Small Craft Advisory 112, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1257 PM AKST TUE FEB 5 2013

.ANALYSIS AND UPPER LEVELS...UPPER LEVEL FLOW IS PROGRESSIVE WITH
SYSTEMS MOVING RELATIVELY QUICKLY FROM WEST TO EAST ACROSS THE
FORECAST AREA. SOUTHCENTRAL ALASKA IS QUIET AT THE MOMENT UNDERNEATH
A WEAK SHORT-WAVE RIDGE WITH SOME MID TO HIGH LEVEL CLOUDS PASSING
OVERHEAD AS WELL AS A FEW ISOLATED AREAS OF FOG. A LOW SPINNING SOUTH
OF THE GULF OF ALASKA HAS PUSHED A WEAK FRONT NORTHWESTWARD ACROSS
THE EASTERN GULF. THIS HAS TIGHTENED UP THE PRESSURE GRADIENT ALONG
THE NORTH GULF COAST JUST ENOUGH TO PRODUCE SOME LOCALIZED GAP WINDS
IN THE USUAL PLACES.

LOOKING UPSTREAM...AN UPPER LEVEL LOW AND SHARP SHORT-WAVE ARE
MAKING THERE WAY ACROSS SOUTHWEST ALASKA PRODUCING AREAS OF
SNOW...WITH RAIN ALONG THE NORTHERN ALASKA PENINSULA. WITH LIGHT
WINDS AND A STABLE AIRMASS (AS SCENE IN THE BETHEL AND MCGRATH
SOUNDINGS) AREAS OF FOG AND STRATUS HAVE ALSO DEVELOPED ACROSS THE
REGION.

MEANWHILE A VERY LARGE AND STRONG LOW SOUTH OF THE ALEUTIANS HAS
BOTTOMED OUT AROUND 950 MB AND IS REALLY BEGINNING TO WRAP UP. THE
OCCLUDED FRONT IS SPREADING NORTH AND EASTWARD TOWARD THE ALEUTIANS.

.MODEL DISCUSSION...THE 12Z NAM WAS QUITE A BIT FARTHER NORTH THAN
OTHER MODELS WITH TRACK OF SHORT-WAVE ACROSS SOUTHCENTRAL TONIGHT
AND WEDNESDAY. 18Z HAS TRENDED SOUTHWARD GIVING MORE CONFIDENCE IN
THE SOUTHERN SOLUTION. MODELS SHOW GOOD AGREEMENT WITH HANDLING OF
THE SYSTEM SOUTH OF THE ALEUTIANS THROUGH ABOUT THURSDAY MORNING.
DIFFERENCES ARISE AS THE TRIPLE POINT MOVES INTO THE WESTERN GULF
ON THURSDAY. THE WESTERN MOST SOLUTIONS (NAM/ECMWF) TRACK THE TRIPLE
POINT TO NEAR THE BARREN ISLANDS WHICH WOULD PRODUCE STRONG
DOWNSLOPING WINDS AND WARMER TEMPERATURES FOR THE WESTERN
KENAI/ANCHORAGE/MAT VALLEY. THE EASTERN MOST SOLUTION (GFS) TRACKS
THE TRIPLE POINT INTO THE NORTHERN GULF WHICH WOULD MEAN WEAKER
DOWNSLOPING WINDS AND COLDER TEMPERATURES. FOR THE TIME BEING WILL
GO WITH AN INTERMEDIATE SOLUTION UNTIL GAIN MORE CONFIDENCE IN WHERE
THIS TRIPLE POINT WILL TRACK.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...EXPECT LOCALIZED GAP WINDS ALONG THE NORTH
GULF COAST TO DISSIPATE THIS EVENING AS THE LOW SOUTH OF THE GULF
EXITS TO THE SOUTH. SNOW WILL DEVELOP EARLY TOMORROW MORNING ALONG
THE COOK INLET TO SUSITNA VALLEY CORRIDOR AS THE TROUGH OVER
SOUTHWEST ALASKA ARRIVES. THE TROUGH IS FAIRLY SHARP AND ACCOMPANIED
BY LOW LEVEL COLD ADVECTION. HOWEVER IT WILL BE PROGRESSING EASTWARD
FAIRLY FAST WHICH WILL LIMIT SNOW ACCUMULATION. OBSERVATIONS OVER
SOUTHWEST ALASKA TODAY INDICATE 2 TO 3 INCHES OF SNOW. EXPECT
SIMILAR AMOUNTS AS THE TROUGH CROSSES SOUTHCENTRAL WITH ISOLATED
HIGHER AMOUNTS ALONG THE WEST SIDE OF THE MOUNTAINS THANKS TO WEAK
UPSLOPE FLOW. THIS TROUGH WILL QUICKLY EXIT WEDNESDAY NIGHT AS A
SHORT-WAVE RIDGE MOVES IN. THIS WILL BE CONDUCIVE TO FORMATION OF
AREAS OF FOG. HOWEVER FRONTAL SYSTEM WILL QUICKLY MOVE IN FROM THE
BERING ON THURSDAY BRINGING PRECIP BACK INTO THE AREA. EVEN WITH
POTENTIAL FOR DOWNSLOPING WINDS...MODELS INDICATE UPPER FLOW WILL
BE SOUTHERLY...SO STILL EXPECT SOME PRECIP IN THE TYPICAL DOWNSLOPE
AREAS. AS MENTIONED IN THE MODEL DISCUSSION THERE IS SOME UNCERTAINTY
WITH THE PLACEMENT OF THE TRIPLE POINT WHICH WILL AFFECT EXTENT OF
DOWNSLOPING WINDS...TEMPERATURES...AMOUNT OF PRECIP...AND
PRECIP-TYPE.

