Small Craft Advisory 29, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKST WED JAN 7 2009

.MODEL DISCUSSION...
MODELS CONTINUE TO HAVE PROBLEMS REGARDING THE NORTH PACIFIC LOW
EXPECTED TO AFFECT THE CENTRAL ALEUTIANS BY WEDNESDAY NIGHT. WHILE
MODELS ARE IN GENERAL AGREEMENT THROUGH FRIDAY...SIGNIFICANT
DIFFERENCES ARISE AFTERWARDS. MODEL DISAGREEMENT PERTAINS MAINLY TO
THE STRENGTH...TIMING AND EVOLUTION OF THE LOW AS IT MOVES INTO THE
GULF THURSDAY AFTERNOON INTO FRIDAY. THE FORECAST PACKAGE THIS
AFTERNOON IS BASED ON THE ECMWF...AS IT HAS BEEN THE MOST CONSISTENT
PERFORMER RECENTLY.

.ANALYSIS AND UPPER LEVELS...
SURFACE HIGH PRESSURE OVER INTERIOR ALASKA CONTINUES TO SUPPLY COLD
AIR OVER THE SOUTHERN MAINLAND. A TROUGH IN THE GULF OF ALASKA IS
WEAKENING...GRADUALLY RELAXING THE PRESSURE GRADIENT ALONG THE
MOUNTAINS. ELSEWHERE LOW PRESSURE SOUTH OF THE CENTRAL ALEUTIANS IS
MOVING TOWARD THE NORTHEAST.

AT THE UPPER LEVELS A LOW IS CENTERED OVER THE YUKON TERRITORY...WITH
A TROUGH EXTENDING THROUGH CENTRAL ALASKA. THIS TROUGH WILL SLOWLY
DROP SOUTH THROUGH THURSDAY AS THE PARENT UPPER LOW LIFTS TOWARD THE
NORTHEAST.

.SHORT TERM FORECAST...

.SOUTHCENTRAL...
CLEAR...COLD AND DRY CONDITIONS WILL PERSIST THROUGH THE END OF THE
WEEK. TEMPERATURES ACROSS THE MOUNTAINS AND COPPER RIVER BASIN REMAIN
IN THE NEGATIVE 20 TO 50 RANGE. GIVEN SUCH COLD TEMPERATURES ONLY
LIGHT WINDS ARE NEEDED TO DROP WIND CHILLS BELOW -40 DEGREES.
ACCORDINGLY...A WIND CHILL ADVISORY IS IN EFFECT THROUGH FRIDAY FOR
THOMPSON PASS. CLOUDS SHOULD BEGIN FILTERING INTO THE AREA BY
THURSDAY NIGHT AS THE LOW MOVES INTO THE NORTHERN GULF. SNOW WILL
BEGIN TO IMPACT KODIAK BY THURSDAY AFTERNOON ALTHOUGH LIGHT
ACCUMULATIONS ARE EXPECTED. TEMPERATURES ALONG THE REST OF THE GULF
COAST WILL BE ON THE UPSWING FRIDAY AS MOISTURE INCREASES AHEAD OF
THE APPROACHING LOW. INLAND AREAS WILL ALSO SEE SOME RELIEF FROM THE
COLD BY FRIDAY...ALTHOUGH TEMPERATURES SHOULD STILL REMAIN BELOW
NORMAL.

.SOUTHWEST...
BRISK NORTHEASTERLY FLOW WILL CONTINUE THROUGH THE END OF THE WEEK
ACROSS MOST OF THE SOUTHWEST MAINLAND. COLD TEMPERATURES COUPLED WITH
MODERATE WINDS HAVE RESULTED IN WIDESPREAD WIND CHILLS OF 20 TO 50
DEGREES BELOW ZERO. A WIND CHILL ADVISORY IS IN EFFECT FOR THE
KUSKOKWIM DELTA THROUGH FRIDAY. CLOUDS AND MOISTURE WILL BE ON THE
INCREASE THURSDAY NIGHT...MAINLY ACROSS THE SOUTHERN ALASKA
PENINSULA...AS THE LOW MOVES INTO THE NORTHERN GULF. OTHERWISE EXPECT
THE REMAINDER OF SOUTHWEST ALASKA TO REMAIN DRY AND COLD AS WE
APPROACH THE WEEKEND.

.ALEUTIANS/BERING SEA...
COLD NORTHEAST FLOW WILL CONTINUE ACROSS MOST OF THE CHAIN THROUGH
FRIDAY. INCREASED COVERAGE OF SNOW SHOWERS WILL OCCUR OVER THE
CENTRAL AND EASTERN ALEUTIANS AS THE NORTH PACIFIC LOW PASSES TO THE
SOUTH THIS AFTERNOON THROUGH THURSDAY. CONDITIONS SHOULD IMPROVE BY
THE END OF THE WEEK...WITH SCATTERED SNOW SHOWERS AND MODERATE WINDS
PREVAILING.

.LONG TERM FORECAST...
AS PREVIOUSLY MENTIONED...CONFIDENCE IN THE LONG TERM REMAINS LOW AS
THE MODELS STRUGGLE WITH THE EVOLUTION OF UPCOMING SYSTEMS. OVERALL
EXPECT STORM SYSTEMS TO MOVE NORTH THROUGH THE GULF. THIS WILL RESULT
IN INCREASED MOISTURE AND WARMING ALONG COASTAL AREAS...EVENTUALLY
SPREADING FURTHER INLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...
MARINE...
FIRE WEATHER...

NRH/AB JAN 09