Ensembles starting to gel for a major east-coast storm this weekend
Posted by JAC on 12/7/2010, 7:57 am
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
359 AM EST TUE DEC 07 2010

VALID 12Z SAT DEC 11 2010 - 12Z TUE DEC 14 2010

ENSEMBLE MEANS HAVE FINALLY COME INTO BETTER AGREEMENT ON THE
LARGE SCALE DETAILS OF THE SIGNIFICANT AMPLIFYING TREND EXPECTED
OVER THE CONUS DURING THE PERIOD... WITH A RIDGE BUILDING INTO THE
WEST SUPPORTING A VERY DEEP/AMPLIFIED TROF REACHING THE EAST COAST
BY THE FIRST HALF OF NEXT WEEK.  ACCOMPANYING THIS EVOLUTION WILL
BE STRENGTHENING LOW PRESSURE FCST TO TRACK FROM THE PLAINS INTO
THE NORTHEAST DURING THE SAT-MON TIME FRAME.  IMPORTANT SMALLER
SCALE SHRTWV DETAIL ISSUES WILL LIKELY TAKE A WHILE TO BE RESOLVED
THOUGH.  THE 00Z GFS SHOWS A FARTHER SWD TRACK THAN CONSENSUS WITH
ITS MID LVL/SFC LOWS FROM THE PLAINS INTO TN VLY... AND THEN
FARTHER NEWD PULLS THE SFC LOW FARTHER NWD INTO ERN CANADA THAN
THE PRIMARY SOLN CLUSTER.  THE GFS SOLN IS NOT TOO FAR FROM ITS
LAGGED AVERAGE OF RECENT CYCLES THOUGH.  ON THE OTHER HAND SOME
RECENT ECMWF RUNS HAVE BEEN ON THE NRN SIDE OF THE SOLN ENVELOPE.
THE 00Z ECMWF HAS ADJUSTED A LITTLE CLOSER TO THE LATEST
GEFS/ECMWF/CMC ENSEMBLE MEANS BUT IS STILL A LITTLE NWD/NWWD OF
ITS 4-CYCLE LAGGED AVERAGE.  THE UKMET/CMC ARE GENERALLY CLOSER TO
THE ENSEMBLE MEANS TO THE W OF THE APLCHNS.  IMPROVED CLUSTERING
OF ENSEMBLE GUIDANCE FAVORS MAJORITY WEIGHTING OF THEIR SOLNS WITH
SOME INCORPORATION OF THE 00Z ECMWF AS ITS MID LVL EVOLUTION
COMPARES SOMEWHAT BETTER TO THE ENSEMBLE MEANS THAN THE GFS.  THUS
THE DAYS 3-7 FCST STARTS WITH A NEARLY EVEN BLEND OF THE 00Z
ECMWF/00Z GEFS MEAN/12Z ECMWF ENSEMBLE MEAN.

MEANWHILE THE MEAN TROF OVER THE NERN PAC WILL GRADUALLY BRING
SOME HGT FALLS INTO THE WEST COAST STATES BY DAYS 6-7 MON-TUE.
AHEAD OF THIS FEATURE EXPECT A SYSTEM TRACKING OVER THE NERN PAC
TO BRING A WARM FRONT ACROSS THE PAC NW DURING THE WEEKEND.
TIMING DIFFS WITH THIS FRONT ARE FAIRLY MODEST BUT THE GFS IS ON
THE FAST EDGE OF THE ENVELOPE WITH THE ANCHORING SFC LOW.  THEN
EXPECT A FRONTAL SYSTEM TO CROSS THE COAST LATE IN THE PERIOD AS
THE TROF ALOFT DRIFTS EWD.  THE BLEND USED FOR THE CNTRL-ERN CONUS
SYSTEM PROVIDES A GOOD ACCOUNT FOR CONSENSUS NEAR THE WEST COAST.

RAUSCH




EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
229 PM EST MON DEC 06 2010

VALID 12Z THU DEC 09 2010 - 12Z MON DEC 13 2010

MEDIUM RANGE GUIDANCE CONSENSUS SHOWS THAT THE MEAN LONGWAVE
PATTERN CONTINUES TO BE DOMINATED BY LARGE CENTERS OF PERSISTENT
EXTREME POSITIVE ANOMALIES: ONE OVER THE WRN ALEUTIANS...THE OTHER
E OF THE SRN TIP OF GREENLAND. THIS STRONG NEGATIVE NAO PATTERN IS
COMPATIBLE WITH A VERY DEEP TROF ALONG THE E COAST...AND WELL
BELOW NORMAL TEMPS OVER MOST OF THE ERN CONUS.  THE PATTERN
UPSTREAM OVER THE CONUS IS ALSO SUPPORTIVE OF A DEEP E COAST TROF.
THE HUGE RIDGE OVER THE ALEUTIANS SUPPORTS A DEEP TROF/RIDGE ALONG
145W AND 110W....RESPECTIVELY. THIS PATTERN...IN TURN...ALSO
SUPPORTS THE MAJOR E COAST TROF. THOUGH IN  AGREEMENT
OVERALL...00Z/12Z GUIDANCE STILL SHOWED SOME DIFFS WITH RESPECT TO
THE VIGOROUS LOW PRESSURE EXPECTED TO AFFECT THE ERN HALF OF THE
CONUS IN RESPONSE TO THE AMPLIFYING TROF ALOFT. FOR EXAMPLE...THE
00Z DETERMINISTIC ECMWF SHOWED A DAY 5-7/SAT-MON SFC TRACK THAT
TRENDED TOWARDS THE NW SIDE OF THE MODEL/ENSEMBLE SPREAD.

