Small Craft Advisory 334, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
630 AM ADT MON APR 14 2008

.ANALYSIS AND UPPER LEVELS...
ACTIVE WEATHER PATTERN CONTINUES OVER MUCH OF ALASKA EARLY THIS
MORNING. THE ACTIVE PATTERN IS A RESULT OF THE POLAR JET FLOWING AT
160 KT FROM THE WESTERN ALEUTIANS TO THE KUSKOKWIM DELTA AND THEN
SOUTHWEST ACROSS SOUTHCENTRAL ALASKA AND INTO THE NORTHERN GULF. A
DISTINCT POSITIVELY TILTED TROUGH IS LOCATED FROM THE SEWARD
PENINSULA TO THE WESTERN ALEUTIANS. THE MOST SIGNIFICANT SURFACE
FEATURE IS A COLD FRONT THAT IS BEGINNING TO TAKE SHAPE ALONG THE
KUSKOKWIM VALLEY. WINDS HAVE SHIFTED TO THE WEST-NORTHWEST ALONG A
LINE FROM BETHEL TO MCGRATH WITH TEMPERATURES FALLING INTO THE 20S.
THE TIMING AND STRENGTH OF THIS COLD FRONT WILL BE THE BIGGEST
CHALLENGE FOR THIS FORECAST PACKAGE.

.MODEL DISCUSSION...
ALTHOUGH MODELS ARE IN AGREEMENT OF MAJOR FEATURES...HAVE NOTICED
SOME INITIALIZATION PROBLEMS THAT WE WILL HAVE TO TAKE INTO
CONSIDERATION. FIRST...BETHELS MORNING SOUNDING INDICATES A MAX WIND
SPEED OF 166 KT. BOTH GFS AND NAM PEAK AT APPROX 140 KT AT 12Z. ALSO
BELIEVE THE TIMING AND THE STRENGTH ARE OFF...BOTH MODELS ARE A BIT
SLOW AS THE COLD AIR IS ARRIVING IN THE KUSKOKWIM DELTA FASTER AND
WITH MORE VIGOR THAN ADVERTISED.

WARM AIR AT THE SURFACE MADE IT MUCH FURTHER INLAND THAN MODELS HAD
INDICATED. A LAYER OF WARM AIR JUST ABOVE THE SURFACE PROVIDED AREAS
FROM ANCHORAGE UP TO TALKEETNA WITH A PERIOD OF FREEZING RAIN EARLY
THIS MORNING WHILE KODIAK ENJOYED 50 DEGREE TEMPERATURES BRIEFLY
OVERNIGHT.

WHILE THIS FORECAST PACKAGE WAS NUDGED TOWARD THE 00Z GFS...HAD TO
MANIPULATE THE FINAL PRODUCT TO ACCOUNT FOR THESE DISCREPANCIES.

.SHORT TERM FORECAST...
SOUTH AND EAST OF THE ALASKA RANGE...
SURFACE TROUGH ROTATING THROUGH SOUTHCENTRAL ALASKA THE MOST LIKELY
CULPRIT FOR THE UNEXPECTED WINTRY MIX EARLY THIS MORNING. WINDS
BRIEFLY SHIFTED FROM SOUTHEAST TO NORTHEAST IN ANCHORAGE ALLOWING
SURFACE TEMPERATURES TO REMAIN BELOW FREEZING WHILE WARM AIR JUST
ABOVE THE SURFACE REMAINED ABOVE FREEZING. A PERIOD OF FREEZING
DRIZZLE MIXED WITH SLEET AND SNOW HIT ANCHORAGE BEFORE SOUTHEASTERLY
WINDS RETURNED AND A RAIN SNOW MIX RESUMED. LIGHT SNOW IS STILL
FALLING ACROSS THE MATANUSKA AND SUSITNA VALLEYS BUT WILL END SOON AS
THE TROF ROTATES EAST.

