Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1
000
FXAK02 KWNH 281809
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
208 PM EDT FRI APR 28 2017

VALID 12Z TUE MAY 02 2017 - 12Z SAT MAY 06 2017

AN UPPER LOW IS FORECAST TO LIFT INTO THE GULF MIDWEEK AND WEAKEN
AS ANOTHER ONE FROM THE WESTERN BERING SEA SLIDES EAST ALONG 50N
NEXT FRI/SAT. THE ENSEMBLES WERE GENERALLY IN AGREEMENT THROUGH
THE PERIOD (06Z GEFS AND 00Z ECMWF ENSEMBLE MEAN) WHICH WOULD
OTHERWISE LEAD TO ABOVE AVERAGE CONFIDENCE, BUT THE EMBEDDED
SYSTEMS REMAIN SOMEWHAT POORLY HANDLED BY RECENT DETERMINISTIC
GUIDANCE. OVERALL, CONFIDENCE IS AVERAGE BUT ABOVE AVERAGE IN THE
SYNOPTIC SETUP. USED A BLEND OF THE 12Z/06Z GFS WITH THE 06Z GEFS
MEAN AND 00Z ECMWF/ECMWF ENSEMBLE MEAN.

LEAD SYSTEM SHOULD MOVE INTO THE GULF AND DEEPEN BUT THE
MODELS/ENSEMBLES DIVERGE N-S (SPEED) AND E-W (TRACK) AS WELL AS
DEPTH (970-990MB) DEPENDING ON HOW AN UPSTREAM VORTICITY
INTERACTS/ADVECTS INTO (OR PAST) THE MAIN SYSTEM. ENSEMBLES
SUGGEST MODEST DEEPENING (CLOSED 984MB ISOBAR IN THE ECMWF
ENSEMBLE MEAN) AND THIS WAS CONSISTENT WITH THE 06Z GFS. PARENT
LOW SHOULD GET LEFT BEHIND IN THE GULF ON THURSDAY AS THE FRONT
PUSHES INTO CANADA.

NEXT SYSTEM SHOULD PUSH INTO THE WESTERN ALEUTIANS AROUND
WEDNESDAY THOUGH THE MODELS/ENSEMBLES CANNOT FIGURE OUT HOW TO
HANDLE THE FLOW OFF EASTERN ASIA (GFS RUNS WERE MORE PROGRESSIVE
WITH NORTHERN STREAM ENERGY UNLIKE THE 00Z ECMWF/UKMET).
NEVERTHELESS, ALL COMES TOGETHER INTO ANOTHER SYSTEM LIKELY JUST
SOUTH OF THE ALEUTIANS THU-SAT. AGAIN, CONSENSUS BLEND SUFFICED
WHICH WAS NEAR WPC CONTINUITY.

RATHER WET PERIOD FOR SE PORTIONS INTO THE PANHANDLE BUT NOTHING
OUT OF THE ORDINARY. THIS SHOULD KEEP DAYTIME TEMPERATURES BELOW
AVERAGE. WESTERN INTERIOR WILL SEE ABOVE AVERAGE TEMPERATURES
UNDER WEAK RIDGING WHILE THE NORTH SLOPE WILL BE CLOSE TO AVERAGE
UNDER WEAK TROUGHING.

FRACASSO


$$





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