Small Craft Advisory 353, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
438 PM AKDT SAT APR 23 2016

.ANALYSIS AND UPPER LEVELS...
THERE IS A LARGE VERTICALLY STACKED LOW IN THE GULF OF ALASKA.
THERE IS ANOTHER EVEN LARGER LOW OVER THE BERING SEA AND
ALEUTIANS THAT IS CENTERED JUST SOUTH OF ADAK. WEAK HIGH PRESSURE
IS IN BETWEEN THESE TWO LOWS...WITH A NORTH-SOUTH AXIS CROSSING
THE ALASKA PENINSULA. HIGH PRESSURE IS OVER MAINLAND ALASKA...AN
EXTENSION OF THE STRONG AND PERSISTENT WESTERN NORTH AMERICA
RIDGE. A WEATHER FRONT ASSOCIATED WITH THE GULF LOW IS MOVING
ONSHORE ALONG THE GULF COAST. A FRONT ASSOCIATED WITH THE
BERING/ALEUTIANS LOW IS OVER THE NORTH PACIFIC AND MOVING NORTH
TOWARDS THE EASTERN ALEUTIANS.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN GOOD AGREEMENT FOR THE SHORT TERM
PORTION OF THE FORECAST (THROUGH MONDAY AFTERNOON). THEY BEGIN TO
DIFFER A LITTLE ON THE TIMING OF FRONTS BY MONDAY...BUT NOT ENOUGH
TO CAUSE TROUBLE WITH THE FORECAST. FORECAST CONFIDENCE IS ABOVE
NORMAL FOR THE AFTERNOON PACKAGE.

&&

.FIRE WEATHER DISCUSSION...
A FRONT PUSHING UP FROM THE GULF OF ALASKA WILL BRING SHOWERS TO
THE WINDWARD SIDE OF THE RANGES...HOWEVER ON THE LEE SIDE
DOWNSLOPING WILL PREVENT WETTING RAINS. WINDS HAVE BEEN GUSTY OUT
OF THE MATANUSKA VALLEY AND MODELS HAVE NOT BEEN HANDLING RH
VALUES WELL IN THIS AREA. ALTHOUGH TEMPERATURES ARE NOT HIGH
ENOUGH FOR RED FLAG CRITERIA...WITH THE WINDS CAUSING RH VALUES
TO DROP TO NEAR RED FLAG CONDITIONS THE CONDITIONS IN THIS AREA
SHOULD BE MONITORED CLOSELY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE FRONT FROM THE LOW IN THE GULF OF ALASKA IN AN ARC THROUGH
KODIAK THEN ALONG THE NORTH GULF COAST WILL CONTINUE TO PUSH NORTH
AND WEST ACROSS THE SOUTH CENTRAL REGION TONIGHT. RAINY COOL
CONDITIONS ARE PREVALENT ACROSS THE SOUND AND OUTER COAST OF THE
KENAI PENINSULA WHILE THE DOWNSLOPE DRYING IS PREVALENT ON THE LEE
SIDE OF THE MOUNTAINS. POST FRONTAL DRYING IS EVIDENT ON THE
SATELLITE IMAGERY AS WELL AS A MORE SHOWERY REGIME. THIS FRONT
WILL CROSS THE COASTAL MOUNTAINS AND DISSIPATE TO A LEE TROUGH
TONIGHT THOUGH IT IS NOT EXPECTED TO PERSIST LONG. THIS WILL HELP
FACILITATE THE STRONG GAP WINDS THROUGH THE CHUGACH MOUNTAINS
TONIGHT. AS WE MOVE INTO SUNDAY NIGHT AND MONDAY A STRONG LOW WILL
BE MOVING TO SOUTH OF THE ALASKA PENINSULA AND PUSH ANOTHER FRONT
TOWARD THE COAST. ANOTHER TROUGH WILL FORM NORTH OF THE COASTAL
MOUNTAINS SETTING UP ANOTHER ROUND OF STRONGER GAP WINDS THROUGH
THE CHUGACH MOUNTAINS SUNDAY NIGHT AND MONDAY. THIS WILL LIKELY
PRODUCE STRONGER WIND ALONG THE COPPER RIVER MONDAY.

