Prognostic Meteorological Discussion
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000
FXUS02 KWBC 241441
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1040 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 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 50 PERCENT BLEND OF THE GFS/ECMWF ENSEMBLE MEANS ALONG WITH
50 PERCENT WPC/NDFD CONTINUITY...
WITH CONTINUITY EMPHASIZED SIGNIFICANTLY UNTIL THE CLOSED LOWS AND
BLOCKING PATTERN DEVELOP AND PATTERN BECOMES MORE ESTABLISHED.
REGARDING THE DETERMINISTIC SOLUTIONS...A MIXTURE OF THE 00Z
GFS/ECMWF SHOULD SUFFICE THROUGH DAY 4/MON...WITH THE GFS THEN
DRIFTING TOWARD THE NORTHERN EDGE OF THE GUIDANCE ACROSS THE
PLAINS AND ECMWF BECOMING SUSPICIOUSLY AMPLIFIED WITH A SHORTWAVE
TROUGH AFFECTING THE NORTHEAST BY DAY 5/TUE.  WHILE INTERACTION OF
THIS SHORTWAVE TROUGH WITH THE CLOSED LOW IS POSSIBLE...THE EXTENT
TO WHICH THE RECENT ECMWF SUGGESTS SEEMS UNLIKELY GIVEN THEIR
SPACING.  ALSO...BY DAY 7/THU THE 00Z GFS IS CONSIDERED AN OUTLIER
WITH A SHORTWAVE TROUGH AGGRESSIVELY LOWERING HEIGHTS ACROSS THE
PACIFIC NORTHWEST.

SCHICHTEL/JAMES


$$




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