Small Craft Advisory 629, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 PM AKDT TUE AUG 11 2009

.MODEL DISCUSSION...
MODELS ARE IN RELATIVELY GOOD AGREEMENT FOR THE SHORT TERM KEEPING
THE UPPER LEVEL LOW IN EASTERN ALASKA THOUGH WEDNESDAY BEFORE THE
RIDGE OVER THE BERING PUSHES IT TO THE NORTH SLOPE WEDNESDAY EVENING.
IN ADDITION...THE KAMCHATKA LOW TO ROTATE INTO THE CENTRAL AND
EASTERN BERING OVER THE NEXT COUPLE DAYS. THE STRONG SHORT WAVE
ROTATING AROUND THE KAMCHATKA LOW TO MOVE THROUGH THE BERING TONIGHT
AND TOMORROW BEFORE CROSSING THE MAINLAND WEDNESDAY NIGHT AND
THURSDAY. THIS WILL BRING PRECIP BACK TO SOUTHWEST AND SOUTHCENTRAL
ALASKA. THE UPPER LOW TO SETTLE INTO THE EASTERN BERING BY FRIDAY.

AT THE SURFACE THE GFS IS SLOW ON THE LOW CROSSING THE ALEUTIANS THIS
AFTERNOON. EVEN THE NAM IS A BIT SLOW. THEREFORE...MOST PRECIPITATION
WILL START EARLIER THAN PREVIOUSLY THOUGHT FOR MOST AREAS IN THE
CENTRAL AND EASTERN BERING THIS AFTERNOON AND TONIGHT.
CONSEQUENTLY...PRECIP WILL END SOONER TO THE WEST OF THE LOW.

.ANALYSIS AND UPPER LEVELS...
A 996 MB LOW IS CROSSING THE ALEUTIAN CHAIN NEAR ADAK THIS AFTERNOON.
MINIMAL GALE FORCE WINDS ARE CIRCLING IT AND SHOULD THROUGH THE EARLY
EVENING AS THE LOW WEAKENS AS IT HEADS TOWARD THE PRIBILOF ISLANDS.
ANOTHER LOW IS SOUTHWEST OF SHEMYA AS WELL AND WILL CROSS ATTU ISLAND
TOMORROW. CLEAR SKIES OVER MUCH OF THE MAINLAND HAS LED TO A DECK OF
STRATUS ALONG THE COAST OF BERING. A COLD UPPER LOW OVER EASTERN
ALASKA BRINGING SHOWERS AND POSSIBLE AFTERNOON/EVENING THUNDERSTORMS
TO THE COPPER RIVER BASIN. SHOWERS EXTEND TO THE NORTHERN GULF COAST
EAST OF THE CHUGACH AND KENAI MOUNTAINS. WINDS ARE LIGHT MOST EVERY
ELSE OUTSIDE OF THE LOWS IN THE BERING AND NORTHERN PACIFIC.

.ALOFT...A DEEP CLOSED LOW EAST OF THE KAMCHATKA PENINSULA WITH A 100
KT JET ROUNDING IT AND SUPPORTING THE SHORT WAVE TROUGH ASSOCIATED
WITH THE SURFACE LOW NEAR ADAK THIS AFTERNOON. THE SHORT WAVE TO PUSH
THE RIDGE IN THE BERING EAST. THE RIDGE WILL FLATTEN OVER THE GULF AS
IT RUNS INTO THE UPPER LOW OVER EASTERN ALASKA. THE KAMCHATKA LOW TO
ROTATE EAST OVER THE NEXT FEW DAYS.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...
MOSTLY CLEAR SKIES DOMINATING MUCH OF THE MATSU VALLEY DOWN THROUGH
ANCHORAGE AND TO THE WESTERN KENAI WITH DRY NORTHERLY FLOW.
HOWEVER...A COLD UPPER LOW CREATING ENOUGH INSTABILITY FOR SHOWERS IN
THE COPPER RIVER BASIN TO THE NORTHERN GULF COAST EAST OF THE KENAI
AND CHUGACH MOUNTAIN CHAINS. THE LOW TO WEAKEN AND LIFT NORTH
TOMORROW. SHOWERS AND ISOLATED THUNDERSTORMS ARE POSSIBLE DURING THIS
TIME FRAME. A FRONT WILL PUSH TO KODIAK ISLAND TOMORROW WITH A TRIPLE
POINT LOW DEVELOPING NEAR THE ISLAND AS WELL TOMORROW NIGHT. SHOWERS
WILL SPREAD FROM KODIAK ISLAND TOMORROW AFTERNOON NORTH IN THE
EVENING. AFTER THIS INITIAL PUSH OF MOISTURE...THE FLOW WILL REMAIN
MOIST AND FROM THE SOUTHWEST FOR THURSDAY. SHOWERS WILL BE MORE
WIDESPREAD THURSDAY AS THE SHORT WAVE TROUGH MOVES THROUGH AS WELL. A
SECONDARY LOW TO MOVE TO KODIAK FRIDAY WITH SOME DRYING TO THE
NORTHERN SUSITNA AND COPPER RIVER BASIN WITH SHOWERS ELSEWHERE.
SATURDAY WILL DRY OUT A BIT AS THE LOW WEAKENS AND PASSES INTO THE
YUKON. COASTAL LOCATIONS SHOULD REMAIN WET THOUGH.

