Storm Warning 169, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1250 PM AKDT TUE OCT 26 2010

.ANALYSIS AND UPPER LEVELS...A VERTICALLY STACKED LOW CENTERED NEAR
KING SALMON THIS MORNING IS TRACKING SLOWLY EASTWARD TOWARD KODIAK
ISLAND. THE BULK OF THE PRECIP WITH THIS LOW IS RIGHT NEAR THE
LOW CENTER FALLING MAINLY AS SNOW. OF NOTE HOWEVER IS AN AREA OF
SHOWERS MOVING NORTHWESTWARD ACROSS THE KENAI PENINSULA. THE SOURCE
OF VERTICAL MOTION IS A VORT-MAX EMBEDDED WITHIN THE ROTATION AROUND
THE BRISTOL BAY LOW. THE NAM IS VERIFYING THE BEST WITH THE NORTHWARD
PROGRESSION OF THESE SHOWERS AND IS THE PREFERRED MODEL FOR TONIGHT
IN TRACKING THESE SHOWERS ACROSS THE ANCHORAGE AREA. UPPER LEVEL
MOISTURE CLEARED OUT THIS MORNING AHEAD OF THIS AREA OF SHOWERS AND
AREAS OF FOG QUICKLY FORMED. WEB CAMS SHOW THAT THIS FOG IS QUITE
SHALLOW SO WOULD EXPECT IT TO BURN OFF EARLY THIS AFTERNOON AND
PROVIDE SOME SUNSHINE FOR MUCH OF SOUTHCENTRAL. OUT WEST A HURRICANE
FORCE LOW BOMBED AS IT MOVED INTO THE WESTERN BERING THANKS TO A
160KT+ UPPER JET. ESTIMATED CENTRAL PRESSURE OF THIS LOW IS AROUND
950 MB. THE STRONG JET IS HELPING TO PUSH THE FRONTAL SYSTEM QUICKLY
EASTWARD ACROSS THE BERING SEA WITH WIDESPREAD RAIN AND GALE TO
STORM FORCE WINDS BEING OBSERVED ACROSS THE WESTERN TO CENTRAL
BERING AND ALEUTIANS THIS MORNING.

.MODEL DISCUSSION...MODELS SOLUTIONS CONTINUE TO SHOW GOOD AGREEMENT
THROUGH THE NEXT FEW DAYS WITH MAJOR FEATURES. THERE HAS BEEN A
CONSISTENT TREND TOWARD A STRONGER BERING LOW AND STRONGER FRONT AS
WELL AS FASTER EASTWARD PROGRESSION OF THE FRONT. MODELS HAVE ALSO
TRENDED STRONGER WITH THE TRIPLE POINT LOW THAT FORMS NEAR KODIAK
ISLAND WEDNESDAY NIGHT WHICH MAKES SINCE CONSIDERING UPPER LEVEL
SUPPORT. FORECASTS WILL BE UPDATED TO REFLECT THESE TRENDS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE SHOWERS MOVING UP THE KENAI PENINSULA
ARE FALLING MAINLY IN THE FORM OF RAIN. THE AIR MASS FURTHER NORTH
TOWARD ANCHORAGE IS SLIGHTLY COOLER SO EXPECT RAIN AND SNOW SHOWERS
AS THESE PROGRESS NORTHWARD LATER THIS AFTERNOON AND EVENING.
SURFACE TEMPERATURES ARE ABOVE FREEZING SO WOULD EXPECT LITTLE
OR NO ACCUMULATION AS THESE MOVE THROUGH...ESPECIALLY FOR AREAS
AT OR NEAR SEA LEVEL. OUTSIDE OF THESE SHOWERS SKIES WILL BE MOSTLY
CLEAR ACROSS SOUTHCENTRAL ALLOWING TEMPERATURES TO DROP WELL BELOW
FREEZING. MEANWHILE...THE LOW OVER KING SALMON WILL MOVE ACROSS
KODIAK ISLAND RESULTING IN A PERIOD OF RAIN AND SNOW OVERNIGHT.
THIS LOW WILL THEN QUICKLY DISSIPATE WEDNESDAY MORNING AS THE BULK
OF ENERGY WITH THIS LOW DROPS DOWN INTO THE PACIFIC. THERE WILL BE
A BRIEF BREAK WEDNESDAY BEFORE A STRONG FRONT CURRENTLY MARCHING
ACROSS THE BERING SEA ARRIVES. STRONG SOUTHEAST CHINOOK WINDS WILL
DEVELOP AHEAD OF THIS FRONT BUT SOUTH TO SOUTHWEST FLOW ALOFT
COMBINED WITH ABUNDANT MOISTURE AND STRONG DYNAMICS WILL COUNTERACT
SOME OF THESE AFFECTS AND PRODUCE WIDESPREAD PRECIP ACROSS THE
REGION WEDNESDAY NIGHT INTO THURSDAY. A TRIPLE POINT LOW WILL
DEVELOP NEAR KODIAK ISLAND WEDNESDAY NIGHT AND TRACK TO THE VICINITY
OF THE KENAI PENINSULA THURSDAY...WHICH WILL HELP CUT OFF WARM
ADVECTION TO INLAND AREAS OF SOUTHCENTRAL. THE BEST SHOT FOR SNOW
LOOKS TO BE THE WESTERN SUSITNA VALLEY...THOUGH EVEN HERE
TEMPERATURES LOOK BORDERLINE FOR SNOW. IF IT IS IS COLD ENOUGH
FOR SNOW THEN A WINTER WEATHER ADVISORY FOR SNOW WILL HAVE TO
BE CONSIDERED BECAUSE THE STRONG LOW LEVEL SOUTHEAST FLOW WILL
ENHANCE PRECIP AMOUNTS ALONG THE ALASKA RANGE. FOR NOW WILL
INTRODUCE SNOW ACCUMULATION AMOUNTS BELOW ADVISORY THRESHOLDS.
COLDER AIR WILL QUICKLY MOVE IN BEHIND THE SYSTEM THURSDAY NIGHT
INTO FRIDAY...BRINGING POTENTIAL FOR A QUICK SHOT OF SNOW ELSEWHERE
ACROSS SOUTHCENTRAL.

