Small Craft Advisory 201, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
210 PM AKST MON MAR 2 2009

.ANALYSIS AND UPPER LEVELS...
THE LONG WAVE PATTERN REMAINS RELATIVELY UNCHANGED WITH AN ANCHOR
UPPER LOW POSITIONED OVER EASTERN SIBERIA. A HIGH AMPLITUDE UPPER
LEVEL RIDGE IS IN PLACE OVER THE EASTERN BERING SEA AND SOUTHWEST
ALASKA MAINLAND. AN ACTIVE SOUTHWESTERLY JET FLOWING BETWEEN THE TWO
FEATURES IS SERVING AS THE FOCAL POINT FOR CYCLOGENESIS NEAR THE
CENTRAL ALEUTIANS.

AT THE SURFACE...PRESSURE GRADIENT THIS MORNING REMAINS STRONG ALONG
THE COASTAL MOUNTAINS IN SOUTHCENTRAL ALASKA. THIS IS WEAKENING AS
THE BROAD AREA OF LOW PRESSURE OVER THE NORTHEASTERN GULF MOVES
SOUTHEAST INTO THE PANHANDLE. WINDS WILL CONTINUE TO DIMINISH
TODAY AS A RESULT OF THE WEAKENING GRADIENT. HIGH PRESSURE IS
RESPONSIBLE FOR THE CLEAR SKIES ACROSS THE REGION BUT WILL QUICKLY
GIVE WAY TO HIGH CLOUDS AS THE BAROCLINIC LEAF FROM A DEVELOPING LOW
OUT WEST CROSSES THE ALASKA PENINSULA TONIGHT.

.MODEL DISCUSSION...MODELS CONTINUE TO DO A FAIRLY GOOD JOB HANDLING
ALL MAJOR FEATURES. ONE AREA OF CONTENTION IS A WEAK LOW PRESSURE
SYSTEM AND ASSOCIATED UPPER LEVEL TROUGH MOVING ACROSS THE EASTERN
ALEUTIANS THIS AFTERNOON. THE GFS IS SLIGHTLY STRONGER THAN THE NAM
WHICH APPEARS TO BE THE CASE BASED ON SATELLITE AND SURFACE
OBSERVATIONS. WILL BE INCREASING THE CHANCE OF SNOW ACROSS
SOUTHCENTRAL WITH THIS SYSTEM TUESDAY BASED ON THESE LATEST TRENDS.
STILL PREFER THE GFS/ECMWF SOLUTION WITH THE DEVELOPING LOW MID WEEK
BUT ALTOGETHER NO MAJOR CHANGES ARE IN STORE FOR THE UPCOMING
FORECAST PACKAGE.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE BAROCLINIC LEAF ASSOCIATED WITH THE
AFOREMENTIONED WEAK LOW PRESSURE SYSTEM WILL BE SPREADING ACROSS
SOUTHCENTRAL THIS EVENING. LATEST THINKING IS THAT
PRECIPITATION...WHILE LIGHT...IS NOW LIKELY WITH THIS SYSTEM.
ISENTROPIC LIFT MAXES OUT AT 18Z WITH SUFFICIENT PRESSURE ADVECTION
FROM THE SURFACE UP TO 290K OR SO. ONE INGREDIENT THAT MAY BE LACKING
WILL BE MOISTURE. THINKING THAT IT MAY TAKE A WHILE TO SATURATE THE
ATMOSPHERE...SO AT THIS TIME WILL BE BUMPING UP PROBABILITY OF
PRECIPITATION BUT KEEPING ACCUMULATION LESS THAN 1 INCH.

THE SYSTEM QUICKLY EXITS THE REGION TUESDAY NIGHT AND CLEAR SKIES
AGAIN PREVAIL BY WEDNESDAY MORNING. THE ACTIVE PATTERN WILL BRING THE
AFFECTS OF THE NEXT SYSTEM INTO SOUTHCENTRAL BY WEDNESDAY
NIGHT. SOUTHWESTERLY FLOW ALOFT AND AN IMPRESSIVE FETCH OF MOISTURE
WILL LEAD TO A GOOD CHANCE OF MORE SUBSTANTIAL SNOW
ACCUMULATION...ESPECIALLY OVER THE SUSITNA VALLEY. WILL HAVE TO WATCH
AS THIS DEVELOPS THE NEXT 48 HOURS.

SOUTHWEST ALASKA...SNOW WILL SPREAD INLAND THIS EVENING ASSOCIATED
WITH THE FIRST AREA OF LOW PRESSURE. THE SPEED OF THE SYSTEM WILL
HELP KEEP SNOW TOTALS RELATIVELY LIGHT. WARM AIR ON THE SOUTH SIDE OF
THE SYSTEM WILL KEEP PRECIPITATION TYPE RAIN ALONG THE ALASKA
PENINSULA AND EASTERN ALEUTIANS. HIGH PRESSURE QUICKLY BUILDS IN LATE
TONIGHT. THE NEXT OCCLUDED FRONT WILL BRING RAIN AND SNOW BACK TO THE
SOUTHWEST COAST TUESDAY NIGHT WITH SHOWERS PERSISTING THROUGH LATE
WEEK AS THE MAIN LOW MOVES NORTH TOWARD THE SEWARD PENINSULA.

BERING SEA ALEUTIANS....RELATIVELY BENIGN WEATHER...BY BERING SEA
STANDARDS...WILL PERSIST THROUGH TONIGHT WHEN THE NEXT NORTH PACIFIC
LOW DEVELOPS SOUTH OF THE WESTERN ALEUTIANS. THE NEXT STORM WILL
SPREAD GALES AND MINIMUM STORM FORCE WINDS ACROSS MOST OF THE BERING
SEA THROUGH LATE IN THE WEEK. WARM AIR SOUTH AND EAST OF THE LOW WILL
KEEP PRECIP TYPE ALL RAIN FOR MOST OF THE AREA...THE EXCEPTION WILL
BE THE WESTERN ALEUTIANS TUESDAY NIGHT WHEN COLD AIR BEGINS TO ADVECT
SOUTHWARD ON THE BACK SIDE OF THE LOW. WILL BE MENTIONING STRONGER
WINDS AND THE POSSIBILITY OF BLIZZARD CONDITIONS BUT WILL HOLD OFF ON
A WATCH OR WARNING FOR NOW.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...170 172 175 176.
FIRE WEATHER...NONE.

AB MAR 09