Small Craft Advisory 399, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
434 AM AKDT MON MAY 9 2016

.ANALYSIS AND UPPER LEVELS...

THE MAIN LARGE SCALE SYNOPTIC FEATURES THAT ARE GOING TO PLAY A
LARGE ROLE IN THE FUTURE WEATHER PATTERN OVER ALASKA ARE TAKING
SHAPE THIS MORNING. THE FIRST IS A LARGE TROUGH OVER THE WESTERN
BERING...WITH THE SECOND BEING A DEVELOPING REGION OF HIGH
PRESSURE OVER THE NORTHEAST PACIFIC OCEAN. IN BETWEEN THESE TWO
LARGE SCALE SYNOPTIC SYSTEMS IS A DEAMPLIFYING SHORTWAVE LENGTH
TROUGH TRACKING ACROSS SOUTHWEST ALASKA AND TOWARD COOK INLET.
THIS SOUTHWEST FLOW PATTERN IS USHERING IN RATHER WIDESPREAD LIGHT
RAIN FROM BRISTOL BAY TO THE EASTERN GULF COAST. THIS REPRESENTS
THE FIRST WIDESPREAD RAIN EVENT FOR SOUTHERN ALASKA IN OVER A
MONTH. EVEN SO...RAINFALL AMOUNTS ARE ON THE LIGHT SIDE ACROSS
MOST AREAS. A GALE FORCE FRONT ASSOCIATED WITH THE AFOREMENTIONED
WESTERN BERING TROUGH WILL RAPIDLY MOVE EAST FROM WEST OF THE
PRIBILOF ISLANDS THIS MORNING TO THE COAST OF SOUTHWEST ALASKA BY
TUESDAY MORNING.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN EXCELLENT AGREEMENT WITH THE SYNOPTIC SCALE
PATTERN. THEY REMAIN IN EXCELLENT AGREEMENT WITH THE SHORTWAVE
TROUGH MOVING ACROSS SOUTHERN ALASKA...AS WELL AS THE FRONT MOVING
INTO THE BERING SEA. THEY REMAIN IN GOOD AGREEMENT THROUGH NEXT
WEEKEND...WITH VERY HIGH CONFIDENCE IN THE FORECAST AND THE
EXPECTED DRAMATIC CHANGE IN THE OVERALL PATTERN BY LATE WEEK.

&&

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

A WEAK FRONTAL TROUGH APPROACHING COOK INLET THIS MORNING MOVES
INTO WESTERN CANADA TONIGHT. RAIN ASSOCIATED WITH THIS FEATURE
SHOULD TAPER OFF TO SHOWERS ACROSS COOK INLET AND THE WESTERN
KENAI PENINSULA THIS AFTERNOON. PRECIPITATION WILL DIMINISH FROM
THE WEST THROUGH THIS EVENING AND SHOULD FINALLY CLEAR THE COPPER
RIVER BASIN AFTER MIDNIGHT TONIGHT. A LOW AMPLITUDE RIDGE RIDING
ON THE HEALS OF THE FRONT WILL BRING STABLE CONDITIONS ACROSS MUCH
OF THE AREA TONIGHT ALLOWING FOR LOW STRATUS AND FOG DEVELOPMENT.
RIDGING WILL SHIFT EASTWARD SOME ON TUE ALLOWING FOR BROAD
SOUTHERLY FLOW ALOFT TO BRING INCREASING CLOUDS AND CHANCES OF
LIGHT RAIN WEST OF THE COPPER RIVER BASIN.

WINDS WILL BE RELATIVELY LIGHT ACROSS MUCH OF MAINLAND
SOUTHCENTRAL TODAY WITH SEABREEZES ALONG THE COASTS AND WEAK GAP
FLOWS. WINDS WILL INCREASE OVER THE WESTERN GULF TUE...BUT SHOULD
REMAIN BELOW GALES.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3)...

STEADY RAIN ACROSS BRISTOL BAY WILL BE MOVING OUT THIS
MORNING AS THE ASSOCIATED SHORTWAVE TROUGH MOVES EAST INTO
SOUTHCENTRAL. IN ITS WAKE WILL BE EXTENSIVE BERING CLOUDS AND A
CONTINUED SOUTHERLY WIND...WITH ONLY SPORADIC AND LIGHT
RAIN/SHOWERS TODAY.

