Small Craft Advisory 31, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 AM AKST THU JAN 9 2014

.ANALYSIS AND UPPER LEVELS...

LITTLE TO NO CHANGE IN THE LARGE SCALE PATTERN...WITH A BLOCKING HIGH
OVER EASTERN SIBERIA AND THE SIBERIAN SEA...AND AN ACTIVE PACIFIC JET
STREAM SOUTH OF THE ALEUTIAN CHAIN AND SOUTHERN ALASKA. A LONGWAVE
TROUGH CENTERED OVER 170W IS TRACKING EASTWARD...WITH A LEADING
SHORTWAVE TROUGH RAPIDLY TRANSLATING TOWARD THE EASTERN PANHANDLE OF
ALASKA. OVER THE BERING SEA...A BROAD AND WEAKENING AREA OF STACKED
LOW PRESSURE EXISTS...WITH A WEAK EMBEDDED WAVE TRACKING OVER THE
ALASKA PENINSULA. OVER SOUTHCENTRAL ALASKA...THE REMNANTS OF A
SHEARED AND WEAKENING UPPER LEVEL WAVE IS SLOWLY MIGRATING EAST INTO
CANADA. A NORTHERN STREAM VORTEX NEAR BANKS ISLAND WILL DROP
SOUTHEAST INTO NORTHERN ALASKA...REINFORCING THE COLD AIRMASS ALREADY
IN PLACE.

WITH TIME...THE ENTIRE WAVE PATTERN WILL CONTINUE TO SLOWLY SHIFT
EAST...WITH NUMEROUS WEAK WAVE FEATURES TRACKING OVER THE AREA. THE
MAIN PACIFIC STORM TRACK WILL REMAIN SHUNTED TO THE SOUTH...WITH COLD
AIR FROM THE NORTH SLOWLY FILTERING IN THROUGH THE WEEKEND.

.MODEL DISCUSSION...

MODELS REMAIN IN EXCELLENT AGREEMENT WITH THE LARGE SCALE SYNOPTIC
PATTERN...AND LESS SO WITH THE LOW AMPLITUDE PACIFIC WAVE
DISTURBANCES BREAKING OFF THE JET. WITH THAT SAID...THEY ARE IN
BETTER AGREEMENT WITH THE LOW AMPLITUDE WAVE PATTERN THAN THE
PREVIOUS FEW DAYS...ALTHOUGH THE ERROR SPREAD GROWS RAPIDLY BY SUNDAY
AFTERNOON. IN THE SHORT TERM...THE GFS AND ECMWF REMAIN THE FAVORED
GUIDANCE.

THEREAFTER...THE GLOBAL MODELS CONTINUE TO SHOW SUPERB CONSISTENCY
LATE INTO NEXT WEEK...WITH THE GFS...GFS ENSEMBLE...THE ECMWF...AND
THE ECMWF ENSEMBLE DEPICTING A DRAMATIC SHIFT IN THE PATTERN OVER
ALASKA (SEE EXTENDED DISCUSSION).

.SHORT TERM FORECAST...

SOUTHCENTRAL...
SCATTERED SNOW SHOWERS WILL LINGER THROUGH THE LATE MORNING AND EARLY
AFTERNOON HOURS ACROSS PARTS OF THE MAT-SU VALLEY AND COPPER RIVER
BASIN. SNOW WILL ALSO CONTINUE ALONG THE GULF COAST...WITH OCCASIONAL
MIXING OF RAIN AROUND CORDOVA. AN UNSETTLED WEATHER PATTERN IN THE
NORTHERN GULF WILL CONTINUE TO BRING CHANCES FOR SNOW TO COASTAL
AREAS FROM PRINCE WILLIAM SOUND EASTWARD THROUGH THE FIRST HALF OF
THE WEEKEND. FOR THE REMAINDER OF SOUTHCENTRAL ALASKA...PARTLY TO
MOSTLY CLOUDY SKIES WILL CONTINUE TO BE SEEN WITH TEMPERATURES
GRADUALLY COOLING TOWARD NORMAL LEVELS.

SOUTHWEST...
WAVES OF MOISTURE WITH A WEAK ONSHORE FLOW WILL KEEP THE REGION UNDER
THE THREAT OF ISOLATED TO SCATTERED SNOW SHOWERS THROUGH TONIGHT
BEFORE MOST OF THE AREA GRADUALLY DRIES OUT. AREAS OF FOG WILL
PERSIST THROUGH THE DAY AND TONIGHT AS WELL...WITH LOCAL AREAS OF
DENSE FOG THIS MORNING. TEMPERATURES WILL VERY SLOWLY DECREASE
THROUGH THE WEEKEND AS COLD HIGH PRESSURE BUILDS IN.

BERING SEA AND ALEUTIANS...
RAIN AND SNOW SHOWERS WILL CONTINUE OVER THE AREA THROUGH TODAY. A
STRONG LOW WILL MOVE INTO THE WESTERN ALEUTIANS ON FRIDAY...WITH A
FRONT TRACKING OVER THE CENTRAL AND EASTERN ALEUTIANS...BRINGING MORE
RAIN AND SNOW. STRONGER MAX GALE FORCE SOUTHWEST WINDS WILL IMPACT
THE CENTRAL ALEUTIANS AS THE LOW SLOWLY TRACKS EAST INTO
SATURDAY...SLOWLY WEAKENING AS THE LOW TRACKS EAST.

.LONG TERM FORECAST...

A DRAMATIC SHIFT IN THE PATTERN IS BECOMING ALMOST A CERTAINTY BY THE
MIDDLE AND LATE PORTIONS OF NEXT WEEK AS A POWERFUL 220 KNOT EAST
ASIAN JET STREAM MEANDERS EAST...SETTING UP A +PNA PATTERN OVER
ALASKA AND NORTH AMERICA. RAPID AMPLIFICATION OF THE ALREADY
PERSISTENT NPAC RIDGE WILL ENSUE...WITH STRONG CYCLOGENESIS FORMING
ALONG THE LEFT EXIT OF THIS POWERFUL JET. DETAILS ARE STILL
UNCERTAIN...BUT THE POTENTIAL EXISTS FOR SIGNIFICANT RAINFALL ALONG
THE COAST...A VIGOROUS CHINOOK TRACKING DEEP INTO THE INTERIOR...AND
EXTENSIVE AND WIDESPREAD STORMINESS ACROSS THE GULF AND BERING SEA.
INLAND LOCATIONS WILL SEE A MYRIAD OF PRECIPITATION TYPES...INCLUDING
RAIN AND POSSIBLY FREEZING RAIN...DEPENDING ON THE TRACK AND STRENGTH
OF VARIOUS LOWS. ALTHOUGH DETAILS ARE UNCERTAIN...THE LIKELIHOOD OF A
SIGNIFICANT AND WIDESPREAD PERIOD OF WEATHER IS INCREASING.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 173-177 185.
         HEAVY FREEZING SPRAY 185.
FIRE WEATHER...NONE.

AHSENMACHER/CLAY JAN 14