787  
FXUS02 KWNH 210646  
PREEPD  
 
PRELIMINARY EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
145 AM EST TUE FEB 21 2017  
 
VALID 12Z FRI FEB 24 2017 - 12Z TUE FEB 28 2017  
   
..OVERVIEW
 
 
THE ERN PAC/WRN U.S. CONTINUES TO BE AN AREA OF HIGH FCST  
SENSITIVITY FOR SPECIFIC DETAILS WITHIN AN OVERALL MEAN TROUGH  
ALOFT DOWNSTREAM FROM A STRONG NERN PAC RIDGE. ISSUES WITHIN THIS  
REGION WILL THEN HAVE AN IMPACT ON THE REMAINDER OF THE LOWER 48  
WHERE MEAN FLOW SHOULD EVOLVE TOWARD A SWLY ORIENTATION.  
MEANWHILE THERE ARE STILL DETAIL UNCERTAINTIES FOR A STRONG SYSTEM  
TRACKING NEWD FROM THE MIDWEST FRI ONWARD.  
   
..MODEL EVALUATION/PREFERENCES
 
 
AFTER GUIDANCE HAD APPEARED TO START THE PROCESS OF CONVERGING  
TOWARD A COMMON SOLN FOR THE EVOLUTION OF ERN PAC/WEST COAST  
ENERGY ALOFT BY THE WEEKEND... 12Z/18Z MODEL RUNS ADJUSTED TOWARD  
TAKING NWRN NOAM ENERGY AND WRAPPING UP A FAIRLY DEEP SYSTEM JUST  
OFF THE WEST COAST. MANY OF THESE MODELS ALSO INCORPORATED ENERGY  
FROM A CLOSED LOW FARTHER OFFSHORE. GIVEN THE DIFFICULTY THAT  
GUIDANCE HAS IN RESOLVING DETAILS OF FLOW IN THIS KIND OF PATTERN  
IT WOULD NOT BE SURPRISING FOR FURTHER CHANGES TO OCCUR IN THE  
FCST. ALSO THERE IS STILL WIDE SPREAD IN ENSEMBLE MEMBERS BY DAY  
5 SUN. SOME MEMBERS LOOKED MORE SIMILAR TO THE LATEST OPERATIONAL  
CLUSTER WHILE OTHERS REPRESENTED THE QUICKER EJECTING SOLNS THAT  
WERE THE MAJORITY 24-36 HRS AGO. THIS DIVERGENCE LED TO A 12Z SUN  
FCST THAT HAD ENSEMBLES RANGING ANYWHERE FROM RIDGE TO TROUGH OVER  
THE INTERIOR WEST/ROCKIES. OVER SOME AREAS SPREAD ACTUALLY  
DAMPENED OUT A LITTLE BY DAYS 6-7 MON-TUE AS AGREEMENT IMPROVED  
TOWARD A POSITIVELY TILTED MEAN TROUGH SETTING UP OVER THE WEST  
WITH SOME EJECTING ENERGY SUPPORTING A WAVE THAT REACHES THE  
MIDWEST/UPR MS VLY BY NEXT TUE. CONFIDENCE IS NOT VERY HIGH THAT  
CURRENT CONSENSUS WILL VERIFY BUT THESE MODEL RUNS PROVIDED ENOUGH  
OF A COMMON SIGNAL TO INCORPORATE A PORTION OF THE OPERATIONAL  
MODEL EVOLUTION WITH THE WEAKER ENSEMBLE MEANS AS THE BEST OPTION  
FOR THE DETERMINISTIC FCST UPDATE. THE 00Z GFS/UKMET/CMC AT LEAST  
MAINTAIN A REASONABLE DEGREE OF CONTINUITY.  
 
