Gale Warning 1097, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKST THU DEC 30 2010

.MODEL DISCUSSION...

MODELS ARE IN GOOD AGREEMENT OVERALL...ESPECIALLY IN THE SHORT TERM.
PREFERRED THE NAM FOR ITS HIGHER RESOLUTION ON THE EAST SIDE WITH
WINDS. OUT WEST...THERE ARE TIMING DIFFERENCES WITH RESPECT TO A
NORTH PACIFIC LOW APPROACHING THE EASTERN ALEUTIANS THURSDAY NIGHT
INTO FRIDAY MORNING...SO A BLEND OF THE GFS AND EC WAS PREFERRED.
OTHERWISE...MODEL DIFFERENCES ARE RELATIVELY MINOR...YIELDING A
MEDIUM TO HIGH CONFIDENCE FORECAST FOR THE NEXT COUPLE OF DAYS.

.ANALYSIS AND UPPER LEVELS...

UPPER LEVEL LOW PRESSURE SYSTEM CONTINUES TO DIG SOUTH AND WESTWARD
THROUGH THE BERING SEA. THE POLAR FRONT CONTINUES TO BE SITUATED FROM
NEAR JAPAN NORTH AND EAST TO NEAR THE EASTERN ALEUTIANS AND ALASKA
PENINSULA AND EXTENDING FROM THERE TO THE GULF OF ALASKA. THE JET
STREAM ALOFT WILL CONTINUE TO MOVE SYSTEMS QUICKLY ALONG THE POLAR
FRONT OVER THE NEXT SEVERAL DAYS TOWARDS SOUTHERN ALASKA...KEEPING
THE PATTERN VERY ACTIVE THROUGH THE WEEKEND INTO THE EARLY PART OF
NEXT WEEK.

FOR BREVITY AND CLARITY...SYSTEM #1 IS OVER SOUTHCENTRAL ALASKA THIS
MORNING AND IS CURRENTLY RESPONSIBLE FOR THE LIGHT SNOW FALLING
ACROSS MOST OF THE REGION. SYSTEM #2 FEATURES A DEVELOPING LOW ALONG
THE COLD FRONT SOUTH OF THE ALASKA PENINSULA...WHICH WILL MOVE NORTH
AND EAST ACROSS KODIAK ISLAND LATE THIS AFTERNOON AND UP THROUGH THE
COOK INLET REGION TONIGHT. SYSTEM #3 WILL APPROACH THE CENTRAL
ALEUTIANS THROUGH SOUTHERN AKPEN LATE THURSDAY NIGHT INTO FRIDAY
MORNING BEFORE MOVING NORTH ACROSS THE KUSKOKWIM DELTA ZONE FRIDAY
NIGHT THROUGH SATURDAY. AN ASSOCIATED FRONT WITH THIS LOW WILL MOVE
SOUTHWEST TO NORTHEAST ACROSS THE GULF AND INTO SOUTHCENTRAL ALASKA
ON SUNDAY.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...

WIDESPREAD LIGHT SNOW CONTINUES IN ASSOCIATION WITH SYSTEM #1 OVER
SOUTHCENTRAL ALASKA THIS MORNING...AS SOUTHWEST FLOW ALOFT IS
PROVIDING PLENTY OF MOISTURE AMPLE LIFT. A FRONTAL BOUNDARY CAN BE
SEEN ON RADAR IMAGERY MOVING NORTH UP THE INLET...AND WITH FRONTAL
PASSAGE MOST PLACES WILL LIKELY SEE A VERY BRIEF TRANSITION TO MORE
SHOWERY CONDITIONS LATER TODAY BEFORE A RETURN TO STEADY SNOW. HEAVY
SNOW CONTINUES OVER WESTERN PRINCE WILLIAM SOUND ALONG WITH STRONG
WINDS...WITH A BLIZZARD WARNING CONTINUING THROUGH EARLY AFTERNOON
FOR NORTH OF MOOSE PASS. TEMPERATURES WILL CONTINUE TO WARM...AND
WILL EVENTUALLY CHANGE THE PRECIPITATION OVER TO RAIN MOST PLACES
ALONG PRINCE WILLIAM SOUND IN THE AFTERNOON.

