Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1
000
FXAK02 KWNH 231955
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 PM EST THU FEB 23 2017

VALID 12Z MON FEB 27 2017 - 12Z FRI MAR 03 2017

MODELS ARE IN GENERAL AGREEMENT IN THE LARGE SCALE PATTERN, WHERE
THE ANOMALOUS BLOCKING UPPER RIDGE SOUTH OF ALASKA WILL BEGIN TO
RETREAT SOUTHWARD DURING THE MEDIUM RANGE AS AN ANOMALOUS UPPER
TROUGH AMPLIFIES OVER THE STATE. MEANWHILE, A BLOCKING RIDGE WILL
BUILD OVER THE BERING SEA AND NORTHEASTERN ASIA. BETWEEN THE TWO
RIDGES SLIGHTLY NEGATIVE HEIGHT ANOMALIES WILL PERSIST ACROSS MUCH
OF MAINLAND ALASKA THROUGH MUCH OF NEXT WEEK. THE ONE EXCEPTION
WILL BE THE WEST COAST WHICH MAY KEEP SOME INFLUENCE FROM THE
BUILDING RIDGE OVER NORTHEASTERN ASIA. MODELS SHOW SOME
DIFFERENCES WITH RESPECT TO THE TIMING AND AMPLITUDE OF THE ENERGY
CROSSING ALASKA BETWEEN THE RIDGES. SPECIFICALLY, THERE HAVE BEEN
VARYING DEGREES OF PHASING BETWEEN THE TROUGH/UPPER LOW ACROSS
ALASKA MON NIGHT/TUES AND THE CUTOFF LOW FARTHER SOUTH IN THE
NORTH PACIFIC. THE 12Z GFS WAS AN IMPROVEMENT OVER ITS 06Z RUN,
AND JOINED THE ENSEMBLE MEANS AND THE 00Z ECMWF IN SHOWING LESS
PHASING AND KEEPING THE STREAMS MORE SEPARATE. WPC FAVORED A BLEND
OF THE 06Z GEFS/00Z ECMWF ENS MEANS ALONG WITH THE 12Z GFS AND 00Z
ECMWF, WITH MORE WEIGHT ON THE DETERMINISTIC SOLUTIONS INITIALLY
AND THEN ON THE ENSEMBLE MEANS AFTER DAY 6.

THE IMPLICATIONS IN TERMS OF SENSIBLE WEATHER IMPACTS ACROSS
ALASKA AS A RESULT OF THIS PATTERN ARE GENERALLY COLD AND DRY
CONDITIONS FOR MUCH OF THE STATE. THE LOW HEIGHTS ACROSS THE STATE
SHOULD SUPPORT 850 HPA TEMPS 1 TO 3 STANDARD DEVIATIONS BELOW
AVERAGE BETWEEN NEXT TUES AND FRI. ADDITIONALLY, PWAT ANOMALIES
WILL BE 1 TO 2 STANDARD DEVIATIONS BELOW AVERAGE THROUGH MOST OF
THE MEDIUM RANGE. THE EXCEPTION WILL BE THE ALASKA PANHANDLE,
WHERE PWATS WILL BE NEAR OR SLIGHTLY ABOVE CLIMATOLOGICAL NORMS,
AND MOISTURE FLUX MAY BE ENHANCED AS THE MID/UPPER TROUGH DIGS AND
POTENTIALLY CLOSES OFF IN THE GULF OF ALASKA. THE MOST SIGNIFICANT
FLUX OF MOISTURE COULD POTENTIALLY REACH THE PANHANDLE DURING DAYS
7-8 / NEXT THUR AND FRI, INDICATING THE POTENTIAL FOR HEAVY
PRECIPITATION.

RYAN


$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.