Snow Advisory 8, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
100 PM AST SUN JAN 27 2008

.ANALYSIS AND UPPER LEVELS...A HIGH AMPLITUDE RIDGE OVER MAINLAND
ALASKA IS SLOWLY BEING NUDGED EASTWARD AS AS SHORT-WAVES EMBEDDED
IN THE BERING SEAS TROUGH PUSH UP AGAINST IT. COLD AIR IS STILL
FIRMLY ENTRENCHED OVER ALL MAINLAND ALASKA EXCEPT THE SOUTHWEST
COAST. COLD ADVECTION HAS ENDED AND FLOW IS BEGINNING TO SHIFT
TO THE SOUTH AS RIDGE AXIS SLIDES EASTWARD. THEREFORE...WINDS
HAVE DIMINISHED TO BELOW WARNING LEVEL THROUGH THOMPSON PASS AND
THE COPPER RIVER DELTA. AT THE SURFACE A FRONT IS APPROACHING THE
SOUTHWEST ALASKA COAST. RADAR IMAGERY SHOWS WIDESPREAD SNOW
OVERSPREADING SOUTHWEST ALASKA AND WEAK RETURNS BEGINNING TO MOVE
UP COOK INLET. REPORTS FROM A FEW LOCALES NEAR THE SOUTHWEST COAST
INDICATE ONE HALF INCH TO ONE INCH PER HOUR. SNOW ADVISORIES HAVE
BEEN ISSUED FOR THE KUSKOKWIM DELTA AND BRISTOL BAY ZONES. OUT TO
THE WEST...WATER VAPOR IMAGERY SHOWS A SHARP SHORT-WAVE FROM WEST
OF THE PRIBILOFS SOUTHWARD ACROSS THE CENTRAL ALEUTIANS. A DECENT
LOW TO MID LEVEL JET BEHIND THE SHORT-WAVE IS PUSHING IT EASTWARD
RIGHT INTO THE MAINLAND RIDGE. SURFACE TEMPERATURES OVER THE CENTRAL
TO EASTERN BERING ARE ABOVE FREEZING WITH PRECIPITATION IN THE FORM
OF RAIN. MODERATE COLD ADVECTION IS OCCURRING BEHIND THE SHORT-WAVE
AND CONTRIBUTING TO STRONG GUSTY WINDS ACROSS THE ALEUTIANS.
OBSERVATIONS INDICATE GUSTS TO AROUND 50 KT WITH RAIN SHOWERS
CHANGING TO SNOW SHOWERS.

.MODEL DISCUSSION...MODELS ALL INITIALIZED FAIRLY WELL AND ARE IN
GOOD AGREEMENT THROUGH THE SHORT-TERM. THE 12Z NAM WAS SLOWER WITH
THE PROGRESSION OF THE FRONT AND MOVEMENT OF PRECIP INTO SOUTHCENTRAL
BUT 18Z RUN IS CLOSER TO GFS. STUCK CLOSE TO GFS THROUGH ABOUT MONDAY
NIGHT. BEYOND THAT THERE ARE LARGE MODEL DIFFERENCES WITH LOW
DEVELOPING SOUTH OF EASTERN ALEUTIANS/AKPENN. GFS/NAM SEEM TO BE THE
OUTLIERS COMPARED WITH THE FASTER AND WEAKER ECMWF/UKMET. GFS HAS
ALSO TRENDED TOWARD ECMWF SOLUTION AND GFS ENSEMBLE MEAN IS FASTER
THAN OPERATIONAL RUN. SO...HAVE STUCK WITH CURRENT GRIDS WHICH ARE
CLOSE TO THE ECMWF SOLUTION.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE FRONT WILL MOVE ACROSS KODIAK ISLAND
TONIGHT AND THEN STALL AS A TRIPLE POINT LOW FORMS JUST NORTHEAST OF
KODIAK CITY. PRECIPITATION IS CURRENTLY ALL SNOW ON KODIAK BUT WARMER
AIR WILL ACCOMPANY THE FRONT AND PRECIPITATION SHOULD MIX WITH OR
CHANGE TO RAIN BY THIS EVENING...ESPECIALLY ACROSS THE SOUTH END OF
THE ISLAND. COLDER AIR WILL MOVE BACK IN BY MONDAY MORNING ALONG WITH
GUSTY WESTERLIES. THERE IS THE POTENTIAL FOR LOCALIZED BLIZZARD
CONDITIONS IN THE MORNING...ESPECIALLY SOUTH END OF ISLAND (INCLUDING
AKHIOK) WHERE WINDS WILL BE STRONGEST. KACHEMAK BAY AREA WILL
INITIALLY SEE SOME DOWN-SLOPING WITH STRONG SOUTHEAST FLOW AHEAD OF
THE FRONT. THIS SHOULD MINIMIZE SNOW ACCUMULATION. HOWEVER...AS
TRIPLE POINT LOW FORMS EXPECT WINDS TO BACK TOWARD THE NORTH AND
STEADIER SNOW TO MOVE IN. WILL UP SNOW AMOUNTS FROM CURRENT FORECAST
AND CONSIDER A SNOW ADVISORY ONCE 18Z GFS GETS IN. SINCE FRONT STALLS
OVER GULF SNOW AMOUNTS INLAND WILL BE LIGHT WITH A BIT MORE AROUND
PRINCE WILLIAM SOUND. SOUTHCENTRAL WILL GRADUALLY DRY OUT MONDAY
NIGHT AND TUESDAY AS THE LOW TRACKS OFF TO THE SOUTHEAST.

