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000
FXAK68 PAFC 231447
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
547 AM AKST FRI JAN 23 2015

.ANALYSIS AND UPPER LEVELS...
THE MAJOR PLAYERS IN THIS EVENT REMAIN THE SAME WITH A BROAD
TROUGH SOUTH OF THE ALEUTIANS PUSHING AN ACTIVE SOUTHERLY FLOW
TOWARD AND OVER THE SOUTHCENTRAL MAINLAND. THE MOST NOTABLE
FEATURE ON WATER VAPOR IMAGERY AND ONE THAT DESCRIBES THE WHOLE
EVENT WELL IS A CLEAR DEMARCATION BETWEEN THE COLD/DRY ARCTIC AIRMASS
OVER THE INTERIOR...NORTH SLOPE...SOUTHWEST ALASKA AND THE
WARM/MOIST MARINE AIRMASS ON THE EAST/SOUTH SIDE OF THE ALASKA
RANGE. THE CLASH BETWEEN THESE TWO AIRMASSES ON THE LARGE SCALE IS
WHAT IS DRIVING THE ACTIVE WEATHER AROUND THE AREA...HOWEVER MANY
FINER DETAILS ON THE SMALLER SCALE WILL AFFECT SNOWFALL MAGNITUDE
AND DISTRIBUTION. THE FRONTAL BOUNDARY/DEFORMATION ZONE THAT MOVED
OVERHEAD ANCHORAGE YESTERDAY AFTERNOON AND EVENING IS NOW PARKED
TO THE WEST OVER COOK INLET...EXTENDING NORTHWARD INTO THE SUSITNA
VALLEY. A FRONTAL LIKE FEATURE IS MOVING FROM SOUTH TO NORTH OVER
THE KENAI PENINSULA WITH PAIH/PAHG RADARS SUGGESTING SPATIAL
CONTINUITY...LIKELY ABOVE MOUNTAIN TOP. THIS FEATURE LOOKS TO BE
WELL CORRELATED TO THE 300K ISENTROPIC SURFACE AND SHOULD CONTINUE
TO SPREAD SNOW OVER MOST AREAS INDEPENDENT OF THE AFOREMENTIONED
BAROCLINIC ZONE. THE PROGRESSION OF THE FORECAST THIS MORNING
LOOKS TO BE OVERRUNNING PRECIPITATION FOLLOWED BY WESTERLY COLD
ADVECTION AND FINALLY UPPER TROUGH PASSAGE.

