROF EDGING TOWARD THE PAC NW NEXT

TUE. NEITHER THE GFS NOR ECMWF COMPARE PARTICULARLY WELL WITH

ESTABLISHED CONSENSUS FOR THE MEANINGFUL DETAIL DIFFS ASSOC WITH

EACH SYSTEM. AS A RESULT... THE FCST EMPHASIZES ENSEMBLE MEAN

GUIDANCE... ESPECIALLY BY MID-LATE PERIOD.

DURING THE LATTER HALF OF THE SHORT RANGE PERIOD THE 00Z GFS WRAPS

UP A SHARP SHRTWV/CLOSED LOW ALOFT OVER THE EAST TO YIELD AN

OUTLIER DEEP/WWD SFC LOW OVER THE NRN MID ATLC AS OF EARLY DAY

3/FRI. THE 06Z AND 12Z GFS RUNS ARE STILL A BIT OF OUTLIERS WITH

THE DEEP SFC LOW OFF THE MID-ATLANTIC COAST... BUT NOT AS EXTREME

AS THE 00Z RUN. REMAINING GUIDANCE... INCLUDING THE GEFS

MEAN/ECMWF/UKMET/CMC STILL OFFER BETTER CLUSTERING. THE GFS

TRENDS CLOSER TO OTHER SOLNS BY DAY 4/SAT THOUGH.

WITH THE SYSTEM PROGRESSING ACROSS THE CONUS DAYS 4-7 SAT-TUE...

THE 00Z GFS IS GENERALLY ON THE FAST SIDE OF THE GUIDANCE SPREAD

FROM LATE IN THE SHORT RANGE PERIOD THRU THE MEDIUM RANGE. ON THE

OTHER HAND... BOTH THE 00Z ECMWF AND 12Z GFS HAVE DEPARTED

SIGNIFICANTLY FROM PREVIOUS OPERATIONAL RUNS AND LATEST ENSEMBLE

MEANS IN HOLDING BACK MORE ENERGY OVER THE SRN ROCKIES/PLAINS BY

DAYS 6-7 MON-TUE... LEADING TO A MUCH MORE SUPPRESSED CNTRL-ERN

CONUS SFC EVOLUTION VERSUS MOST OTHER GUIDANCE. THE CANADIAN GLBL

HINTS AT THIS IDEA... BUT IN THIS CURRENT PATTERN WHICHEVER SOLNS

HAVE BEEN ON THE SLOW/SWRN SIDE OF THE SPREAD WITH THEIR MID LVL

ENERGY HAVE ULTIMATELY TRENDED FASTER/FLATTER. THE ECMWF/CMC ARE

ALSO OCCASIONALLY BIASED TO THE SLOW/AMPLIFIED SIDE IN THE MEDIUM

RANGE. HOWEVER... WITH THE LATE PERIOD TROF NEARING THE PAC NW...

THE 00Z ECMWF IS ONE OF THE FASTER SOLNS WHILE THE 00Z GFS BECOMES

MORE AMPLIFIED THAN THE AVERAGE OF GUIDANCE.

FOR THE PRELIM PRODUCTS... THE DAY 3-7 FORECASTS STARTED WITH A

50/50 BLEND OF THE 00Z GEFS MEAN/00Z ECMWF ENSEMBLE MEAN. MANUAL

ADJUSTMENTS WERE MADE TOWARDS THE 00Z ECMWF EARLY IN THE FORECAST

PERIOD... WHILE THE BLEND OF THE MEANS OFFERED A GOOD COMPROMISE

IN THE CNTRL-ERN CONUS BETWEEN THE FASTER 00Z GFS AND SLOWER 00Z

ECMWF FOR DAYS 5-7/SUN-TUE. FOR THE FINAL PRODUCTS...SOME OF THE

AVAILABLE 12Z MODEL GUIDANCE SUPPORTED THE 00Z ECMWF SOLUTION OF

POTENTIALLY HOLDING BACK ENERGY OVER THE SRN ROCKIES/PLAINS LATE

IN THE FORECAST PERIOD...SO THE 00Z ECMWF WAS INCORPORATED INTO

THE FORECASTS. A 50/30/20 BLEND OF THE 00Z ECMWF ENSEMBLE

MEAN/ECMWF/GEFS MEAN WAS USED FOR THE FINAL MEDIUM RANGE ISSUANCE.

[ag3]

SREF's came in wetter, but are still very warm

850's are colder then any model.

Surface shows warmer because precip amounts arent as explosive as other models yet.

[CoastalWx]

Agreed, but interpretation of the guidance has to be filtered through lens of climo, so to speak, especially with respect to snow in April in coastal areas. It appears the chances of snow in NYC are increasing that notwithstanding, so let's see how this plays out.

Noreaster85 do us all a favor and just don't address me or refer to me again. Thanks.

That's why soundings are important. They were pretty cold on the GFS..even given the time of year.

[IsentropicLift]

850's are colder then any model.

Surface shows warmer because precip amounts arent as explosive as other models yet.

I actually edited my post to say at the surface, but yes I agree with your point

[tornadojay]

any bets on when the NAM will actually show a storm?

if it reverts back to it's 6Z solution, it will definitely show a storm. It was on it's way to showing a big one.. it was just happening much later than other guidance.

[ag3]

if it reverts back to it's 6Z solution, it will definitely show a storm. It was on it's way to showing a big one.. it was just happening much later than other guidance.

Considering that srefs just came in with the storm, NAM should most definitely follow suit.

[tornadojay]

Considering that srefs just came in with the storm, NAM should most definitely follow suit.

cool! Was it showing the storm within the same timeframe as other guidance or was it still coming in later?

[eduggs]

That's why soundings are important. They were pretty cold on the GFS..even given the time of year.

