Small Craft Advisory 434, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
353 PM AKDT WED MAY 20 2015

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL FLOW OVER THE FORECAST AREA IS HIGHLY AMPLIFIED
TODAY WITH A SHARP RIDGE EXTENDING OUT OF THE PACIFIC UP THE 145W
PARALLEL ALL THE WAY OVER THE COPPER RIVER BASIN INTO THE
INTERIOR OF THE STATE. THE UPPER LEVEL TROUGH EXTENDS OUT OF
EASTERN RUSSIA INTO THE CENTRAL BERING SEA AND THEN OVER DUTCH
HARBOR. THIS COMBINATION IS BRINGING THE JET STREAM OVER SOUTHWEST
MAINLAND ALASKA WHICH IS CONTINUING THE RAINFALL IN THAT AREA.
THE SURFACE FRONT EXTENDS FROM NEAR THE BERING STRAIT INTO BRISTOL
BAY AND THEN NEAR THE SOUTHWESTERN GULF OF ALASKA. THE SURFACE
RIDGE IN THE GULF IS BEGINNING THE GET SQUEEZED BY THIS FRONT
AS IT APPROACHES FROM THE WEST. THIS IS SHIFTING THE ORIENTATION
OF THE RIDGE TO BECOME MORE PARALLEL TO THE NORTH GULF COAST
WHICH HELPS TO INCREASE THE GUSTY WINDS THROUGH CHANNELED TERRAIN
IN SOUTHCENTRAL ALASKA AND THE COPPER RIVER BASIN.

FARTHER WEST THE JET STREAM IS RUNNING FROM OVER JAPAN TOWARD ATTU
BEFORE CURVING AGAIN TO THE SOUTHEAST AROUND THE SOUTHERN
PERIPHERY OF THE UPPER LEVEL TROUGH. THE REMNANTS OF FORMER
TYPHOON DOLPHIN ARE CURRENTLY EAST OF JAPAN AND ARE BEING CAUGHT
UP IN THIS JET STREAM. WHAT THIS MEANS IS THAT THE STORM WILL
STRENGTHEN AGAIN AS IT BECOMES EXTRA-TROPICAL AND MOVES INTO THE
WESTERN BERING SEA THURSDAY. AT THIS TIME MAXIMUM WINDS APPEAR TO
BE STORM FORCE IN THE CENTRAL TO WESTERN BERING SEA AND ALEUTIAN
ISLANDS.

&&

.MODEL DISCUSSION...
THERE ARE ONLY MINOR DIFFERENCES IN MODELS OVER THE SOUTHERN MAINLAND
PART OF THE STATE. IN THE WESTERN PART OF THE STATE THE MODELS
HAVE CONVERGED ON A VERY SIMILAR SOLUTION FOR THE REMNANTS OF
FORMER TYPHOON DOLPHIN AS IT ENTERS THE WESTERN BERING SEA
THURSDAY AND THEN TREKS SLOWLY INTO THE CENTRAL BERING SEA THROUGH
EARLY NEXT WEEK. THE ONLY DIFFERENCE ON NOTE RIGHT NOW IS THAT THE
ECMWF CONTINUES TO RUN 5 TO 8 MB WEAKER THAN THE OTHER
MODELS...KEEPING IT IN THE MID 960S INSTEAD OF A LOWEST PRESSURE
IN THE UPPER 950S. IN EITHER CASE IT WILL BE A STRONGER STORM THAN
IS TYPICAL FOR THIS TIME OF YEAR.

&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

ONSHORE MOIST FLOW WILL CONTINUE TO BRING RAIN TO KODIAK ISLAND
THROUGH FRI AND SOME SHOWERS TO THE SOUTHERN KENAI PENINSULA INTO
THU. OTHERWISE HIGH PRESSURE BUILDING OVER SOUTHCENTRAL AK WILL
BRING WARMER AND DRIER CONDITIONS THROUGH FRI. LOCAL BREEZY
CONDITIONS THROUGH CHANNELED AREAS WILL ALSO DIMINISH THROUGH THE
PERIOD.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...