SYSTEM #2 IS CURRENTLY DEVELOPING SOUTH OF THE AKPEN THIS MORNING
ALONG A COLD FRONT DRAPED NORTH-SOUTH ALONG THE 160TH WEST MERIDIAN.
THIS LOW PRESSURE SYSTEM WILL MOVE THROUGH SHELIKOF STRAIT LATER THIS
AFTERNOON AND THEN UP THROUGH COOK INLET. RAIN AND SNOW RATES IN
STRONG SOUTHERLY FLOW...ESPECIALLY OVER SOUTH AND SOUTHEAST FACING
SLOPES...WILL INCREASE DRAMATICALLY. IMPACTS FROM THIS EVENT WILL BE
THE POTENTIAL FOR HEAVY SNOW FOR THE SUSITNA VALLEY WEST OF THE PARKS
HIGHWAY...AND ALSO IN NORTHEAST PRINCE WILLIAM SOUND. VALDEZ MAY SEE
THE COLD AIR HANG IN JUST LONG ENOUGH FOR SIGNIFICANT ACCUMULATIONS
OF SNOW BEFORE POSSIBLY CHANGING OVER TO RAIN. WILL NEED TO WATCH TO
FOR THE POSSIBILITY OF WINDS AND SNOW PRODUCING BLIZZARD CONDITIONS
THROUGH THOMPSON PASS...BUT CONFIDENCE IS STILL NOT HIGH ENOUGH TO
WARRANT A WATCH THERE YET. WINTER STORM WATCH FOR HEAVY SNOW IN THE
SUSITNA VALLEY WEST OF THE PARKS HIGHWAY HAS BEEN ISSUED WITH THE
MORNING PACKAGE AND WILL YIELD TO THE FOLLOWING FORECAST PACKAGE TO
DECIDE WHETHER TO UPGRADE TO A WINTER WEATHER ADVISORY OR WINTER
STORM WARNING.

THE OTHER POTENTIAL SIGNIFICANT IMPACT WILL BE HIGH WINDS THROUGH
TURNAGAIN ARM. THE STRENGTH OF THE DISTURBANCE ALOFT AND LOW PRESSURE
AT THE SURFACE AS IT MOVES NORTH THROUGH THE COOK INLET REGION WILL
INCREASE THE PRESSURE GRADIENT SUBSTANTIALLY ACROSS TURNAGAIN ARM. AS
OF RIGHT NOW WE ARE EXPECTING WINDS TO POSSIBLY REACH HIGH WIND
CRITERIA BEGINNING LATE EVENING THROUGH LATE THURSDAY NIGHT. HAVE
ISSUED HIGH WIND WATCHES BOTH FOR THE ANCHORAGE ZONE AND
WESTERN PRINCE WILLIAM SOUND ZONES TO COVER THIS WITH THE MORNING
FORECAST PACKAGE.

WITH THE ONSET OF WINDS THROUGH TURNAGAIN ARM WE WILL LIKELY SEE
DOWNSLOPE CONDITIONS COMMENCE ACROSS THE ANCHORAGE BOWL...WHICH WILL
MOST LIKELY RESULT IN WARMING TEMPERATURES AND LITTLE PRECIPITATION.
WHAT PRECIPITATION DOES FALL...HOWEVER...HAS THE POTENTIAL TO FALL AS
SOME LIGHT RAIN OR FREEZING RAIN...SO WILL CERTAINLY HAVE TO KEEP AN
EYE ON THIS ASPECT FOR THIS SYSTEM. BY LATE FRIDAY MORNING AS THE LOW
PRESSURE AT THE SURFACE MOVES FARTHER INTO THE INTERIOR...WE WILL
LIKELY SEE A BRIEF PERIOD OF SNOW ACROSS ANCHORAGE AS COLD AIR BUILDS
BACK INTO THE AREA THROUGH THE AFTERNOON.