500mb geopotential heights and various thickness values are very low/cold for this time of year on the GFS! A cold pool aloft is so helpful in terms of transitioning to snow. But even with anomalous cold, an offshore storm track, and snow occurring in the middle of the night, the surface has trouble cooling to freezing in NYC metro.

[CooL]

if it reverts back to it's 6Z solution, it will definitely show a storm. It was on it's way to showing a big one.. it was just happening much later than other guidance.

true, i expect the nam to start showing the lead off wave bomb out like every other model either 18z or 00z tonight..Its just late to the party, and it will be good to have another model in our arsenal right now..

[eduggs]

if it reverts back to it's 6Z solution, it will definitely show a storm. It was on it's way to showing a big one.. it was just happening much later than other guidance.

Yeah it was developing the subsequent shortwave.

[RUNNAWAYICEBERG]

Considering that srefs just came in with the storm, NAM should most definitely follow suit.

yea tru.....srefs showed a miss this morning and NAM followed suit.

[IsentropicLift]

Thru 18hrs on the new NAM, the first S/W looks weaker over MO than the 12z run at 21hrs.

[ag3]

cool! Was it showing the storm within the same timeframe as other guidance or was it still coming in later?

Same timeframe. A little weaker with qpf but much colder with 850's then other models. Lots of members leaning west.

[pazzo83]

500mb geopotential heights and various thickness values are very low/cold for this time of year on the GFS! A cold pool aloft is so helpful in terms of transitioning to snow. But even with anomalous cold, an offshore storm track, and snow occurring in the middle of the night, the surface has trouble cooling to freezing in NYC metro.

I wouldn't be surprised if this morning was the last time the city itself dropped below 32 until the Fall/Winter.

[tornadojay]

500mb geopotential heights and various thickness values are very low/cold for this time of year on the GFS! A cold pool aloft is so helpful in terms of transitioning to snow. But even with anomalous cold, an offshore storm track, and snow occurring in the middle of the night, the surface has trouble cooling to freezing in NYC metro.

yep.. and very steep lapse rates in the lowest levels.. some of that cold air aloft needs to be dragged down as far as possible.. when we get those days where it's snowing at like 40-45 degrees, we usually are under a very deep upper low.

[tornadojay]

Same timeframe. A little weaker with qpf but much colder with 850's then other models. Lots of members leaning west.

nice! thanks!!

[pazzo83]

yep.. and very steep lapse rates in the lowest levels.. some of that cold air aloft needs to be dragged down as far as possible.. when we get those days where it's snowing at like 40-45 degrees, we usually are under a very deep upper low.

with heavy enough precip rates, that could occur in NYC with this storm. Better than rain.

[Momza]

How do the models know that Friday is April(fools)?

[eduggs]

true, i expect the nam to start showing the lead off wave bomb out like every other model either 18z or 00z tonight..Its just late to the party, and it will be good to have another model in our arsenal right now..

I still don't think it's certain which shortwave will be dominant. Probably the lead (technically the 2nd in line), but the GFS, Euro, and GGEM all hint that the kicker could amplify right behind. We've been playing this game for days with the models continuing to delay the amplification of any one wave. It's got to happen soon now that we have a strong longwave trof developing, but there are several small waves that could either phrase or interfere, and the timing is not yet clear. The NAM probably moves toward the consensus, but we could end up with a compromise solution where the waves interfere.

[RUNNAWAYICEBERG]

How do the models know that Friday is April(fools)?

technology is bad arse....a computer won jeapordy, april fools is chump change to them.

[tornadojay]

it's funny... for those of you who use Storm Vista - did you notice that there is an error with the date. It goes from March 31st back to March 1st again.. LOL.. when the model interpreted the solution, it figured there's no way this could be April 1st.

EDIT: it was only doing this on the NAM, but still pretty funny.

[A-L-E-X]

I've seen multiple snowfalls of 18"+ in April... in Utah. So what? April snowfall at NYC is rare. 6" would undoubtedly be historic.

General rule of thumb for sea-level snow in April.... take 1/3 of what you'd estimate the model to show in terms of snowfall if it were January.

I don't consider a 6 inch snowfall historic-- maybe in NYC with it's UHI. But not outside the urban areas.

[A-L-E-X]

with heavy enough precip rates, that could occur in NYC with this storm. Better than rain.

it probably wont stick in that case.... I think it was March 2009, we had a snow squall when it was like upper 40s and low 50s-- even down to ACY.

[A-L-E-X]

accupro snow maps have the 1"+ qpf as snow, touching NYC, Northern Queens and all of SWCT

Must be using the GFS, which had 9" at LGA and 8" at JFK

[ag3]

Must be using the GFS, which had 9" at LGA and 8" at JFK

No. Accupro snow maps for EURO model show 1"+ of qpf as snow for NYC, SWCT, Northern Queens.

[tornadojay]

18Z NAM is still kicking that initial system well south and east.. it looks like it wants to wait for the next piece of energy.

[eduggs]

I don't consider a 6 inch snowfall historic-- maybe in NYC with it's UHI. But not outside the urban areas.

Not historic in general. Just for the month of April. It's extremely rare, dating back to the mid-1850s. It's also rare up here in Putnam County.

Gotta go up to the elevations of the Catskills and Berkshires before 6" April snows become a fairly routine occurrence.

[A-L-E-X]

Not historic in general. Just for the month of April. It's extremely rare, dating back to the mid-1850s. It's also rare up here in Putnam County.

Gotta go up to the elevations of the Catskills and Berkshires before 6" April snows become a fairly routine occurrence.

If you had to quantify it, what would you consider historic for early April-- let's say, a once in 10 year event? In that case, 6 inches may well be historic because (using my example) on the south shore of Long Island, I've seen 3 6 inch snowfalls in the past 30 years.