SOUTHWEST ALASKA...UPPER TROUGH WILL CONTINUE EASTWARD ACROSS
SOUTHWEST ALASKA TONIGHT. COLDER AIR WILL MOVE IN THIS AFTERNOON
AND CHANGE PRECIP TO ALL SNOW ALONG THE NORTHERN ALASKA PENINSULA.
PRECIP WILL END FROM WEST TO EAST AS THE TROUGH MOVES TO SOUTHCENTRAL
ON WEDNESDAY. THE COMPLETE LOSS OF MID AND UPPER LEVEL MOISTURE
BEHIND THE TROUGH COMBINED WITH VERY MOIST LOW LEVELS WILL LEAD
TO WIDESPREAD AREAS OF STRATUS AND FOG. THESE AREAS OF LOW CLOUDS
AND FOG WILL PERSIST UNTIL THE FRONT EXTENDING FROM THE ALEUTIAN
LOW ARRIVES WEDNESDAY NIGHT INTO THURSDAY. THE FRONT WILL BE
WEAKENING AS IT ARRIVES...BUT WINDS MAY BE STRONG ENOUGH TO PRODUCE
SOME BLOWING SNOW ISSUES ALONG THE KUSKOKWIM DELTA. TRIPLE POINT WILL
TRACK ALONG THE ALASKA PENINSULA WHICH MEANS AIRMASS WILL STAY COLD
ENOUGH FOR ALL SNOW WITH THE POSSIBLE EXCEPTION OF THE NORTHERN
ALASKA PENINSULA/ALEUTIAN RANGE.

BERING SEA/ALEUTIANS...THE GREATEST IMPACT FROM THE ALEUTIAN LOW
WILL BE WIDESPREAD GALE TO STORM FORCE WINDS AS THE FRONTAL SYSTEM
SLOWLY PROGRESSES NORTH AND EASTWARD. WARMER AIR WILL ACCOMPANY THE
OCCLUSION AND RESULT IN PRIMARILY RAIN ALONG THE ALEUTIANS AND
SOUTHERN ALASKA PENINSULA. THE PRIBILOFS HOWEVER WILL REMAIN ON THE
COLD SIDE OF THE FRONT. EVEN THOUGH EASTERLY FLOW IS NOT THE MOST
FAVORABLE FOR BLIZZARD CONDITIONS...SURFACE TEMPERATURES WILL REMAIN
IN THE 20S AND PRECIPITATION WILL BE FAIRLY HEAVY AS THE MAIN
PRE-FRONTAL BAND MOVES THROUGH WEDNESDAY AFTERNOON AND EVENING.
THE PRESENCE OF SEA ICE IN THE VICINITY CAN ALSO CONTRIBUTE TO LESS
OF A MARINE INFLUENCE...HELPING MAINTAIN COLDER AND DRIER CONDITIONS
WHICH ARE MORE FAVORABLE FOR BLOWING SNOW. THEREFORE...WILL ISSUE A
BLIZZARD WARNING WITH THE AFTERNOON PACKAGE.

.LONG TERM FORECAST...THE ALEUTIAN STORM SYSTEM WHICH WILL AFFECT
MOST OF THE FORECAST AREA AS OCCLUDED FRONT TRACKS TO SOUTHCENTRAL
THURSDAY...WILL QUICKLY WEAKEN ON FRIDAY. MODELS ARE IN FAIRLY GOOD
AGREEMENT ON THE SYNOPTIC EVOLUTION AFTER THIS POINT WITH TWO MAJOR
LOWS MOVING INTO THE REGION...ONE OVER THE NORTHWEST
PACIFIC/ALEUTIANS AND ANOTHER MOVING FROM THE PACIFIC NORTHWARD TO
THE MAINLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...172 175 176.
         GALE WARNING...160 170 171 179 180 185.
FIRE WEATHER...NONE.

SERB FEB 13