ALASKA EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
300 PM EDT SAT JUL 04 2009
 
VALID 12Z WED JUL 08 2009 - 12Z SUN JUL 12 2009
 
SOME ELEMENTS OF THE MEDIUM RANGE FORECAST CONTINUE TO BE
RELATIVELY PREDICTABLE...ESPECIALLY OVER THE NORTHEAST PACIFC INTO
SOUTH CENTRAL ALASKA BUT THERE CONTINUES TO BE CONSIDERABLE
COMPLEXITY WITH THE EVOLUTION OF TROUGHS OVER THE NORTH CENTRAL
PACIFIC INTO THE BERING SEA AND THE EFFECT OF A CUTOFF LOW
NORTHEAST OF THE ARCTIC COAST. THE 12Z OPERATIONAL MODEL RUNS SHOW
THAT THE MEAN TROUGH REMAINS OVER THE NORTH PACIFIC/BERING SEA AND
RIDGE REMAINS OVER THE NORTHEAST PACIFIC.

OVER THE PAST COUPLE DAYS...IT HAS NOT BEEN THAT CLEAR WHETHER A
SHORTWAVE TROUGH THAT NOW BEGINS IN THE SHORT RANGE OVER THE
BERING SEA WOULD SIMPLY ROTATE NORTHWESTWARD INTO NORTHEAST
SIBERIA ALONG THE WESTERN PERIPHERY OF AN UPPER RIDGE HANGING
TOUGH OVER ALASKA OR HEAD NORTHEASTWARD ACROSS THE BERING STRAIT
AND THEN EASTWARD TOWARD THE BEAUFORT SEA OR PERHAPS NORTHERN
CANADA. OVERNIGHT...THIS SYSTEM APPEARS TO BE TRENDING TOWARD THE
LATTER ON DAYS 4 THROUGH 6/WEDNESDAY THROUGH FRIDAY.

THERE HAS ALSO BEEN A TREND FOR TWO SYSTEMS...ONE OVER THE NORTH
CENTRAL PACIFIC AND ANOTHER NEAR KAMCHATKA TO INTERACT OVER THE
NORTH CENTRAL PACIFIC INTO THE BERING SEA.  THIS INTERACTION IS
STILL NOT CLARIFIED BY THE OVERNIGHT MODELS. IN ADDITION...A THIRD
SYSTEM MOVING EAST OFF THE EAST COAST OF ASIA ALSO APPEARS TO
INTERACT IN A MANNER THAT IS DIFFICULT TO PREDICT.  THE 12Z MODELS
ARE SUGGESTING THAT ALL THREE SYSTEMS TEND TO REINFORCE THE MEAN
TROUGH OVER THE BERING SEA/NORTH PACIFIC.

THE OVERNIGHT OPERATIONAL MODELS ALSO WERE SUGGESTIVE THAT THE
POOL OF COLDER AIR LOCATED WITH THE UPPER LOW NORTHEAST OF ALASKA
COULD MAKE ITS WAY INTO THE NORTHERN SECTION OF THE STATE...BUT
RELATIVELY LATE IN THE FORECAST...WHICH CONTINUES TO MAKE IT
SUSPECT.  YESTERDAYS 12Z EUROPEAN BROUGHT A STRONG SHOT OF COLDER
AIR INTO THE STATE...WHICH APPEARED TO BE AN OUTLIER AT THE TIME. 
HOWEVER...WHILE NOT NEARLY AS IMPRESSIVE AS THAT RUN APPEARED TO
BE...OTHER OPERATIONAL MODELS INCLUDING THE OVERNIGHT
EUROPEAN...06Z GFS...00Z CANADIAN CONTINUE TO SUGGEST THE
POSSIBILITY...AS WELL AS THE GFS AND EUROPEAN ENSEMBLE MEANS. 
HOWEVER...THE 00Z GFS AND UKMET DO NOT BRING COLDER AIR ANYWHERE
NEAR NORTHERN ALASKA. THE 12Z RUNS SHOW THAT COLDER AIR WILL BE
POISED ALONG THE NORTHERN SLOPES BUT DOES NOT NOW APPEAR TO DRIVE
MUCH FARTHER SOUTH...AT LEAST FOR NOW.

AT THE START OF THE MEDIUM RANGE FORECAST...THE 12Z GFS HAS
TRENDED TOWARD THE 00Z EUROPEAN IN THE STRUCTURE OF THE UPPER
TROUGH OVER THE NORTH CENTRAL AND NORTHWEST PACIFIC ON
WEDNESDAY/DAY 4...MAINTAINING 2 SEPARATE LOWS.  HOWEVER...IT ALSO
IS FAR LESS PROGRESSIVE ON ENERGY MOVING INTO WESTERN ALASKA BY
DAY 6/FRIDAY...AS THE 00Z EUROPEAN HAD DONE AND APPEARS TO BE MORE
IN SYNC WITH THE OVERNIGHT ENSEMBLE FORECASTS.  

FOR THE MANUAL GRAPHICS...HAVE GONE WITH A BLEND OF THE
OPERATIONAL 12Z GFS AND 00Z EUROPEAN ON DAYS 4 AND 5 BUT HAVE USED
MORE THE 12Z GFS AS THE OPERATIONAL COMPONENT OF THE FORECAST ON
DAYS 6 AND BEYOND...COMBINING IT WITH THE 00Z ENSEMBLE GFS AND
EUROPEAN ENSEMBLE MEANS.

THE 12Z EUROPEAN SHOWS THE INTERACTION OF TWO WEAKENING SYSTEMS
OVER THE NORTH CENTRAL PACIFIC/SOUTHERN BERING SEA AT THE EXPENSE
OF A DEEPENING LOW MOVING TOWARD THE NORTH CENTRAL PACIFIC BY DAY
6.  THEREFORE...THE 12Z EUROPEAN IS SHOWING THAT THE DEEP UPPER
TROUGH IS TRENDING TOWARDS REMAINING IN PLACE ACROSS THE NORTH
PACIFIC AND BERING SEA.

KOCIN