Prognostic Meteorological Discussion
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FXAK02 KWNH 271814
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
213 PM EDT TUE SEP 27 2016

VALID 12Z SAT OCT 01 2016 - 12Z WED OCT 05 2016

A MODESTLY POSITIVE MID-LEVEL HEIGHT ANOMALY IS EXPECTED TO
PREVAIL OVER THE ALASKA MAINLAND DAYS 4-8 WHILE COMPENSATING
NEGATIVE MID LEVEL HEIGHT ANOMALIES DEVELOP OVER RUSSIA AND
BRITISH COLUMBIA. THE MAIN IMPACTS OF THIS PATTERN ARE GENERALLY
ABOVE NORMAL TEMPERATURES AND DRY CONDITIONS FOR THE MAINLAND WITH
MORE SEASONABLE TEMPERATURES AND PRECIPITATION ELSEWHERE...WHILE
THE PRIMARY SYSTEM TO MONITOR WILL BE A SURFACE LOW AND
ACCOMPANYING PRESSURE GRADIENT THAT ARE LIKELY TO AFFECT THE
WESTERN AND CENTRAL ALEUTIANS WITH STRONG WINDS/HIGH SEAS/HEAVY
RAIN DAY 4/SAT.

CONFIDENCE IN THE LOW AFFECTING THE ALEUTIANS AS DEPICTED BY
CURRENT GUIDANCE IN AROUND 70 PERCENT...WITH THE 00Z ECMWF MOST
CONSISTENT FROM RUN-TO-RUN AND WITH ITS HIGHER SPATIAL RESOLUTION
AND MORE SOPHISTICATED INITIALIZATION FAVORED OVER THE
COARSER-GRIDDED AND FASTER/WEAKER 00-06-12Z GFS. BY DAY
5/SUN...MODELS DIVERGE QUICKLY AS THE LOW ENCOUNTERS THE BLOCK
OVER THE MAINLAND AND SPLITS. HAVE THEREFORE MOVED QUICKLY TOWARD
THE ENSEMBLE MEANS WITH MODEL BLENDING USING A NEARLY EQUAL
DISTRIBUTION OF THE ENSEMBLE SYSTEMS THAT GENERALLY AGREE ON THE
RIDGE PORTION OF THE BLOCK CONTINUING OR SPREADING NORTHWARD FROM
THE MAINLAND ALONG WITH AN UPPER TROUGH CONTINUING OVER THE BERING
SEA. CONFIDENCE ON THE DAY-TO-DAY DETAILS FALLS BELOW AVERAGE BY
SUNDAY GIVEN THE GROWING SPREAD.

JAMES



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