Blizzard Watch 18, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
115 PM AKST MON MAR 4 2013

.ANALYSIS AND UPPER LEVELS...
THE OVERALL WEATHER PATTERN HAS BECOME VERY AMPLIFIED WITH A HIGH
LATITUDE RIDGE OVER THE MAINLAND THAT EXTENDS ABOVE 70N.
MEANWHILE...A DEEP TROUGH OVER THE NORTH PACIFIC IS IN PLACE OVER THE
WESTERN 2/3 OF THE BERING SEA. A LONG AND SLOW-MOVING WEATHER FRONT
OVER THE EASTERN BERING IS MOVING SLOWLY AWAY FROM THE PRIBILOFS AND
TOWARD THE SOUTHWEST MAINLAND WITH SNOW AND GALE FORCE WINDS. AHEAD
OF THIS FRONT IS A SHORTWAVE TROUGH OVER BRISTOL BAY THAT IS CLASHING
WITH THE STRONG RIDGING TO THE EAST TO GENERATE A NARROW BUT INTENSE
BAND OF PRECIPITATION OVER INTERIOR PORTIONS OF BRISTOL BAY.

.MODEL DISCUSSION...
MODELS ARE IN GOOD SYNOPTIC AGREEMENT...WHICH IS NOT UNCOMMON WITH A
HIGHLY AMPLIFIED AND GENERALLY SLOW-EVOLVING WEATHER PATTERN. THE
FRONT OVER THE EASTERN BERING WILL WEAKEN AS IT CONTINUES TO PROGRESS
TOWARD THE MAINLAND COAST THIS EVENING. GALE FORCE WINDS WILL BE
LIMITED TO THE COAST AS THE FRONT FALLS APART AND PUSHES INLAND
DURING THE DAY TUESDAY. BY WEDNESDAY...THE PRESSURE GRADIENT ALONG
THE FRONT CONTINUES TO WEAKEN AS THE REMNANTS OF THE FEATURE MOVE
INTO SOUTHCENTRAL WITH A BRIEF PERIOD OF SNOW TO MOST AREAS WITH
GENERALLY MINIMAL SNOW ACCUMULATION. BY WEDNESDAY NIGHT ALL EYES TURN
TO A LARGE PACIFIC LOW THAT ALL MODELS BRING NORTHWARD TOWARD THE
BRISTOL BAY REGION ON THURSDAY. THIS STORM WILL BECOME A MAJOR
WEATHER-MAKER AS IT USHERS IN STRONG WINDS AND WARM TEMPERATURES FOR
THE END OF THE WEEK...ESPECIALLY OVER SOUTHCENTRAL ALASKA. THE GFS IS
A BIT OF AN OUTLIER BEING SLOWER WITH THE LOW MOVEMENT...WHILE THE
GEM IS THE FASTEST MODEL. THE EC/NAM SOLUTION IS THE MIDDLE GROUND
AND LOOKS THE MOST REASONABLE FOR THIS AFTERNOONS FORECAST.
SIGNIFICANT UNCERTAINTY ALSO STILL EXISTS INVOLVING THE DEVELOPING
AND STRENGTH OF ANY TRIPLE-POINT LOW AS THE FRONT MOVES INTO THE GULF
OF ALASKA. THINK SOME WEAK TRIPLE POINT DEVELOPMENT DEFINITELY SEEMS
POSSIBLE...BUT WILL OPT FOR MORE OF A BROAD-BRUSHED APPROACH UNTIL
MODELS COME INTO BETTER AGREEMENT AS THE STORM GETS CLOSER IN TIME.

.SHORT TERM FORECAST...
SOUTHCENTRAL...SIGNIFICANT PERIODS OF SUNSHINE WILL GIVE WAY TO
CLOUDY CONDITIONS ACROSS THE REGION BY TOMORROW MORNING AS THE BERING
FRONT PROGRESSES EASTWARD. PERSISTENT RAIN SHOWERS FROM KODIAK TO
SOUTHERN COOK INLET WILL DISSIPATE THIS EVENING AS THE MID-LEVEL
SHORTWAVE OVER BRISTOL BAY MOVES NORTHWARD. AS THE FRONT APPROACHES
THE REGION WEDNESDAY WINDS ALONG THE FRONT WILL DROP SIGNIFICANTLY.
MOST OF THE PRECIPITATION WILL GET CAUGHT UP ON THE COASTAL
MOUNTAINS...HOWEVER WITH WEAKENING CROSS-BARRIER FLOW THINK EVEN
INLAND AREAS WILL BE ABLE TO SEE A BRIEF PERIOD OF SNOW OR RAIN/SNOW
MIX DURING THE DAY WEDNESDAY. BY THURSDAY THE AFOREMENTIONED MAJOR
LOW APPROACHES THE REGION. THERE REMAINS SOME UNCERTAINTY IN THE KEY
DETAILS OF HOW THIS STORM WILL EVOLVE AS IT APPROACHES THE SOUTHERN
MAINLAND...INCLUDING TIMING OF THE LOW CENTER POSITION AND WHETHER OR
NOT THERE WILL BE SIGNIFICANT TRIPLE POINT LOW DEVELOPING IN THE
NORTHERN GULF. WHILE CONFIDENCE IS GROWING THAT TURNAGAIN ARM WILL
LIKELY BE APPROACHING WARNING-LEVEL WINDS ON THURSDAY...THESE KEY
DETAILS WILL HAVE A MORE SIGNIFICANT IMPACT ON HOW MUCH IF ANY WIND
MAKES IT INTO ANCHORAGE DURING THIS EVENING. SUFFICE IT TO SAY...STAY
TUNED TO THE LATEST FORECAST FOR THE MOST UP TO DATE INFORMATION
THROUGHOUT THE WEEK.

