significant/very significant Snowstorm/Blizzard for Northeast Tue/Wed??
Posted by Fred on 1/8/2011, 5:19 pm
FXUS61 KOKX 082105
AFDOKX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW YORK NY
405 PM EST SAT JAN 8 2011


LONG TERM /TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --...POTENTIAL FOR SIGNIFICANT SNOW STORM FROM LATE TUESDAY INTO
WEDNESDAY INCREASING...

LOOKING AT THE 12Z SUITE OF MODELS...IT APPEARS THE GFS IS A
SOUTHERN/EASTERN OUTLIER...AND THE 9Z SREF A NORTHERN/WESTERN
OUTLIER WITH THE STORM WHEN COMPARED TO THE GEFS ENSEMBLE MEAN AND
ECWMF. THE 12Z GEFS MEAN TRACKS THE STORM OVER THE 40N/70W BENCHMARK
AT 6Z WEDNESDAY...WITH ECMWF JUST TO THE NW OF THE BENCHMARK AT 12Z
WEDNESDAY. BASED ON THIS HAVE OPTED FOR A ECMWF/GEFS ENSEMBLE MEAN
BLEND FOR THE EXTENDED. OTHER THAN THE SREF SOLUTION...THERE IS A
CLEAR CONSENSUS FOR AN ALL SNOW EVENT...WITH THIS IDEA BEING
FOLLOWED.

THE FIRST PART OF THE STORM...A CUTOFF LOW CURRENTLY OVER EASTERN
AZ...IS WELL RESOLVED BY LAND BASED OBSERVATIONS...AND IS HANDLED
FAIRLY SIMILARLY BY ALL MODELS. THE SECOND PIECE OF THE EQUATION
ENERGY FORECAST TO DIVE DOWN FROM THE PACIFIC NORTHWEST BY
TONIGHT/SUNDAY IS STILL OVER THE NE PACIFIC...SO HOPEFULLY EITHER
THE 00Z OR 12Z SUNDAY BALLOON LAUNCHES WILL CAPTURE THIS FEATURE AND
PROVIDE INCREASED CONFIDENCE. THE GFS IS A FAST/SHEARED OUTLIER WITH
THIS SYSTEM...AND AS A RESULT DOES NOT STRENGTHEN THE DOWNSTREAM
RIDGING THAT MOVES OVER THE AREA TUESDAY SHARPLY ENOUGH (THIS IS A
KNOWN GFS BIAS - NOT SHARPENING THE DOWNSTREAM RIDGING ENOUGH). THE
RESULT IS A MORE SOUTHERN/EASTERN SOLUTION IN THE GFS. THE OTHER
MODELS HANDLE THIS DOWNSTREAM RIDGING BETTER...SO HAVE THE SETUP FOR
A LOW TRACKING CLOSER TO THE COAST AND INTENSIFYING MORE THAN THE
GFS.

BASED ON THE ABOVE HAVE CHANCE POPS SW 1/2...SLIGHT CHANCE POPS NE
1/2 OF AREA BY TUESDAY AFTERNOON. INCREASE POPS TO LIKELY THROUGHOUT
BY LATE TUESDAY NIGHT...AND CONTINUE INTO WEDNESDAY MORNING FOR ALL
BUT FAR NW ZONES...WHERE UNCERTAINTY IN TIMING GIVES PRUDENCE TO
HIGH END CHANCE POPS AT THIS TIME. TAPER POPS OFF FROM NW TO SE INTO
WEDNESDAY NIGHT...WITH THURSDAY BEING DRY.

WHILE IT IS TOO EARLY TO DISCUSS AMOUNTS...THE POTENTIAL IS
INCREASING FOR A SIGNIFICANT TO VERY SIGNIFICANT SNOWFALL ACROSS THE
REGION FROM LATE TUESDAY INTO WEDNESDAY...ESPECIALLY OVER EASTERN
PORTIONS OF THE REGION. IF THE STRONGER ECMWF SOLUTION IS
CORRECT...THERE IS ALSO THE POTENTIAL FOR STRONG GUSTY WINDS...WHICH
WOULD ALSO CAUSE BLOWING AND DRIFTING OF SNOW...WITH THE BEST CHANCE
FOR THIS OVER EASTERN PARTS OF THE AREA. THIS LATTER IDEA IS THE
LOWEST CONFIDENCE PART OF THE FORECAST AT THIS TIME. BASED ON THIS
WILL ENHANCE WORDING IN THE HWO...INCLUDING THE POTENTIAL FOR
BLOWING AND DRIFTING SNOW - EMPHASIZING THE BEST POTENTIAL FOR THIS
IDEA IS OVER EASTERN PARTS OF THE AREA FOR NOW.
STILL PLENTY OF TIME FOR THINGS TO CHANGE...BUT GIVEN SOLID
CONSISTENCY OF GEFS ENSEMBLE MEAN SOLUTION OVER THE PAST FEW
DAYS...AND THE ECMWF OVER ITS PAST FEW RUNS...CONFIDENCE IN A WINTER
STORM...POSSIBLY A MAJOR ONE...IS INCREASING IN THE LATE
TUESDAY/WEDNESDAY TIME FRAME. STAY TUNED.

WITH THE STORM PULLING SLOWLY NE INTO THE CANADIAN MARITIMES
THURSDAY...MEAN ZONAL FLOW SETS UP INTO FRIDAY...WITH POSSIBLY SOME
SHORTWAVES PASSING...BUT NOTHING SIGNIFICANT ENOUGH AT THIS TIME TO
WARRANT EVEN SLIGHT CHANCE POPS. RIDGING BUILDS IN FRIDAY
NIGHT...GIVING WAY TO AN APPROACHING 500 HPA TROUGH SATURDAY. HAVE
SLIGHT CHANCE POPS WESTERN 1/4 OF THE AREA SATURDAY TO REFLECT
APPROACHING TROUGH.

FOR TEMPERATURES...STARTED WITH A MEX/MEX ENSEMBLE MEAN
BLEND...TWEAKED TOWARDS ECMWF LOW LEVEL THERMAL FIELDS...AND
UNDERCUT A BIT ESPECIALLY FROM WEDNESDAY ON WITH IMPACT OF POTENTIAL
SNOW COVER. EXPECT BELOW NORMAL TEMPERATURES THROUGHOUT THE PERIOD. -- End Changed Discussion --
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significant/very significant Snowstorm/Blizzard for Northeast Tue/Wed?? - Fred, 1/8/2011, 5:19 pm
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