Another Major Northeast snowstorm?
Posted by
Fred on 12/26/2009, 1:37 pm
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
804 AM EST SAT DEC 26 2009
VALID 12Z WED DEC 30 2009 - 12Z SAT JAN 02 2010
BUILDING RIDGING ACROSS WESTERN CANADA WILL LEAD TO TROUGHING
MID-CONTINENT. SYSTEMS MOVING THROUGH THE FLOW SHOULD REMAIN
PROGRESSIVE DUE TO THE PRESENCE OF A POLAR VORTEX OVER NUNAVUT.
WITH ARCTIC HIGH PRESSURE OVER MUCH OF THE EASTERN TWO-THIRDS OF
THE CONTINENT... A GULF LOW SHOULD BE GUIDED THROUGH THE NORTHEAST
GULF AND SOUTHEAST COAST TO NEAR THE 40N/70W BENCHMARK BY THE
BEGINNING OF 2010...SIMILAR TO THE CYCLONE THAT MOVED OUT OF THE
GULF AND UP THE EAST COAST JUST OVER A WEEK AGO. THE MODELS AND
ENSEMBLE MEANS SHOW GENERAL AGREEMENT ON THESE IDEAS. EARLY
PRELIM PRESSURES WERE INITIALLY BASED ON A 00Z GFS/00Z ECMWF
COMPROMISE TO ACCOUNT FOR TIMING ISSUES IN THE EASTERN PACIFIC AND
ALONG THE EAST COAST OF THE UNITED STATES BEFORE MANUAL
CORRECTIONS TOWARDS THE NORTHWEST SIDE OF THE MULTI-MODEL ENSEMBLE
CLUSTERING WAS MADE.
UPDATED MORNING PRELIMS ARE READJUSTED SOMEWHAT IN TIMING AND
POTENTIAL INTENSITY FROM EARLIER NIGHT THOUGHTS. LAST WEEKS
SIMILAR GULF/ATLC COAST SYSTEM WAS POORLY FORECAST BY MODEL
GUIDANCE AT LONGER RANGES AND NOT UNTIL THE SHORT RANGE WAS IT
HANDLED WELL. OVERALL GUIDANCE OF ALL MODELS WAS SLOW. TDAS GFS
RUNS EMPHASIZE A FLAT SHORTWAVE EXITING INTO THE EAST COAST/WEST
ATLC RIDGE INDUCING OFF SHORE MID ATLC REGION CYCLOGENESIS WITH A
TRACK NEWD SOUTH OF THE 40/70 BENCHMARK. 12Z/25/00Z 26E ECMWF RUNS
AND ENSEMBLES WAIT FOR THE MAIN MID LEVEL TROF WITH LOWER HT
ANOMALIES TO BRING IN GREATER HT FALLS ACROSS THE GULF COAST. AS
THE MORE AMPLIFIED MID LEVEL TROF SWINGS EWD TO THE SOUTH ATLC
COAST ADDITIONAL HT FALLS OCCUR AS A POLAR TROF DROPS INTO THE OH
VALLEY WITH PHASING POTENTIAL INTO A CLOSED MID LEVEL LOW OVER THE
MID ATLC REGION ROTATING UP THE NORTHEAST COAST SATURDAY. LAST TWO
RUNS AND ENSEMBLE AGREE ON THIS SOLUTION. BASED ON THE PERSISTENT
STRONG NEG AO/NAO...A MEAN + PNA AND A CLOSED MID LEVEL LOW EAST
OF NEWFOUNDLAND NEAR 50N/50W IT SEEMS INGREDIENTS ARE IN PLACE FOR
AT LEAST A SIGNIFICANT NORTHEAST SNOW STORM WITH SOME MID ATLC
INTRUSION OF COLDER PCPN. SEVERAL PERSISTENT COMPOSITE ANALOG
DATES FOR THE PATTERN EXPECTED BETWEEN DAYS 6-10 ARE FOR JAN 1996
AND 1961. DATES OF SIGNIFICANT EAST COAST STORMS WITH PERHAPS NOT
AS MUCH COLD AIR IN PLACE AS THOSE AHEAD OF THIS SYSTEM. OVERALL
TREND/DATES OF THE COMPOSITE ANALOGS HAVE BEEN FOR PAST STRONG
ARCTIC OUTBREAKS PENTRATING VERY FAR SOUTH AS CURRENTLY SEEN IN
ALL OF MODELS AND MEANS BY NEXT WEEKEND. HIGHEST CONFIDENCE ON
COLD AIR OUTBREAK SET UP. RESERVED FAIR CONFIDENCE ON
TIMING/TRACK/INTENSITY OF A COASTAL LOW AFFECTING THE EAST COAST
OVER NEW YEARS WEEKEND.FOR REASONS STATED ABOVE UPDATED BLEND CONSISTS OF 00Z ECMWF AND
00Z ECMWF ENS MEAN.
ROTH/ROSENSTEIN |
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