Prognostic Meteorological Discussion
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FXAK02 KWNH 202018
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
318 PM EST FRI JAN 20 2017

VALID 12Z TUE JAN 24 2017 - 12Z SAT JAN 28 2017

...WET PERIOD IN STORE FOR MUCH SOUTHERN TO SOUTHEASTERN AK...

A MEAN UPPER RIDGE ALONG THE WEST COAST OF NORTH AMERICA WILL BE
THE MOST PERSISTENT FEATURE TO BASE THE FORECAST ON. UPSTREAM OF
THIS POSITIVE HEIGHT ANOMALY...INITIALLY AMPLIFIED FLOW WILL
GRADUALLY FLATTEN BY 25/0000Z LEADING TO A SHORTER WAVELENGTH
BETWEEN INDIVIDUAL IMPULSES. THE LEAD SHORTWAVE AND ITS ASSOCIATED
DEEP SURFACE CYCLONE SHOULD CROSS THE CENTRAL ALEUTIANS BY
WEDNESDAY MORNING WITH ADDITIONAL SUCH LOWS TRACKING ACROSS THE
NORTHEASTERN PACIFIC THROUGHOUT THE PERIOD. THROUGH DAY 5...THE
12Z GFS AND 00Z ECMWF/CMC AFFORD A REASONABLE SOLUTION TO UTILIZE
BEFORE SPREAD BEGINS TO INCREASE. WHILE CONFIDENT IN THE GENERAL
DETAILS OF THE UPPER RIDGE ALONG WESTERN NORTH AMERICA...THERE ARE
ENOUGH DETAIL DIFFERENCES IN THE UPSTREAM FLOW TO MIGRATE TOWARD
AN ENSEMBLE PATH. GIVEN SOMEWHAT SIMILAR FORECASTS...TOOK A SPLIT
BETWEEN THE 06Z GEFS AND 00Z ECMWF/NAEFS ENSEMBLE MEANS TO
CONCLUDE THE PERIOD.

THE CONTINUED CASCADE OF SHORTWAVE ENERGY MOVING FROM THE
ALEUTIANS TO SOUTHEASTERN AK WILL MAINTAIN A WET PATTERN OVER THIS
REGION. THIS IS PARTICULARLY THE CASE BETWEEN 24/1200Z AND
25/1200Z AS THE AFOREMENTIONED DEEP WAVE MOVES ACROSS THE CENTRAL
ALEUTIANS. LOOKING AT TEMPERATURE TRENDS...THERE WILL BE A MARKED
WARM UP COMPARED TO RECENT DAYS. LOWS ACROSS NORTHERN AK WHICH ARE
FORECAST TO BE IN THE -20S TO -30S WILL REBOUND TO THE NEGATIVE
SINGLE DIGITS BY LATE NEXT WEEK.


RUBIN-OSTER

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