SYSTEM #3 FOLLOWS IMMEDIATELY ON THE HEELS OF SYSTEM #2 AND BEGINS TO
AFFECT THE REGION FRIDAY NIGHT. THE LOW PRESSURE SYSTEM WILL MOVE
MUCH FARTHER NORTH AND WEST ACROSS SOUTHWEST ALASKA THAN SYSTEM #2
AND WILL LIKELY ALSO HAVE MORE WARM AIR TO DRAW UPON AS A RESULT.
THUS...WE COULD BE LOOKING AT A MESSY SITUATION THIS WEEKEND WITH
TEMPERATURES REACHING WELL INTO THE 30S WITH PERHAPS A PERIOD OF
RAIN. STAY TUNED.

SOUTHWEST ALASKA...

LIGHT SNOW...WITH ISOLATED POCKETS OF FREEZING RAIN NEAR KING
SALMON...WILL CONTINUE TO MOVE ACROSS THE BRISTOL BAY AND MIDDLE
KUSKOKWIM VALLEY ZONES IN ASSOCIATION WITH SYSTEM #1 THIS
MORNING...AND WILL MOSTLY CLEAR THE AREA BY THIS AFTERNOON. SYSTEM #2
WILL LIKELY BRING A GOOD DOSE OF SNOW TO CENTRAL AND EASTERN PARTS OF
THE BRISTOL BAY ZONE NORTH INTO THE MIDDLE KUSKOKWIM VALLEY.
FORECASTED PRECIPITATION AMOUNTS SUGGEST THAT ENOUGH SNOW WILL FALL
TO WARRANT WINTER WEATHER ADVISORIES FOR SNOW...ESPECIALLY FOR
CENTRAL AND EASTERN SECTIONS OF THESE ZONES AS WRAP-AROUND MOISTURE
DEVELOPS ON THE BACKSIDE OF THE LOW PRESSURE SYSTEM MOVING THROUGH
SHELIKOF STRAIT NORTH THROUGH THE SUSITNA VALLEY. SYSTEM #3 WILL
BEGIN TO MOVE INTO THE REGION FRIDAY EVENING THROUGH SATURDAY...WITH
MODELS SUGGESTING THERE WILL BE LOTS OF MOISTURE ALONG WITH GOOD
ONSHORE AND UPSLOPE FLOW. WILL CONTINUE TO MONITOR FOR THE POTENTIAL
OF ADDITIONAL WATCHES...ADVISORIES...AND/OR WARNINGS IN ASSOCIATION
WITH THIS EVENT.

BERING SEA/ALEUTIANS...

BLIZZARD CONDITIONS SHOULD BEGIN TO WANE THIS AFTERNOON ACROSS THE
PRIBILOFS AS WINDS WEAKEN ON THE BACK SIDE OF A DISSIPATING LOW
MOVING TOWARDS BRISTOL BAY. NORTHERLY FLOW WILL PREDOMINATE THROUGH
THE REST OF THE SHORT TERM...WHICH WILL RESULT IN COLD ADVECTION SNOW
SHOWERS ACROSS THE REGION UNDER PARTLY TO MOSTLY CLOUDY SKIES.

.LONG TERM FORECAST...

ZONAL FLOW ACROSS THE NORTH PACIFIC LOOKS TO CONTINUE THROUGH THE
EXTENDED...WHICH WILL LIKELY KEEP THE WEATHER PATTERN QUITE ACTIVE
THROUGH THE MIDDLE OF NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING...125 195
         WINTER WEATHER ADVISORY...152 161
         WIND CHILL ADVISORY...155
         HIGH WIND WATCH...101 125
         WINTER STORM WATCH...145
MARINE...GALES...120 125 129 132 138 140 179 185
         STORMS...130
         HVY FRZG SPRY...140 179 185
FIRE WEATHER...NONE.

CC DEC 10