Prognostic Meteorological Discussion
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FXAK02 KWNH 262026
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
326 PM EST SUN FEB 26 2017

VALID 12Z THU MAR 02 2017 - 12Z MON MAR 06 2017

AN IMPRESSIVE UPPER RIDGE WILL REMAIN THE DOMINANT FEATURE
INFLUENCING THE PATTERN ACROSS AK DURING THE FIRST WEEK OF MARCH.
RECENT GFS SOLUTIONS ADVERTISE 500-MB HEIGHT ANOMALIES IN THE 3 TO
4 SIGMA ABOVE AVERAGE RANGE. THIS DOMINANT SYSTEM IS FORECAST TO
BE CENTERED OVER THE BERING SEA AND INTO SIBERIA WHILE GRADUALLY
SLIDING WESTWARD IN TIME. TO THE EAST OF THE POSITIVE HEIGHT
ANOMALY...THE HIGHLY MERIDIONAL PATTERN WILL ALLOW A SERIES OF
SHORTWAVES TO DIVE SOUTHWARD ACROSS THE WESTERN HALF OF MAINLAND
AK AND INTO THE NORTHEAST PACIFIC. THESE SYSTEMS SEEM TO SQUEEZE
BETWEEN THE MEAN UPPER RIDGE TO THE WEST AND A CLOSED LOW
LINGERING ACROSS THE ARCTIC OCEAN. WHILE THERE ARE GENERAL
DIFFERENCES IN THE DETAILS WITH THIS PATTERN...THE LONGWAVE
PATTERN IS REASONABLY AGREED UPON. THIS IS IN STARK CONTRAST OF
WHAT WAS SEEN IN THE PAST FEW DAYS WHICH SAW DETERMINISTIC
SOLUTIONS AT ODDS WITH ONE ANOTHER. THE BIGGEST DIFFERENCE NOTED
WAS TOWARD THE END OF NEXT WEEKEND WHERE SPREAD BECAME EVIDENT
ALONG THE SOUTHWEST FLANK OF THE LONGWAVE TROUGHING. THIS
PRIMARILY AFFECTED THE POSITION OF THE UPPER TROUGH ACROSS THE
NORTHEAST PACIFIC ON DAY 7/8...MARCH 5/6 WHERE THE 12Z GFS WAS
WEST OF THE MODEL CONSENSUS.

GIVEN THE STRONGER DETERMINISTIC AGREEMENT...WAS ABLE TO MAINTAIN
SOME FRACTION OF SUCH MODELS THROUGH DAY 6/SATURDAY. THE GENERAL
APPROACH WAS TO UTILIZE 60 PERCENT OF THE 00Z ECMWF SUITE WITH THE
REMAINING PORTION OF THE BLEND DEDICATED TO THE 12Z GFS/06Z GEFS
MEAN. EACH DAY LOWERED THE INFLUENCE OF THE 12Z GFS/00Z ECMWF AS
UNCERTAINTIES IN THE FORECAST DETAILS BEGAN TO INCREASE. THE
RESULTANT PATTERN WILL FAVOR RATHER COLD TEMPERATURES ACROSS THE
STATE GIVEN THE INFLUENCE OF SURFACE HIGH PRESSURE ON THE SENSIBLE
WEATHER. SOME RATHER COLD OVERNIGHT LOWS ARE FORECAST ACROSS
NORTHERN/EASTERN AK WITH SOME MINIMA GOING BELOW -40 DEGREES
DURING THE PERIOD. IT SHOULD ALSO BE QUITE BREEZY AT
TIMES...PARTICULARLY EARLY IN THE FORECAST PERIOD WHERE MODERATE
EAST-SOUTHEASTERLY WINDS AFFECT THE WESTERN/CENTRAL ALEUTIANS. IN
TERMS OF PRECIPITATION...THE INFLUENCE OF CONTINENTAL ARCTIC AIR
MASSES SHOULD KEEP MUCH OF MAINLAND AK DRY ALTHOUGH THE 12Z GFS
WAS A TAD WETTER WITH THE SYSTEM DIVING THROUGH WESTERN AK ON
FRIDAY/SATURDAY. OTHERWISE...THE HIGHEST PROBABILITIES FOR
PRECIPITATION REMAIN OVER SOUTHEASTERN AK GIVEN THE PERSISTENT
NEGATIVE HEIGHT ANOMALIES IN THE NORTHEAST PACIFIC.


RUBIN-OSTER


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