HPC Discussion - Tapping the GOM
Posted by JAC on 2/3/2010, 4:15 pm
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
338 AM EST WED FEB 03 2010

VALID 12Z WED FEB 03 2010 - 12Z SAT FEB 06 2010

DAY 1


NM INTO AZ/TX PANHANDLE...
SRN STREAM TROF WILL CONTINUE TO DEVELOP OVER BAJA CA AS IT SLIDES
EWD INTO THE SW CONUS/NRN MEXICO BY THU MORNING.  IT WILL BE
LARGELY UN-PHASED WITH THE NRN STREAM TODAY...AND WILL THEREFORE
HAVE TIME TO SPREAD ENERGY/UVV IN THE SW FLOW AHEAD OF IT.
COPIOUS PAC MSTR WILL BE INVOLVED FROM THE ONSET...THEN INCREASING
GULF MSTR INFLUX IS PROGGED TO SIGNIFICANTLY RAMP UP PRECIP
THROUGH THE SRN ROCKIES AND ADJACENT PLAINS TONIGHT.  COOLING
EFFECTS OF THE DYNAMIC TROF/HT FALLS WILL DROP SNOW LVLS TO AOA
6KFT TODAY IN NM...THEN CONTINUE TO FALL DOWN TO AROUND 2-3KFT
OVERNIGHT INTO THE TX PANHANDLE.  ROEBBER SLR ON SEVERAL MODELS IS
INDICATING GENERALLY LESS THAN 10 TO 1 RATIO SO TOTALS WILL BE
ONLY A FEW INCHES DESPITE THE HIGH QPF...EXCEPT FOR TX PANHANDLE
WHERE UPSLOPE/MSTR FLUX WILL BE MAXIMIZED AND 8 INCHES COULD FALL.
HPC PREFERS AN ECMWF/NAM BLEND HERE ALTHOUGH MASS FIELDS ARE
FAIRLY CONGRUENT ON DAY 1 ANYWAY.  SREF WAS A LITTLE LIGHT ON
PRECIP WHERE TRRN HAD AN INFLUENCE...SO NAM WAS USED TO CAPTURE
THAT ASPECT.

PAC NW AND INTER-MOUNTAIN WEST...
EXPECT ONLY LIGHT SNOWFALL...AN INCH OR TWO...TO THE HIGH TRRN
THROUGH THURSDAY MORNING ASSOCIATED WITH A SHRTWV SLIDING EWD
THROUGH THE REGION.  COLD AIR ALOFT WILL KEEP INSTABILITY SHWRS
ALIVE THROUGH THE PD...BUT PAC MSTR IS MEAGER HERE.


THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT


DAYS 2 AND 3

WEST...
PRONOUNCED HT FALLS AND A POWERFUL CDFNT WILL BRING A STRONG SHOT
OF PAC MSTR AND COOLER TEMPS TO THE PAC NW SWD INTO CA. AN UPPER
VORTEX OVER THE NERN PAC WILL STEER A POTENT SHORT WAVE TOWARD NRN
CA AND UP THE NW COAST... WHILE THE IMPRESSIVE 700 MB MOISTURE
TRANSPORT INUNDATES NRN CA AND THE SIERRA WITH TREMENDOUS UPSLOPE
FLOW. IT IS HERE... THE SHASTA/SISKIYOUS AND ENTIRE SPINE OF THE
CA SIERRA WHERE SPOTS COULD SEE WELL OVER A FOOT OF SNOW...PERHAPS
CLOSER TO 2 FEET. HPC GENERALLY FOLLOWED THE 00Z NAM/GFS HERE
SINCE THE ECMWF WAS ON THE FAST SIDE OF GUIDANCE BRINING IN THE
SYSTEM.  

