Gale Warning 759, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
235 PM ADT TUE OCT 23 2007

.ANALYSIS AND UPPER LEVELS...
AGREE WITH THE PREVIOUS FORECAST DISCUSSION THAT A RELATIVELY BENIGN
PATTERN IS IN PLACE OVER MUCH OF ALASKA BY OCTOBER STANDARDS BUT
STILL SEVERAL FEATURES CREATING FORECAST CHALLENGES IN BOTH DOMAINS.
AT THE UPPER LEVELS...AN UPPER TROUGH EXTENDS NW TO SE FROM NORTON
SOUND TOWARD SOUTHCENTRAL ALASKA. AHEAD OF THE TROF AXIS IS THE SHORT
WAVE THAT BROUGHT THE SNOW TO SOUTHCENTRAL EARLY THIS MORNING NOW
LOSING STEAM AS IT CROSSES THE ALASKA RANGE. JUST ALONG AND BEHIND
THE TROF AXIS IS A AN ELONGATED VORTICITY MAXIMUM WHICH IS HELPING TO
PUSH THE TROF EAST TODAY. AND THEN FURTHER WEST IS ANOTHER SHORT WAVE
ASSOCIATED WITH A WARM FRONT NEARING THE PRIBILOF ISLANDS.

AT THE SURFACE...A WEAK AREA OF CIRCULATION IS EVIDENT ON THE
MIDDLETON ISLAND RADAR JUST SOUTH OF MONTAGUE ISLAND. LIGHT SNOW
ASSOCIATED WITH THE ELONGATED SHORT WAVE MOVING INTO THE UPPER
KUSKOKWIM VALLEY AND ACROSS THE ALASKA PENINSULA AS WELL AS A NICE
FRONTAL BOUNDARY EVIDENCED BY A SHARP WIND SHIFT IN DILLINGHAM LAST
HOUR. BEHIND THE WARM FRONT WHICH IS APPROACHING THE EASTERN BERING
SEA IS A BROAD AREA OF LOW PRESSURE IN THE WESTERN BERING.

.MODEL DISCUSSION...
MODELS IN EXCELLENT AGREEMENT FOR THE FIRST 24 HOURS...THEN DIFFER ON
TIMING AND EVOLUTION OF THE BROAD LOW IN THE WESTERN BERING AND ITS
ASSOCIATED WEATHER FRONT. GFS HAS A BETTER TRACK RECORD AND IS IN
FAIR ALIGNMENT WITH EUROPEAN MODELS SO HAVE TRENDED THE FORECAST
TOWARD THIS SOLUTION. THIS WILL HAVE LITTLE IMPACT ON THE EASTERN
DOMAIN UNTIL THURSDAY NIGHT WHEN THE FRONT MOVES ACROSS KODIAK ISLAND
AND INTO THE NORTHERN GULF. BEYOND 72 HOURS...GFS HAS POOR RUN TO RUN
CONSISTENCY SO CONFIDENCE IS LOW.

.SHORT TERM FORECAST...
SOUTHCENTRAL...
CHALLENGING FORECAST AS MODEL QPF NOT MATCHING OUR CONCEPTUAL MODEL.
SHORT WAVE CROSSES THE SOUTHERN END OF THE ALASKA PENINSULA AND
SWINGS UP COOK INLET THIS EVENING AND INLAND OVERNIGHT. THIS FEATURE
COUPLED WITH WEST TO SOUTHWESTERLY FLOW WITH WEAK COLD AIR ADVECTION
LENDS ITSELF TO AT LEAST THE CHANCE FOR SNOW OVER THE THE NORTHERN
KENAI, ANCHORAGE BOWL, AND MATSU VALLEY. THE 12Z RUN INSISTS THAT THE
MOISTURE WILL NOT CROSS THE ALASKA RANGE LEAVING SOUTHCENTRAL AK DRY
TONIGHT. HISTORY SAYS OTHERWISE SO WE WILL CONTINUE WITH THE FORECAST
OF LIGHT SNOW BEGINNING THIS EVENING AND ENDING AS THE UPPER TROF
SWINGS THROUGH TONIGHT. WE WILL BE WATCHING THE KENAI RADAR CLOSELY
THIS EVENING WAITING FOR THE SNOW TO DEVELOP.

A WARMER TREND BEGINS TOMORROW AS THE SECOND SHORT WAVE MOVES THROUGH
AND ALLOWS SLIGHTLY WARMER AIR ALOFT UP THE INLET. SOUTHWESTERLY FLOW
AT ALL LEVELS BEHIND THIS FEATURE WILL RESULT IN SHOWERS...TOO CLOSE
TO CALL RIGHT NOW SO WILL LEAN TOWARD A HEALTHY MIX OF RAIN AND SNOW.
A STRONG FRONT MOVES INTO THE NORTHERN GULF THURSDAY AND BRINGS GUSTY
WINDS THROUGH TURNAGAIN ARM AND PLENTY OF MOISTURE ALONG THE COAST.

SOUTHWEST ALASKA AND BERING SEA...THE AFOREMENTIONED TWO DISTINCT
SHORT WAVES AND SUBSEQUENT SOUTHWESTERLY FLOW ALOFT WILL ENSURE MOST
OF SOUTHWEST ALASKA MAINLAND REMAINSW MOIST. THE FIRST WAVE HAS
DROPPED MINIMAL AMOUNTS OF SNOW SO NOT EXPECTING MORE THAN A COUPLE
INCHES IN THE UPPER KUSKOKWIM VALLEY TONIGHT FROM THAT SYSTEM.
BELIEVE OVERRUNNING MOISTURE WILL SET UP NICELY ON WEDNESDAY
AFTERNOON OVER THE KUSKOKWIM VALLEY RESULTING IN A SIGNIFICANT
SNOWFALL. COASTAL AREAS WILL HAVE TOO MUCH WARM AIR AT THE SURFACE SO
MOST OF THE KUSKOKWIM DELTA AND BRISTOL BAY ZONES WILL TRANSITION
OVER TO RAIN BY TOMORROW. A TRIPLE POINT LOW WILL DEVELOP TOMORROW IN
THE CENTRAL BERING SEA AND AS THE PRESSURE GRADIENT TIGHTENS AHEAD OF
THE FRONT...EXPECTING GALE FORCE WINDS ALONG AND AHEAD OF THE
BOUNDARY. BEHIND THE LOW IN THE WESTERN BERING...COLD AIR WILL ADVECT
SOUTHWARD BEGINNING TOMORROW AFTERNOON RESULTING IN A STRONG
GALE...POSSIBLY STORM FORCE WINDS OVER THE WESTERN ALEUTIANS. AGAIN
CONFIDENCE DECREASES ALONG THE ALEUTIAN CHAIN PAST 36 HOURS OR SO
WHEN MODELS DIVERGE SIGNIFICANTLY ON THE SOLUTIONS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 155 160 165 170 172 176 180 185
FIRE WEATHER...NONE

AB OCT 07