Prognostic Meteorological Discussion
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FXUS02 KWBC 250625
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
224 AM EDT MON MAY 25 2015

VALID 12Z THU MAY 28 2015 - 12Z MON JUN 01 2015

...OVERVIEW...
SUMMER-LIKE CONDITIONS WILL PREVAIL ACROSS THE EASTERN PORTION OF
THE NATION BENEATH A DEEP-LAYERED RIDGE ANCHORING ACROSS THE
SOUTHEAST MOST OF THIS MEDIUM RANGE PERIOD -- WEDNESDAY THRU NEXT
SUNDAY. SPLIT-FLOW PATTERN IN THE EASTERN PACIFIC DOWNSTREAM FROM
A VERY BLOCKY/AMPLIFIED PATTERN ACROSS ALASKA --- SHOULD DIRECT
THE MAJORITY OF THE SENSIBLE WEATHER AND PRECIPITATION TOWARDS THE
PACIFIC NORTHWEST AND NORTHERN ROCKIES.

...MODEL PREFERENCES/UNCERTAINTY ASSESSMENT...
ALTHOUGH THE FLOW PATTERN ACROSS THE LOWER 48 IS TAKING ON A
SLOWER --- SUMMER-LIKE PROGRESSION AND APPROACH --- THE 24/12Z
ECENS...NAEFS AND GEFS MEANS HAVE A DECENT HANDLE ON THE FEATURES.
AND THOUGHT THEY WERE IN GOOD MASS FIELD AGREEMENT THROUGH DAY 5
(31/00Z). HAVE LEANED ON THE DETERMINISTIC ECMWF FOR SOME OF THE
DETAILS OVER THE PAST 3-4 DAYS --- AND THOUGH NOT A PERFECT PROG
--- IT`S RUN-TO-RUN CONTINUITY WITH THE KEY FEATURES OF THIS
PATTERN ---HAVE BEEN BETTER THAN ONE COULD REASONABLY EXPECT. AND
THIS PACKAGE --- WAS NO EXCEPTION WITH THE SMALLER-SCALE DETAILS
HEADING INTO DAY 6

THE MEANS GENERALLY DEPICT ---WITH SOME PRECISION --- THE
`UNDERCUTTING` OF THE QUASI-STATIONARY UPPER RIDGE OVER ALASKA AND
ITS MIGRATION ACROSS THE PACIFIC NORTHWEST AND NORTHERN ROCKIES
HEADING INTO DAY 5-6 TIME FRAME. LIKEWISE... I THOUGHT THE MEANS
WERE HANDLING THE NATURE OF THE RIDGE IN THE EAST AND THE
SLOW-MOVING EAST-NORTHEASTWARD MIGRATION OF THE SURFACE FRONT INTO
SOUTHEAST CANADA AND NEW ENGLAND (PRIMARILY THE DAY 3-4 PERIOD)
WITHOUT MUCH FANFARE --- WITH THE DETERMINISTIC ECMWF GENERALLY
CAPTURING THE OSCILLATION OF THE SHALLOW COLD ADVECTION SEQUENCE
(UNDERNEATH THE UPPER RIDGE) --- AND ITS IMPACTS ON TEMPERATURES
FOR THE NORTHEAST.

THE 24/12Z DETERMINISTIC ECMWF DID NOT OFFER MANY SURPRISES AND
THOUGHT IT GENERALLY FITS ITS MEAN IN THE GULF OF ALASKA --- IN
THE EAST CENTRAL PACIFIC --- AND OFF THE SOUTHWEST COAST OF MEXICO
(INVOF 110W LONGITUDE). THESE THREE AREAS SEEMED TO BE WHERE THE
SPLIT-FLOW HAS THE BEST CHANCE TO `INJECT` MOISTURE AND ENERGY
DOWNSTREAM --- AND ALTER THE FLOW PATTERN AND FORECAST ACROSS THE
LOWER 48 (IN THE DAY 6-7 AND D+8 TIME FRAMES).

...SENSIBLE WEATHER HIGHLIGHTS...
WARM/HOT AND MORE HUMID IN THE EAST WITH HIT-N-MISS AFTERNOON AND
EVENING AIRMASS POP-UP SHOWERS/THUNDERSTORM ACTIVITY. OVERNIGHT
TEMPS MAY BE CLOSE TO RECORD `HIGH MIN` VALUES. THE MORE ORGANIZED
AREAS OF PRECIPITATION WILL FOLLOW THE WEST THROUGH NORTHWEST
FLANKS OF THE MID-LEVEL RIDGE --- INCLUDING THE SOUTH CENTRAL
PLAINS... OZARKS... MID-MS & WESTERN OHIO VALLEYS AND EASTERN
LAKES/NORTHERN NEW ENGLAND --- WHERE THE MID-CONTINENT FRONT HAS A
PATHWAY TO MIGRATE IN NORTHEASTWARD FASHION TOWARDS THE ST
LAWRENCE VALLEY AND NORTHERN NEW ENGLAND.

CONVECTION SHOULD BE ON THE INCREASE ACROSS THE OKANAGAN REGION OF
BC/WA... THE NORTHERN DIVIDE... AND ADJACENT NORTHERN HIGH PLAINS
THIS MEDIUM RANGE PERIOD AS MID-LEVEL ENERGY MIGRATES SLOWLY
SOUTHEASTWARD FROM THE MOUNTAINS OF SOUTHWEST CANADA AND THROUGH
THE SOUTHERN ALASKA PANHANDLE.

ALONG THE WEST COAST THE SPLIT-FLOW PATTERN WILL PROVIDE A GRADUAL
WARMING/DRYING TREND ACROSS THE SOUTHWEST DESERTS AND INTERIOR
CALIFORNIA AND THE EMERGENCE OF A NORTHWARD-MOVING THERMAL TROUGH
COULD MAKE A BRIEF APPEARANCE ACROSS THE PACIFIC NORTHWEST TOWARDS
THE END OF THIS FORECAST PERIOD.

VOJTESAK

$$




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