Prognostic Meteorological Discussion
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FXUS02 KWBC 061559
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1159 AM EDT WED MAY 06 2015

VALID 12Z SAT MAY 09 2015 - 12Z WED MAY 13 2015

...OVERVIEW...
THE FLOW PATTERN ALOFT APPEARS TO BE IN TRANSITION EAST OF THE
DIVIDE AND SOUTHEAST CANADA THIS MEDIUM RANGE PERIOD. A
HIGHLY-AMPLIFIED TROUGH PATTERN ACROSS EASTERN NORTH AMERICA---AND
SPECIFICALLY A PATTERN THAT HAS PERSISTED ACROSS SOUTHEAST
CANADA-NEW ENGLAND---WILL MAINTAIN A WESTERLY FLOW ALOFT---AND A
DISTINCT SEPARATION---FROM TWO UPPER-LEVEL CUTOFF CIRCULATIONS
BETWEEN 30N AND 40N LATITUDE.

IN THE WEST...THE EASTWARD MIGRATION OF A SLOW-MOVING UPPER-LEVEL
TROUGH CURRENTLY SOUTH OF THE ALEUTIANS---SHOULD DICTATE THE
EVOLVING PATTERN AND ONSHORE FLOW `SEQUENCING` ACROSS THE WEST
COAST OF NORTH AMERICA.

...MODEL PREFERENCES...
HAD NO ISSUE WITH USING A BLEND OF THE 6/00Z ECENS/NAEFS MEANS FOR
THE ENTIRE PERIOD FROM WEST TO EAST---AND CONSIDERING THE
COMPLEXITIES OF THE FLOW PATTERN ACROSS THE LOWER 48---THE 6/00Z
DETERMINISTIC ECMWF/GFS WERE DECENT PIECES OF MODEL GUIDANCE
THROUGH DAY 4 (11/00Z). THIS SHOULD ALLOW A DISTURBANCE ALONG THE
EAST COAST OF FLORIDA TO SLOWLY MIGRATE NORTHWARD INTO THE
CAROLINAS AT/BEYOND DAY 3.

THE MODEL DIFFERENCES IN THE WEST AND NORTHERN PLAINS AFTER DAY
4---CONCERN THE TRANSFER OF MID-LEVEL ENERGY BETWEEN TWO PROMINENT
MID-LEVEL CYCLONES. LEANED A TAD CLOSER TO THE DETERMINISTIC ECMWF
INTO DAY 5---FROM OREGON EASTWARD INTO SOUTHERN WYOMING.

...UNCERTAINTY ASSESSMENT...
ALONG THE EAST COAST---PREFER SOMETHING THAT RESEMBLES A SLOWER
SOLUTION AT THE SURFACE---WITH THE IDEA THAT THE SOUTHEAST COAST
CLOSED UPPER-LEVEL SYSTEM REMAINS DETACHED/SEPARATED FROM THE
PREVAILING NORTHERN STREAM FLOW PATTERN. THIS THOUGHT PROCESS
WOULD LEND TO A BROAD CYCLONIC CIRCULATION THAT ALLOWS FOR A
SERIES OF MID-LEVEL WAVES (AND EMBEDDED CONVECTIVE ELEMENTS)
ROTATE ONSHORE IN A COUNTER-CLOCKWISE FASHION VERSUS A TRUE
`VERTICALLY-STACKED` CYCLONE. A DAY 5-6 FRONTAL PROGRESSION SHOULD
BEGIN HAVING SOME IMPACT ON THE SOUTHEAST UPPER-LEVEL SYSTEM`S
MIGRATORY TRACK---ON OR JUST AFTER DAY 5. OF NOTE---DID HAVE A
CONVERSATION WITH NHC REGARDING THE EVOLVING SYSTEM---AND PLEASE
FOLLOW NHC FOR ADDITIONAL INFORMATION THIS EVOLVING SYSTEM.
VOJTESAK

...SENSIBLE WEATHER HIGHLIGHTS...
THE COOLER THAN AVERAGE WEST AND WARMER THAN AVERAGE EAST PATTERN
WILL SHIFT EASTWARD IN TIME THIS PERIOD. RECORD MAX OR HIGH MIN
TEMPS MAY BE POSSIBLE AHEAD OF THE SFC FRONT. PRECIPITATION WILL
FOCUS AROUND AND DOWNSTREAM OF THE EXITING CLOSED LOW FROM THE
FOUR CORNERS REGION -- CENTRAL ROCKIES/PLAINS SOUTHWARD AND THEN
NORTHEASTWARD TOWARD THE GREAT LAKES. GEFS REFORECAST DATA SHOWS
NE COLORADO INTO WESTERN AND CENTRAL NEBRASKA IN THE 99.5
PERCENTILE -- M-CLIMATE RELATIVE -- WHICH LINES UP WITH THE ECMWF
AND ECENS MEAN RELATIVE MAX QPF AMOUNTS. NEXT TROUGH INTO THE PAC
NW EARLY NEXT WEEK WILL BRING SOME SHOWERS TO WA/OR/ID AND
NORTHERN CA/NV. ALONG THE CAROLINA COAST... MODELS CONTINUE TO BE
ALL OVER THE PLACE FROM SEVERAL TENTHS OF AN INCH OF RAIN TO
SEVERAL INCHES OF RAIN... SOME OFFSHORE AND SOME INLAND. WILL
CONTINUE TO BE SUSPICIOUS OF ANY ONE RUN AND WILL FOLLOW THE
ENSEMBLES UNTIL THIS IS BETTER RESOLVED... PROBABLY IN THE SHORT
RANGE. FRACASSO



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