A STATIONARY BUT WEAKENING FRONTAL ZONE OVER SOUTHWEST WILL
CONTINUE TO SPREAD RAIN OVER MUCH OF THE BRISTOL BAY AND LOWER
KUSKOKWIM REGIONS INTO MONDAY. THE FRONT WILL SLOWLY WEAKEN AND
DRIFT EAST...DRYING OUT FIRST OVER THE KUSKOKWIM DELTA. WITH WEAK
ONSHORE FLOW AND SOME CLEARING OUT OF HIGHER CLOUDS OVER THE
KUSKOKWIM DELTA...SOME FOG IS POSSIBLE OVERNIGHT. THE FRONT WILL
FALL APART TOMORROW AFTERNOON WITH A CHANGE TO SHOWERS. WEAK
DISTURBANCES ALOFT WILL SUPPORT MORE PERIODS OF LIGHTER RAIN AGAIN
ON FRIDAY...BUT IT WILL NOT BE AS WIDESPREAD OR INTENSE AS THE
FRONTAL RAIN OVER THE LAST DAY. STRONG SOUTHEAST WINDS WILL WANE
OVERNIGHT TONIGHT AS THE FRONT WEAKENS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

THE BIG STORY FOR THE BERING SEA WILL BE THE DEVELOPMENT OF A
STRONG LOW (STORM FORCE) DEVELOPING OVER THE WESTERN BERING SEA
AND ALEUTIANS AS THE REMNANTS OF FORMER TYPHOON DOLPHIN INTERACT
WITH A NORTHERN STREAM BAROCLINIC WAVE. WHILE SOME DISCREPANCY
EXISTS IN CENTRAL PRESSURE...THIS STORM WILL BE RATHER ANOMALOUSLY
STRONG FOR THIS TIME OF YEAR. THE STORM WILL REACH MAX INTENSITY
ON THURSDAY EVENING BEFORE SLOWLY WEAKENING FRIDAY. THE MAIN
IMPACT WITH THIS STORM WILL BE OVER THE WESTERN AND CENTRAL BERING
SEA/ALEUTIANS WITH STORM FORCE WINDS (UP TO 50 KTS) AND HEAVY RAIN.
THE EASTERN ALEUTIANS WILL REMAIN WELL EAST OF THE LOW WITH
SOUTHERLY FLOW AND GUSTY GAP WINDS THROUGH THE TERRAIN...AND
PERIODIC RAIN SHOWERS.

&&

.LONG TERM FORECAST (SATURDAY THROUGH WEDNESDAY)...

BEGINNING THE EXTENDED FORECAST ON SATURDAY...THE REMNANTS OF
FORMER TYPHOON DOLPHIN WILL BE SPINNING OVER THE FAR WESTERN
BERING...WITH A STRONG NORTH AMERICAN RIDGE CENTERED OVER THE
YUKON. A WEAKENING LOW IN THE NORTH PACIFIC WILL MERGE WITH THE
LARGE LOW OVER THE BERING...EFFECTIVELY ENDING THE LONG PERIOD OF
WARMTH AND DRY WEATHER FOR SOUTHCENTRAL. THAT SAID...THE FRONT
WILL BE FALLING APART AS IT MOVES EAST...WITH THE WETTEST WEATHER
ON SATURDAY AND SUNDAY BEFORE DRYING OUT AND BECOMING MORE SHOWERY
TUESDAY AND WEDNESDAY...WITH TEMPERATURES ONCE AGAIN SLOWLY
REBOUNDING. THE PATTERN BECOMES A LITTLE LESS CERTAIN BY
MIDWEEK...BUT THE GENERAL IDEA IS HIGH PRESSURE ALOFT WILL SLOWLY
BEGIN TO EXERT ITS INFLUENCE OVER MOST OF MAINLAND ALASKA...WITH
THE MAIN STORM TRACK REMAINING OVER THE BERING SEA.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 175 177 178.
   GALE WARNING 173 174 176 185.
FIRE WEATHER...RED FLAG WARNING 141.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...JA