Prognostic Meteorological Discussion
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FXAK02 KWNH 051859
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 PM EST THU MAR 05 2015

VALID 12Z MON MAR 09 2015 - 12Z FRI MAR 13 2015

THE MEDIUM RANGE FORECAST STARTS OUT WITH A PROGRESSIVE FLOW
PATTERN ALOFT OVER NORTHEAST SIBERIA AND EASTWARD ACROSS THE
ARCTIC CIRCLE PORTION OF ALASKA. BUT BY DAY 5
(10/12Z-11/00Z)---THE PATTERN ALOFT BEGINS TO BREAK DOWN---WITH
THE DETERMINISTIC GUIDANCE HAVING SOME TROUBLE HANDLING THE
AMPLITUDE OF THE 500MB WAVE MIGRATING ACROSS THE PANHANDLE AND
DOWNSTREAM INTO WEST CENTRAL CANADA. IN THE WAKE OF THIS MID-LEVEL
ENERGY---THE PATTERN ATTEMPTS TO AMPLIFY---WITH A LARGE
UPPER-LEVEL RIDGE BUILDING ALONG THE DATELINE FROM THE WESTERN
ALEUTIANS INTO NORTHEAST SIBERIA. THERE IS SOME VARIANCE WITH
RESPECT TO THE AMPLITUDE OF THE UPPER-LEVEL RIDGE AND THE
CORRESPONDING DOWNSTREAM AMPLITUDE OF A MIGRATORY TROUGH AXIS
BETWEEN 140W-160W. THIS WILL BE THE FORECAST CHALLENGE FOR THE
NEXT SEVERAL DAYS--- IN THAT---A CUTOFF 500MB LOW FORMING NEAR THE
BASE OF THE TROUGH AXIS---INVOF OF 40N-45N AND 160W---WILL HAVE
ROOM TO `SPLIT` AND MIGRATE EASTWARD AND/OR EJECT ENERGY
NORTHEASTWARD INTO THE EASTERN GULF OF ALASKA.

WITH THE ENSEMBLE SPREAD BEING VERY HIGH---ALONG 150W BY DAY 8---I
OPTED TO FOLLOW THE 5/00Z ECENS/NAEFS MEANS WITH THE MEDIUM RANGE
GRAPHICS. THESE CHOICES DID NOT ALTER CONTINUITY AND
MINIMALLY-CHANGED THE PREVIOUS SET OF WPC PRODUCTS FOR ALASKA.

VOJTESAK

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