ALASKA EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
257 PM EDT FRI MAY 16 2008
 
VALID 12Z TUE MAY 20 2008 - 12Z SAT MAY 24 2008
 
THE ENSEMBLE MEANS INDICATE THAT A WEAK RIDGE WILL PERSIST OVER
MUCH OF THE STATE NORTH OF THE SOUTH COAST DURING MOST OF THE
MEDIUM RANGE PERIOD.  NO LARGE CHANGES ARE EXPECTED ACROSS MUCH OF
THE INTERIOR OF ALASKA.

MEANWHILE...THE DOMINANT UPPER CUTOFF LOW NEAR THE ALEUTIANS WILL
BECOME A PROGRESSIVE TROUGH DURING THE MEDIUM RANGE PERIOD BUT
WILL PASS MOSTLY SOUTH OF 60N.  IN THE WAKE OF THIS TROUGH...AN
UPPER RIDGE WILL MOVE EASTWARD FROM THE EAST COAST OF ASIA ON DAY
4/TUESDAY TO NEAR THE ALEUTIANS/BERING SEA BY DAY 8/SATURDAY.  A
STRONG RIDGE WILL DEVELOP OVER THE EASTERN PACIFIC WEST OF THE US
MAINLAND BETWEEN DAYS 4 AND 6/TUESDAY AND THURSDAY.

THE EVOLUTION OF INDIVIDUAL SHORTWAVES/CYCLONES SOUTH OF ALASKA IS
STILL RELATIVELY UNCERTAIN EVEN AS EARLY AS DAY 4/TUESDAY.  THE
ENSEMBLE MEANS POINT TO A SIGNIFICANT LOW DEVELOPING IN THE LATE
SHORTRANGE NEAR 40N 170W BY DAY 3/MONDAY TO NEAR 50N 160W BY DAY
4/TUESDAY.  CONTINUITY FROM PREVIOUS FORECASTS ISSUED HERE WOULD
SUGGEST THAT A SIGNIFICANT LOW WOULD MOVE NE TOWARD THE ALASKA
PENINSULA...BUT TRENDS OF THE OPERATIONAL GFS AND CONTINUITY OF
THE EUROPEAN RATHER SUGGEST THAT THE MEAN LOW REFLECTS 2 OR MORE
SEPARATE SYSTEMS...ONE WEAK LOW UNDER THE UPPER LOW NEAR THE
ALEUTIANS...AND THE OTHERS MOVING ENE TOWARD THE SOUTHERN GULF OF
ALASKA.  

THE OPERATIONAL MODELS EXHIBIT A WIDE RANGE OF SOLUTIONS WITH THIS
SYSTEM...MOVING SOUTH AND EAST OF A WEAK LOW NEAR THE ALEUTIANS.
THIS MORNINGS 12Z GFS IS SIMILAR TO LAST NIGHTS EUROPEAN...LENDING
CREDENCE TO THE 00Z EUROPEAN SOLUTION.  HAVE ELECTED TO USE BLEND
OF 60/40 12Z GFS AND 00Z EUROPEAN BECAUSE OF THIS.   HOWEVER...AM
TAKING A CALCULATED RISK SINCE 12Z CANADIAN REMAINS SIMILAR WITH
THE ENSEMBLE MEANS AND REPRESENTS MORE CONTINUITY...WILL SEE
TOMORROW IF RISK PAID OFF OR NOT. IN ANY EVENT...12Z EUROPEAN IS
SLIGHTLY DIFFERENT THAN ITS PREVIOUS SOLUTION WITH LOW PRESSURE
MOVING NEAR THE GULF...BUT THE TREND IS STILL TOWARD RELATIVELY
WEAK...FLAT LOWS MOVING SOUTH OF ALASKA PRIOR TO DAY 6/THURSDAY.

WHILE THE OPERATIONAL 00Z AND 12Z GFS AND EUROPEAN MODELS AMPLIFY
THE SOUTHERN PORTION OF THE TROUGH SOUTH OF THE ALEUTIANS FROM
DAYS 6 THRU 8/THURSDAY THRU SATURDAY AND PRODUCE A SIGNIFICANT
CYCLONE HEADED TOWARD THE SOUTHWEST ISLANDS...THE ENSEMBLE MEANS
ONLY MAINTAIN A PROGRESSIVE TROUGH WITH NO INDICATION THAT THERE
WOULD NECESSARILY BE AN INTENSIFYING CYCLONE. AT THIS
TIME...MANUAL PROGS WILL NOT EMPHASIZE ANYTHING NECESSARILY MAJOR
AFFECTING THE SW ISLANDS BY DAY 8.

12Z EUROPEAN ALSO BRINGS UPPER TROUGH EASTWARD ACROSS BERING SEA
INTO NORTHERN ALASKA...INDICATING POSSIBILITY OF COOLING DAYS 7 TO
8 IN THE NW.  THIS IS ACTUALLY A LARGE CHANGE FROM THE PREVIOUS
RUN...WHICH KEEPS UPPER LOW OVER SIBERIA...AS DO THE OTHER
OPERATIONAL MODELS.  WHILE THIS WOULD REFLECT A SIGNIFICANT CHANGE
TO THE WEATHER ACROSS THE NW PART OF THE STATE...IT IS STILL TOO
EARLY TO GIVE IT MUCH WEIGHT YET BUT IMPORTANT TO POINT IT OUT.

KOCIN