Small Craft Advisory 848, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
517 AM AKDT TUE OCT 27 2015

.ANALYSIS AND UPPER LEVELS...
ON THE GENERAL LARGE SCALE...THE FLOW PATTERN ALOFT IS GOVERNED BY
A LARGE BROAD AREA OF LOW PRESSURE OVER AND SOUTH OF THE ALEUTIANS
AND RIDGING FROM THE PANHANDLE THROUGH THE NORTHERN
BERING/KAMCHATKA. THE JET STREAM LIES WELL TO THE SOUTH IN THE
NORTHERN PACIFIC. EACH OF THESE BROAD UPPER LEVEL LOW/HIGHS HAS
MULTIPLE CENTERS OF CIRCULATION COMPLICATING THE PATTERN A BIT
BUT FOR THE MOST PART ARE ACTING AS ONE. THE MAIN AREA OF ACTIVITY
IS BETWEEN THE UPPER LOW CENTER SOUTH OF THE ALASKA PENINSULA AND
THE MAINLAND RIDGING. WHAT IS LEFT OF A FRONTAL BOUNDARY WITH THE
UPPER SYSTEM STRETCHES FROM THE SOUTHERN GULF THROUGH KODIAK
ISLAND AND INTO THE BERING SEA.

AN IMPRESSIVE CLOUD SHIELD FROM THE MOIST FLOW BETWEEN THE UPPER
LEVEL SYSTEMS ENCOMPASSES MUCH OF MAINLAND ALASKA. THE GRADIENT
BETWEEN THE HIGH PRESSURE CENTERED OVER THE CANADIAN YUKON AND
NORTH PACIFIC LOW PRESSURE IS BRINGING VERY GUSTY WINDS THROUGH
THE BARREN ISLANDS...ALEUTIAN RANGE AND INTO THE BERING. THE
SOUTHWEST MAINLAND IS STAYING MOSTLY DOWNSLOPED AND DRY AS THE
FRONTAL ENERGY IS TO THE SOUTH BUT SOME LIGHT RAIN IS MAKING IT TO
THE GROUND. THAT FRONTAL BOUNDARY WRAPS ALL THE WAY TOWARD THE
WESTERN ALEUTIANS INTO THE REMNANTS OF TYPHOON CHAMPI.

&&

.MODEL DISCUSSION...
GUIDANCE IS IN GOOD AGREEMENT WITH THE OVERALL EVOLUTION OF THE
SYNOPTIC PATTERN ALOFT...HOWEVER IN NOT GREAT AGREEMENT WITH THE
FINE SCALE DETAILS OF THE PATTERN. ALOFT...ALL OF THE UPPER LOW
CENTERS WILL CONGEAL INTO ONE BROAD TROUGH AS THE JET PROPAGATES
IT EASTWARD. THE SMALLER SCALE EMBEDDED SHORT-WAVES AND THEIR
ASSOCIATED SURFACE REFLECTIONS ARE WHAT MODELS ARE NOT HANDLING SO
WELL.

&&

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

THE MAIN IMPACTS THROUGH THE FORECAST PERIOD ARE WINDS ACROSS MUCH
OF THE GULF AND RAINFALL TOTALS ACROSS THE WESTERN GULF...SPECIFICALLY
KODIAK ISLAND. THE OCCLUDED FRONT MOVING NORTH ACROSS THE GULF
MAKES LANDFALL ALONG THE NORTH COAST WED. WIDESPREAD GALES ARE
EXPECTED ALONG AND AHEAD OF THE FRONT WITH A NARROW BAND OF STORMS
ACROSS THE BARREN ISLAND AND SHELIKOF STRAIT MARINE AREAS. WINDS
WILL SLOWLY DIMINISH FROM THE SOUTH TONIGHT...THOUGH A WAVE MOVING
ENE ACROSS THE GULF WED AFTERNOON WILL TEND TO KEEP SMALL CRAFT TO
LOW END GALES IN THE NORTHERN GULF UNTIL WED EVENING.

STRONG EASTERLY FLOW ACROSS THE WESTERN GULF AND ABUNDANT MOISTURE
WITH THE FRONT WILL PROVIDE FOR PROLONGED MODERATE TO HEAVY
RAINFALL ACROSS EASTERN KODIAK ISLAND. MODEL ACCUMULATED RAINFALL
TOTALS PRIOR TO FRONTAL PASSAGE TONIGHT RANGE FROM 1.5-2.5 INCHES
ALONG THE NORTHERN COAST TO 3 TO AROUND 5.5 INCHES SOUTH OF KODIAK
CITY. PRECIPITATION ACROSS KODIAK WILL BECOME SHOWERY AND DIMINISH
SIGNIFICANTLY AFTER FRONTAL PASSAGE TONIGHT. THE BRUNT OF THE RAIN
THEN SHIFTS NORTH TO THE EASTERN KENAI WHERE RAINFALL TOTALS RANGE
FROM 1.5 TO 3 INCHES...THOUGH THE 00Z GFS20 SHOWS VALUES REACHING
NEARING 4.5 INCHES WED NIGHT.