THE NEXT SYSTEM IS ALREADY APPROACHING THE PRIBILOF ISLANDS...AND
WILL REACH THE COAST BY LATE THIS EVENING. THIS FRONT HAS MUCH
MORE UPPER LEVEL JET ENERGY...AND THIS WILL BRING MORE WIDESPREAD
RAIN AND STRONGER SOUTH-SOUTHEAST WINDS TO THE REGION THROUGH
WEDNESDAY. THE FRONT WILL SLOWLY DRIFT EAST WEDNESDAY
EVENING...LEAVING A BULK OF THE PRECIPITATION ACROSS INTERIOR
BRISTOL BAY AND THE LOWER KUSKOKWIM VALLEY. HOWEVER...SOUTHEAST
WINDS NEAR THE ALASKA/ALEUTIAN RANGES WILL KEEP LOCATIONS
IMMEDIATELY DOWNWIND SOMEWHAT RAIN SHADOWED AND DRIER. SOUTHEAST
WINDS WILL BE STRONGEST ACROSS THE REGION TUESDAY AND TUESDAY
NIGHT BEFORE SLOWLY WEAKENING WEDNESDAY AND THURSDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH 3)...

A BERING TROUGH CENTERED OVER THE WESTERN ALEUTIANS...IN
ASSOCIATION WITH A STRONG PACIFIC UPPER LEVEL JET STREAM...WILL
QUICKLY MOVE A GALE FORCE FRONT THROUGH THE CENTRAL AND EASTERN
BERING SEA BY TONIGHT. SOUTHERLY WINDS WILL BE ENHANCED THROUGH
FAVORED GAPS ACROSS THE EASTERN ALEUTIANS AND ALONG THE WESTERN
ALASKA PENINSULA. RAIN ALONG THE FRONT WILL MOVE THROUGH
QUICKLY...LEAVING SPORADIC/INTERMITTENT LIGHT RAIN AND SHOWERS AS
THE UPPER LOW MOVES EAST BEHIND THE FRONT...WHICH WILL STALL OVER
THE SOUTHWEST MAINLAND. THE LOW WILL THEN WEAKEN THROUGH WEDNESDAY
NIGHT...WITH QUIESCENT WEATHER ENCOMPASSING THE BERING DURING THIS
TIME. HOWEVER...FOG AND LOW STRATUS WILL LIKELY INCREASE AS THE
WINDS/PRESSURE GRADIENT WEAKEN.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

LATER ON THURSDAY A CONSOLIDATED BLOCKING HIGH WILL FORM OVER THE
EASTERN PART OF THE STATE AND ELONGATE AND BUILD TO THE WEST. THIS
WILL CLEAR OUT THE SKIES AND RESULT IN WARM AND SUNNY AFTERNOONS
THROUGH SUNDAY. TEMPERATURES WILL SOAR TO THEIR HIGHEST LEVELS
THIS YEAR ON SATURDAY AND SUNDAY. BY EARLY NEXT WEEK...THERE IS
STILL UNCERTAINTY REGARDING HOW QUICKLY THE RIDGE MAY BREAK
DOWN...BUT THE GLOBAL MODELS ARE BEGINNING TO SHOW WEAK RIDGING
REMAINING THROUGH TUESDAY...WITH SHOWER AND THUNDERSTORM THREATS
OVER THE MOUNTAINS...BUT OTHERWISE STILL WARMER THAN AVERAGE
CONDITIONS ACROSS MUCH OF SOUTHERN ALASKA AS THE NORTH PACIFIC JET
BEGINS TO WEAKEN AND DRIFT SOUTH UNDER THE INFLUENCE OF STRONG
BLOCKING FARTHER WEST.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 165 170 173 180 414.

&&

SYNOPSIS AND MODEL DISCUSSION...AHSENMACHER
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AHSENMACHER
LONG TERM...AHSENMACHER/KRAMER