Prognostic Meteorological Discussion
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FXAK02 KWNH 311905
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
203 PM EST SAT JAN 31 2015

VALID 12Z WED FEB 04 2015 - 12Z SUN FEB 08 2015

VERY LITTLE CHANGE FROM THE PREVIOUS WPC MEDIUM RANGE FORECAST FOR
ALASKA.

THE LATTER HALF OF THIS PARTICULAR MEDIUM RANGE PERIOD---FEBRUARY
4-8---REMAINS AN ACTIVE PERIOD FOR THE GULF OF ALASKA---AND A
COLD/DRY PATTERN FOR MUCH OF THE INTERIOR. NOT AN UNFAMILIAR FLOW
PATTERN FOR THE NORTHEAST PACIFIC THIS WINTER---CHARACTERIZED BY
AN UPPER-LEVEL TROUGH ALONG 150W-160W...AND A SLOW...GRADUAL
`UNDERCUTTING` OF THE TROUGH AXIS---WITH FAST-WESTERLY FLOW
MIGRATING ACROSS THE MID-LATITUDE PACIFIC (THIS CURRENT
SCENARIO---BETWEEN 35N AND 45N). THE FLOW---STEERING A SERIES OF
MODERATELY-INTENSE SHORTWAVES TOWARDS THE PANHANDLE AND NORTHEAST
GULF OF ALASKA---THEN DIRECTING A HIGHLY-SHEARED PORTION OF THE
WAVE DOWNSTREAM INTO THE WEST COAST OF NORTH AMERICA.

THE FORECAST CHALLENGES WILL BE WITH THE DEPTH OF ONSHORE
FLOW---AS THE SURFACE CYCLOGENESIS REGION (INVOF 42N 140W) WILL BE
QUITE ACTIVE AND RATHER INTENSE AT TIMES. OWNING TO A MOISTURE
SOURCE ORIGINATING IN THE SUBTROPICS...A SERIES OF APPRECIABLY
MOIST WARM FRONTS WILL ATTEMPT TO MIGRATE NORTHWARD BETWEEN 130W
AND 140W---AND MODIFY SIGNIFICANTLY AS THEY ROTATE
COUNTERCLOCKWISE AROUND THE NORTHERN `RIM` OF THE GULF OF ALASKA.
NO PERFECT PROGS OUT THERE---EVEN WITH THE 31/00Z GEFS/ECENS MEANS
IN VERY GOOD AGREEMENT WITH THE AMPLITUDE OF THE WAVELENGTH.

THE BROAD FETCH OF ZONAL WESTERLY FLOW ALOFT---ALONG
35N-40N---WILL ATTEMPT TO SHEAR SOUTHEASTWARD--- `RE-DIRECTING`---
AREAS OF MODERATE-TO-HEAVY PRECIPITATION ALONG A VERY SLOW-MOVING
PACIFIC COLD FRONT. INITIALLY... ANTICIPATE THE BULK OF THE
PRECIPITATION TO MIGRATE INTO THE NORTHEASTERN GULF OF ALASKA AND
SOUTHWEST CANADA---THEN AS THE UPPER-LEVEL TROUGH BEGINS TO
MIGRATE AND `WOBBLE` SOUTHEASTWARD---THE BULK OF THE
CONCENTRATED...JET-DRIVEN PRECIPITATION---IS PROJECTED TO "STEER
AWAY" FROM THE SOUTHEAST COAST/PANHANDLE AND FOCUS ALONG THE
BC/WASHINGTON BORDER.

THE 31/00Z ECENS AND GEFS MEANS CONTINUE TO FEATURE THIS RATHER
`STABLE` UPPER-LEVEL PATTERN---WITH SOME OBVIOUS SPREAD IN THE
INDIVIDUAL SHORTWAVE DETAILS THAT BEGIN TO INTERACT WITH
DOWNSTREAM RIDGE. THESE TIMING/TRACK DIFFERENCES TIED TO INTENSITY
OF THE INDIVIDUAL SURFACE CYCLONE. THE FACT THAT THERE WILL BE A
SERIES OF RATHER INTENSE SURFACE CYCLONES EMERGING BENEATH THE
BASE OF THE UPPER-LEVEL TROUGH--- THE DETERMINISTIC RUNS CONTINUE
TO DIFFER ON LAT/LONG POSITION---AS EARLY AS DAY 4-5 ALONG
140W---WITH THE NORTHEASTWARD PROGRESSION OF THE INITIAL WARM
FRONT. THE WPC CURRENT GRAPHICS DID UTILIZE SOME ASPECTS OF THE
31/00 DETERMINISTIC ECMWF. ITS BEEN A RATHER CONSISTENT SOLUTION
IN THE CENTRAL AND NORTHEAST PACIFIC OVER THE LAST 3-4 DAYS WORTH
OF FORECAST CYCLES.

VOJTESAK

$$





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