Small Craft Advisory 996, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
535 AM AKST SUN DEC 14 2014

.ANALYSIS AND UPPER LEVELS...
TWO LOW PRESSURE SYSTEMS ARE THE MAIN FEATURES FOR THE AREA. ONE
HAS MOVED INTO THE SOUTHERN BERING AND IS TRACKING EAST TOWARDS
BRISTOL BAY. THE FRONT ASSOCIATED WITH THIS SYSTEM IS MOVING
THROUGH THE ALASKA PENINSULA. THE OTHER LOW IS IN THE SOUTHERN
GULF AND IS HEADED TOWARDS KODIAK ISLAND. IT IS BRINGING UP MORE
WARM AIR FROM THE SOUTH AND ITS ASSOCIATED FRONT IS ALREADY
BRINGING RAIN TO THE NORTHERN GULF COAST.

&&

.MODEL DISCUSSION...
MODELS ARE INITIALIZING POORLY WITH IDENTIFICATION OF FEATURES ON
WATER VAPOR IMAGERY. THIS SHOWS UP IN POOR AGREEMENT BETWEEN THE
DIFFERENT MODELS BY 30 HOURS OUT AND GETS WORSE IN THE MID TERM.
THE PATTERN BECOMES COMPLEX WITH VARIOUS LOWS MOVING THROUGH THE
BERING AND GULF AND THE MODELS ARE HAVING TROUBLE WITH PLACEMENT
OF THESE LOWS. OVERALL MODEL CONFIDENCE IS LOW.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A SOLID RAIN SHIELD SITS OVER THE GULF THIS MORNING AT THE
LOW/FRONT APPROACH. THE MAJORITY OF THIS PRECIPITATION IS CONFINED
TO COASTAL AREAS BUT SOME FLURRIES ARE SURVIVING THE DRY AIR
INDUCED BY THE DOWNSLOPE WINDS ACROSS THE CHUGACH. THE 12Z
ANCHORAGE SOUNDING INDICATED A WARM LAYER SO FREEZING RAIN IS NOT
OUT OF THE QUESTION...HOWEVER ANY PRECIPITATION THAT FALLS SHOULD
BE VERY LIGHT AND NOT IMPACTFUL. DEEP LAYER SOUTHEASTERLY FLOW
WILL CONTINUE FOR THE NEXT COUPLE DAYS WHICH SHOULD KEEP MOST
AREAS MAINLY DRY IN THE COOK INLET REGION WITH SEASONALLY MILD
TEMPERATURES AND LIGHT NORTHERLY WINDS EXCEPT FOR ALONG THE INLET
TODAY WHERE SOME GUSTS TO 30 MPH REMAIN POSSIBLE. A STRONG UPPER
LEVEL JET PUSHING INTO THE COPPER RIVER BASIN TODAY WILL BRING
LIGHT ACCUMULATION SNOW TO MANY AREAS BEFORE TAPERING OFF THIS
EVENING AND OVERNIGHT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (SUNDAY AND MONDAY)...
PRECIPITATION CHANCES WILL BE ON THE RISE THIS MORNING AS AN AREA
OF LOW PRESSURE OVER THE EASTERN BERING SEA MOVES TOWARD THE
BRISTOL BAY AREA. PRECIPITATION OVER THE ALASKA PENINSULA WILL
BEGIN AS SNOW THIS MORNING BUT TRANSITION TO A RAIN SNOW MIX OR
POSSIBLY ALL RAIN DURING THE AFTERNOON HOURS AS "WARMER" AIR GETS
ADVECTED NORTHWARD. HOWEVER...A CHANCE FOR FREEZING RAIN WILL
EXTEND FROM DILLINGHAM NORTHWARD INTO THE LOWER KUSKOKWIM VALLEY
TODAY AS NORTHERLY WINDS AT THE SURFACE KEEP SURFACE TEMPERATURES
BELOW FREEZING. THE BIGGEST QUESTION FOR FREEZING RAIN POTENTIAL
EXISTS WITH THE WARM LAYER JUST OFF THE SURFACE. THE 12Z PAKN RAOB
SHOWS A VERY SHALLOW AREA ABOVE FREEZING...WHICH HINTS AT
PRECIPITATION STAYING IN THE FORM OF SNOW. AS SOME OF THE WARMER
AIR ADVECTS NORTHWARD...WE COULD SEE THAT WARM NOSE BECOME DEEPER
AND POSE THE THREAT FOR FREEZING RAIN. OTHERWISE...SNOW SHOWERS
WILL OVERSPREAD THE AREA TODAY AND INTO MONDAY...WITH GREATEST
CHANCES FOR SNOW BEGINNING LATE TONIGHT AND LASTING THROUGH
MONDAY. SNOW ACCUMULATION OF 2-4 INCHES WILL BE SEEN ALONG THE
ALASKA RANGE AND NEAR THE AHKLUN MOUNTAINS...WITH 1 TO 2 INCHES
SEEN AROUND THE REST OF THE AREA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (SUNDAY AND MONDAY)...
AN AREA OF LOW PRESSURE PRESENTLY RESIDES JUST TO THE NORTH OF
DUTCH HARBOR/UNALASKA AND IS NEARLY AT PEAK INTENSITY. WEAK
RIDGING IS TRYING TO DEVELOP IN THE NORTH PACIFIC TO THE SOUTH AND
WEST OF THE CENTRAL ALEUTIANS. THIS HAS CREATED A COMPACT PRESSURE
GRADIENT ON THE BACKSIDE OF THE LOW CURRENTLY NORTH OF UNALASKA.
ISALLOBARIC FLOW WILL CREATE A PERIOD OF STRONG WINDS UP TO 65 MPH
(ALREADY OBSERVED AT NIKOLSKI) IN THE DUTCH HARBOR AREA THIS
AFTERNOON AND LINGER THROUGH A MAJORITY OF THE OVERNIGHT PERIOD.
HAVE UPPED THE COASTAL WATERS NORTH OF DUTCH HARBOR TO STORM FORCE
WINDS DUE TO THE STRONG PRESSURE RISES. OTHERWISE...RAIN IS
EXPECTED TO CONTINUE ACROSS THE EASTERN ALEUTIANS AND SOUTHERN TIP
OF THE ALASKA PENINSULA THROUGH MONDAY BEFORE BEGINNING TO TAPER
OFF TO RAIN AND SNOW SHOWERS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE JET STREAM MAINTAINS A STRONG WESTERLY FLOW JUST SOUTH OF THE
ALEUTIANS WHICH KEEPS AN ACTIVE WEATHER PATTERN THROUGH THE END OF
NEXT WEEK AS IT PUSHES MULTIPLE LOW PRESSURE SYSTEMS FROM THE
WESTERN BERING TO THE EASTERN GULF. MODEL SOLUTIONS WERE IN DECENT
AGREEMENT WITH LONG RANGE SOLUTIONS...HOWEVER THE ECMWF WAS
PREFERRED AS IT PERFORMED BETTER ON THE LATEST RUN TO RUN
CONSISTENCY.

