Heavy Freezing Spray Warning 124, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 PM AKST MON MAR 5 2012

.ANALYSIS AND UPPER LEVELS...
INTERESTING UPPER LEVEL PATTERN SHAPING UP WITH A LARGE CLOSED LOW
JUST EAST OF KAMCHATKA...A RIDGE STRETCHING FROM THE CENTRAL PACIFIC
NORTHEASTWARD INTO MAINLAND ALASKA...AND A TROUGH JUST EAST OF THE
PANHANDLE. A CUT-OFF UPPER LOW MEANDERS IN THE CENTRAL PACIFIC. A
MOIST SOUTHWESTERLY FLOW EXISTS FROM THE NORTHWESTERN PACIFIC ACROSS
THE ALEUTIANS AND INTO MAINLAND ALASKA. LIGHT SNOW HAS SPREAD OVER
MUCH OF SOUTH CENTRAL THIS AFTERNOON AS WARM AIR PUSHES IN FROM THE
SOUTHWEST.

.MODEL DISCUSSION...
NAM IS TOO SLOW IN BEGINNING THE SNOW TODAY FOR MUCH OF THE KENAI
PENINSULA AND ANCHORAGE BOWL. MUCH OF THE FORCING WITH THE UPPER
LEVEL TROUGH HAS BEEN TRENDING TO THE NORTH WITH EACH CONSECUTIVE
MODEL RUN. SNOW WILL STILL STAY PRETTY CONSISTENT ACROSS THE SOUTH
CENTRAL AS THE OVERRUNNING SOUTHWESTERLY FLOW WILL PROVIDE FOCUS FOR
ASCENT. AS THE WARM AIR PUSHES OVER THE BARREN ISLANDS INTO WESTERN
PRINCE WILLIAM SOUND A WEAK TRIPLE POINT LOW WILL FORM. AT THE VERY
LEAST AN OPEN WAVE ON THE FRONT WHICH WILL BE ENOUGH TO TURN THE LOW
LEVEL FLOW TO THE SOUTH-SOUTHEAST DIRECTION. THE IMPLICATIONS BEING A
DOWNSLOPE COMPONENT TO THE WIND FOR THE NORTHERN KENAI PENINSULA
THROUGH THE MATANUSKA VALLEY...MAINLY FOR A SHORT PERIOD DURING THE
EVENING. AS THE LOW PROGRESSES INLAND THE LOW LEVEL FLOW WILL FLIP TO
THE SOUTHWEST AND INCREASE THE SNOW THROUGH THE OVERNIGHT HOURS.
WHILE ALL GUIDANCE IS SUGGESTING THAT THE SNOW WILL CONTINUE THROUGH
THE EARLY MORNING...THE NAM IS SUGGESTING THAT WARM DRY AIR ALOFT
WILL WORK OVERHEAD AND SWITCH THE PRECIPITATION TO FREEZING DRIZZLE
FOR A TIME. PAST TODAY THE NEXT SYSTEM WILL BE DEVELOPING IN THE
NORTH CENTRAL PACIFIC AND MOVE UP INTO THE GULF.

.SHORT TERM FORECAST...
SOUTH CENTRAL ALASKA...LIGHT SNOW WILL CONTINUE THROUGH THE MORNING
HOURS ON TUESDAY AS THE WARM FRONT PUSHES THROUGH. SNOW COULD REALLY
LIGHTEN UP IN THE NEXT FEW HOURS AS SOUTHEASTERLY FLOW DRIES THE LOW
LEVELS OUT FOR A PERIOD. IT IS POSSIBLE IN THE EARLY MORNING FREEZING
DRIZZLE COULD BE THE PREDOMINANT PRECIPITATION TYPE FOR SHORT
PERIODS. ACCUMULATING SNOW WILL BE DONE BY MID MORNING BUT SNOW
SHOWERS ALONG THE MOUNTAINS REMAIN POSSIBLE.

SOUTHWEST ALASKA...THE WESTERN SLOPES OF THE KILBUCKS AND ALASKA
RANGE WILL SEE SNOW LINGER THROUGH TOMORROW. OTHERWISE EXPECT
SCATTERED SNOW SHOWERS AS THE AIR BEHIND THE COLD FRONT REMAINS
UNSTABLE ENOUGH TO SUPPORT CELLULAR CONVECTION. THE THREAT FOR SNOW
SHOWERS WILL CONTINUE TILL THE UPPER TROUGH PUSHES THROUGH ON
WEDNESDAY.

BERING SEA AND ALEUTIANS...COLD AIR BEHIND THE DEPARTING LOW PRESSURE
WITHIN THE UPPER TROUGH IS SUPPORTING RAIN SHOWERS OVER THE OPEN
WATER. AS SURFACE TEMPERATURES COOL THIS EVENING SNOW WILL BEGIN TO
MIX IN AND EVENTUALLY BECOME THE DOMINANT PRECIPITATION TYPE. THESE
CONDITIONS WILL STAY IN PLACE THROUGH WEDNESDAY BEFORE THE NEXT WARM
FRONT SURGES NORTHWARD OVER THE WESTERN ALEUTIANS WEDNESDAY
AFTERNOON.

.LONG TERM FORECAST...
THE EXTENDED PERIOD LOOKS QUITE DIFFERENT THAN THE PATTERN OF THE
LAST FEW WEEKS. A TROUGH WILL BECOME ESTABLISHED OVER MUCH OF
MAINLAND ALASKA. THIS PATTERN WILL BE CONDUCIVE FOR LOW PRESSURE
SYSTEM DIGGING FROM THE BERING SEA ACROSS THE ALEUTIANS THEN INTO THE
GULF OF ALASKA TO FILL.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 155 172 175 176
FIRE WEATHER...NONE

MTL MAR 12