Gale Warning 174, NWS Anchorage, AK

AREA FORECAST DISCUSSION ...UPDATED
SOUTHCENTRAL AND SOUTHWEST ALASKA
257 PM AKST SUN FEB 28 2010

UPDATED TO ADD HEAVY FREEZING SPRAY WARNINGS

.ANALYSIS AND UPPER LEVELS...
COMPLICATED SURFACE WEATHER PATTERN UNDER THE DEEP UPPER LEVEL TROF
WITH AXIS NEAR 150W. THE JET STREAM IS FLOWING AROUND THE MASSIVE
TROF WITH PEAK SPEEDS AROUND 120 KT IN THE EXIT REGION OVER THE
PANHANDLE...AND 165 KT ON THE COLD AIR SIDE OVER THE SOUTHERN BERING
SEA. MULTIPLE EMBEDDED SHORTWAVES FLOWING AROUND THE TROF WITH THE
MOST POTENT NEARING THE GULF COAST AROUND YAKUTAT EARLY THIS
AFTERNOON. AN ELONGATED WAVE ACROSS THE SOUTHERN BERING IS ASSOCIATED
WITH A WEAKENING FRONTAL BOUNDARY. ANOTHER STRONG WAVE IS NEARING THE
SOUTHERN TIP OF THE KAMCHATKA PENINSULA. THIS LAST ONE WILL PLAY A
MAJOR ROLE IN THE FORECAST THROUGH EARLY NEXT WEEK.

AT THE SURFACE...THE MAIN SURFACE LOW IN THE EASTERN PACIFIC IS A
VERTICALLY STACKED AND DECAYING 971 MB LOW. AN OCCLUDED LOW IS
LOCATED JUST SOUTH OF KODIAK ISLAND. A FRONTAL BOUNDARY EXTENDS NORTH
AND EAST TOWARD THE GULF COAST WITH STRONG GALE FORCE WINDS ALONG AND
AHEAD OF THIS BOUNDARY. PRECIPITATION IS WIDESPREAD FROM THE GULF
COAST TO BRISTOL BAY ASSOCIATED WITH THE OCCLUSION. STRONG COLD AIR
CONTINUES TO SPILL SOUTHWARD FROM THE KUSKOKWIM DELTA DOWN ACROSS THE
ALASKA PENINSULA AND EASTERN ALEUTIANS. ACROSS THE CENTRAL AND
WESTERN BERING SEA...A FRONTAL BOUNDARY ORIENTED NW TO SE CONTINUES
TO WEAKEN.

.MODEL DISCUSSION...
MODELS SEEM TO BE FINALLY COMING INTO AGREEMENT WITH THE FEATURES
OVER THE EASTERN DOMAIN. THE DIFFERENCES OVER THE PAST COUPLE OF DAYS
ARE EVIDENT NOW BECAUSE OF A SECONDARY LOW THAT DEVELOPED ALONG THE
OCCLUSION. THE MODELS WERE TRYING TO PICK ONE OR THE OTHER AS THE
MAIN LOW INSTEAD OF THE DUAL HEADED SYSTEM THAT DEVELOPED. BECAUSE OF
THE DIFFERENT LOCATION OF THE SURFACE FEATURES...SOUTHEASTERLY FLOW
ALOFT BECAME MORE ESTABLISHED OVERNIGHT AND ESSENTIALLY DOWNSLOPED
THE ANCHORAGE BOWL AND WESTERN KENAI PENINSULA.

SOME MINOR DIFFERENCES IN THE SHORT TERM ARE EVIDENT WITH THE
INITIALIZATION OF THE APPROACHING FRONTAL BOUNDARY. WINDS ALONG THE
GULF COAST ARE PUSHING 50 KT WHEREAS ONLY 30 KT WAS INITIALLY
EXPECTED IN THIS AREA. SNOW HAS ALSO SPREAD MUCH FURTHER WEST TOWARD
BRISTOL BAY THAN THE MODELS PROJECTED. THESE ARE INDICATORS OF A MORE
POTENT SYSTEM WITH MUCH MORE DYNAMICS THAN EXPECTED...SO FORECASTS
WILL BE ADJUSTED TO ACCOUNT FOR THIS.