SOUTHWEST ALASKA...SKIES WILL GRADUALLY CLEAR OUT TONIGHT ACROSS
SOUTHWEST ALASKA AS THE KING SALMON LOW MOVES TO KODIAK ISLAND.
THE BERING FRONT WILL REACH THE SOUTHWEST COAST BY WEDNESDAY
MORNING AND SPREAD INLAND DURING THE DAY. WARM AIR ADVECTION
AHEAD OF THE FRONT WILL PRODUCE MAINLY RAIN FROM BRISTOL BAY TO
THE KUSKOKWIM DELTA. THE SOUTHERN KUSKOKWIM VALLEY WON'T SEE AS
MUCH WARM AIR...SO PRECIP WILL FALL MAINLY AS SNOW. THE FRONT
WILL MOVE THROUGH FAIRLY QUICKLY SO DON'T EXPECT MINOR SNOW
ACCUMULATION. COLDER AIR WILL MOVE BACK IN BEHIND THE FRONT ON
THURSDAY SO SHOWERS MOVING IN FROM THE BERING WILL BE MAINLY IN
THE FORM OF SNOW.

BERING SEA/ALEUTIANS...THE LOW OVER THE WESTERN BERING WILL BE
SLOW TO WEAKEN AS IT SITS OVER THE NORTHERN BERING MID TO LATE
WEEK. THEREFORE...EXPECT A PROLONGED PERIOD OF WESTERLY GALES.
SEAS WILL ALSO BUILD TO OVER 30 FEET ACROSS MUCH OF THE BERING
BY MID WEEK AND THEN VERY SLOWLY BEGIN TO SUBSIDE LATER THIS WEEK.
COLDER AIR ALOFT WILL MOVE IN BEHIND THE FRONT TONIGHT AND WEDNESDAY
SO THAT SHOWERS WILL MIX WITH OR CHANGE TO SNOW.

.LONG TERM FORECAST...MEDIUM RANGE MODELS ARE SHOWING A LITTLE
BETTER CONSISTENCY AND AGREEMENT LATE THIS WEEK THROUGH EARLY
NEXT WEEK. A PERSISTENTLY STRONG SUBTROPICAL JET WILL LEAD TO
ACTIVE CYCLOGENESIS ACROSS THE NORTH PACIFIC AND INTO THE ALASKAN
REGION. WHILE THE NORTHERN LOW CONTINUES TO WEAKEN MODELS INDICATE
A SHORT-WAVE EXITING ASIA AND LEADING TO LOW DEVELOPMENT ALONG
THE ALEUTIANS NEXT WEEKEND. BY EARLY NEXT WEEK THERE IS GENERAL
AGREEMENT ON A MAJOR LOW DEVELOPING OVER THE NORTHEAST PACIFIC
AND MOVING INTO THE GULF. THE SOUTHERN STORM TRACK WILL ALLOW
ARCTIC AIR TO PROGRESS SOUTHWARD ACROSS ALASKA...WHICH COULD SET
UP POTENTIAL FOR WIDESPREAD SNOW DEPENDING HOW THESE SOUTHERN
STORMS INTERACT WITH ALASKA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...176 180 185.
         GALE WARNING...130 138 150 160 170 172 175 179.
FIRE WEATHER...NONE.

SEB OCT 10