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FXUS02 KWNH 210658
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT MON APR 21 2014

VALID 12Z THU APR 24 2014 - 12Z MON APR 28 2014

...GUIDANCE PREFERENCES/UNCERTAINTY ASSESSMENTS...

THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A
COMPOSITE BLEND OF THE 18 UTC GFS/GFS ENSEMBLE MEAN AND 12 UTC
ECMWF AND ECMWF/NAEFS ENSEMBLE MEANS DAYS 3-5/THU-SAT.  FORECAST
SPREAD AND UNCERTAINTY REMAINS SLIGHTLY LOWER THAN NORMAL
NATIONALLY...ALBEIT WITH HARD TO DIAGNOSE SMALLER SCALE
SYSTEM/INTERACTION VARIANCE LOCALLY.  PREFER A 18 UTC GEFS MEAN
AND 12 UTC NAEFS/ECMWF ENSEMBLE MEANS BASED FORECAST APPROACH DAYS
6-7 NEXT SUN/MON IN LUE OF EMBRACING ANY PARTICULAR DETERMINISTIC
MODEL IN A PERIOD WITH STEADILY GROWING FORECAST
SPREAD/UNCERTAINTY.

THIS WPC SOLUTION OVERALL NOW LEANS SLIGHTLY MORE IN THE DIRECTION
OF AMPLITUDE COMPARED TO WPC CONTINUITY FOLLOWING PRONOUNCED
ENSEMBLE MEAN TRENDS AND FAVORABLE PACIFIC AND NORTH AMERICAN
WATER VAPOR IMAGERY LOOPS.

...PATTERN OVERVIEW AND SENSIBLE WEATHER HIGHLIGHTS...

A STRONG MID-UPPER LEVEL TROUGH AND DEEP SURFACE SYSTEM AMPLIFIES
OFF THE NERN US/CANADIAN MARITIMES INTO THU AFTER SHORT RANGE
PASSAGE OFFSHORE...WITH WINTERY PCPN WRAPPING BACK INTO NRN NEW
ENG AS THE EAST COOLS WITH POST-FRONTAL HIGH PRESSURE.

MEANWHILE...QUITE AMPLIFIED MID-UPPER LEVEL TROUGH/POTENT HEIGHT
FALLS WORKS OUT FROM THE WEST TO STEADILY CROSS THE CENTRAL THEN
ERN US THU-NEXT SUN BEFORE SHIFTING OFFSHORE. THIS SHOULD SET THE
STAGE FOR A WELL ORGANIZED LOW/FRONT TO DEVELOP AND INCREASINGLY
FOCUS MOISTURE/PCPN ALONG WITH POST-FRONTAL COOLING.  HEAVIEST
PCPN POTENTIAL SEEMS CLOSER TO THE MAIN LOW TRACK ACROSS THE
N-CENTRAL US...BUT DYNAMIC SUPPORT/MOISTURE RETURN/INSTABILITY
OFFERS AN ADDITIONAL HEAVY CONVECTIVE SPARK DOWN OVER THE
S-CENTRAL AS PER SPC AND TO A LESSER EXTENT THEN SPREAD ACROSS THE
ERN US.

UPSTREAM...EXPECT ANOTHER DYNAMIC MID-UPPER LEVEL TROUGH AND
SURFACE SYSTEM WITH ENHANCED PCPN FOR THE US WEST COAST BY FRI IN
WPC PROGS.  THIS SYSTEM IS KICKED INLAND ACROSS AN
UNSETTLED/COOLING WRN US BY ADDITIONAL ERN PACIFIC ENERGIES AND
MAY WORK ACROSS THE PLAINS NEXT SUN/MON IN A DEVELOPING RETURN
FLOW CONVECTIVE PATTERN.

SCHICHTEL





$$






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