306  
FXUS02 KWBC 070645  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
144 AM EST WED MAR 07 2018  
 
VALID 12Z SAT MAR 10 2018 - 12Z WED MAR 14 2018  
 
...PATTERN HIGHLIGHTS/THREATS AND GUIDANCE/PREDICTABILITY  
ASSESSMENT...  
 
SPLIT FLOW DEVELOPS FROM THE PACIFIC TO THE WEST COAST OF NORTH  
AMERICA AS HIGHLIGHTED BY A NRN STREAM MID-UPPER LEVEL TROUGH OVER  
THE NERN PACIFIC AND A MORE PROGRESSIVE LOW-MID LATITUDE SRN  
STREAM. THIS SETS THE STAGE FOR A SWATH OF ORGANIZED WEEKEND  
PRECIPITATION MAINLY INTO S-CENTRAL CA AND THE SOUTHWEST/SRN  
ROCKIES WITH APPROACH AND PASSAGE OF SRN STREAM IMPULSE ENERGIES  
AND MOISTURE. THE FLOW AMPLIFIES UPSTREAM OVER THE ERN PACIFIC  
EARLY-MID NEXT WEEK AS NRN STREAM TROUGHING BECOMES DOMINANT OVER  
THE ERN PACIFIC. THERE IS A STRONG GUIDANCE SIGNAL THAT PATTERN  
TRANSITION LEADS TO INCREASED POTENTIAL FOR SIGNIFICANT SYSTEM  
ENERGY TO REACH THE WEST COAST IN WET AND UNSETTLED DEEP LAYERED  
SOUTHERLY FLOW WITH HEAVIEST QPF POTENTIAL OVER PAC NW/NRN CA  
COASTAL AREAS AND TERRAIN.  
 
DOWNSTREAM...ENERGY PROGRESSION IN TWO STREAMS LENDS SYSTEM  
DEVELOPMENT AND RAISED PRECIPITATION POTENTIAL OVER THE CENTRAL US  
SATURDAY. EXPECT MODEST NRN STREAM MOISTURE/SNOWS FOR THE  
N-CENTRAL US OVER A FRONTAL DRAPE WITH SHORTWAVE PASSAGES. A SRN  
STREAM SYSTEM SHOULD MEANWHILE DEVELOP OVER THE SRN PLAINS/LOWER  
MS VALLEY SAT AND ORGANIZE OVER THE SOUTHEAST SUN WITH QUITE  
UNCERTAIN NRN STREAM INTERACTION. INCREASING MOISTURE RETURN FROM  
THE GULF OF MEXICO WOULD ENHANCE PRECIPITATION CHANCES FROM THE  
LOWER MS VALLEY/CENTRAL GULF COAST/MID-SOUTH TO THE OH  
VALLEY...WITH SOME ENHANCED RAINFALL/THUNDERSTORMS OVER THE  
SOUTHEAST. DETAILS ARE UNCERTAIN WITH SIGNIFICANT MODEL TO MODEL  
VARIANCE...BUT THE MAJORITY OF GEFS/ECMWF ENSEMBLE MEMBERS REMAIN  
DECENTLY CLUSTERED IN SUPPORT FOR SUBSEQUENT COASTAL STORM  
POTENTIAL. A TRACK NORTHEASTWARD UP OFF THE ERN SEABOARD LATER SUN  
INTO TUE OFFERS A THREAT OF INLAND WRAPPING PRECIPITATION  
INCLUDING A CHANCE FOR MID-ATLANTIC TO NEW ENGLAND HEAVY SNOWS  
ALONG WITH THE POTENTIAL FOR COASTAL FLOODING AND HIGH WINDS/WAVES  
FOR MARITIME INTERESTS.  
 
OVERALL...THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED  
FROM A BLEND OF REASONABLY COMPATABLE GUIDANCE FROM RECENT  
GEFS/ECMWF ENSEMBLE MEANS...THE 00 UTC NATIONAL BLEND OF  
MODELS...AND WPC CONTINUITY. DETERMINISTIC MODEL GUIDANCE OFFERS  
SIMILAR THEMES TO THE LARGER SCALE PATTERN OF THE ENSEMBLE  
MEANS...BUT RUN TO RUN VARIANCE HAS INCREASED MORE OVER TIME SO  
ONLY LIMITED INPUT WAS BLENDED INTO THE WPC FORECAST.  
 
SCHICHTEL  
 

 
 
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