Prognostic Meteorological Discussion
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FXAK02 KWNH 301958
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
357 PM EDT TUE AUG 30 2016

VALID 12Z SAT SEP 03 2016 - 12Z WED SEP 07 2016

ON SATURDAY MORNING...THE INITIAL SYNOPTIC SETUP FEATURES A BROAD
UPPER LOW JUST WEST OF THE ALEUTIANS WHILE A CLOSED RIDGE EXTENDS
OVER THE CHUKCHI SEA. FARTHER DOWNSTREAM...A MEAN TROUGH IS SET UP
OVER THE NORTH POLE WITH A CASCADE OF SHORTWAVES SINKING SOUTHWARD
INTO THE YUKON TERRITORY AND NORTHWEST TERRITORIES. ONE OF THE
MORE UNCERTAIN ASPECTS OF THE FORECAST IS RESOLVING EACH OF THESE
IMPULSES AS THEY SKIRT NORTHEASTERN/EASTERN AK. CURRENTLY THE 00Z
ECMWF AND ITS ENSEMBLE MEMBERS ARE MORE AMPLIFIED COMPARED TO THE
MORE CONSERVATIVE GFS/CMC/NAEFS SOLUTIONS. LOOKING CLOSER TO THE
AK FORECAST DOMAIN...THE BIG SYSTEM OF INTEREST IS THE SLOW MOVING
UPPER LOW WHICH IS FORECAST TO TRACK ALONG THE ALEUTIANS. AT FIRST
GLANCE...THE 00Z ECMWF SOLUTION APPEARED TO BE ON THE SLOWER SIDE.
HOWEVER...THE 12Z GFS EVENTUALLY DID SHIFT WESTWARD WHICH BROUGHT
IT CLOSER TO THE ECMWF FORECAST. REGARDLESS OF TIMING...THE
PATTERN FAVORS A RATHER WET PATTERN FOR SOUTHEASTERN AK GIVEN THE
INCREASE IN WESTERLY ONSHORE FLOW. WHILE THERE IS SOME VARIANCE IN
THE EASTWARD EJECTION OF THIS SYSTEM...FURTHER UNCERTAINTY LOOMS
UPSTREAM WITH THE NEXT SHORTWAVE. MODELS DEPICT SOME SORT OF
CUT-OFF LOW OVER SIBERIA WHICH ATTEMPTS TO DIP SOUTHWARD WITHIN
THE BROAD MID-LEVEL CYCLONIC FLOW. MODEL-TO-MODEL DIFFERENCES
PRECLUDE ANY USE OF DETERMINISTIC SOLUTIONS AT THAT POINT.
OVERALL...FELT THE 12Z GFS/00Z ECMWF WAS A REASONABLE STARTING
POINT FOR DAY 4/SATURDAY BEFORE LEANING MORE TOWARD THE 00Z ECMWF
SUITE. FOR THE REMAINDER OF THE PERIOD...UTILIZED APPROXIMATELY 75
PERCENT OF THE 00Z ECMWF/ECMWF ENSEMBLE MEAN COMBINATION WHILE
INCORPORATING A QUARTER OF THE 00Z NAEFS MEAN TO ACCOUNT FOR
PATTERN UNCERTAINTIES. GROWING SYNOPTIC-SCALE DIFFERENCES LED TO
FULL USE OF ENSEMBLE MEANS BY DAY 7/TUESDAY.


RUBIN-OSTER

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