HOWEVER...ENSEMBLE SPAGHETTI PLOTS...TELECONNECTIONS...AND A
FAVORABLE UPSTREAM LONGWAVE PATTERN NOW SEEM TO POINT INCREASINGLY
TOWARDS A MAJOR STORM FOR THE E COAST STATES SHAPING UP NEXT
WEEKEND. FINAL PROGS FOLLOWED THE CONTINUITY OF THE
PRELIMS....SAVE FOR BEING SLIGHTLY FASTER DAY DAY 6 WITH THE
DEEPENING SYS OVER THE ERN STATES.  THE CONTINUITY OF THE NEW
00Z/06 ECMWF ENSEMBLE MEAN WAS VERY GOOD FROM THE CORRESPONDING
12Z/05 MEAN. PERHAPS THE MOST MEANINGFUL PIECE OF NEW INFORMATION
FROM, 00Z/06 GUIDANCE IS THAT NEW ENSEMBLE SPAGHETTI PLOTS
SUPPORTED THE MORE AMPLIFIED SCENARIO FOR SAT-MON AS A MAJOR STORM
DEVELOPS OVER THE OH VLY/CENTRAL APPALACHIANS/MID AND N ATLANTIC
COAST STATES. IN FACT...THE DETERMINISTIC GFS WAS IN THE PREFERRED
AMPLIFIED ECMWF FAMILY OF SOLUTIONS! THE AMPLIFIED ECMWF FAMILY OF
SOLUTIONS IS CLEARLY PREFERRED OVER THE FLATTER GEFS MEAN SOLUTION
FOR SUN/MON DAYS 6-7.  

12Z MODELS:

DETERMINISTIC 12Z/06 GUIDANCE IS STILL ON TRACK IN MOVING A
WEAKENING STORM ACROSS THE UPPER MS VLY/GREAT LAKES THU-SAT....AND
WITH DEVELOPING A NEW MAJOR ERN CONUS STORM NEXT WEEKEND. BY SUN
DAY 6...THE GFS IS ON THE FAST SIDE OF THE ENVELOPE OF SOLUTIONS
WHILE THE UKMET IS ON THE SLOW SIDE. ECMWF WAS FARTHER N WITH THE
PRIMARY LOW MOVING INTO THE GREAT LAKES REGION NEXT WEEKEND AND
NOT QUITE AS FAR E AS THE GFS WITH THE SECONDARY CENTER DEVELOPING
DAY 6 VICINITY OF VA/NC. I WILL NUDGE THE DAY 6 FINAL LOW POSITION
JUST A TAD TO THE E  OVER KY. THIS SYS WILL BE A MAJOR WEATHER
PRODUCER AS SYNOPTIC HEAVY SNOWFALL NEXT WEEKEND IN THE GREAT
LAKES LAKES REGION GIVES WAY TO MORE EFFECT SN BY DAY 7. FARTHER
S...SN MAY CHANGE TO RAIN FROM THE CENTRAL APPALACHIANS TO SE NEW
ENG BEFORE QUICKLY CHANGING BACK TO SN OVER THE
APPALACHIANS/NY/INTERIOR NEW ENG AS THE SYS MOVES FROM THE OH VLY
INTO NY STATE. WHILE SOME HEAVY SN IS EXPECTED TO THE LEFT OF THE
STORM TRACK...PERHAPS EVEN MORE IMPORTANT WILL BE THE DANGEROUS
WIND CHILLS THAT WILL HOWL IN ON NORTHWESTERLY WINDS E OF THE MS
RIVER BEHIND THE STORM. FURTHERMORE THERE IS A RISK OF SOME NEAR
RECORD LOW TEMPS DAMAGING CITRUS CROPS IN FL EARLY NEXT WEEK.


BEFORE THE BIG ERN STORM GETS UNDER WAY...THERE WAS REASONABLE
CLUSTERING OF SOLNS WITH THE WEAKER SYSTEM FCST TO TRACK ACROSS
THE NRN TIER/GRTLKS AND OVER THE NORTHEAST DAYS 3-5 THU-SAT.  THE
GFS LOOKED TOO FAST BY DAY 5 SAT.  A DETERMINISTIC GFS/ECMWF BLEND
WAS USED FOR DAYS 3-4 THU-FRI TO REPRESENT GUIDANCE CONSENSUS WITH
THIS SYSTEM...WITH THE DAY 5 BLEND PROVIDING THE DESIRED MINORITY
WEIGHTING OF THE GFS.

ORIGINATING PAC ENERGY IS CARRIED BY PROGRESSIVE FLOW ALOFT BUT
DOES NOT REACH THE WEST COAST UNTIL EARLY DAY 4 FRI. EXPECT
MULTIPLE SYSTEMS TO AFFECT THE PACIFIC NORTHWEST DURING THE PERIOD
IN RESPONSE TO BUNDLES OF ENERGY BEING CARRIED ALONG BY THE FAST
PAC FLOW.  THE GFS/UKMET ARE ON THE FAST SIDE OF THE GUIDANCE
SPREAD WITH A SYSTEM FCST TO TRACK INTO THE NERN PAC AROUND DAY 5
FRI.  THE AFOREMENTIONED BLEND AT THAT TIME REFLECTS A CONSENSUS
THAT IS SOMEWHAT SLOWER THAN THE GFS.  

FLOOD



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Waaay Toooo Cold - JAC, 12/6/2010, 7:23 am
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