ALASKA EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
202 PM EST SUN NOV 22 2009
 
VALID 12Z THU NOV 26 2009 - 12Z MON NOV 30 2009
 
VERY ACTIVE CYCLONE PATTERN OVER THE NORTHEAST PACIFIC TO CONTINUE
THRU THE MEDIUM RANGE. THERE IS MORE UNCERTAINTY TODAY THAN RECENT
DAYS AS MODEL DIFFERENCES APPEAR TO INCREASE. THERE APPEARS MORE
UNIFORMITY IN THE FORECASTS ON DAYS 7 AND 8/SUNDAY AND MONDAY.

THE 00Z OPERATIONAL EUROPEAN AND THE 06Z GFS APPEAR TO TREND
TOWARD THE OVERNIGHT CANADIAN ENSEMBLES WHICH ARE DRIVING THE 00Z
NAEFS ENSEMBLES MUCH MORE SO THAN THE GFS...WHICH IS NOT A COMMON
OCCURRENCE. ESPECIALLY...SINCE THE 00Z OPERATIONAL CANADIAN DOES
NOT LOOK MUCH LIKE THE 00Z CANADIAN ENSEMBLE MEANS.

THERE APPEARS TO BE MORE UNCERTAINTY WITH THE EVOLUTION OF THESE
CYCLONES DURING THE MEDIUM RANGE THAN DURING THE PAST COUPLE DAYS.
 THESE DIFFERENCES SHOW UP EVEN IN THE ENSEMBLE MEANS...WITH THE
OVERNIGHT ENSEMBLE MEANS SHOWING A CYCLONE SOMEWHERE OVER THE
SOUTHEAST BERING SEA ON THURSDAY/DAY 4 WITH A POSSIBLE SIGNIFICANT
TRIPLE POINT LOW...BUT NO CONSENSUS...SOUTH OF THE ALASKA
PENINSULA. WHILE THE 00Z AND 06Z GFS SHOW THIS TRIPLE POINT
LOW...THE 12Z GFS DOES NOT WHILE THE 12Z EUROPEAN HAS A SMALL
CENTER.

ANOTHER LOW THAT DEVELOPS IN THE SHORT RANGE APPEARS TO BE
WEAKENING IN THE GULF ON THURSDAY/DAY 4. NOT MUCH OF AN ISSUE
THERE.

BY FRIDAY/DAY 5...THE 00Z EUROPEAN HAS THE REMNANT LOW OVER SW
ALASKA...BUT IS FARTHER EAST THAN THE MAJORITY OF ENSEMBLE MEMBERS
FOR THIS SYSTEM...BUT IS SIMILAR TO THE 0Z UKMET AND 06Z GFS
FORECAST. 

MOST OF THE ENSEMBLE MEMBERS INDICATE THE LOW IS STILL LOCATED IN
THE EAST CENTRAL BERING SEA...WHICH IS CONSISTENT WITH THE
ENSEMBLE MEANS.  ONCE AGAIN...LOW CONFIDENCE HERE. THE 12Z
EUROPEAN IS CONSISTENT WITH THIS IDEA THAN THE PREVIOUS RUN BY
PLACING THIS LOW MUCH FARTHER WEST AND NORTH OVER THE BERING SEA.

THE OVERNIGHT GFS ALSO SHOOTS A SYSTEM FROM WESTERN ALASKA
NORTHEAST INTO THE BEAUFORT SEA BY SATURDAY/DAY 6. THIS SOLUTION
IS AN OUTLIER WITH RESPECT TO THE ENSEMBLE MEANS AND TO THE OTHER
MODELS. THE 12Z GFS NO LONGER HAS THIS FEATURE.

THE NEXT SYSTEM HAS ITS ROOTS JUST EAST OF JAPAN BY WEDNESDAY/DAY
3 AND IS NOT PARTICULARLY WELL DEFINED IN THE ENSEMBLE MEANS
SOMEWHERE SOUTH OF THE EASTERN ALEUTIANS BY FRIDAY/DAY
5...ALTHOUGH SEVERAL OF THE OVERNIGHT OPERATIONAL MODELS INDICATED
THE POTENTIAL FOR A STRONGLY DEVELOPING SYSTEM OR SYSTEM WITH
MULTIPLE CENTERS.  THIS SYSTEM IS DEFINED BY A FAIRLY DISPERSED
CLUSTER OF LOW PRESSURE CENTERS...AS FORECAST BY THE MANY ENSEMBLE
MEMBERS.

