Prognostic Meteorological Discussion
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FXAK02 KWNH 291847
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 PM EDT SAT APR 29 2017

VALID 12Z WED MAY 03 2017 - 12Z SUN MAY 07 2017

...STRONG STORM IN THE GULF OF ALASKA ON WEDNESDAY...

AN UPPER LOW IS FORECAST TO WEAKEN IN THE GULF WED-FRI AS ANOTHER
ONE SLIDES ENE ALONG 50N NEXT FRI-SUN. THE GEFS/ECMWF ENSEMBLES
WERE GENERALLY IN AGREEMENT THROUGH THE PERIOD THOUGH THE SECOND
SYSTEM SHOWS MUCH MORE UNCERTAINTY IN DETAILS. USED A BLEND OF THE
12Z GFS WITH THE 00Z ECMWF TO START, ADDING DETAIL TO THE
LEAD/DEEP SYSTEM IN THE GULF ON WEDNESDAY, BEFORE ADDING IN ABOUT
HALF WEIGHTING FROM THE 06Z GEFS MEAN AND 00Z ECMWF ENSEMBLE MEAN
LATER IN THE FORECAST TO ADDRESS THE UNCERTAINTY.

LEAD SYSTEM IN THE GULF SHOWS MUCH TIGHTER CLUSTERING OF MODEL
SOLUTIONS AND AS SUCH HAVE DEEPENED THE CENTRAL PRESSURE SINCE THE
FORECAST YESTERDAY BY ABOUT 10MB INTO THE LOW 970S MB. PLEASE
CONSULT THE LATEST OCEAN PREDICTION CENTER PRODUCTS FOR ADDITIONAL
INFORMATION INCLUDING WAVE HEIGHT FORECASTS. PARENT LOW SHOULD GET
LEFT BEHIND IN THE GULF  AND SLOWLY WEAKEN AS THE FRONT PUSHES
INTO CANADA. JUST SOUTH OF HAIDA GWAII, THE ECMWF/UKMET SHOW A SFC
WAVE DEVELOPING ALONG THE COLD FRONT MOVING INTO THE SOUTHERN
PANHANDLE WHEREAS THE CANADIAN AND GFS WERE FARTHER EAST. BLENDED
SOLUTION CARRIED AT LEAST A WEAK WAVE PERHAPS JUST GRAZING THE
PANHANDLE THU INTO FRI. ENSEMBLES WERE NOT CRAZY ABOUT THIS WAVE
(NOT MANY L STAMPS IN THE MEMBERS) BUT GIVEN ITS EXISTENCE IN THE
MODELS (DESPITE THE LACK OF LOCATION AGREEMENT) FELT IT WAS
PRUDENT TO AT LEAST SHOW A REFLECTION.

NEXT SYSTEM SHOULD PUSH JUST SOUTH OF THE WESTERN ALEUTIANS BY
THURSDAY. 12Z GFS FINALLY GAVE UP ON THE NORTHERN STREAM LOW AND
JOINED THE ECMWF ET AL. (INCLUDING THE ENSEMBLES) AND FOCUSED ON
THE SOUTHERN LOW. THIS SHOULD TRACK EASTWARD THEN NORTHEASTWARD
NEXT WEEKEND PER THE ENSEMBLES WITH TYPICAL SPEED DIFFERENCES SEEN
IN THE GUIDANCE. CONSENSUS BLEND MAINTAINED GOOD CONTINUITY.

RATHER WET PERIOD FOR SE PORTIONS INTO THE PANHANDLE TO START BUT
INCREASED RIDGING LATER NEXT WEEK INTO THE WEEKEND SHOULD BRING A
DRIER PERIOD TO THAT REGION. EXPECT MORE PRECIPITATION TO SPREAD
EASTWARD COINCIDENT WITH AND AHEAD OF THE NEXT SYSTEM IN THE
ALEUTIANS, EVENTUALLY INTO SOUTH CENTRAL.


FRACASSO


$$





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