&&

.MODEL DISCUSSION...
THE DIFFERENCES THAT PLAGUED INDIVIDUAL GUIDANCE SOLUTIONS
YESTERDAY CONTINUE TO DO THE SAME TODAY. MOST OF THE DISCREPANCY
SEEMS TO BE CENTERED ON HOW MUCH PRECIPITATION FALLS FROM KENAI
THROUGH THE MATANUSKA VALLEY TO THE EAST OF THE FRONTAL
BOUNDARY/DEFORMATION ZONE. THE APPEARANCE ON RADAR SUGGESTS THE
ZONE IS TOO FAR TO THE WEST AND NEEDS TO MIGRATE EAST BEFORE
INFLUENCING THE COOK INLET REGION. FOR THE MOST PART FEATURES ON
THE SYNOPTIC SCALE ARE PRETTY WELL AGREED UPON. THE NAM SEEMS TO
BE A FEW HOURS SLOWER WITH THE UPPER TROUGH PASSAGE ON SATURDAY
AFTERNOON...WHICH WOULD LEAVE FAVORABLE DYNAMICS OVER ANCHORAGE
AND THE MATANUSKA VALLEY LONGER. THERE IS MUCH BETTER AGREEMENT ON
PRECIPITATION AMOUNTS WITH COLD ADVECTION/TROUGH PASSAGE WITH THE
00Z/06Z MODELS SAVE THE GFS WHICH CONTINUES TO SEEMINGLY
UNDERPERFORM WITH PRECIPITATION AMOUNTS THOUGH THE SAME DYNAMICS
REMAIN IN PLACE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
ANOTHER SHOT OF OVERRUNNING SNOW LOOKS TO HIT THE KENAI PENINSULA
THROUGH THE MATANUSKA VALLEY THIS MORNING. SOME UNCERTAINTY STILL
EXISTS FOR THE AFTERNOON HOURS BUT PERIODS OF SNOW THROUGHOUT THE
DAY LOOK LIKELY IN MOST AREAS WITH ACCUMULATIONS. THE FRONT STILL
SITS OFF TO THE WEST OVER THE INLET AND WILL BEGIN TO TRACK EAST
DURING THE LATE AFTERNOON AND EVENING HOURS. AT THIS POINT COLD
ADVECTION WILL BEGIN TO WORK IN THE LOW LEVELS AND START THE
HEAVIEST PERIOD OF SNOW THROUGH THE OVERNIGHT HOURS INTO SATURDAY
MORNING. SNOW WILL TAPER OFF FROM WEST TO EAST SATURDAY
AFTERNOON/EVENING. ONCE THE SYSTEM PROGRESSES EASTWARD SNOW WILL
PICK UP IN THE COPPER RIVER BASIN ON SATURDAY FOR ANOTHER ROUND OF
ACCUMULATING SNOW.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TODAY THROUGH SATURDAY)...
THE LOW WIND CHILLS OVER THE SOUTHWEST MAINLAND WILL SLOWLY
IMPROVE LATER THIS MORNING AS THE NORTHERLY FLOW AND COLD AIR
ADVECTION DIMINISH. THIS WILL LEAVE CLEAR SKIES AND SOME OF THE
COLDEST TEMPERATURES OF THE SEASON FOR THE NEXT TWO
NIGHTS...ESPECIALLY FOR THE USUAL COLD SPOTS IN THE KUSKOKWIM
VALLEY AND INTERIOR KUSKOKWIM DELTA WHERE OVERNIGHT LOW
TEMPERATURES WILL APPROACH 30 BELOW ZERO. SNOW WILL CONTINUE OVER
EXTREME EASTERN BRISTOL BAY THROUGH LATE THIS MORNING AS THE
DEFORMATION BAND SLOWLY CLEARS FROM THE WEST. THIS BAND WILL
LIKELY REMAIN JUST OFF TO THE EAST...KEEPING SNOW SHOWERS OVER THE
ALEUTIAN AND ALASKA RANGES INTO SATURDAY...BUT THESE SHOULD REMAIN
EAST OF THE POPULATED AREAS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TODAY THROUGH SATURDAY)...
MOST OF THE REGION WILL REMAIN UNDER THE CURRENT NORTHERLY FLOW
AND COLD AIR ADVECTION REGIME INTO SATURDAY. THE ONE EXCEPTION TO
THIS WOULD BE THE WESTERN ALEUTIANS WHICH WILL SEE MORE WIDESPREAD
SNOW SHOWERS TODAY WITH A WEAK SHORTWAVE PASSING JUST OFF TO THE
NORTH. AFTER A BRIEF PERIOD OF CLEARING TOMORROW...THE NEXT
ALEUTIAN LOW WILL THEN APPROACH THE WESTERN ALEUTIANS ON LATE
SATURDAY BEFORE SPREADING INTO THE CENTRAL ALEUTIANS FOR SUNDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THIS TIME FRAME WILL BE KNOWN FOR THE MUCH COLDER AIR ACROSS MUCH
OF THE FORECAST AREA. GENERALLY DRY AND COLD CONDITIONS CAN BE
EXPECTED AFTER THE UPPER TROUGH AXIS PASSES OFF TO THE EAST.
BELOW ZERO TEMPERATURES ARE FORECAST FOR MUCH OF THE SOUTHERN
MAINLAND...EXCEPT MAINLY COASTAL AREAS...WITH FRESH SNOWCOVER AND
A COLD AIRMASS SPREADING EASTWARD OVER THE AREA. ACROSS THE BERING
SEA AND ALEUTIANS...A LARGE LOW WILL PASS BY TO THE SOUTH OF THE
ALEUTIANS...BRINGING PERIODS OF RAIN AND SNOW LATE THIS WEEKEND
AND EARLY NEXT WEEK.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY 101 111 121 125 131 141 145.
MARINE...GALE WARNING 130 131 150 155 160 165 170 172 173 174 180.
         HEAVY FREEZING SPRAY 130 138 160 165 170 180 185.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...ML
SOUTHCENTRAL ALASKA...ML
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...MBS