Small Craft Advisory 324, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
524 AM AKDT MON APR 13 2015

.ANALYSIS AND UPPER LEVELS...

TROUGHING OVER THE REGION CONTINUES TO EXERT ITS INFLUENCE THIS
MORNING. WITH A LARGE POOL OF ARCTIC AIR PUSHING INTO THE NORTH
PACIFIC FROM THE BERING SEA...THE ENHANCED BAROCLINIC ZONE IS
STRENGTHENING THE ALREADY POTENT NORTH PACIFIC JET STREAM. A
STRONG STORM FORCE LOW CAN BE SEEN ON WATER VAPOR AND INFRARED
SATELLITE IMAGERY TRACKING TOWARD THE CENTRAL ALEUTIAN
CHAIN...WITH ANOTHER STRONG LOW FORMING NEAR SITKA. ACROSS
ALASKA...A WEAK AND ILL-DEFINED DEFORMATION ZONE REMAINS OVER THE
SOUTHERN PORTION OF THE STATE. THIS FEATURE WILL WEAKEN AS THE
PARENT TROUGH...CURRENTLY IN THE VICINITY OF KODIAK
ISLAND...WEAKENS AND MOVES TOWARD THE PANHANDLE OF ALASKA. SHOWERS
OVER THE GULF AND SOUTHERN ALASKA WILL DIMINISH TODAY AND BECOME
RELEGATED TO THE MOUNTAINS. EVENTUALLY THE STRONG LOW TRACKING
SOUTH OF THE ALEUTIAN CHAIN WILL WEAKEN AND MOVE INTO THE GULF OF
ALASKA LATE MONDAY THROUGH WEDNESDAY...KEEPING THE ACTIVE PATTERN
IN PLACE OVER MUCH OF ALASKA.

&&

.MODEL DISCUSSION...

THE NUMERICAL MODELS ARE IN EXCELLENT AGREEMENT IN THE SHORT TERM
WITH FEW IF ANY MAJOR DISCREPANCIES NOTED. BY LATE
WEEK...DISCREPANCIES WITH THE UPPER AIR PATTERN OVER THE STATE
BEGIN TO BECOME NOTABLE AS THE REMNANT GULF LOW MERGES WITH A
COMPLEX TROUGH OVER SOUTHWEST ALASKA. THIS WILL INFLUENCE
PRECIPITATION PATTERNS ACROSS SOUTHERN ALASKA LATE WEDNESDAY INTO
LATE FRIDAY. FOR NOW...A GENERAL ENSEMBLE APPROACH OF THE GFS AND
ECMWF WAS UTILIZED TOWARD THE END OF THE SHORT TERM FORECAST OWING
TO HIGHER UNCERTAINTY BY THAT TIME PERIOD. FORECAST CONFIDENCE IS
HIGH THROUGH DAY TWO...THEN BECOMES MODERATE FOR THE REMAINDER OF
THE SHORT TERM FORECAST.