THE 12Z GFS IS SLOWER THAN PREVIOUS RUNS WITH THIS DEVELOPING LOW.
THEREFORE...THERE IS QUITE A BIT OF UNCERTAINTY WITH WHERE AND HOW
STRONG THIS SYSTEM WILL BE. WILL STICK WITH THE 00Z EUROPEAN/00Z
CANADIAN AND 06Z GFS BECAUSE THERE IS SOME CONSISTENCY WITH THESE
RUNS. THE 12Z EUROPEAN HAS THIS SYSTEM FARTHER SOUTH THAN THE
PREVIOUS RUN BY FRIDAY/DAY 5 AND A GOOD 600 MILES EAST OF THE
MANUAL GRAPHICS CENTER BY SATURDAY/DAY 6. LOOKS LIKE A BIG STORM
BUT TOO MUCH VARIABILITY TO PINPOINT WHERE AT THIS POINT.

WITH THE LARGE VARIABILITY IN MODEL SOLUTIONS...CONTINUED USING A
SIGNIFICANT COMPONENT OF THE ENSEMBLE MEANS IN THE MANUAL GRAPHICS
BEING MODIFIED BY AN ASSORTMENT OF OPERATIONAL MODELS AND LOTS OF
MANUAL ADJUSTMENTS.  

THE OPERATIONAL COMPONENT OF THE BLEND CONSISTED OF THE 12Z GFS
AND 00Z EUROPEAN ON DAY 4...THE 6Z GFS AND 00Z UKMET ON DAY 5 AND
THE 6Z GFS AND 00Z EUROPEAN ON DAY 6...WITH THE 00Z NAEFS AND
EUROPEAN ENSEMBLE MEANS FILLING IN THE REST OF THE BLEND.  DAYS 7
AND 8 WERE GUIDED BY THE 00Z EUROPEAN...WHICH WAS NOT THAT
DIFFERENT THAN THE 12Z GFS.

KOCIN  












THE COLD CONDITIONS WILL CONTINUE TO MODERATE SLOWLY INTO THE
MEDIUM RANGE PERIOD AS A PARADE OF STORMS CONTINUE TO MOVE FROM
THE NORTH CENTRAL PACIFIC TOWARD THE NORTHEAST PACIFIC. THE MEAN
UPPER FLOW REMAINS WITH A DEEP TROUGH OVER THE BERING SEA AND A
RIDGE OVER WESTERN CANADA.

WHILE YESTERDAYS ENSEMBLE MEANS POINTED TOWARD A DEEP CYCLONE
CLOSER TO THE SOUTHERN ALASKA COAST OVER THE GULF BY WEDNESDAY/DAY
4...THE OPERATIONAL EUROPEAN TRENDED TOWARDS THE CENTER REMAINING
FARTHER SOUTH.  OVERNIGHT...THE EUROPEAN ENSEMBLES FOLLOWED SUIT
AND THE 00Z OPERATIONAL RUN CONTINUES TO KEEP THE CENTER NEARLY
600 MILES SOUTH OF CAPE SUCKLING.

MEANWHILE...THE 00Z CANADIAN KEEPS THE CENTER CLOSER TO SOUTHERN
ALASKA WHILE THE 00Z UKMET IS MORE SIMILAR TO THE EUROPEAN AND THE
00Z/06Z GFS HAS A COMPROMISE WITH TWO CENTERS...ONE NEAR THE COAST
AND ONE FARTHER SOUTH.

THE NEXT CYCLONE IS MOVING EASTWARD ACROSS THE SOUTHERN BERING SEA
ON DAY 4/WEDNESDAY WITH THE 00Z EUROPEAN CONTINUING MOVING IT
EASTWARD TOWARD THE EASTERN ALEUTIANS BY EARLY THURSDAY/DAY 5 AND
TO THE WESTERN TIP OF THE ALASKA PENINSULA BY EARLY FRIDAY/DAY 6.
THIS MOVEMENT RESEMBLES THE AVERAGE OF THE 00Z
EUROPEAN/GFS/CANADIAN/NAEFS ENSEMBLE MEANS...WITH THE GFS/NAEFS
FARTHER NORTH AND THE CANADIAN FARTHER SOUTH.