.SOUTHWEST...
THE DRY NORTHWESTERLY FLOW WILL BE REPLACED BY A MOIST SOUTHWESTERLY
FLOW WEDNESDAY. EXPECT STRATUS THAT IS IN PLACE OVER THE EASTERN
BERING TO DISSIPATE TOMORROW AS A FRONT WORKS TO THE COAST TOMORROW
AFTERNOON. WINDS TO INCREASE AS WELL WITH THE FRONT. PRECIP WILL WORK
TO THE AKPEN LATE TONIGHT AND MAKE ITS WAY TO THE COAST TOMORROW. DO
NOT EXPECT ANY PRECIP FURTHER INLAND UNTIL WEDNESDAY NIGHT. WITH THE
UPPER LOW AND SURFACE LOW REMAINING IN THE BERING...MOIST CONDITIONS
ARE EXPECTED THROUGH FRIDAY. PRECIP WILL WANE A BIT SATURDAY. WE
COULD SEE SHOWERS BEGINNING TO DEVELOP IN THE APKEN REGION AS EARLY
AS TONIGHT AND MOVE INTO THE MAINLAND WEDNESDAY NIGHT INTO THURSDAY.

.BEING SEA AND ALEUTIANS...
LOW CROSSING THE ALEUTIANS THIS AFTERNOON EAST OF ADAK AND HEADED
TOWARD THE PRIBILOF ISLANDS. STRATUS IN PLACE OVER THE EASTERN BERING
TO BE SHOVED ASIDE AS THIS LOW WORKS TO THE NORTH AND EAST. AN
ASSOCIATED FRONT MOVING THROUGH THE CENTRAL BERING NOW TO WORK TO THE
WEST COAST. JET SUPPORT TO WEAKEN AS THE LOW MOVES FARTHER FROM THE
PARENT STACKED LOW IN THE WESTERN BERING. THE LOW WILL THEREFORE
WEAKEN AS IT MOVES INTO THE EASTERN BERING TOMORROW. GALE FORCE WINDS
WILL BE ASSOCIATED WITH THE LOW THROUGH THE EARLY EVENING HOURS. THE
STACKED LOW IN THE WESTERN BERING TO MOVE INTO THE CENTRAL BERING
THURSDAY AND SETTLE IN THE EASTERN BERING FRIDAY. SOME MODERATE WINDS
TO ACCOMPANY THIS LOW AS IT HAS AMPLE JET SUPPORT ROTATING AROUND THE
BASE OF THE LOW. SHOWERS TO REMAIN ACROSS THE ENTIRE BERING AND
ALEUTIAN CHAIN WITH THIS LOW.

.LONG TERM FORECAST...
THE GFS AND ECMWF AGREE ON THE IDEA SETTLING THE CLOSED UPPER LOW
OVER THE EASTERN BERING THIS WEEKEND BEFORE PROGRESSING ONCE AGAIN IN
THE LATE WEEKEND EARLY NEXT WEEK. THEREFORE...THE MAINLAND WILL BE
UNDER A MOIST SOUTHWEST FLOW WITH MANY SHORT WAVES ROTATING THROUGH.
THE PROGRESSION STARTS AS A RESULT OF PHASING UP WITH A POLAR LOW
MOVING INTO THE ARCTIC OCEAN NORTH OF ALASKA. THIS WOULD PUT MUCH OF
THE BERING AND MAINLAND UNDER COLD NORTHERLY FLOW AND A TROUGH AXIS
IN THE MIDDLE OF THE STATE.

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

JN AUG 09