ON TUESDAY MORNING AN UPPER LOW CENTERED OVER THE NORTHEAST BERING
EXTENDS A TROUGH AXIS THROUGH THE SOUTHWEST MAINLAND AND INTO THE
NORTHERN GULF OF ALASKA. THIS ESSENTIALLY KEEPS THE SOUTHERN
MAINLAND IN A SHOWERY PATTERN THROUGH MID WEEK. MIXED
PRECIPITATION ACROSS SOUTHCENTRAL MID WEEK CHANGES OVER TO MAINLY
SNOW WEDNESDAY INTO THURSDAY AS THE TROUGH ADVECTS COLDER AIR FROM
THE BERING. THURSDAY AND FRIDAY PRESENTS THE BIGGEST WEATHER
CHALLENGE AS TWO LOW PRESSURE SYSTEMS...ONE SOUTH OF THE WESTERN
ALEUTIANS AND THE OTHER MOVING ACROSS THE GULF...BRING GUSTY WINDS
AND MEASURABLE PRECIPITATION THROUGH THE SOUTHERN MAINLAND AND
SURROUNDING WATERS. HOWEVER...WITH CURRENT MODEL INCONSISTENCIES
AND DIFFERENCES THERE REMAINS SOME UNCERTAINTY WITH THE TIMING AND
STRENGTH OF THE WINDS AND PRECIPITATION ASSOCIATED WITH THESE
FEATURES AS WE MOVE INTO THE LATER PART OF THE WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORMS 119 170
         GALES 120 125 129 130 139 150 155 165 171 172 173 174
               175 176 177 179 180 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...MTL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...TP