Small Craft Advisory 890, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
251 PM AKST SUN NOV 9 2014

.ANALYSIS AND UPPER LEVELS...A HIGHLY AMPLIFIED UPPER LEVEL PATTERN
IS DEVELOPING OVER ALASKA WITH A DEEP VERTICALLY STACKED LOW
SPINNING OVER THE BERING SEA AND A 175 KT SUBTROPICAL JET/DIGGING
TROUGH OVER THE NORTH CENTRAL PACIFIC INDUCING DOWNSTREAM RIDGING
OVER THE NORTHEAST PACIFIC AND EASTERN GULF OF ALASKA. STRONG
SOUTHERLY FLOW HAS SET UP ON THE WEST SIDE OF THE AMPLIFYING
RIDGE...TRANSPORTING DEEP MOISTURE NORTHWARD ACROSS THE WESTERN
GULF INTO SOUTHCENTRAL ALASKA AND INTERIOR SOUTHWEST ALASKA.

THE REMNANTS OF THE OCCLUDED FRONT FROM THE BERING SEA LOW ARE
PUSHING INLAND ACROSS SOUTHWEST ALASKA...ENHANCED BY UPPER WAVES
MOVING ALONG THE FRONT. THERE IS STRONG SOUTHEASTERLY FLOW AHEAD
OF THE FRONT..BUT IT IS FAIRLY SHALLOW WITH DEEP SOUTHERLY FLOW
ABOVE. THIS IS ALLOWING PRECIP TO REACH THE GROUND IN TYPICAL
DOWNSLOPE AREAS. WARMER AIR IS ALSO ARRIVING WITH THE OCCLUDED
FRONT AND SOUTHERLY FLOW ALOFT. THE COASTAL ZONE HAS CHANGED TO
ALL RAIN WITH TEMPERATURES NOW WELL INTO THE 30S AND 40S. INTERIOR
SOUTHCENTRAL AND SOUTHWEST ALASKA ARE STILL COLD ENOUGH FOR SNOW
OR FREEZING RAIN (AS IS BEING OBSERVED IN THE SOUTHERN SUSITNA
VALLEY THIS MORNING)...BUT TEMPERATURES WILL CONTINUE TO SLOWLY
CLIMB IN ALL AREAS.

THE LOW OUT IN THE BERING SEA IS STILL STRONG WITH AN ESTIMATED
CENTRAL PRESSURE SOMEWHERE AROUND 950 MB AS OF EARLY THIS MORNING.
HOWEVER THE STRONGEST WINDS NOW TOP OUT AT GALE FORCE. THE IMPACTS
ARE QUITE NORMAL FOR THIS TIME OF YEAR WITH STRONG GUSTY WINDS
BEING OBSERVED ACROSS MUCH OF THE BERING SEA AND ALEUTIANS.

