Prognostic Meteorological Discussion
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FXAK02 KWNH 242009
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
308 PM EST FRI FEB 24 2017

VALID 12Z TUE FEB 28 2017 - 12Z SAT MAR 04 2017

THE DOMINANT FEATURE DURING THE PERIOD WILL BE AN EXPANSIVE UPPER
RIDGE WHICH SHOULD GRADUALLY RETROGRADE WESTWARD LATER NEXT WEEK.
STANDARDIZED ANOMALIES FROM THE GFS/ECMWF SHOW 500-MB HEIGHTS IN
THE 2 TO 3 SIGMA BELOW AVERAGE RANGE GENERALLY CENTERED OVER THE
BERING SEA. HOW THIS RIDGE BEHAVES AND FLATTENS THROUGHOUT THE
PERIOD IS ONE OF THE MORE UNCERTAIN ASPECTS OF THE FORECAST. MUCH
OF THIS REVOLVES AROUND A BAND OF HEIGHT FALLS MOVING OUT OF
SIBERIA WITH SOLUTIONS DEPICTING A PAIR OF SCENARIOS.
FURTHER...THE PAST SEVERAL RUNS OF THE GFS AS WELL AS THE 00Z
UKMET ARE MORE AMPLIFIED WHICH HELPS BREAK DOWN THE NORTHERN
EXTENT OF THIS BERING SEA RIDGE. ON THE CONTRARY...THE 00Z
ECMWF/CMC ARE LESS AGGRESSIVE AND HELP MAINTAIN THE PRESENCE OF
THIS RIDGE FOR MUCH OF THE PERIOD. HOW THIS OCCURS HAS LARGE
IMPACTS ON THE RESULTANT FLOW AND TIMING OF FEATURES CIRCULATING
AROUND THE UPPER HIGH. EVALUATING THE 50 ECMWF ENSEMBLE
MEMBERS...THERE APPEARED TO BE DECENT CONSISTENCY AMONG THESE
SOLUTIONS WHICH BOOSTED CONFIDENCE IN ITS FORECAST.
ADDITIONALLY...GIVEN THE POSITIVE HEIGHT ANOMALIES IN
PLAY...BELIEVE THE RIDGE MAY STAY INTACT LONGER THAN THE GFS/CMC
WERE INDICATING. CONSEQUENTLY...A CASCADE OF SHORTWAVES SHOULD
CONTINUE TO SWEEP SOUTHWARD ACROSS THE AK AND EVENTUALLY INTO THE
NORTHEASTERN PACIFIC. THIS WILL ENSURE A DRIER PATTERN ACROSS THE
REGION WITH BELOW AVERAGE TEMPERATURES INFILTRATING THE STATE. THE
BEST CHANCE FOR PRECIPITATION SHOULD BE ACROSS SOUTHEASTERN AK
WHERE ACCUMULATING SNOWS ARE LIKELY. THE CORRESPONDING GRIDS WERE
CREATED BY A COMBINATION OF THE 06Z GFS/00Z ECMWF GLOBAL SUITES
WITH MUCH STRONGER EMPHASIS ON THE LATTER GIVEN THE HANDLING OF
THE INTERACTION OF THE SIBERIAN SHORTWAVES WITH THE STOUT UPPER
RIDGE.


RUBIN-OSTER


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