Gale Warning 823, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
225 PM AKST SUN NOV 1 2009

.ANALYSIS AND UPPER LEVELS...
ANOTHER PATTERN SHIFT IS TAKING PLACE AS THE HIGH AMPLITUDE BLOCKING
RIDGE OVER THE EASTERN BEING SEA AND WESTERN INTERIOR IS BEING
UNDERCUT BY A DEEPENING TROF IN THE CENTRAL BERING. THE JET STREAM AT
ABOUT 175 KNOTS IS FLOWING OUT OF A RELATIVELY FLAT UPPER LEVEL RIDGE
ACROSS THE NORTH PACIFIC INTO THE NEGATIVELY TILTED TROF NEAR 175W.

AT THE SURFACE...A BROAD AREA OF LOW PRESSURE PERSISTS OVER THE
NORTHERN GULF WITH MULTIPLE SMALLER VORTICES. THE STRONGEST IS
PASSING SOUTH OF THE KENAI PENINSULA LATE THIS MORNING AND WILL
EVENTUALLY WEAKEN AS IT DRIFTS BACK EAST TOWARD YAKUTAT. SHOWERS
ASSOCIATED WITH THIS FEATURE WILL BE LIMITED TO THE GULF WATERS WITH
ONLY A FEW AFFECTING THE COAST. WINDS HAVE DIMINISHED SIGNIFICANTLY
FROM PREVIOUS DAYS AS THE RIDGE BREAKS DOWN TO THE WEST...BRINGING AN
END TO THE UPPER LEVEL SUPPORT. OUT WEST...THE INTERIOR IS MOSTLY
CLEAR OUTSIDE OF SOME STRATUS LINGERING OVER BRISTOL BAY. A
WEAKENING FRONTAL BOUNDARY HAS STALLED OVER THE CENTRAL ALEUTIANS
WHILE THE NEXT BIG STORM DEVELOPS OVER THE NORTH PACIFIC.

.MODEL DISCUSSION...MODEL SYNOPTIC MSLP AND UPPER AIR INITIALIZATIONS
ARE REASONABLE. THE SOLUTIONS DIVERGE ON THE DEVELOPING LOW IN THE
DATA SPARSE REGION OF THE NORTH PACIFIC...ALTHOUGH THE GFS IS CLEARLY
THE OUTLIER ON THE SPEED OF THE FRONT MOVING ACROSS THE ALEUTIANS
MONDAY AND TUESDAY. UKMET/NAM/ECMWF SOLUTION IS MORE CONSISTENT WITH
PREVIOUS RUNS AND IN GOOD AGREEMENT. THIS HAS BEEN THE FORECAST
CHALLENGE OF THE DAY...FINE TUNING THE TIMING OF THE FRONT. MODELS
COME BACK INTO AGREEMENT MID WEEK WHEN A LARGE LOW DEVELOPS SOUTH OF
THE ALASKA PENINSULA. THIS WAS ALREADY WELL COVERED IN THE INHERITED
FORECAST SO WE WILL NOT MAKE ANY CHANGES BEYOND TUESDAY NIGHT.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...SHOWERS AND CLOUDS ASSOCIATED WITH THE LAST OF THE
POTENT LOWS IN THE GULF HAVE BEEN CONFINED TO COASTAL SECTIONS OF
SOUTHCENTRAL ALASKA...RESULTING IN A PLEASANT DAY OVER THE INTERIOR.
WHILE THE UPPER TROF WILL REMAIN OVER THE COPPER RIVER BASIN...DRY
AIR CONTINUES TO FILTER SOUTHWARD ON THE BACKSIDE OF THE LOW WHICH
WILL LEAD TO ANOTHER CLEAR NIGHT AND FAIR WEATHER DAY MONDAY...WITH
TEMPERATURES NEAR CLIMATOLOGICAL NORMS.

CLOUDS ASSOCIATED WITH THE NEXT FRONTAL BOUNDARY WILL INVADE
SOUTHCENTRAL TUESDAY EVENING. LIGHT SNOW IS POSSIBLE AS WARM AIR WILL
OVERRUN THE COLD AIR THAT IS IN PLACE AT THE SURFACE. IT WILL TAKE
SOME TIME TO SATURATE THE VERY DRY COLUMN...BUT THERE COULD BE A
BRIEF PERIOD OF LIGHT SNOW IN ANCHORAGE BEFORE THE DOWNSLOPING TAKES
OVER. THE LARGE LOW DEVELOPS SOUTH OF KODIAK ON WEDNESDAY...BRINGING
WITH IT ABUNDANT MOISTURE AND STORM FORCE WINDS. TOO MUCH UNCERTAINTY
IS SURROUNDING THIS STORM RIGHT NOW BUT MODELS HAVE CONSISTENTLY BEEN
PLACING IT SOMEWHERE IN THE 950S...WITH THE GFS THE STRONGEST AT 946
MB. A LOW THIS STRONG IS NOT OUT OF THE QUESTION FOR THIS TIME OF
YEAR...AND WILL BEAR WATCHING FOR POTENTIAL HIGH WIND WARNINGS INLAND
AND HURRICANE FORCE WIND WARNINGS OVER THE MARINE ZONES.

.SOUTHWEST INTERIOR AND BERING SEA/ALEUTIANS...RELATIVELY BENIGN
WEATHER PATTERN FOR THE FIRST DAY OF NOVEMBER WILL BECOME MUCH MORE
ACTIVE THIS WEEK. OUTSIDE OF A FEW AREAS OF STRATUS...CLEAR SKIES
WILL CONTINUE TO PREVAIL THROUGH MONDAY NIGHT WHEN CLOUDS AND THEN
PRECIPITATION SPREADS INLAND. PRECIPITATION WILL BE IN THE FORM OF
SNOW INITIALLY...POSSIBLE MIXING WITH FREEZING RAIN ALONG THE
ALEUTIAN RANGE. SOUTHEASTERLY GAP WINDS WILL INCREASE AS
WELL...EVENTUALLY TURNING NORTHEAST AND FINALLY NORTHWEST AS LOW
PRESSURE MOVES SOUTH OF THE ALASKA PENINSULA AND INTO THE GULF. COLD
AIR WILL ADVECT SOUTH BACK ACROSS THE REGION WEDNESDAY NIGHT
RESULTING IN NUMEROUS SNOW SHOWERS...SIGNIFICANT ACCUMULATION AT THIS
POINT WILL BE LIMITED TO THE UPSLOPE MOUNTAIN RANGES. A BROAD TROF
WITH AXIS JUST EAST OF THE SOUTHWEST INTERIOR WILL STALL OVER THE
REGION...RESULTING IN BLUSTERY BUT RELATIVELY NORMAL FOR THIS TIME OF
YEAR.

THE RAPIDLY DEVELOPING AREAS OF LOW PRESSURE AIDED BY A STRONG JET
STREAM WILL SPREAD GALES THROUGH MOST OF THE BERING
SEA...OCCASIONALLY REACHING STORM FORCE WINDS...MAINLY ON THE COLD
ADVECTION SIDE LOW PRESSURE SYSTEMS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM 176 411 412 413
         GALES 172 175 179 185 414.
FIRE WEATHER...NONE.

AB NOV 09