Small Craft Advisory 1027, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
511 AM AKST TUE DEC 23 2014

.ANALYSIS AND UPPER LEVELS...

IT IS TWO DIFFERENT STORIES ACROSS THE FORECAST AREA TODAY. OUT
WEST...WE HAVE A MODERATELY STRONG LOW SPINNING STORM FORCE WINDS
THROUGH THE WESTERN ALEUTIANS. THIS LOW HAS DROPPED THE PRESSURE
TO 959 MB AT SHEMYA AND IT SHOULD CONTINUE TO FALL TOWARDS THE
MID 950 MB RANGE THROUGH THE DAY. THIS LOW WILL BE SOMEWHAT OF A
PATTERN CHANGER IN THE SENSE THAT IT WILL DOMINATE THE WEATHER FOR
THE BERING AND AT LEAST THE SOUTHWEST MAINLAND THROUGH THE WEEK.
FOR THE EAST...WEAK...SMALL SCALE FEATURES DOMINATE THE SENSIBLE
WEATHER. AN UPPER LEVEL TROUGH WITH PLENTY OF COLD AIR RESIDES
OVER THE NORTHWEST PORTION OF THE MAINLAND. EMBEDDED WITHIN THIS
TROUGH IS A WEAK SURFACE LOW THAT CONTINUES TO SPIN IN BRISTOL
BAY. THIS LOW WAS ABLE TO TAP INTO SOME MOISTURE AND PRODUCE A
QUICK BURST OF SNOW OVER KING SALMON AND PARTS OF THE ALASKA
PENINSULA. THE WEAK SURFACE CYCLE WITH A SUPPORTING UPPER LEVEL
VORTICITY MAXIMUM NEAR KODIAK HAS DRIFTED INLAND WEST OF THE PARKS
HIGHWAY. THIS BROUGHT SOME SNOW SHOWERS TO PARTS OF THE SUSITNA
VALLEY. BUT IT LEFT MOST OF THE ANCHORAGE BOWL AND MATSU VALLEY
PINCHED IN A SMALL POCKET OF NEGATIVE VORTICITY ADVECTION. THIS IS
LEADING TO SINKING AIR PUSHING SOME OF THE CEILINGS DOWN WITH LOW
STRATUS AND FOG INCREASING AROUND THE AREA.

&&

.MODEL DISCUSSION...

THE BIG STORY HERE...MODELS ARE IN MUCH BETTER AGREEMENT THROUGH
THE FIRST 60 HOURS WITH SYNOPTIC FEATURES. NONE OF THE MODELS...TO
INCLUDE THE HI-RES VARIETALS...ARE HANDLING THE LOW STRATUS AND
FOG THROUGH THE MATSU VALLEY AND ANCHORAGE BOWL THIS MORNING. SO
WE ARE RELYING HEAVILY ON OBSERVATIONS AND SATELLITE TO TRY TO
NOWCAST HOW LOW IT WILL LAST. ALL MODELS NOW PAINT A VERY SIMILAR
STORY WITH THE DOMINANT LOW OVER THE WESTERN ALEUTIANS. THE LOW
WILL STAY FAIRLY CONCENTRIC AS IT DEEPENS TODAY...THEN IT WILL
QUICKLY ELONGATE BY THIS EVENING AS THE FIRST IN A SERIES OF
FRONTS SWEEPS ACROSS THE BERING. MODELS NOW AGREE THAT THE
PRECIPITATION ASSOCIATED WITH THE WARM OCCLUSION WILL REACH THE
SOUTHWEST COAST LATE TONIGHT INTO EARLY WED. WHILE IT DOES LOOK
LIKE MOST OF THE PRECIPITATION WILL SPREAD TOWARDS THE ANCHORAGE
BOWL LATE WED...IT REMAINS TO BE SEEN HOW MUCH CROSS BARRIER FLOW
THERE WILL BE AND HOW MUCH...IF ANY PRECIPITATION WILL REACH THE
GROUND. THE ECMWF WAS FAVORED IN HANDLING THIS AS IT HAS REMAINED
THE MOST CONSISTENT IN TIMING OVER THE PAST FEW DAYS.