SOUTHWEST MAINLAND...THE MAIN FORECAST CHALLENGE WITH THE FRONT
IMPACTING THE AREA TONIGHT AND TOMORROW WILL BE HOW MUCH TEMPERATURES
WARM AND POTENTIAL FOR BLOWING SNOW ALONG THE KUSKOKWIM DELTA COAST.
THERE IS NOT A LOT OF WARM AIR REMAINING ALOFT WITH THIS FRONT...SO
NOT EXPECTING TEMPERATURES TO WARM TO ABOVE FREEZING AT MOST
LOCATIONS. THIS WILL KEEP PRECIPITATION TYPE GENERALLY AS SNOWFALL
NORTH OF CAPE NEWENHAM. THE FRONTAL PRECIP BAND IS NOT VERY
WIDE...BUT IS MOVING SLOWLY ENOUGH THAT SOME ACCUMULATIONS OF SNOW
ARE LIKELY AS WELL AS LOCALIZED AREAS OF BLOWING SNOW ALONG THE COAST
ANYWHERE TEMPERATURES STAY IN THE UPPER 20S. ON TUESDAY THE FRONT
PUSHES INLAND AND WEAKENS DRAMATICALLY...WITH A FEW INCHES OF SNOW
LIKELY IN INLAND AREAS OF BRISTOL BAY AND THE KUSKOKWIM VALLEY. THE
STORM ON THURSDAY WILL LIKELY BRING STRONG WINDS TO PORTIONS OF
BRISTOL BAY AND SNOW/BLOWING SNOW TO THE KUSKOKWIM DELTA AS THE LOW
TRACKS INLAND LATE THURSDAY. HOWEVER...THESE WEATHER IMPACTS WILL BE
VERY DEPENDENT ON THE EXACT TRACK OF THE LOW WHICH IS STILL IN
QUESTION AT THIS TIME.

BERING SEA AND ALEUTIANS...WITH THE FRONT MOVING OFF TO THE EAST MOST
OF THE BERING SEA WILL SEE BROAD BUT FAIRLY LIGHT SOUTHWESTERLY WINDS
WITH SCATTERED SHOWERS THROUGH WEDNESDAY. BY WEDNESDAY NIGHT THE
EASTERN HALF OF THE ALEUTIANS WILL BE THE FIRST TO FEEL THE EFFECTS
OF THE APPROACHING STORM. STRONG NORTH TO NORTHEAST WINDS WILL SPREAD
FROM DUTCH HARBOR TO THE ALASKA PENINSULA WITH STEADY PRECIP MOVING
IN FROM SOUTH. AT THIS TIME IT LOOKS LIKE THE RAIN/SNOW LINE WILL
LIKELY SETUP SOMEWHERE AROUND COLD BAY...WITH RAIN TO THE EAST AND
SNOW TO THE WEST.

.LONG TERM FORECAST...
THE AFOREMENTIONED MAJOR LOW WILL FALL APART RAPIDLY AS IT MOVES
SLOWLY INLAND THROUGH FRIDAY NIGHT. LONG RANGE MODELS ARE HINTING AT
A RIDGE BUILDING OVER THE BERING ON SATURDAY AND MOVING INTO INTERIOR
ALASKA BY SUNDAY EVENING BEFORE CONTINUING EASTWARD FOR THE START OF
NEXT WEEK. OVERALL...FAIRLY PROGRESSIVE FLOW WITH A SOUTHWESTERLY JET
STREAM WILL CONTINUE TO BRING ACTIVE WEATHER AND ABOVE NORMAL
TEMPERATURES INTO MUCH OF ALASKA.

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

AMD MAR 13