Prognostic Meteorological Discussion
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FXUS02 KWBC 240655
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EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 AM EDT THU APR 24 2014

VALID 12Z SUN APR 27 2014 - 12Z THU MAY 01 2014

...A STORMY AND AMPLIFIED/BLOCKY LATE APRIL PATTERN...

...PATTERN OVERVIEW AND WEATHER HIGHLIGHTS/THREATS...

A MAJOR COOLING/UNSETTLING MID-UPPER LEVEL S-CENTRAL
ROCKIES/PLAINS TROUGH AND DEEP LEAD CYCLOGENESIS SUN/MON SETS THE
STAGE FOR A SPRING N-CENTRAL ROCKIES/HIGH PLAINS SNOW THREAT IN A
COOLED AIRMASS WRAPPED BACK FROM THE NRN HALF OF THE CENTRAL AND
ERN US.  SPC ALSO SHOWS MULTI-DAY SEVERE WEATHER POTENTIAL IN A
WELL DEFINED WARM SECTOR OVER THE S-CENTRAL PLAINS/MS VALLEY INTO
SUN/MON INCLUDING A STRONG TORNADO THREAT.

THE CLOSED TROUGH/LOW AND WELL ORGANIZED SURFACE SYSTEM SHOULD
SUBSEQUENTLY BE FORCED GRADUALLY EASTWARD ACROSS THE EAST-CENTRAL
US TUE-THU DAYS 5-7 IN A DEVELOPING REX BLOCK SETUP AS WARMING
RIDGES BUILD STRONGLY UPSTREAM OVER THE WRN US AND OVERTOP OVER
S-CENTRAL CANADA.  THIS OCCURS AS A LEAD NERN US/CANADIAN MARITIME
CLOSED LOW LOSES INFLUENCE.  SLOW/WRAPPED SYSTEM TRANSLATION AND
INCREASINGLY DEEP MOISTURE INFLUX FROM THE GULF OF MEXICO THEN WRN
ATLANTIC WILL FUEL A WIDESPREAD CONVECTIVE AND OVERRUNNING HEAVY
TO EXCESSIVE RAINFALL THREAT SPREADING SLOWLY ACROSS THE
EAST-CENTRAL TO ERN US AS DEPICTED ON RECENT/UPCOMING WPC MEDIUM
RANGE DAYS 4-7 QPF PROGS.

...GUIDANCE/UNCERTAINTY ASSESSMENT...

THE WPC MEDIUM RANGE GUIDANCE SUITE HAS BEEN PRIMARILY DERIVED
FROM A COMPOSITE BLEND OF THE GFS/ECMWF/CANADIAN AND GFS/ECMWF
ENSEMBLE MEANS ALONG WITH WPC/NDFD CONTINUITY DAYS 3-5 SUN-TUE.  A
FORECAST PLAN BASED CLOSEST TO THE 12 UTC ECMWF ENSEMBLE MEAN AND
TO LESSER DEGREE THE 12 UTC ECMWF WAS INVOKED DAYS 6/7 TO MAINTAIN
MAX PATTERN AMPLITUDE/IDENTITY THAT SEEMS WELL SUPPORTED BY
LEAD-IN WATER VAPOR LOOP IMAGERY.

CONSIDERING THE CLOSED/BLOCKY NATURE OF THE MAIN WEATHER FEATURES
AND THREATS AS DESCRIBED ABOVE...GUIDANCE OVERALL REMAINS WELL
CLUSTERED WITH FORECAST CONFIDENCE ABOVE NORMAL.  A NOTABLE
EXCEPTION WAS EVIDENT FROM THE ERN PACIFIC INTO WRN NOAM DAYS 6/7
AS THE 12 UTC GFS AND GEFS/CANADIAN/NAEFS ENSEMBLE MEANS WERE
SIGNIFICANTLY FASTER TO BRING AMPLE PACIFIC MID-UPPER LEVEL TROUGH
ENERGY INLAND THROUGH THE AMBIENT WRN US RIDGE THAN THE 12 UTC
ECMWF/CANADIAN/ECMWF ENSEMBLE MEAN.   WE SEE MINIMAL COMPELLING
REASON TO CRASH THE AMPLIFIED RIDGE IN A BLOCKY PATTERN AND MORE
RECENT 18/00 UTC GFS AND 00 UTC ECMWF TRENDS BLEND WELL INTO THE
WPC BLENDED SOLUTION.

SCHICHTEL


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