Prognostic Meteorological Discussion
Issued by NWS

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FXUS02 KWBC 011553
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1152 AM EDT MON JUN 01 2015

VALID 12Z THU JUN 04 2015 - 12Z MON JUN 08 2015

...OVERVIEW...
UPPER-FLOW PATTERN `RESHUFFLE` AT HIGH LATITUDE `COMMENCES` THIS
MEDIUM RANGE PERIOD. ACROSS THE NORTH AMERICAN CONTINENT ---
TROUGH EMERGES OVER EASTERN CANADA AND AN UPPER-LEVEL RIDGE
EMERGES OVER WESTERN CANADA.

FOR THE LOWER 48 --- THE WEATHER PATTERN FOCUS WILL BE IN THE
SOUTHWEST --- WITH ENERGY `UNDERCUTTING` THE WESTERN CANADA UPPER
RIDGE --- PRODUCING AN ACTIVE CUTOFF LOW --- THAT MIGRATES SLOWLY
FROM CALIFORNIA TO THE GREAT BASIN. A PROMINENT SHORTWAVE RIDGE
WILL PREVAIL ALONG 100W FORCING CONFINING CONVECTIVE INITIATION IN
A MORE SEASONAL "HIGH PLAINS/LEE OF THE ROCKIES" CONFIGURATION.

...UNCERTAINTY ASSESSMENT...
CRUCIAL TIME FRAME AND MEDIUM RANGE FORECAST CHALLENGE WILL OCCUR
BETWEEN DAYS 4-5 --- OVER THE MISSOURI VALLEY --- WHEN THE
NORTHWEST FLOW ASSOCIATED WITH THE EMERGING EASTERN CANADA TROUGH
MIGRATES INTO THE US. AS MENTIONED IN THE PREVIOUS PMDEPD --- THE
DAY 8+ ANOMALY IS SHOWING THE AMPLIFIED PATTERN "WE HAVE BECOME
FAMILIAR WITH" --- RETURNING TO NORTH AMERICA BY PERIOD`S END.

IN THE EAST---THE CHALLENGE WILL BE EARLY IN THE PERIOD --- WITH A
SLOW-MOVING MID-LEVEL SHORTWAVE THAT MEANDERS OVER CENTRAL AND
SOUTHERN APPALACHIA.

IN THE WEST---THE FORECAST SHOULD BE STRAIGHT-FORWARD EARLY IN THE
PERIOD UNTIL DAY 5 --- THEN QUESTIONS ARISE WITH THE PROJECTED
PATH AND `CHARACTER` OF THE CUTOFF ONCE IT REACHES THE CENTRAL
GREAT BASIN (INVOF CENTRAL UTAH/EAST CENTRAL NEVADA).

...MODEL PREFERENCES...
THE 1 JUNE/00Z MODEL CYCLE WAS A REASONABLE FORECAST SOLUTION AND
SOME ASPECTS OF THE DETERMINISTIC GUIDANCE COULD BE RELIED UPON
HEADING INTO EARLY DAY 6 --- THOUGH THE ECENS/NAEFS MEANS WILL BE
THE PREFERRED FORECAST APPROACH FOR THE ENTIRE PERIOD.

THE DETERMINISTIC APPROACH HAS ITS WEAKEST MOMENTS OVER THE
NORTHERN DIVIDE ON DAY 3 --- AND IN SHORT --- WITH THE SHEARING
OUT OF ENERGY DOWNSTREAM ACROSS THE DAKOTAS FOR DAY 4 INTO THE
EASTERN CANADA TROUGH. WHAT WOULD BE `PREFERRED` IS FOR THIS
`EASTWARD-MIGRATING` ENERGY TO FORM AN `MCS-TYPE` SYSTEM OVER
NORTHEAST WYOMING/EASTERN MONTANA---THEN HAVE IT SWEEP OVER THE
UPPER-LEVEL RIDGE AND HEAD EAST-SOUTHEASTWARD INTO THE MIDWEST.
THAT WOULD BE A `TYPICAL` EARLY JUNE NOCTURNAL PRECIPITATION
PATTERN FOR THE PLAINS. BUT AM NOT QUITE SURE AT A DAY 4-5 TIME
SCALE--- I COULD PIN-POINT THE EXACT PLACE WHERE CONVECTIVE
INITIATION TAKES PLACE AND THE `NEXT` MCS ROLLS OUT. WOULD SUGGEST
(FROM PERSONAL EXPERIENCE/OBSERVATION)--- THE 1/00Z GFS IS THE
FASTER SOLUTION OVER CENTRAL CANADA ON DAY 3-4 AND THAT WOULD
POSSIBLY GENERATE FORECAST `FLIP-FLOP` DOWN THE ROAD---THAT FOR
NOW --- IS NOT WORTH THE TROUBLE. FOR ITS THAT FASTER APPROACH ---
THAT REALLY QUESTIONS WHAT THE EASTERN CONUS TROUGH LOOKS LIKE AT
DAY 7---AND THE GFS LOOKS VERY DIFFERENT VERSUS THE ECMWF. ALL THE
RESULT OF A SHORTWAVE THAT UNDERCUTS THE RIDGE IN THE ALASKA
PANHANDLE

...SENSIBLE WEATHER HIGHLIGHTS...
VERY MUCH A SUMMER `LOOK` TO THE PRECIPITATION DISTRIBUTIONS
NATION WIDE --- WITH CONVECTIVE FOCUS ACROSS THE NORTHERN PLAINS
AND INTERMOUNTAIN WEST DURING THE AFTERNOON AND EVENING HOURS. AS
IS THE CASE IN EARLY JUNE--- EXPECT THE OCCASIONAL ORGANIZED
CLUSTER OF SHOWERS AND THUNDERSTORMS TO MIGRATE DOWNSTREAM OF THE
ROCKIES AND WEAKEN AS THEY MOVE INTO THE MISSOURI AND UPPER
MISSISSIPPI VALLEYS.

THE EXCEPTIONS --- ALONG THE WEST COAST WITH THE PACIFIC `FRONT`
AND UPPER-LEVEL CUTOFF MOVING INLAND. AND ALONG THE SOUTHEAST
COAST --- WITH RESIDUAL FRONTAL BOUNDARY MOISTURE AND WEAK SURFACE
TO MID-LEVEL WAVE ENERGY GENERATING SOME ORGANIZED RAINFALL INVOF
THE CAROLINAS AND DELMARVA.

VOJTESAK

$$




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