NRN/CNTRL PLAINS AND MID MS VLY...
SYSTEM INITIALLY IN THE WEST WILL EJECT INTO THE PLAINS ON
THURSDAY AND DIVE SEWD PARTIALLY PHASING WITH THE STRONG SRN
STREAM WAVE.  A SIGNIFICANT PORTION OF THE SRN ROCKIES/PLAINS MSTR
WILL BE ENTRAINED INTO THE DIGGING NRN SYS FOSTERING PRECIP
THROUGH THE PLAINS ALL THE WAY TO ND.  00Z MODELS RESOLVED MANY OF
THEIR EARLIER TIMING/STRENGTH DIFFERENCES WITH THE UPR WAVE...AS
WELL AS DIFFERENCES IN THE SFC REFLECTION IN THE CNTRL HI PLAINS.
THERE SHOULD BE A BROAD AXIS OF SNOW FROM NRN OK TO SRN SD EWD
THROUGH THE MID MS VLY THURS INTO FRIDAY WITH WIDESPREAD 4-6 FM KS
NWD AND 6-8 LOCALLY 4-6 FOCUSED INTO NEB/SD.    

MIDWEST TO MID-ATLANTIC AND CNTRL/SRN APPALACHIANS...
HIGH-IMPACT STORM SYSTEM STILL APPEARS IN THE OFFING FOR LATE WEEK
AS A SURGE OF GULF MSTR BECOMES INVOLVED WITH A SEMI-SPLIT STREAM
TROF MOVING THROUGH THE CNTRL/ERN CONUS.  SRN STREAM SFC
REFLECTION IN THE NRN GULF LATE THURS WILL INITIATE THE INFLUX OF
MSTR TO THE REGION...AND THE STRONG WAA PATTERN WILL TEND TO RAISE
SNOW LVLS AND MAKE FZRA THE DOMINANT PTYPE FOR THE COLDER
HIGH-ELEVATIONS...AOA 2-3KFT...OF THE SRN APPS/ADJACENT FOOTHILLS.
VERY AGREEABLE GUIDANCE FOR LATE THURS INTO FRIDAY GIVING OVER A
HALF INCH OF ICE HERE.  AS THE MSTR CONTINUES NEWD...TREMENDOUS
UVV AND EMBEDDED ENERGY WILL OVERSPREAD THE MID
ATLANTIC/APPALACHIANS ON FRIDAY.  THE WAA PATTERN SHOULD BE MOSTLY
OFFSET BY HT FALLS/DYNAMIC COOLING...YET ADMITTEDLY IF MODELS WERE
NOT SO AGREEABLE HERE IT WOULD BE A VERY TENUOUS FORECAST
THERMALLY SPEAKING.  NONETHELESS...PTYPE ANALYSIS FROM THE
SREF/NAM/GFS/GEFS AND 12Z ECMWF ALL SHOW AN IMPRESSIVE SWATH OF
HVY SNOW CENTERED ON NRN VA.  THE 00Z ECMWF INDICATED A MORE SLY
TRACK...BUT THIS DID NOT AGREE WITH ITS OWN ENSEMBLE MEAN.  THE
QUESTION MARK IS FRIDAY AFTERNOON/EVNG WHEN SNOW WILL DEPEND ON
WHETHER THE COLD AIR PLACE WILL REMAIN LONG ENOUGH TO OVERCOME THE
STRONG MID LVL WARMING.  THE ASSOCIATED COASTAL LOW WILL DRAW
COLDER AIR SWD EARLY SATURDAY TURNING THE REGION TO SNOW
REGARDLESS...BUT THE NATURE OF THE HVY QPF FRIDAY NIGHT WILL MAKE
A HUGE DIFFERENCE IN TOTALS.  MDL DIAG PREFERS THE 00Z NAM/12Z
ECMWF/21Z SREF FOR THE MASS FIELDS...AND THOSE CLUSTERED WELL WITH
THE INDIVIDUAL GUIDANCE FROM ALL THE MODELS MENTIONED.  SO FOR
NOW...HPC INDICATES 10 INCHES FOR NRN VA/MD AND GRADUALLY TAPERING
AMTS WESTWARD INTO OH...WITH LCLY HIGHER AMTS IN THE COMPLEX TRRN
OF WV/PA/VA.
 

SOWKO

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Possible Significant Storm Friday - IN to VA to FL - JAC, 2/2/2010, 3:59 pm
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