Freezing Rain Advisory 9, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AKST THU DEC 18 2008

.ANALYSIS AND UPPER LEVELS...
A MEAN LONGWAVE RIDGE IS OVER THE ENTIRE REGION AND WILL PERSIST FOR
AT LEAST ANOTHER WEEK. THIS MEANS FAIRLY TAME WEATHER WILL CONTINUE.
A VERTICALLY STACKED CUTOFF LOW IS CENTERED ATKA EARLY THIS MORNING
AND IS UNDERCUTTING THE OVERALL MEAN RIDGE OF HIGH PRESSURE OVER THE
REGION. THIS LOW HAS BROUGHT BLIZZARD CONDITIONS TO ADAK WEDNESDAY
NIGHT. A SHORTWAVE UPPER LEVEL RIDGE OF HIGH PRESSURE IS POSITIONED
FROM THE GULF OF ALASKA NORTH TOWARD DEADHORSE...WITH ANOTHER RIDGE
CENTERED OVER THE WESTERN BERING/ALEUTIANS. THE MAJOR FEATURES ARE
PROGRESSING SLOWLY EASTWARD.

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT OVERALL EVEN INTO THE EXTENDED. WHERE
DIFFERENCES ARISE...PREFER THE ECMWF DUE TO ITS BETTER RUN TO RUN
CONSISTENCY LATELY. PROBABLY THE TRICKIEST FORECAST ISSUE THROUGH
SATURDAY WILL BE FORECASTING THE DEVELOPMENT AND DISSIPATION OF WEAK
TRIPLE POINT LOWS WHICH WILL FORM ALONG A FRONT EXTENDING FROM THE
EASTERN BERING TO THE AKPEN TO THE WESTERN AND SOUTHERN GULF. THIS
FRONT WILL PROGRESS SLOWLY EAST AND REMAIN POSITIONED OUT AHEAD OF
THE MAIN VERTICALLY STACKED LOW CENTER.

.SHORT TERM FORECAST...
SOUTHCENTRAL...
A NORTHWEST/SOUTHEAST ORIENTED FRONT WRAPPED SEVERAL TIMES INTO THE
ATKA LOW IS POSITIONED FROM THE EASTERN BERING TO SOUTH OF THE AKPEN
THIS MORNING AND WILL CONTINUE TO MOVE SLOWLY EAST...BECOMING MORE
EAST/WEST ORIENTED ACROSS THE GULF ON FRIDAY AND SHEARING APART AND
DISSIPATING FRIDAY NIGHT AND SATURDAY. PRECIPITATION THROUGH
SATURDAY WILL BE CONCENTRATED IN THE GULF INCLUDING KODIAK...AND
HAVE MORE TROUBLE REACHING THE MAINLAND. PRECIPITATION IS EXPECTED
TO MAKE IT TO THE EASTERN KENAI FRIDAY THROUGH SATURDAY AND THEN
RETREAT AS DRIER OFFSHORE FLOW TAKES OVER. HOWEVER...ELSEWHERE ON
THE MAINLAND PRECIPITATION IS EXPECTED TO BE VERY LIGHT OR
NONEXISTENT AS THE RIDGE OVER THE MAINLAND IS JUST TOO STRONG AND
WILL LIMIT THE NORTHEASTWARD PROGRESS OF THE FRONT.

SOUTHWEST MAINLAND...
LIGHT PRECIPITATION...MAINLY AS RAIN OR A RAIN SNOW MIX...WILL
CONTINUE OVER THE SOUTHWEST MAINLAND THROUGH FRIDAY NIGHT AS MOIST
SOUTH TO SOUTHEAST FLOW CONTINUES ON THE EAST SIDE OF THE LOW
COMPLEX MOVING EAST THROUGH THE ALEUTIANS. THE FLOW WILL SHIFT MORE
NORTHERLY FRIDAY NIGHT AND SATURDAY WITH SOME DRYING. THE AIRMASS
WILL REMAIN QUITE MILD OVER THE SOUTHWEST MAINLAND INTO THE WEEKEND
THOUGH IT WILL COOL SOMEWHAT AFTER TODAY.

BERING SEA/ALEUTIANS...
A POTENT VERTICALLY STACKED LOW NEAR ATKA THIS MORNING IS DRIFTING
EAST INTO THE NORTH PACIFIC AND WILL SLOWLY WEAKEN AS IT MOVES TO
SOUTH OF SAND POINT FRIDAY NIGHT. THE LOW REACHED ITS PEAK WEDNESDAY
NIGHT WITH SOME STORM FORCE WINDS ON ITS WEST SIDE AND BLIZZARD
CONDITIONS FOR ADAK. STRONG WINDS WILL PERSIST FOR THE CENTRAL
ALEUTIANS INTO TONIGHT ALTHOUGH PRECIPITATION INTENSITY WILL
DECREASE SOMEWHAT. A COUPLE OF WEAK TRIPLE POINT LOWS WILL FORM
NORTH AND EAST OF THE MAIN LOW INTO FRIDAY. HIGH PRESSURE OVER THE
WESTERN BERING/ALEUTIANS TODAY GRADUALLY MOVES INTO THE EASTERN
BERING/ALEUTIANS SATURDAY AS A FRONT MOVES EAST INTO THE WESTERN
BERING/ALEUTIANS FRIDAY AND CENTRAL BERING/ALEUTIANS SATURDAY.

.LONG TERM FORECAST...
THE MEAN RIDGE OF HIGH PRESSURE WILL PERSIST INTO NEXT WEEK. SOME
INCREASED UPPER LEVEL JET INVOLVEMENT SHOULD BRING SOME FASTER AND
WARMER WESTERLY FLOW ESPECIALLY OUT WEST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING ZONE 187.
MARINE...STORM WARNING ZONE 172.
         GALE WARNING ZONES 130 132 140 175 176 351 352 411 412 413.
FIRE WEATHER...NONE.

FOISY DEC 08