Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2
000
FXAK02 KWNH 161942
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
242 PM EST SAT DEC 16 2017

VALID 12Z WED DEC 20 2017 - 12Z SUN DEC 24 2017

DETERMINISTIC AND ENSEMBLE GUIDANCE ARE SHOWING GOOD AGREEMENT
THAT STRONG UPPER RIDGING BUILDING IN THE EAST/NORTHEAST PACIFIC
WILL EXTEND NORTHWARD INTO THE ALASKA REGION DURING THE LATER HALF
OF NEXT WEEK, DOMINATING THE WEATHER PATTERN NEXT WEDNESDAY
THROUGH FRIDAY.  DESPITE HIGH CONFIDENCE IN THE BUILDING RIDGE,
THE SPREAD AMONG ENSEMBLE MEMBERS AND UNCERTAINTY IN THE FORECAST
QUICKLY INCREASES WHILE THE MEAN RIDGE AXIS POTENTIALLY SHIFTS
EASTWARD NEXT WEEKEND.  ALSO, WEST OF THE RIDGE, THERE REMAINS
SOME UNCERTAINTY WITH THE DETAILS OF IMPULSES OF ENERGY ROTATING
AROUND A RELATIVELY STAGNANT UPPER LOW OVER FAR EASTERN RUSSIA,
WHICH WILL IMPACT THE FORECAST ACROSS THE ALEUTIANS AND BERING SEA
THROUGHOUT THE FORECAST PERIOD.  THE LATEST 00Z/12Z GUIDANCE
SUGGEST THE POTENTIAL FOR A SURFACE WAVE TO TRACK ACROSS THE
WESTERN/CENTRAL ALEUTIANS WEDNESDAY BEFORE DEEPENING AND LIFTING
THROUGH THE BERING SEA ON THURSDAY, BUT AGAIN, CONFIDENCE IN THE
EXACT STRENGTH/EVOLUTION OF THIS FEATURE REMAINS LOW.

A BLEND OF THE 00Z ECMWF/00Z CMC/12Z GFS WAS USED EARLY IN THE
FORECAST PERIOD IN ORDER TO SMOOTH OUT DETAIL DIFFERENCES WITH
ENERGY ROTATING AROUND THE UPPER LOW IN FAR EASTERN RUSSIA.  THE
FORECAST THEN TRANSITIONED TO MORE ENSEMBLE MEAN GUIDANCE BY DAY
7-8 (SATURDAY-SUNDAY) DUE TO DETERIORATING CONFIDENCE AND MODEL
AGREEMENT WITH THE RIDGE AXIS POSSIBLY SHIFTING EASTWARD NEXT
WEEKEND.


GERHARDT


$$




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