Small Craft Advisory 948, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKST THU NOV 19 2009

.ANALYSIS AND UPPER LEVELS...
AMPLIFIED PATTERN CONTINUES WITH A DEEP TROUGH ANCHORED OVER THE
MAINLAND AND GULF OF ALASKA WHILE A RIDGE OVER SOUTHWEST ALASKA AND
THE EASTERN BERING SEA IS BEING UNDERCUT BY A LARGE STORM IN THE
WESTERN BERING. THE JET IS BECOMING MORE ZONAL...FLOWING WEST TO EAST
JUST SOUTH OF THE ALEUTIAN CHAIN AT ABOUT 135 KT. THE FRONTAL
BOUNDARY ASSOCIATED WITH THE 955 MB LOW IN THE WESTERN BERING IS
RACING ACROSS THE EASTERN ALEUTIANS AND THE PRIBILOFS THIS AFTERNOON.
MULTIPLE MESO LOWS ARE SPINNING ABOUT IN THE GULF OF ALASKA.

.MODEL DISCUSSION...SOME MINOR DIFFERENCES BETWEEN THE MODELS IN THE
SHORT TERM BUT OVERALL...ALL SYNOPTIC FEATURES ARE WELL REPRESENTED
AND IN RELATIVE AGREEMENT. THIS FORECAST PACKAGE IS LEANING TOWARD
THE ECMWF AS IT HAS BEEN THE MODEL OF CHOICE FOR THE LAST SEVERAL
RUNS DUE TO ITS MORE CONSISTENT APPROACH TO THE EVOLUTION OF THE
DEVELOPING LOWS SOUTH OF THE CHAIN.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...COMPLEX AREA OF LOW PRESSURE IN THE GULF
CONTINUES TO SLIDE SOUTH. THE FEATURES THAT WILL BE IMPACTING
SOUTHCENTRAL OVER THE NEXT COUPLE OF DAYS WILL BE SUBTLE WHICH WILL
LEAD TO A TRICKY FORECAST. A TROUGH OVER THE NORTHERN HALF OF THE
STATE WILL DROOP SOUTHWARD OVER SOUTHCENTRAL. THE INCREASED SOUTHWEST
FLOW ALOFT COUPLED WITH THE REMNANTS OF THE FRONT THAT IS MOVING
ACROSS THE BERING WILL COMBINE TO GIVE MANY AREAS A CHANCE OF SNOW
THIS WEEKEND. WHILE THE MAIN TRIPLE POINT LOW SLIPS SOUTH OF THE
GULF...A TROUGH WILL EXTEND NORTHWARD AND A SURFACE LOW WILL LIKELY
DEVELOP BETWEEN MIDDLETON ISLAND AND THE EASTERN KENAI PENINSULA
FRIDAY NIGHT AND SATURDAY MORNING. THERE WILL BE JUST ENOUGH
DEFORMATION ALOFT AND MOISTURE AT THE SURFACE TO RESULT IN LIGHT SNOW
ACROSS THE AREA...ESPECIALLY ALONG THE CHUGACH RANGE. WHILE
CONFIDENCE IS GROWING...WE ARE STILL NOT EXPECTING A SIGNIFICANT
EVENT WITH ANY ACCUMULATION GREATER THAN AN INCH OR SO...SO WILL NOT
UPDATE THE WORDING TO LIKELY QUITE YET.

.SOUTHWEST ALASKA...
HIGH PRESSURE WILL PREVENT ANY WEATHER OF SIGNIFICANCE FROM MOVING
ONSHORE ACROSS BRISTOL BAY AND THE KUSKOKWIM DELTA. THE TRIPLE POINT
LOW WILL SLIP SOUTH OF THE ALASKA PENINSULA...RESULTING IN NORTH TO
NORTHEAST WIND ACROSS THE REGION AND DRIER AIR FILTERING SOUTHWARD
FROM THE YUKON VALLEY. IT IS NOT UNTIL SATURDAY EVENING THAT THE NEXT
AREA OF LOW PRESSURE AND ITS ASSOCIATED WEATHER FRONT MAKES ANY
PROGRESS INLAND...BRINGING SNOW ALONG THE COAST SATURDAY NIGHT AND
SPREADING UP THE KUSKOKWIM VALLEY SUNDAY MORNING.

.BERING SEA AND ALEUTIANS...
THE MOST ACTIVE WEATHER REMAINS OUT WEST WHERE A LARGE LOW AND ITS
ASSOCIATED FRONTAL BOUNDARY IS BRINGING HURRICANE FORCE WINDS TO MUCH
OF THE CENTRAL AND WESTERN BERING. TEMPERATURES AHEAD OF THE
FRONT...EVEN THOUGH WINDS WERE SOUTHEASTERLY...DID NOT INCREASE AS
EXPECTED...RESULTING IN ACCUMULATING SNOW IN DUTCH HARBOR AND
BLIZZARD CONDITIONS ACROSS THE PRIBILOF ISLANDS. WARMER AIR BEHIND
THE FRONT WILL BRING AN END TO THE BLIZZARD AND THE SNOWFALL THIS
EVENING. WINDS ACROSS THE AREA WILL ALSO DIMINISH AS THE UPPER LEVEL
SUPPORT BECOMES FAR REMOVED FROM THE SURFACE FEATURES...ALTHOUGH THE
NEXT WAVE WILL DEVELOP OVER THE NORTH PACIFIC AND MOVE ACROSS THE
CENTRAL ALEUTIANS FRIDAY NIGHT...BRINGING ANOTHER ROUND OF STORM
FORCE WINDS TO THE CENTRAL AND WESTERN ALEUTIANS THROUGH THE WEEKEND.

.LONG TERM FORECAST...NO CHANGE TO THE INHERITED LONG RANGE FORECAST
TONIGHT DUE TO THE LARGE VARIABILITY AND LOW RELATIVE MEASURE OF
PREDICTABILITY BASED OFF OF ENSEMBLE GUIDANCE...STILL APPEARS THE
COLD AND RELATIVELY DRY WEATHER OVER SOUTHCENTRAL AND THE GULF WILL
COME TO AN END AS ACTIVE WEATHER FROM THE BERING SLIDES EASTWARD FOR
THE START OF NEXT WEEK. THIS WILL ALSO USHER IN A RETURN TO MUCH MORE
SEASONAL TEMPERATURES.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 195
         HIGH WIND WARNING 191
MARINE...STORM 175 176 411
         GALE 127 128 170 172 180 185 179
         HEAVY FREEZING SPRAY 121 126 127 128 129 140 141 160 180
FIRE WEATHER...NONE.

AB NOV 09