ALASKA EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
253 PM EDT TUE MAY 05 2009
 
VALID 12Z SAT MAY 09 2009 - 12Z WED MAY 13 2009
 
A STABLE NW-SE ORIENTED UPPER RIDGE IS FORECAST TO REMAIN
ENTRENCHED OVER SOUTHWESTERN ALASKA UP TO NORTHEASTERN RUSSIA OVER
THE MEDIUM RANGE PERIOD. TWO UPPER LEVEL CLOSED LOWS WILL SKIRT
THE DOMAIN BUT SHOULD NOT HAVE A MEANINGFUL IMPACT. A COLD FRONT
WILL SINK INTO CENTRAL ALASKA BY THE WEEKEND AND SLOWLY FADE AS
UPPER SUPPORT SLIDES EASTWARD INTO NORTHERN CANADA. 

THE 06Z/12Z GFS SQUASH THE UPPER RIDGE OVER THE BERING STRAITS
UNLIKE THE CONSENSUS OF THE 12Z UKMET/CANADIAN AND 00Z
ECMWF/UKMET/CANADIAN AS WELL AS THE 00Z ECMWF ENSEMBLE MEAN AND
SOMEWHAT THE 06Z GEFS MEAN. THE ECMWF HAS BEEN PRETTY CONSISTENT
KEEPING A SHARPER RIDGE WEST OF 160W ITS PAST THREE RUNS WHEREAS
THE GFS WANTS TO SEND ENERGY UP AND OVER IT TO FLATTEN THE RIDGE.
OTHER GUIDANCE OUTSIDE THE 12Z GFS AND CANADIAN KEPT SOME
TROUGHING OVER NORTHEASTERN ALASKA REFLECTED AS THE SURFACE
FRONTAL BOUNDARY... BUT THE 00Z ECMWF APPEARS PERHAPS TOO
STRONG/COLD AT THE SURFACE. 

THIS WEEKEND... AN UPPER LOW WILL MOVE SOUTHEASTWARD TOWARD
BC/QUEEN CHARLOTTE ISLANDS WITH ITS ASSOCIATED COLD POOL MAINLY
OVER THE OCEAN. TO THE WEST... ANY SYSTEMS SOUTHWEST OF THE
ALEUTIANS /INCLUDING THE REMNANTS OF KUJIRA/ WILL LIKELY BE HELD
AT BAY AND DEFLECTED TO THE NNW OR SE AND WEAKEN. THE ONE SYSTEM
THAT HAS POTENTIAL TO EVENTUALLY COME CLOSER TO THE GULF OF ALASKA
IS A SLOWLY MOVING CLOSED LOW SOUTH OF 50N THAT MAY CREEP
NORTHEASTWARD BY WED/DAY 8. MOST GUIDANCE HAS GENERAL LOW PRESSURE
IN THE VICINITY BUT THERE IS AMPLE TIME TO MODIFY THE FORECAST.

THE SFC FEATURES WERE GENERALLY MODELED AFTER THE 00Z ECMWF AND
00Z ECMWF ENSEMBLE MEAN IN ORDER TO TAME DOWN SOME FEATURES IN THE
DOMAIN. NEARLY EVERY NEW RUN OF THE ECMWF/GFS/CANADIAN OFFERS A
DIFFERENT WAY TO KILL SYSTEMS OVER THE WESTERN BERING SEA OVER THE
NEXT WEEK /ALSO SEEN QUITE COLORFULLY IN THE 500 MB SPAGHETTI
CHARTS/ BUT AT LEAST THE IDEA IS CONSISTENT THAT WHATEVER ENERGY
APPROACHES WILL EVENTUALLY BE SHEARED APART IN SOME WAY. 

THE 12Z ECMWF TAKES SOME ENERGY OVER THE TOP OF THE RIDGE THROUGH
THE ARCTIC OCEAN BY MON/DAY 6 UNLIKE ITS 00Z/05 AND 00Z/04 RUNS
BUT CLOSE TO ITS 12Z/04 RUN. HOWEVER... IT IS STILL NOT AS BULLISH
AS THE 12Z GFS. THIS BRINGS IN LOWER HEIGHTS TO THE PANHANDLE BY
TUE/DAY 7 IN SIMILAR FASHION TO THE 12/04 RUN. OVERALL IT REMAINS
WITHIN THE SPECTRUM OF POSSIBILITIES.

FRACASSO