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

ONSHORE FLOW THIS MORNING WILL WEAKEN BY AFTERNOON AS WEAK HIGH
PRESSURE BUILDS OVER THE STATE. CONVECTIVE SHOWERS OVER THE GULF
OF ALASKA WILL CONTINUE TO IMPACT COASTAL LOCATIONS ALONG THE
KENAI PENINSULA...BUT WILL OTHERWISE WEAKEN AND WANE THROUGH THE
DAY. ELSEWHERE...SOME LOCAL AREAS OF PATCHY FOG AND LOW STRATUS
ACROSS SOUTHCENTRAL WILL GRADUALLY BURN OFF BY MIDDAY...LEAVING
MUCH OF SOUTHCENTRAL UNDER THE INFLUENCE OF INCREASING SUNSHINE
AND OVERALL QUIESCENT WEATHER. SHOWERS WILL GENERALLY REMAIN
RELEGATED TO THE MOUNTAINS WITH ONLY A FEW ISOLATED SHOWERS MOVING
INLAND DURING THE LATE AFTERNOON AND EVENING. ON TUESDAY...A
MODERATE GALE FORCE FRONT WILL RAPIDLY MOVE INTO THE GULF OF
ALASKA...SPREADING MOISTURE AND PRECIPITATION TO COASTAL
LOCATIONS. KODIAK ISLAND AND PORTIONS OF THE GULF COAST SEE A
PERIOD OF SNOWFALL TUESDAY BEFORE RAPIDLY CHANGING OVER TO RAIN
TUESDAY NIGHT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...MONDAY AND
TUESDAY)...LIGHT SNOW CONTINUES TO LINGER IN A SMALL AREA NORTH
OF KING SALMON AND EAST OF DILLINGHAM. SOME LIGHT SNOW WILL LIKELY
CONTINUE IN THIS AREA THROUGH AT LEAST THE MORNING HOURS TODAY AS
THE UPPER LEVEL WAVE PIVOTS ALONG THE ALEUTIAN RANGE. THE SNOW
SHOWERS COULD MEANDER A BIT FURTHER WEST AIDED BY SOME LOW LEVEL
CONVERGENCE CAUSED BY A WEAK TROUGH SLIDING TO THE EAST THROUGH
THE YUKON KUSKOKWIM DELTA. THIS SYSTEM SHOULD WEAKEN INTO EARLY
TUESDAY AS A MID-LEVEL RIDGE APPROACHES IN ADVANCE OF THE DEEP
NORTH PACIFIC LOW. THEN FLOW SWITCHES AROUND TO MORE OF A
NORTHEASTERLY DIRECTION TUESDAY WHICH SHOULD LEAD TO SOME DRYING
AND A FEW MORE BREAKS OF THE SUN OVER THE LOWER KUSKOKWIM VALLEY.
AS THE PRECIPITATION ASSOCIATED WITH THAT LOW APPROACHES THE
ALEUTIAN RANGE DURING THE DAY TUESDAY...SOUTHEAST CROSS BARRIER
FLOW SHOULD KEEP MOST LOCATIONS THROUGH BRISTOL BAY DRY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...MONDAY
AND TUESDAY)...OUR NORTH PACIFIC LOW IS JUST ABOUT AT ITS MAXIMUM
INTENSITY THIS MORNING IN THE LOW 970 MB RANGE. SO FAR GALE FORCE
WINDS HAVE BEEN REPORTED FROM ADAK OVER TO BUOY 72. THESE WINDS
COUPLED WITH SOME MODERATELY HEAVY PRECIPITATION RATES HAVE
BROUGHT VISIBILITIES BELOW ONE MILE AT TIMES. SIMILAR CONDITIONS
ARE EXPECTED TO SPREAD EAST TOWARD DUTCH HARBOR AND EVENTUALLY
COLD BAY AS WE GO THROUGH THE DAY. THE SEVERITY OF BLOWING SNOW
WILL BE LIMITED BY TEMPERATURES AT OR JUST ABOVE FREEZING. THE
GOOD NEWS WITH THIS SYSTEM IS THAT IT DOES CONTINUE TO MOVE ALONG
THE CHAIN QUITE QUICKLY AND SHOULD BE SOUTH OF KODIAK BY TUE
NIGHT. IT WILL LEAVE ANOTHER ROUND OF GUSTY NORTHWEST WINDS AND
PLENTY OF COLD AIR ADVECTION SNOW SHOWERS AS IT DEPARTS...WITH
THE FAVORED LOCATIONS FOR THE WORST CONDITIONS ONCE AGAIN BEING ON
THE BERING SIDE.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A PROGRESSIVE PATTERN WILL CONTINUE THROUGH THE END OF THE WEEK.
THE MAIN LOW IN THE GULF WILL PUSH INTO THE NORTH GULF COAST
BRINGING RAIN WITH IT INTO FRIDAY. THE NEXT LOW WILL BEGIN TO
AFFECT THE WESTERN ALEUTIANS WED...TRACKING ALONG 50N UNTIL EARLY
FRI. SOME DISCREPANCIES THEN DEVELOP WITH THE TRACK OF THIS LOW
ON FRIDAY AS THE EC AND GEM BRING IT INTO THE BERING WHILE THE GFS
KEEPS IT SOUTH OF THE ALEUTIANS. THIS RESULTS IN TIMING
DIFFERENCES WITH THE ASSOCIATED FRONT. THE FORECAST UTILIZES THE
WPC/EC SOLUTION THAT BRINGS THE LOW INTO THE EASTERN BERING FRI
NIGHT...WITH THE ASSOCIATED FRONT MOVING INTO THE MAINLAND ON
SAT.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...
STORMS 172 174 176
GALES 119 120 130-132 136-139 150 155 165 170 171 173 175 177
HEAVY FREEZING SPRAY 179
FIRE WEATHER...NONE.

&&

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