FOR THE SYSTEM TRACKING NEWD FROM THE MIDWEST AN AVG AMONG THE 18Z  
GFS/GEFS MEAN AND 12Z ECMWF/ECMWF MEAN PROVIDED THE MOST STABLE  
SOLN FOR TRACK AND TIMING. IN VARYING WAYS UKMET/CMC RUNS HAVE  
TENDED TO DEVIATE MORE FROM THE MAJORITY CLUSTER THOUGH THEY  
ILLUSTRATE SOME OF THE LINGERING DETAIL UNCERTAINTIES WITH THE  
SUPPORTING ENERGY ALOFT. AS THE TRAILING COLD FRONT HEADS  
TOWARD/INTO NEW ENGLAND... ONE TREND OF NOTE FROM YDAY IS TOWARD  
SOMEWHAT MORE POTENTIAL THAT FLOW COULD TAP SOME OF THE MSTR ASSOC  
WITH A FEATURE TRACKING FROM THE GULF OF MEXICO ACROSS THE FL  
PENINSULA AND INTO THE ATLC DURING THE SHORT RANGE TIME FRAME.  
 
CONSIDERATIONS OVER AREAS OF INTEREST LED TO STARTING WITH A BLEND  
OF THE 18Z GFS/12Z ECMWF AND THEIR MEANS FOR DAYS 3-5 FRI-SUN WITH  
A TRANSITION MOSTLY TO THE MEANS THEREAFTER AS OPERATIONAL RUNS  
DIVERGED MORE GREATLY WITH SOME DETAILS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THERE ARE PERSISTENT UNCERTAINTIES WITH SPECIFICS BUT IN PRINCIPLE  
THE FCST IS STILL ON TRACK FOR THE STORM TRACKING NEWD FROM THE  
MIDWEST FRI INTO THE WEEKEND. YDAYS SPC OUTLOOK MAINTAINED A  
FOCUS ON AN AREA OVER AND AROUND INDIANA AS BEST POTENTIAL FOR  
SEVERE CONVECTION IN THE FRI-FRI NIGHT PERIOD. CONSULT LATEST SPC  
PRODUCTS FOR UPDATED INFO. SNOW TO THE NW OF THE SFC LOW TRACK  
MAY BE HVY AT TIMES WHILE THERE MAY ALSO BE AREAS OF MDT-HVY RAIN  
AHEAD OF THE COLD FRONT CROSSING THE EAST. HOW MUCH ATLC MSTR MAY  
REACH NEW ENGLAND BY SAT-SAT NIGHT WILL HAVE TO BE MONITORED.  
SOME LOCATIONS MAY SEE STRONG WINDS. ALONG THE WEST COAST THE  
LATEST EVOLUTION SFC/ALOFT SHOWN IN MOST GUIDANCE HAS INCREASED  
THE POTENTIAL FOR A PERIOD OF HEAVIER RAIN/HIGHER ELEV SNOW  
FOCUSED OVER CALIFORNIA... MOST LIKELY DURING THE WEEKEND... WITH  
A PERIOD OF STRONG WINDS ALSO A PSBL THREAT. SOME MSTR WILL  
EXTEND INTO FAVORED TERRAIN OF THE INTERIOR WEST/ROCKIES. THEN  
BEYOND THE ROCKIES ONE OR MORE AREAS OF PCPN MAY DEVELOP WITH THE  
AID OF IMPULSES EMBEDDED WITHIN FLOW ALOFT THAT SHOULD BE TURNING  
SWLY AS WELL AS A WAVY FRONT GRADUALLY LIFTING NWD OVER THE  
CNTRL-ERN STATES. NRN AREAS MAY SEE SOME WINTRY PCPN TYPES WITH  
RAIN FARTHER S.  
 
ON FRI MUCH OF THE ERN U.S. SHOULD SEE TEMPS 15-30F ABOVE NORMAL  
WITH WARMTH HANGING ON INTO SAT ALONG THE EAST COAST. EXPECT SOME  
LOCATIONS TO SEE RECORD WARM VALUES FOR MAX/MIN READINGS. IN  
SPITE OF A SIGNIFICANT COOLING TREND... TEMPS SHOULD ONLY DROP TO  
NEAR OR SLIGHTLY BELOW NORMAL LEVELS BRIEFLY BEFORE REBOUNDING  
ABOVE NORMAL AGAIN EARLY NEXT WEEK. THE WARMING TREND SHOULD  
START ON SUN OVER THE SRN PLAINS. MUCH OF THE WEST AND INTO THE  
N-CNTRL PLAINS WILL LIKELY SEE BELOW NORMAL TEMPS WITH SOME  
LOCATIONS SEEING MINUS 10-15F OR SO ANOMALIES ONE OR MORE DAYS.  
 
RAUSCH  
 

 
 
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