Storm Warning 131, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 PM AKDT WED SEP 29 2010

.MODEL DISCUSSION...MODELS ARE DOING WELL THROUGH THURSDAY NIGHT AND
THEN IMPACTIVE DIFFERENCES OCCUR. IN MANY CASES THE DIFFERENCES IN
THE MODELS WOULD NOT BE THAT BIG OF AN ISSUE. HOWEVER THE DIFFERENCE
IN BRINGING THE LOW OVER THE MAIN PART OF KODIAK ISLAND WHICH THE 12
GFS IS SHOWING TO OTHER MODELS BRINGING IT OVER THE HOMER AREA TO
OTHERS SHOWING THE BARREN ISLANDS IS LARGE. THESE SOLUTIONS CONTINUE
TO DIFFER EVEN AFTER THE FRIDAY DAY PERIOD SO THERE IS SOME
UNCERTAINTY EXACTLY WHERE THE WORST OF THE WEATHER WILL OCCUR. BEST
GUESS AT THIS TIME IS THAT THE STORM WILL MOVE THROUGH THE BARREN
ISLAND REGION...BUT THAT EXPECTATION COULD CHANGE AS IT APPROACHES.

.ANALYSIS AND UPPER LEVELS...A SIGNIFICANT UPPER LEVEL TROUGH EXTENDS
OUT OF THE ARCTIC OCEAN THROUGH THE BERING STRAIT AND THEN ALL THE
WAY SOUTH TO AROUND 40N 165W. THE 250 MB JET STREAM EXTENDS FROM THE
TIP OF KAMCHATKA TO THE WESTERN ALEUTIANS WHERE IT DIVES RAPIDLY
SOUTHWARD AROUND THIS TROUGH. THERE IS A SHARP BEND IN THE JET AS IT
HEADS BACK TO THE NORTHEAST AND OVER THE SOUTHEAST GULF OF ALASKA.
THIS SECTION OF THE JET IS DISTINCTLY SEEN ON SATELLITE IMAGERY FROM
40N 160W THROUGH 50N 150W. THE IR IMAGERY IS ESPECIALLY IMPRESSIVE
SHOWING THE BAROCLINIC ZONE WITH THE ASSOCIATED VERTICAL MOTION.
THIS IS THE AREA WHERE A NEW SURFACE LOW WILL START TO DEVELOP
OVERNIGHT AND THEN RAPIDLY STRENGTHEN AS IT MOVES INTO THE
NORTHWESTERN GULF FRIDAY.
THE CYCLONIC MOTION SEEN ON THE SATELLITE NEAR THE SOUTHERN END OF
SHELIKOF STRAIT IS THE REMNANTS OF TYPHOON MALAKAS WHICH IS SLOWLY
WEAKENING AS IT BRINGS RAINFALL AND WARMER AIR INTO THE BRISTOL BAY
REGION THROUGH SOUTH CENTRAL ALASKA AND KODIAK.

.SHORT TERM FORECAST...THE SHORT TERM FOCUS IS ON THE LOW NEAR
SHELIKOF STRAIT THAT WILL MOVE INTO BRISTOL BAY OVERNIGHT AND THEN
REMAIN STATIONARY AND WEAKEN BEFORE THE DEVELOPING GULF LOW ABSORBS
IT TOMORROW. THIS WARM SYSTEM WILL CONTINUE TO BRING MOSTLY RAIN TO
THE AREA. THE EXCEPTIONS TO THIS ARE IN THE COPPER RIVER BASIN AND
FROM THE KILBUCK MOUNTAINS AND FARTHER WEST. WITH A SIGNIFICANT
INFLUX OF WARM AIR THE COPPER RIVER BASIN SHOULD TURN TO ALL RAIN BY
THIS EVENING. THE KILBUCK MOUNTAINS AND WESTWARD WILL SEE A SLOW WARM
UP INTO TOMORROW AS THE LOW MOVES NORTHWESTWARD BUT AREAS WEST OF
BETHEL WILL LIKELY STAY IN THE COLDER NORTHERLY FLOW. ELSEWHERE
PRECIPITATION WILL BE ALL RAIN EVEN FOR THE OVERNIGHT PERIODS.

.LONG TERM FORECAST...THURSDAY NIGHT INTO FRIDAY IS WHEN THINGS GET
REALLY INTERESTING FOR THE AREA FROM THE ALASKA PENINSULA TO THE
NORTH GULF COAST AS WELL AS SOUTH CENTRAL ALASKA INTO BRISTOL BAY.
THE DEVELOPING STORM THAT WAS DISCUSSED EARLIER IS STILL GIVING THE
MODELS FITS AND THEREFORE QUESTIONS REMAIN AS TO WHERE THE STRONGEST
WINDS WILL BE. WHAT CAN BE COUNTED ON IS THAT THE NORTH GULF COAST
WILL GET HIT HARD WITH A BARRIER JET DEVELOPING ALONG THE COAST OF
THE EASTERN KENAI PENINSULA ON FRIDAY. THIS WILL INCLUDE THE AREA
JUST OUTSIDE RESURRECTION BAY. PRINCE WILLIAM SOUND AND PASSAGE CANAL
MIGHT SEE STORM FORCE WINDS IF THE STORM TRACK MOVES FARTHER TO THE
NORTH...BUT WILL ONLY SEE GALES IF IT PROCEEDS OVER KODIAK ISLAND.
THE MAIN DIFFERENCE BETWEEN THIS LOW AND THE ONE FROM A WEEK AGO THAT
CAUSED THE WIND STORM IN SOUTH CENTRAL ALASKA IS THAT THE STORM LAST
WEEK WAS PUSHING INTO A WELL ESTABLISHED RIDGE THAT WAS OVER THE
MAINLAND PART OF THE STATE. THIS CAUSED A VERY TIGHT PRESSURE
GRADIENT. THE STORM APPROACHING ON FRIDAY WILL FOLLOW THE TROUGH
TOWARD THE CURRENT LOW AND THEREFORE THE TIGHTEST PRESSURE GRADIENTS
WILL BE ALONG THE GULF COAST AND OVER THE GULF OF ALASKA AND NOT OVER
THE LAND AREAS OF SOUTH CENTRAL ALASKA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES FROM GULF OF ALASKA REGION THROUGH EASTERN ALEUTIANS.
FIRE WEATHER...NONE

SEP 10