SOUTHWEST ALASKA...COMBINATION OF SNOW ALONG SLOW MOVING FRONT AND
SNOW ASSOCIATED WITH UPPER LEVEL SHORT-WAVE MOVING ACROSS THE BERING
WILL RESULT IN A PROLONGED PERIOD OF SNOW ACROSS MOST OF SOUTHWEST
ALASKA. IN ADDITION TO SNOW ADVISORIES IN EFFECT FOR KUSKOKWIM DELTA
AND BRISTOL BAY ZONES ALSO PLAN TO ISSUE ONE FOR THE KUSKOKWIM VALLEY
ZONE. APPROXIMATE STORM TOTAL ACCUMULATION OF 6 TO 16 INCHES IS
EXPECTED ACROSS SOUTHWEST ALASKA WITH HEAVIEST AMOUNTS OVER INLAND
BRISTOL BAY WHERE SNOW IS BEING ENHANCED BY UPSLOPE FLOW. YET ANOTHER
SHORT-WAVE WILL MOVE TO SOUTHWEST ALASKA LATE MONDAY...SO AREAS OF
SNOW OR SNOW SHOWERS WILL CONTINUE THROUGH MONDAY NIGHT AND THEN
CONDITIONS SHOULD FINALLY DRY OUT ON TUESDAY AS A SHORT-WAVE RIDGE
BUILDS OVER THE REGION.

BERING SEA/ALEUTIANS/AKPENN...SNOW SHOWERS AND STRONG GUSTY
SOUTHWESTERLY WINDS WILL DOMINATE THE WEATHER BEHIND THE UPPER LEVEL
SHORT-WAVE. THE PRESSURE GRADIENT AND COLD AIR ADVECTION WILL WEAKEN
MONDAY NIGHT INTO TUESDAY...BUT SCATTERED SNOW SHOWERS WILL CONTINUE
AS THE REGION REMAINS UNDER MAINLY CYCLONIC FLOW ALOFT. DEVELOPING
PACIFIC LOW MAY COME CLOSE ENOUGH TO EASTERN ALEUTIANS AND AKPENN
TUESDAY TO PRODUCE SNOW AND BLOWING SNOW...BUT WITH GREAT UNCERTAINTY
IN THE TRACK OF THAT LOW WILL WAIT UNTIL MODELS GET A BETTER HANDLE
ON IT BEFORE TAKING A CLOSER LOOK AT BLIZZARD POTENTIAL.

.LONG TERM FORECAST...GFS 500MB 5-WAVE SHOWS A FAIRLY ZONAL LONG-WAVE
PATTERN THROUGH THE EXTENDED PERIOD. SO EXPECT STORMS TO MOVE FAIRLY
FAST FROM WEST TO EAST ACROSS THE FORECAST AREA WITH LITTLE
FLUCTUATION IN TEMPERATURES AND A SHOT OF PRECIPITATION EVERY FEW
DAYS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 120 130 132 150 155 160 165 170 171 172 175 176 179
               180 185.
         HEAVY FREEZING SPRAY...130 140 141.
FIRE WEATHER...NONE.

SEB JAN 08