NO SIGNIFICANT CHANGES HAVE BEEN MADE FROM THE PREVIOUS FORECAST
PACKAGE AS THE EMPHASIS TODAY HAS BEEN ON THE LOCAL WIND AND
PRECIP AREAS AND DETAILS FOR TERRAIN AFFECTS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
WEAK RIDGING OVER THE INTERIOR WILL CONTINUE TO BRING SUNNY
SKIES TO THE KUSKOKWIM VALLEY/DELTA THIS EVENING. TO THE SOUTH...A
SHORTWAVE OVER BRISTOL BAY WILL KEEP RAIN SHOWERS OVER THAT REGION
THROUGH THIS EVENING WITH OTHERWISE LIGHT WINDS. AS THIS SHORTWAVE
DIVES TO THE SOUTH TONIGHT...A WEAK THERMAL TROUGH WILL BUILD INTO
THE AREA FOR SUNDAY...WHICH WILL BRING CONVECTIVE RAIN SHOWERS TO
THE REGION DURING THE AFTERNOON/EVENING. INSTABILITY IS VERY WEAK
WITH THIS HOWEVER...SO NO LIGHTNING STRIKES ARE EXPECTED. BY
SUNDAY EVENING...A FRONTAL MOVING INTO THE AREA FROM THE SOUTH
WILL BRING GUSTY WINDS TO BRISTOL BAY AND THE ALASKA RANGE INTO
MONDAY WITH INCREASING CLOUD COVER.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE FOCUS FOR THE WEATHER THROUGHOUT THE ALEUTIANS HAS SHIFTED TO
A DEVELOPING LOW WELL SOUTH OF THE CENTRAL ALEUTIANS THAT WILL
MOVE INTO THE AREA FOR SUNDAY-MONDAY. THERE REMAINS GOOD
CONFIDENCE THAT THIS SYSTEM WILL BRING GALE FORCE WINDS AND RAIN TO
THE EASTERN ALEUTIANS/AKPEN INTO MONDAY. OVER THE NORTHERN EDGE OF
THIS LOW RIDGING FROM THE INTERIOR WILL BEGIN TO MOVE INTO THE
NORTHERN BERING...CREATING A TIGHT PRESSURE GRADIENT AND ALLOWING
FOR GUSTY NORTHERLY WINDS AND SHOWERS TO DOMINATE THE WEATHER
THROUGH THE WESTERN BERING/ALEUTIANS THROUGH MONDAY.

&&

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

BEGINNING THE EXTENDED PERIOD MONDAY EVENING...THERE WILL BE A
LARGE LOW CENTERED SOUTH OF THE ALASKA PENINSULA...WITH RIDGING
OVER THE NORTHWEST BERING SEA. THIS PATTERN WILL SOUND
SIMILAR...AS IT HAS BEEN THE DOMINANT WEATHER PATTERN FOR THE
ENTIRE WINTER AND THE EARLY PART OF THIS SPRING. A WARM FRONT WILL
BE ARCING FROM THE NORTHEAST PACIFIC TO THE NORTHERN GULF
COAST...WITH MOST OF THAT PRECIP IMPACTING THE COAST AND THE KENAI
PENINSULA. DEEP LAYER SOUTHEAST FLOW WILL RESULT IN A STRONG
DOWNSLOPE SHADOW INLAND...WITH MOST SHOWERS AND LIGHT RAIN OVER
SOUTHWEST ALASKA. EVENTUALLY THE LOW WILL WEAKEN AND DRIFT EAST
WITH YET ANOTHER LARGE BERING LOW DEVELOPING OVER THE ALEUTIANS
THEN SLOWLY MOVING EAST...WITH WEAKER BUT FAST MOVING LOWS MOVING
INTO THE GULF OF ALASKA ALONG THE PERIPHERY OF THE PARENT BERING
LOW.THIS WILL KEEP A RATHER CLOUDY REGIME OVER INLAND
SOUTHCENTRAL...WITH MOST SHOWERS REMAINING ALONG THE MOUNTAINS.
TEMPERATURES WILL CONTINUE TO REMAIN ABOVE AVERAGE HEADING INTO
THE WEEKEND WITH NO DRAMATIC PATTERN CHANGE IN SIGHT THROUGH DAY
7.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 130 131 132 138 150 155 165 170 172.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...SA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...JA