MORE SIGNIFICANT DIFFERENCES ARE OUT WEST AS A STRONG SHORTWAVE EXITS
THE NORTH PACIFIC ALONG THE JET STREAM AND HELPS DEVELOP A STORM
FORCE LOW ALONG THE ALUETIAN CHAIN MONDAY. THE GFS AND NAM AGREE ON A
TRACK A BIT SOUTH OF WHAT WAS PROJECTED ON SATURDAY MORNINGS MODEL
RUNS. THE ECMWF IS HOLDING ONTO A TRACK THAT TAKES THE LOW CLOSER TO
THE PRIBILOFS AND IS QUITE A BIT SLOWER. THE UKMET IS SOMEWHERE IN
THE MIDDLE. THE MANY MEMBERS OF THE GFS ENSEMBLE ARE CLOSELY PACKED
NEAR THE OPERATIONAL FORECAST ADDING SOME CONFIDENCE IN THE SOUTHERN
TRACK. GIVEN THE UNCERTAINTY AND POOR RUN TO RUN CONSISTENCY...WILL
ONLY NUDGE TOWARD THIS SOLUTION.

.SOUTHCENTRAL ALASKA...
OUTLOOK FOR THE NEXT SEVERAL DAYS LOOKS DRASTICALLY DIFFERENT THAN
YESTERDAY. THE FRONTAL BOUNDARY IS NOW EXPECTED TO MOVE INLAND LATE
THIS AFTERNOON AND EARLY EVENING. BEHIND THE FRONT...SOUTHEASTERLY
WINDS AT ALL LEVELS WILL KEEP PRECIPITATION ALONG THE COAST AND
DOWNSLOPE THE LEEWARD SIDE OF THE MOUNTAIN RANGES THROUGH MID WEEK.
THE EXCEPTION WILL BE A BRIEF PERIOD THIS AFTERNOON AND EVENING WHEN
LIGHT SNOW WILL FALL INLAND. A PERIOD OF HEAVY SNOW IS EXPECTED
AROUND PRINCE WILLIAM SOUND BEFORE THE ARRIVAL OF THE WARMER AIR THIS
EVENING. SNOW WILL CHANGE OVER TO RAIN AT OR NEAR SEA LEVEL AND
REMAIN A MIX OF RAIN AND SNOW THROUGH TUESDAY MORNING WHEN THE
OCCLUSION FINALLY MOVES INLAND...ALLOWING COLDER AIR TO FULLY WRAP
BACK AROUND TO THE COAST.

SOUTHWEST ALASKA...
WEATHER A BIT MORE ACTIVE THAN ANTICIPATED WITH THE PRECIPITATION
SPREADING WEST ACROSS BRISTOL BAY. ARCTIC AIR CONTINUES TO FUNNEL
SOUTH ACROSS THE WESTERN MAINLAND RESULTING IN DANGEROUS WIND CHILLS
40 TO 50 BELOW ALONG THE KUSKOKWIM DELTA. THE AIRMASS CONTINUES TO
MODERATE AS IT BECOMES FURTHER REMOVED FROM THE SOURCE AS WELL AS THE
INCREASED DAYLIGHT...SO CONDITIONS WILL CONTINUE TO SLOWLY IMPROVE
OVER TH NEXT 24 HOURS. OTHERWISE...SNOW WILL SPREAD INTO THE UPPER
KUSKOKWIM VALLEY TONIGHT ASSOCIATED WITH THE MOISTURE OVERRUNNING THE
ARCTIC BOUNDARY.

ALEUTIANS/BERING SEA...FOCUS OUT WEST WILL BE THE STORM FORCE LOW
THAT WILL DEVELOP IN THE NEXT 24 HOURS AND MOVE ACROSS THE CENTRAL
ALEUTIANS MONDAY AFTERNOON. AS PREVIOUSLY MENTIONED...SOME
UNCERTAINTY WITH THE SPEED AND TRACK OF THE LOW IS LEADING TO SOME
REDUCED CONFIDENCE BEYOND THE FIRST 36 HOURS. STILL...EXPECTED
WIDESPREAD STORM FORCE WINDS ALONG THE CHAIN AND POTENTIAL BLIZZARD
CONDITIONS IN THE PRIBILOFS STARTING MONDAY NIGHT.

A REINFORCING SHOT OF COLD AIR WILL MOVE ACROSS THE CENTRAL AND
EASTERN CHAIN LATER IN THE WEEK WITH WIDESPREAD COLD ADVECTION
SHOWERS AND POTENTIAL BLIZZARD CONDITIONS BY WEDNESDAY OVER THE
ALASKA PENINSULA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM WARNING 172 175
         GALE WARNING 120 125 150 155 160 165 170 176 179
         HEAVY FREEZING SPRAY ZONES 138 150 155 160 165 179
FIRE WEATHER...NONE.

AB FEB 10