Heavy Freezing Spray Warning 97, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1145 AM AKST SAT MAR 3 2012

.ANALYSIS AND UPPER LEVELS...UPPER LEVEL FLOW IS AMPLIFIED BUT
PROGRESSIVE...MEANING SYSTEMS WILL NOT LINGER IN ANY ONE PLACE
TOO LONG. THIS MORNING THERE IS A TROUGH CENTERED OVER MAINLAND
ALASKA AND THE GULF...A RIDGE FROM THE NORTH-CENTRAL PACIFIC TO
THE SOUTHERN BERING SEA...AND A TROUGH DROPPING OUT OF ASIA INTO
THE NORTHWEST PACIFIC. A SURFACE LOW OVER THE NORTHERN GULF IS
COMBINING WITH WEAK WAVES EMBEDDED WITHIN THE TROUGH TO PRODUCE
AREAS OF SNOW ACROSS SOUTHCENTRAL. AN UPPER LEVEL LOW/SHORT-WAVE
OVER SOUTHWEST ALASKA IS DROPPING DOWN THE BACK SIDE OF THE GULF
TROUGH AND WILL EVENTUALLY HELP TO KICK THIS LOW EASTWARD. COLD
ADVECTION ALONG WITH A STRONG NORTHWESTERLY JET ARE PRODUCING
STRONG GAP WINDS ALONG THE ALASKA PENINSULA AND INTO THE WESTERN
GULF. OUT WEST A FRONT EXTENDING FROM A WEAK LOW NEAR KAMCHATKA
TO THE CENTRAL ALEUTIANS IS GRADUALLY STRETCHING APART AS IT
PROGRESSES EASTWARD. MUCH WARMER AIR MOVING UP THE WEST SIDE OF
THE RIDGE IS MOVING IN BEHIND THIS FRONT. TEMPERATURES ACROSS THE
CENTRAL ALEUTIANS ARE APPROACHING 40 DEGREES. A DEVELOPING LOW
SOUTH OF THE ALEUTIANS WILL HELP PUMP EVEN WARMER AIR NORTHWARD
INTO THE SOUTHERN BERING SEAS OVER THE NEXT COUPLE DAYS.

.MODEL DISCUSSION...MODELS ARE IN GOOD AGREEMENT FOR THE NEXT FEW
DAYS AND SHOW GOOD RUN-TO-RUN CONSISTENCY. FORECAST CONFIDENCE IS
ABOVE AVERAGE.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...SNOW WILL GRADUALLY COME TO AN END ACROSS
SOUTHCENTRAL TONIGHT INTO SUNDAY MORNING AS UPPER LOW QUICKLY
TRACKS FROM SOUTHWEST ALASKA ACROSS THE GULF TO SOUTHEAST ALASKA.
THIS WILL HELP PULL THE SURFACE LOW OVER THE NORTHERN GULF SOUTHWARD.
CLOUDS WILL THEN DECREASE AS HIGH PRESSURE BUILDS IN BEHIND THE
LOW SUNDAY AFTERNOON THROUGH SUNDAY NIGHT. THIS BREAK WILL BE
SHORT-LIVED HOWEVER. A FRONT ASSOCIATED WITH A LOW OVER THE WESTERN
BERING WILL  ARRIVE AT THE WESTERN GULF MONDAY MORNING AND AND
QUICKLY TRACK ACROSS THE GULF AND SOUTHCENTRAL MONDAY NIGHT AND
TUESDAY. THIS WILL BRING ANOTHER PERIOD OF SNOW TO THE REGION.
DEEP SOUTHWESTERLY FLOW COMBINED WITH AN UPPER LEVEL WAVE IS VERY
FAVORABLE FOR SNOW ON THE WEST SIDE OF THE CHUGACH AND TALKEETNA
MOUNTAINS...FROM ANCHORAGE TO THE MAT-SU. WITH THE FAST SPEED OF
THE SYSTEM IT DOESN'T LOOK LIKE A HUGE DUMP OF SNOW...BUT WHAT
DOES FALL COULD BE INTENSE OVER A SHORT PERIOD OF TIME. BASED ON
CURRENT TIMING...THIS WOULD BRING SNOW TO ANCHORAGE LATE MONDAY
AFTERNOON THROUGH THE EVENING.