MODELS AGREE THE WESTERN ALEUTIAN LOW WILL CONTINUE TO WOBBLE JUST
NORTH OF SHEMYA AND DOMINATE THE PATTERN. THEY DO SLOWLY BEGIN TO
DIVERGE IN THEIR SOLUTIONS WITH EACH SUCCESSIVE FRONT COMING
AROUND THE LOW THOUGH. THE SECOND FRONT WED TRIES TO FORM A
TRIPLE POINT LOW NEAR ADAK AND THEN SWEEP TOWARD NUNIVAK ISLAND
THU. THE NEXT FRONT SWINGS AROUND ON A VERY SIMILAR PATH LATE THU
INTO FRI. AND THEN ANOTHER ONE WILL TRACK ALONG A VERY SIMILAR
PATH FRI INTO SAT. WHILE DISCREPANCIES AMONGST THE MEMBERS
INCREASE WITH EACH FRONT...THE GENERAL PATTERN REMAINS MUCH THE
SAME. THE ECMWF WAS AGAIN FAVORED IN HANDLING THIS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
INSTABILITY IS WEAKENING OVER THE SOUTHCENTRAL BUT STILL REMAINS
ALONG THE NORTH GULF COAST DUE TO A WEAK UPPER LEVEL WAVE MOVING
THROUGH THE AREA. THIS WILL ALLOW FOR CONTINUED LIGHT SHOWERS THAT
WILL DIMINISH IN THE EVENING HOURS AS A WEAK RIDGE MOVES IN FROM
THE WEST. THE RIDGE WILL THEN MOVE IN OVER THE AREA TONIGHT AND
ALLOW FOR TEMPERATURES TO DROP AND MORE FOG TO DEVELOPMENT. AREAS
ALONG COOK INLET ARE ALREADY SEEING FOG DEVELOPING AS THE RIDGE
MOVES CLOSER. THEN ON WEDNESDAY A FRONT WILL MOVE IN FROM THE
SOUTHWEST BRINGING PRECIPITATION BACK TO THE SOUTHCENTRAL.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
AN UPPER LEVEL WEAK SHORTWAVE WILL TRACK THROUGH THIS MORNING
RESULTING IN SCATTERED SNOW SHOWERS THROUGH SOUTHWEST ALASKA. BY
EARLY WEDNESDAY MORNING A WEATHER FRONT WILL TRACK THROUGH THE
EASTERN BERING SEA INTO THE SOUTHWEST COASTLINE. THIS WILL RESULT
IN ONSHORE FLOW AS THE FRONT MOVES INLAND THROUGH WEDNESDAY. THE
TEMPERATURES WILL CONTINUE TO WARM WITH THE CONTINUED ONSHORE
FLOW. THE PRECIPITATION WILL FALL AS A MIXTURE OF RAIN/SNOW ALONG
THE COASTLINE WITH MAINLY SNOW IN THE INLAND AREAS. THERE WILL BE
A SLIGHT CHANCE FOR POCKETS OF LIGHT FREEZING RAIN OVER INLAND
AREAS WITH THE WARM AIR LOFT RIDING OVER THE COLDER TEMPERATURES AT
THE SURFACE FOR WEDNESDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A NORTH PACIFIC STORM FORCE LOW WILL TRACK NEAR SHEMYA THIS EARLY
MORNING BEFORE CROSSING OVER INTO THE WESTERN BERING SEA RESULTING
IN HURRICANE FORCE WINDS IN THE WESTERN BERING SEA BY LATE THIS
MORNING AS THE LOW CONTINUES TO DEEPEN. THIS WILL BRING WARMER
TEMPERATURES PRODUCING A WINTRY MIX OF RAIN AND SNOW BEFORE
CHANGING TO ALL RAIN ALONG THE ALEUTIAN CHAIN GOING INTO THE
AFTERNOON HOURS. A HIGH WIND WARNING HAS BEEN ISSUED FOR THE
WESTERN ALEUTIANS FROM SHEMYA THROUGH ADAK UNTIL EARLY THIS
EVENING. THERE IS A SUBTROPICAL 160 KNOT SOUTHWEST TO NORTHEAST
JET STREAK SOUTH OF THE WESTERN ALEUTIANS THAT WILL CONTINUE TO
TRACK EASTWARD ALONG THE ALEUTIAN CHAIN THROUGH WEDNESDAY. THE
FRONTAL BOUNDARY WITH THE AFOREMENTIONED LOW PRESSURE SYSTEM WILL
BE NEAR ADAK THIS MORNING AND WILL TRACK EASTWARD ALONG THE
ALEUTIAN CHAIN. THE WEATHER FRONT WILL BE PUSHING THROUGH NEAR
UNALASKA THIS AFTERNOON BRINGING GUSTY SOUTHERLY WINDS RESULTING
IN STRONG GAP WINDS ON THE BERING SIDE. BY EARLY WEDNESDAY MORNING
THE FRONT WILL MOVE TO THE NORTHERN BERING SEA WITH GALE FORCE
WINDS. DURING THIS SAME TIME FRAME THE WESTERN ALEUTIANS WILL HAVE
A SECONDARY LOW FORM JUST WEST OF ADAK. THIS WILL BRING MORE GUSTY
WINDS WITH ANOTHER ROUND OF PRECIPITATION THROUGH THE
WESTERN/CENTRAL ALEUTIANS BEFORE SPILLING OVER INTO THE BERING
SEA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE BERING SEA WILL REMAIN IN AN ACTIVE WET AND WINDY PATTERN
THROUGH EARLY NEXT WEEK AS A LONGWAVE TROUGH REMAINS CENTERED OVER
THE WESTERN BERING AND A SERIES OF NORTH PACIFIC SHORTWAVES AND
ASSOCIATED DEEP SURFACE LOWS CONTINUE TO ROTATE AROUND THE BASE OF
THE TROUGH INTO THE CENTRAL BERING. THE NEXT OF THESE FEATURES
LOOKS TO CROSS THE CENTRAL ALEUTIANS LATE THURSDAY...BRINGING
ANOTHER ROUND OF GALE TO POSSIBLY STORM FORCE WINDS TO THE REGION.
ANOTHER SYSTEM WILL FOLLOW QUICKLY ON ITS HEELS TAKING A VERY
SIMILAR PATH BY LATE FRIDAY. GUIDANCE IS THEN HINTING AT YET
ANOTHER SYSTEM TRACKING OVER THE SAME AREA BY EARLY NEXT
WEEK...THOUGH DETAILS AT THAT POINT REMAIN A LITTLE MURKIER.

THIS PATTERN WILL YIELD DEEP SOUTH TO SOUTHWESTERLY FLOW OVER THE
SOUTHERN MAINLAND AS A HIGHLY AMPLIFIED RIDGE SETS UP DOWNSTREAM
OVER THE FAR EASTERN GULF AND ALCAN BORDER THIS WEEKEND...KEEPING
SHOWERY CONDITIONS FOCUSED OVER MUCH OF THE AREA.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 187 191
		 DENSE FOG ADVISORY 101 111
MARINE...HURRICANE FORCE WIND WARNING 411 412
		 STORM WARNING 175 176 177 178 185 413
         GALE WARNING 150 155 165 170 171 172 173 174 179
					  180 181 414
FIRE WEATHER...NONE

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PLD
LONG TERM...CB