&&

.MODEL DISCUSSION...MODELS ARE IN GOOD AGREEMENT OVER THE NEXT
COUPLE DAYS WITH GENERAL EVOLUTION OF THE HIGHLY AMPLIFIED
PATTERN. FORECAST CONFIDENCE IS GENERALLY ABOVE AVERAGE. HOWEVER
THERE ARE SOME FORECAST CHALLENGES INCLUDING EXTENT OF PRECIP IN
DOWNSLOPE AREAS...PRECIP-TYPE OVER INTERIOR AREAS OF SOUTHCENTRAL
AND SOUTHWEST ALASKA...AND EXACT STRENGTH OF GAP WINDS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA...
A WET PATTERN WILL CONTINUE THROUGH THE BEGINNING OF THE WEEK WITH
DEEP SOUTHERLY FLOW ESTABLISHED OVER SOUTHCENTRAL ALASKA AND A
SERIES OF FRONTS APPROACHING THE GULF COAST. THE BULK OF THE
PRECIPITATION WILL BE CONFINED TO THE GULF COAST AS STRONG
SOUTHEASTERLY MID LEVEL FLOW ACROSS THE CHUGACH RANGE KEEPS INLAND
AREAS LIMITED TO MAINLY TO SCATTERED SHOWERS. ONE EXCEPTION WILL
BE THIS EVENING AS A WEAK UPPER TROUGH LIFTS NORTHWARD THROUGH THE
AREA...BRINGING A BRIEF WINDOW OF MORE NUMEROUS SHOWERS TO
ANCHORAGE AND THE MAT-SU. SOME SNOW WILL MIX IN OVER INLAND
LOCATIONS BUT PRECIPITATION TYPE WILL BE MOSTLY RAIN OVER THE
COMING DAYS AS TEMPERATURES CONTINUE TO WARM IN SOUTHERLY
FLOW...WITH ANY LIGHT ACCUMULATIONS MOSTLY LIMITED TO HIGHER
ELEVATIONS SUCH AS TURNAGAIN AND THOMPSON PASSES. THE NEXT FRONT
APPROACHING THE COAST LATE SUNDAY WILL LEAD TO ANOTHER ROUND OF
STRONGER SOUTHEASTERLY WINDS THROUGH FAVORED AREAS SUCH AS
TURNAGAIN ARM. INLAND LOCATIONS WILL THEN SEE AN INCREASED CHANCE
OF PRECIPITATION ON MONDAY AS MID LEVEL FLOW BECOMES MORE
SOUTHERLY AND DOWNSLOPE FLOW WEAKENS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
STEADY RAIN MIXED WITH SNOW AT TIMES WILL TAPER OFF FROM WEST TO
EAST TONIGHT ACROSS BRISTOL BAY AND THE LOWER KUSKOKWIM VALLEY AS
A SHORTWAVE MOVING UP FROM THE NORTH PACIFIC DEPARTS INTO THE
INTERIOR. THIS WILL LEAVE A SHOWERY PATTERN AND ABOVE AVERAGE
TEMPERATURES OVER MUCH OF THE SOUTHWEST MAINLAND FOR THE NEXT
SEVERAL DAYS AS BROAD SOUTHERLY FLOW REMAINS ENTRENCHED OVER THE
AREA. ANOTHER ROUND OF STEADIER RAIN WILL APPROACH THE REGION
FROM THE SOUTH AND EAST LATE TUESDAY INTO WEDNESDAY AS A WARM
FRONT MOVES IN FROM THE NORTH PACIFIC. GUSTY SOUTHEAST WINDS WILL
GRADUALLY DIMINISH TONIGHT BUT THEN RETURN TO AREAS ALONG THE
AKPEN AND ALASKA RANGE AS THIS NEXT SYSTEM APPROACHES LATE
TUESDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
WIDESPREAD SHOWERS AND STRONG WINDS WILL GRADUALLY DIMINISH IN
INTENSITY THROUGH TUESDAY AS THE LARGE DEEP LOW OVER THE CENTRAL
BERING CONTINUES TO MOVE OFF TO THE NORTHWEST AND WEAKEN. WEST TO
SOUTHWESTERLY GALE FORCE WINDS WILL PERSIST ACROSS THE WESTERN
AND CENTRAL ALEUTIANS THROUGH MONDAY NIGHT BEFORE TRENDING
DOWN ON TUESDAY...BUT GUSTY NORTHWEST WINDS WILL REMAIN OVER THE
AREA THROUGH MUCH OF THE WEEK AS THE WEAKENING LOW REMAINS OVER
THE NORTHWEST BERING. ANOTHER WEAKER LOW APPROACHING FROM THE
NORTH PACIFIC WILL BRING AN INCREASE IN SHOWER ACTIVITY TO THE
EASTERN ALEUTIANS AND AKPEN LATE TUESDAY INTO WEDNESDAY...WITH
STRONG SOUTHEASTERLY WINDS ALSO POSSIBLE IN THAT TIME PERIOD.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A BLOCKING RIDGE STRETCHING FROM THE PANHANDLE THROUGH THE ALCAN
BORDER WILL AMPLIFY AND ORIENTATE ITSELF NORTHWEST TO SOUTHEAST
OVER SOUTHCENTRAL BY MID WEEK...AND PERSISTS THROUGH THE WEEKEND.
THIS BLOCKING RIDGE WILL KEEP A SERIES OF WEAK BERING AND NORTH
PACIFIC LOWS CONFINED MAINLY TO THE BERING SEA AND SOUTHWEST
MAINLAND. THE FEW WAVES OF PRECIPITATION THAT WILL MAKE IT INTO
SOUTHCENTRAL BY THE LATER PART OF THIS WEEK WILL MAINLY REMAIN
AROUND THE NORTHERN GULF COAST AND EASTERN KENAI...AS WELL AS
OVER KODIAK ISLAND. GOOD MODEL AGREEMENT REGARDING THE RIDGE
CONTINUES TO BUILD CONFIDENCE IN A GENERAL WARMING TREND OVER
MUCH OF SOUTHCENTRAL...AS WELL AS WHERE PRECIPITATION AND
DOWNSLOPING/DRYING WILL OCCUR THROUGH THE WEEKEND.
HOWEVER...MODELS CONTINUE TO STRUGGLE WITH THE PLACEMENT AND
STRENGTH OF THE MULTIPLE SYSTEMS THAT TRACK UP THE WESTERN PART
OF THE RIDGE THROUGH THE END OF THE WEEKEND. THIS CREATES MUCH
UNCERTAINTY WITH THE TRACKS OF THESE SYSTEMS OVER THE SOUTHWEST
MAINLAND OR BERING SEA...AND HOW STRONG THEY WILL BECOME. MAINLY
SIDED WITH WPC GUIDANCE AND TOOK A MORE BROAD BRUSH APPROACH TO
THESE SYSTEMS UNTIL MODELS COME INTO BETTER AGREEMENT.

OVER THE BERING SEA AND WESTERN GULF...A VERTICALLY STACKED LOW
OVER THE NORTHWEST BERING WILL CONTINUE TO WEAKEN AND TRACK
WESTWARD THROUGH MID WEEK...BEFORE DISSIPATING OVER THE EASTERN
SIBERIAN COAST. THE UPPER LEVEL TROUGH COVERING MUCH OF THE BERING
WILL ELONGATE AND DIVE SOUTH INTO THE NORTH PACIFIC BY MID WEEK.
EXPECT CLOUDY AND SHOWERY CONDITIONS TO CONTINUE THROUGH MID WEEK
WITH WINDS SLOWLY DIMINISHING THROUGH EARLY NEXT WEEK. GALE FORCE
WINDS OVER THE WESTERN BERING/ALEUTIANS WILL DIMINISH BY MID
WEEK...AS JET SUPPORT BEGINS TO DECREASE AND PUSH SOUTH OF THE
CHAIN. A SET OF FRONTAL SYSTEMS WILL APPROACH THE WESTERN
ALEUTIANS FROM THE WEST STARTING FRIDAY...BRINGING PRECIP AND
GUSTY WINDS BACK TO THE AREA THROUGH THE WEEKEND. MODELS CONTINUE
TO STRUGGLE WITH THE TIMING AND STRENGTH OF THESE FRONTAL SYSTEMS
AS THEY MAKE THEIR WAY INTO THE WESTERN AND CENTRAL ALEUTIANS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 119 120 130 131 173 174 175 176 177
              178 179 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...TP