THE 00Z/06Z GFS RUNS PLACE THIS LOW FARTHER NORTH THAN THE MEANS
OVER THE BERING SEA WHILE THE 00Z CANADIAN SEEMS MORE OUT OF SYNC
WITH THE MEANS WITH A LOW MUCH FARTHER WEST THAN ITS ENSEMBLE MEAN
LOCATION.

MEANWHILE...OVER NORTHERN ALASKA...1000/500 THICKNESS VALUES HAVE
COME UP OVER INTERIOR ALASKA AS A CYCLONE MOVES NORTH AND WEAKENS
AS IT ENTERS THE STATE FROM THE SOUTH...PRIOR TO THE ONSET OF THE
MEDIUM RANGE PERIOD. A BAROCLINIC ZONE IS ESTABLISHED NORTH OF THE
STATE SOUTH OF A DEEP UPPER LOW EXTENDING SOUTHWESTWARD INTO
NORTHWEST ALASKA BY WEDNESDAY/DAY 4. THIS BAROCLINIC ZONE REMAINS
AND EVEN SHIFTS FARTHER WEST DURING THE MEDIUM RANGE PERIOD...WITH
THE COLDEST AIR BECOMING WELL ESTABLISHED OVER EASTERN
SIBERIA...WHILE THICKNESS VALUES RISE OVER ALASKA AS AN UPPER
RIDGE IS FAVORED OVER NORTHWEST CANADA.

A SHORTWAVE TROUGH EAST OF JAPAN BY DAY 4/WEDNESDAY AMPLIFIES AS
IT MOVES EASTWARD BUT ITS EVENTUAL IMPACT ON THE ALASKA DOMAIN IS
STILL VERY MUCH A QUESTION LATE IN THE FORECAST...WITH THE 00Z
EUROPEAN CONTINUING TO SHOW IT DEVELOPING A SIGNIFICANT CYCLONE
SOUTH OF THE ALEUTIANS BY FRIDAY/DAY 6 AND THEN SPINNING IT UP
OVER THE GULF NEXT WEEKEND ON DAYS 7 AND 8. THE MEANS DO NOT
SUPPORT THIS SYSTEM WHILE THE 00Z GFS/CANADIAN/EUROPEAN MEANS
DIVERGE SHARPLY BY DAY 8 SHOWING HIGH UNCERTAINTY.

THE 12Z GFS CONTINUES TO SHOW A DOUBLE LOW MOVING INTO THE
NORTHEAST PACIFIC ON WEDNESDAY/DAY 4...WHICH IS NOT CONSISTENT
WITH THE 00Z ENSEMBLE MEANS.  IT ALSO APPEARS TO BE AN OUTLIER
WITH THE NORTHERLY LOCATION OF THE NEXT LOW OVER THE NORTH BERING
SEA BY THURSDAY AND FRIDAY/DAYS 5 AND 6.  FOR THOSE
REASONS...ELECTED A COMBINATION OF THE 00Z EUROPEAN AND THE 00Z
EUROPEAN AND NAEFS ENSEMBLE MEANS FOR THE MANUAL FORECAST.

THERE ARE SOME SIGNIFICANT CHANGES TO THE 12Z EUROPEAN. WHILE THE
RUN IS CONSISTENT WITH THE FIRST STORM MOVING INTO THE NORTHEAST
PACIFIC ON WEDNESDAY/DAY 4...THE NEXT SYSTEM CUTTING ACROSS THE
SOUTHERN BERING SEA IS FLATTER THAN EARLIER FORECASTS ON WEDNESDAY
AND THURSDAY/DAYS 4 AND 5. BY FRIDAY/DAY 6...A NEW STORM SOUTH OF
THE ALEUTIANS IS SLOWER AND STRONGER THAN THE EARLIER RUN AND IS
SIMILAR TO THAT IN THE 12Z GFS.

KOCIN