SOUTHWEST ALASKA...HIGH PRESSURE OVERHEAD COMBINED WITH MOSTLY
CLEAR SKIES WILL RESULT IN TEMPERATURES DROPPING WELL BELOW ZERO
ACROSS SOUTHWEST ALASKA TONIGHT. THESE DRY AND COLD CONDITIONS
WILL COME TO AN END MONDAY NIGHT AND TUESDAY AS A FRONT ARRIVES
FROM THE BERING. THERE MAY BE AN INITIAL PERIOD OF LOW VISIBILITY
IN SNOW AND BLOWING SNOW ALONG THE KUSKOKWIM DELTA...BUT EXPECT
WINDS TO DIMINISH QUICKLY AS THE FRONT WEAKENS ALONG THE COAST.
WINDS DON'T LOOK LIKE THEY WILL BE STRONG ENOUGH TO PRODUCE A
BLIZZARD. HOWEVER A BLOWING SNOW ADVISORY WILL LIKELY BE NEEDED.
THE FRONT WILL HEAD QUICKLY INLAND MONDAY AFTERNOON AND EVENING...
BUT THE PARENT LOW WILL WANDER INTO THE REGION TUESDAY MAINTAINING
AREAS OF LOW CLOUDS AND SNOW.

BERING SEA/ALEUTIANS...THE TROUGH DIGGING OUT OF ASIA WILL CAUSE
AMPLIFICATION IN THE DOWNSTREAM RIDGE OVER THE NORTH-CENTRAL PACIFIC.
THIS WILL PROVIDE A GOOD ENVIRONMENT FOR THE LOW SOUTH OF THE
ALEUTIANS TO DEEPEN. THE DOWNSTREAM RIDGE WILL FORCE IT TO TRACK
NORTHWARD ACROSS THE WESTERN BERING. THIS WILL ALLOW VERY WARM AIR
TO SURGE NORTHWARD ON THE EAST SIDE OF THE LOW WHICH WILL CHANGE
PRECIPITATION OVER TO RAIN ACROSS MOST OF THE REGION. THE PRIBILOFS
WILL INITIALLY BE COLD ENOUGH FRO BLOWING SNOW. HOWEVER...WITH A
WEAKENING FRONT AND RAPIDLY RISING TEMPERATURES ON SUNDAY DON'T
EXPECT VISIBILITIES TO GET LOW ENOUGH FOR A BLIZZARD. A TRAILING
COLD FRONT WILL PROGRESS EASTWARD ACROSS THE EASTERN BERING SUNDAY
NIGHT AND MONDAY SETTING UP A SHOWERY PATTERN AND CHANGING
PRECIPITATION BACK TO MOSTLY SNOW.

.LONG TERM FORECAST...UPPER FLOW WILL REMAIN PROGRESSIVE UNTIL THE
END OF THE WEEK WHEN IT LOOKS LIKE A DEEP TROUGH WILL SET UP FROM
MAINLAND ALASKA TO THE NORTHEAST PACIFIC AND HELP TO SLOW DOWN THE
PROPAGATION OF WAVES. PRIOR TO THAT THE REMNANTS OF THE BERING SEA
SYSTEM WILL MOVE INTO SOUTHCENTRAL AND THE GULF MID WEEK BRINGING
YET ANOTHER SHOT OF SNOW TO THE REGION...ALTHOUGH IT SHOULD
GENERALLY BE ON THE LIGHT SIDE. MODELS INDICATE THAT THE MORE
AMPLIFIED PATTERN WILL BRING A STRONG SYSTEM INTO THE GULF ON
FRIDAY...POSSIBLY BRINGING MORE SIGNIFICANT SNOWFALL TO PORTIONS OF
SOUTHCENTRAL. THE BERING SEA REGION WILL REMAIN IN A SHOWERY REGIME
THROUGH MID WEEK AS COLD AIR ADVECTS SOUTHWARD. THEN EXPECT ANOTHER
SYSTEM TO MOVE ACROSS THE REGION LATE IN THE WEEK FORCING THE ARCTIC
AIR TO MAKE ANOTHER NORTHWARD RETREAT.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...130 185.
         GALE WARNING...132 138 170 172 175 176 179 180.
         HEAVY FREEZING SPRAY WARNING...121 129 130 132 138 140 141
                                        150 165.
FIRE WEATHER...NONE.

SEB MAR 12