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...TUE AND
WED)...WHAT'S LEFT OF THE WARM FRONT IS DRAPED ACROSS THE ALASKA
PENINSULA AND STRETCHES BACK TOWARD THE PRIBILOF ISLANDS. IT IS
KEEPING PLENTY OF RAIN MOVING THROUGH THESE AREAS WITH GUSTY EAST
TO SOUTHEAST WINDS. THE FEW EXCEPTIONS TO THE PRECIPITATION ARE
LOCALIZED SPOTS IN THE LEE OF THE MOUNTAINS. THESE WINDS WILL BE
SLOW TO DIMINISH TODAY AS THE UPPER LEVEL LOW SOUTHWEST OF KODIAK
CONTINUES TO PUSH INTO THIS RIDGE OVER SOUTHCENTRAL AK. THIS IS
KEEPING THE GRADIENT TIGHT OVER MUCH OF THE SOUTHWEST. THE FRONT
PIVOTS AND TAKES ON A MORE EAST TO WEST ORIENTATION THROUGH THE
DAY. THIS WILL CAUSE FLOW TO DEVELOP A BIT MORE OF A NORTHERLY
COMPONENT...ESPECIALLY OVER THE YK DELTA AND LOWER KUSKOKWIM
VALLEY. THIS WILL ALLOW SOME COLDER AIR OVER THE INTERIOR TO
START TO BLEED INTO THE REGION BY WEDNESDAY NIGHT. THIS SHOULD
HELP SOME SNOW TO START TO AT LEAST MIX IN WITH THE RAIN OVER THE
NORTHERN SECTIONS OF THE SOUTHWEST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...TUE AND
WED)...AN UPPER LEVEL LOW WILL TRACK FROM THE CENTRAL TO THE
EASTERN ALEUTIANS WHILE STRONG NORTHEAST FLOW CONTINUES OVER THE
WESTERN AND NORTHERN BERING. BROAD...LIGHT CYCLONIC CIRCULATION
WILL REMAIN OVER THE CENTRAL AND EASTERN ALEUTIANS AS VARIOUS WEAK
LOW CENTERS VIE FOR DOMINANCE. THIS WILL KEEP SHOWERS GOING
THROUGH MUCH OF THE AREA. A BROAD DEFORMATION ZONE WILL SET UP
OVER THE CENTRAL BERING TODAY. THIS WILL SERVE AS THE BOUNDARY FOR
THE HEAVIEST RAIN AND STRONGEST WINDS. THIS FEATURE WILL DRIFT
SLOWLY SOUTH ON WED EVENTUALLY BRINGING MORE STEADY RAIN TO THE
EASTERN ALEUTIANS AND ALASKA PENINSULA LATE WED AFTERNOON. OVER
THE WESTERN ALEUTIANS AND THE PRIBILOFS...HIGH PRESSURE OVER
RUSSIA IS MAKING FOR A TIGHT GRADIENT ON THE WESTERN PERIPHERY OF
THE CYCLONIC FLOW. THIS IS CAUSING INCREASING NORTHEAST WINDS AND
SHOULD START TO FUNNEL SOME COOLER AIR TO THESE PARTS. THIS PATTERN
WILL ONLY LAST FOR A DAY OR SO THOUGH AS THE HIGHER PRESSURE
DRIFTS IN FROM THE WEST BY WED NIGHT AND BRINGS DRIER CONDITIONS
WITH LIGHT WINDS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A SHOWERY REGIME WILL CONTINUE ACROSS MUCH OF THE REGION DURING
THE MIDDLE OF THE WEEK BENEATH AN ELONGATED UPPER TROUGH WITH
SEVERAL EMBEDDED LOWS SPANNING FROM THE MAINLAND TO THE WESTERN
ALEUTIANS. THIS TROUGH WILL BEGIN TO PUSH EASTWARD BY THURSDAY...
WITH DRIER CONDITIONS DEVELOPING ACROSS THE BERING AS HIGH
PRESSURE BUILDS IN FROM THE WEST.

ATTENTION THEN TURNS TO A SHARP ARCTIC TROUGH POISED TO DIG OVER
THE WESTERN MAINLAND LATE IN THE WEEK AND THEN PUSH ACROSS
SOUTHCENTRAL AK FRIDAY INTO SATURDAY. THIS WILL COINCIDE WITH A
NORTH PACIFIC SURFACE LOW MOVING INTO THE NORTHERN GULF...LEADING
TO THE POTENTIAL FOR SNOW AT LOWER ELEVATIONS OF SOUTHCENTRAL
INCLUDING THE ANCHORAGE BOWL AS COLDER AIR BEGINS TO MOVE INTO THE
REGION. CONFIDENCE IN THIS SCENARIO REMAINS LOW AT THIS TIME AS
MODELS CONTINUE TO STRUGGLE WITH FINER DETAILS...BUT THE OVERALL
SYNOPTIC AGREEMENT BETWEEN GFS AND EC GUIDANCE SUGGESTS THAT A
PERIOD OF COLDER TEMPERATURES AND GUSTY NORTH TO NORTHWEST WINDS
MAY BE IN STORE FOR THE WEEKEND. SNOW POTENTIAL WILL CONTINUE TO
BE CLOSELY MONITORED THROUGH THE REMAINDER OF THE WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...
 STORMS 131 138
 GALES 119 120 130 132 136 137 139 150 175 177 178 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...ML
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...CB