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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