172  
FXUS02 KWBC 060601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
100 AM EST TUE MAR 06 2018  
 
VALID 12Z FRI MAR 09 2018 - 12Z TUE MAR 13 2018  
 
...AN ACTIVE PATTERN FOR THE WEST AND EAST-CENTRAL US LEADS INTO  
ANOTHER ERN US WINTER COASTAL STORM THREAT...  
 
...PATTERN HIGHLIGHTS/THREATS AND GUIDANCE/PREDICTABILITY  
ASSESSMENT...  
 
IN THE SHORT RANGE...ANOTHER NOR'EASTER WILL EFFECT THE NORTHEAST  
SO PLEASE REFER TO SHORT RANGE PRODUCTS FROM THE WPC WINTER  
WEATHER DESK AND YOUR NWS FORECAST OFFICE ON THIS SIGNIFICANT  
WINTER STORM. RESIDUAL LOW PRESSURE AND CLOSED MID-UPPER LEVEL LOW  
ENERGY WILL REFORM AND LINGER OVER THE NORTHEAST FRI/SAT AND KEEP  
THINGS UNSETTLED AND WINTERY AS HELD UNDERNEATH AN ERN CANADIAN  
BLOCKING RIDGE.  
 
OUT WEST...AN UPPER LOW AND SURFACE FRONT WILL PUSH AN ASSOCIATED  
SWATH OF TERRAIN ENHANCED RAIN/SHOWERS AND MOUNTAIN ENHANCED SNOWS  
INTO THE PACIFIC NORTHWEST BY FRI AND ACROSS THE N-CENTRAL  
INTERIOR WEST/ROCKIES INTO SAT. ADDITIONAL POTENTIAL ACROSS CA AND  
THE SOUTHWEST DERIVES FROM UNDERCUTTING WEEKEND SRN STREAM ENERGY  
AND MOISTURE.  
THIS SPLIT FLOW HAS BEEN MORE VARIABLE IN GUIDANCE OVER THE PAST  
FEW RUNS SO PREFER AN ENSEMBLE MEAN FORECAST APPROACH...WITH SOME  
INDIVIDUAL SOLUTIONS OFFERING POTENTIAL FOR ORGANIZED MOISTURE AND  
PRECIPITATION POTENTIAL.  
THE FLOW AMPLIFIES/RELOADS UPSTREAM ACROSS THE ERN PACIFIC BY  
LATER IN THE WEEEKND INTO EARLY NEXT WEEK LEADING TO AN INCREASED  
POTENTIAL FOR SIGNIFICANT MID-UPPER LEVEL TROUGH/DEEPENED SYSTEM  
ENERGY TO APPROACH AND BREACH THE WEST COAST IN WHAT WILL LIKELY  
BE AN ENHANCED ACTIVE AND WET/UNSETTLED FLOW REGIME.  
 
OVER THE CENTRAL AND ERN US...ENERGY PROGRESSION IN BOTH STREAMS  
LENDS SYSTEM DEVELOPMENT AND RAISED PRECIPITATION POTENTIAL OVER  
THE CENTRAL US HEADING INTO THE WEEKEND. 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 UNCERTAIN NRN STREAM INTERACTION. INCREASING  
MOISTURE RETURN FROM THE GULF OF MEXICO WOULD ENHANCE  
PRECIPITATION CHANCES MAINLY FROM THE LOWER MS VALLEY/CENTRAL GULF  
COAST/MID-SOUTH TO THE OH VALLEY...WITH SOME ENHANCED  
RAINFALL/THUNDERSTORMS OVER THE SOUTHEAST. WHILE DETAILS ARE  
UNCERTAIN...THE LOW HAS POTENTIAL GIVEN FAVORABLE OVERALL PATTERN  
SUPPORT TO DEEPEN INTO A COASTAL STORM. A TRACK NORTHEASTWARD UP  
OFF THE ERN SEABOARD LATER SUN INTO TUE OFFERS A THREAT OF INLAND  
WRAPPING PRECIPITATION INCLUDING HEAVY SNOW 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 THE LATEST  
GEFS/ECMWF ENSEMBLE MEANS. 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.  
OVERALL...PATTERN EVOLUTION PREDICTABILLITY SEEMS SLIGHTLY BETTER  
THAN AVERAGE.  
 
SCHICHTEL  
 

 
 
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