COLD AIR ADVECTION ENTERS THE PICTURE TUESDAY AFTERNOON WHILE AN
ELONGATED SURFACE LOW DEVELOPS FROM KODIAK ISLAND TO PRINCE WILLIAM
SOUND. THE LOW WILL BECOME BETTER DEFINED TUESDAY AS IT TRACKS ACROSS
MIDDLETON ISLAND AND MOVES NEAR YAKUTAT BY LATE TUESDAY NIGHT. A
VIGOROUS SHORT WAVE WILL MOVE ACROSS SOUTHCENTRAL TUESDAY NIGHT AND
HELP USHER IN THE REST OF THE COLD AIR. AS MENTIONED BEFORE THE
TIMING AND STRENGTH OF THE FRONT IS THE BIGGEST CHALLENGE. THE SYSTEM
IS MOISTURE LADEN ALTHOUGH THE SPEED AT WHICH IT TRAVERSES
SOUTHCENTRAL WILL HELP MITIGATE THE AMOUNT OF PRECIPITATION THAT
FALLS ACROSS THE MOST POPULATED AREAS. AT THIS POINT...FEEL CONFIDENT
THAT ANCHORAGE WILL SEE A BRIEF PERIOD OF SNOW BUT WILL NOT ADD UP TO
MUCH. THE EASTWARD PROGRESSION OF THE SYSTEM AND STRONG WINDS ALOFT
WILL BE TOO MUCH TO OVERCOME FOR SIGNIFICANT SNOWFALL IN ANCHORAGE
AND THE MAT-SU VALLEY. THE COASTAL AREAS SHOULD STILL SEE PLENTY OF
RAIN AND SNOW WITH THIS SYSTEM BUT AGAIN...IT WILL BE SHORT LIVED AS
THE STRONG NORTHWESTERLY FLOW QUIKCLY USHERS THE SYSTEM EAST OF OUR
DOMAIN.

ONE AREA OF CONCERN WILL BE THE STRONG GAP WINDS ON THE BACKSIDE OF
THE TROF. STORM FORCE WINDS THROUGH THE BARREN ISLANDS IS CERTAIN
WITH THE POTENTIAL FOR HURRICANE FORCE GUSTS. FEEL CONFIDENT ENOUGH
TO INCREASE TO STORM FORCE WINDS IN THE 4TH AND 5TH PERIOD OF THE
FORECAST. OTHER AREAS PRONE TO STRONG WINDS WITH COLD AIR ADVECTION
LIKE RESURRECTION BAY AND PASSAGE CANAL WILL CERTAINLY REACH GALE
DURING THIS TIME FRAME.

SOUTHWEST MAINLAND...
COLD FRONT MOVING SOUTHEASTWARD TODAY. THERE IS AN INITIAL PUSH OF
COLD AIR AND THEN A MUCH STRONGER REINFORCEMENT ASSOCIATED WITH THE
UPPER LEVEL TROF SWINGING THROUGH. AHEAD OF THE FRONT...SOUTHWESTERLY
WINDS GUSTING 25 TO 40 MPH WITH TEMPERATURES HOVERING NEAR FREEZING.
BEHIND THE FRONT...NORTHWESTERLY WINDS 15 TO 30 MPH WITH TEMPERATURES
RAPIDLY DROPPING FROM THE 30S TO THE 2OS AND TEENS. THE INITIAL FRONT
MAY STALL A BIT TODAY UNTIL THE TROF CATCHES UP AND HELPS PUSH IT
ACROSS THE ALASKA PENINSULA ON TUESDAY. THIS WILL BRING SOME
CHALLENGES TO THE TAFS TODAY AS IFR CONDITIONS ARE WIDESPREAD AHEAD
OF THE FRONT.

ALEUTIANS AND BERING SEA...
SAME STORY OUT WEST WITH FROPA TODAY AND COLD ADVECTION TONIGHT AND
TOMORROW. HIGH PRESSURE BUILDS OVER THE WESTERN BERING SEA TONIGHT
AND QUICKLY MOVES TO THE CENTRAL ALEUTIANS BY WEDNESDAY AHEAD OF THE
NEXT STORM FORCE LOW.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 150 155 165 170 172 175 176.
FIRE WEATHER...NONE.

AB APR 08