Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1
000
FXAK02 KWNH 151913
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
212 PM EST FRI DEC 15 2017

VALID 12Z TUE DEC 19 2017 - 12Z SAT DEC 23 2017

...STRONG SYSTEM IN THE BERING SEA NEXT WEEK...WITH A SEPARATE LOW
MOVING NORTH TOWARDS THE UPPER ALEUTIANS LATE THIS WEEK...

THE MODELS AND ENSEMBLES INDICATE THE EARLY TO MIDDLE PARTS OF
NEXT WEEK ARE LIKELY TO SEE A CLOSED MID-UPPER LOW OVER THE
NORTHERN BERING SEA AND MID-UPPER LEVEL RIDGE OVER SOUTHEAST
ALASKA.

THE PATTERN EVOLUTION APPEARS TO BE ONE OR MORE WAVES ROTATE SOUTH
OF THE NORTHERN BERING CIRCULATION WITH LOW PRESSURE DEVELOPING
AND THEN CONSOLIDATING IN THE ALEUTIANS TO EASTERN BERING SEA WED
20 DEC -THU 21 DEC.
THE SPREAD REFLECTS DIFFERENCES OF WHERE LOW PRESSURE DEVELOPS
WITHIN THE UPPER TROUGH AXIS.  THE UNCERTAINTY IN HOW THE BERING
SEA EVOLVES TO THE WEST COAST OF AK IS HIGH, SO MANUAL PROGS USED
A 12-00Z ECMWF/06Z-12Z GFS/00Z ECMWF ENSEMBLE MEAN/06Z GEFS MEAN
BLEND NEXT THU-SAT.

THE GFS/ECMWF MODELS HAVE COME INTO BETTER AGREEMENT ON A FRONTAL
WAVE AHEAD OF THE BERING LOW MOVING NORTH FROM THE NORTHERN
PACIFIC TOWARDS THE LOWER ALEUTIANS.  THERE ARE TIMING DIFFERENCES
FROM RUN TO RUN AND MODEL TO MODEL.  THE 12Z ECMWF TRENDED FASTER
THAN ITS OLDER RUN WITH TH LOW NOW MOVING INTO THE UPPER ALEUTIANS
AROUND 00Z FRI 22 DEC...SO CONFIDENCE IS LOW GIVEN IT BROKE
CONTINUITY FROM ITS MEAN AND PRIOR 2 RUNS...WHICH WERE SEVERAL
HOURS SLOWER.

FOR DAYS 4-5, A BLEND OF THE DETERMINISTIC SOLUTIONS
(GFS/ECMWF/CANADIAN) OFFERED GOOD CONTINUITY WITH THE INTENSE
SYSTEM IN THE BERING AND ITS SLOW BUT STEADY FILLING OVER
NORTHEASTERN RUSSIA. STILL EXPECT ITS COLD FRONT TO PUSH INTO
WESTERN ALASKA AND THEN DISSIPATE AS IT ENCOUNTERS THE RIDGING AND
THE UPPER SUPPORT SLIDES NORTHEASTWARD INTO THE ARCTIC.


PETERSEN


$$





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