Gale Warning 777, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
507 AM AKST SUN NOV 15 2015

.ANALYSIS AND UPPER LEVELS...

A GENERALLY COLD AND TROUGHY PATTERN CONTINUES ACROSS THE ENTIRE
REGION. LOW PRESSURE NEAR THE NORTHERN GULF COAST CONTINUES TO
WEAKEN. THE UPPER LEVEL TROUGH THAT INITIATED LIGHT SNOW IN
VALDEZ...CORDOVA...AND GLENNALLEN THE LAST 12 TO 24 HOURS
CONTINUES TO MOVE NORTH AND EAST PAST THE SURFACE LOW...AND THE
MID-LEVEL DEFORMATION ZONE CONTINUES TO MOVE INLAND TOWARD THE
EASTERN INTERIOR AND WESTERN YUKON.

A SECOND LOW PRESSURE SYSTEM CONTINUES TO LOOK QUITE IMPRESSIVE ON
SATELLITE IN THE CENTRAL BERING SEA. THIS LOW HAS REACHED PEAK
INTENSITY AS A LOW-END STORM-FORCE CENTER...AND IS NOW MOVING
SOUTH AND EAST THROUGH THE BERING IN THE GENERAL DIRECTION OF
THE EASTERN ALEUTIANS AND SOUTHERN ALASKA PENINSULA. A WEAK FRONT
EXTENDS FROM THIS LOW EAST AND THEN SOUTH JUST OFFSHORE OF THE
SOUTHWEST MAINLAND...AND IS BRINGING SCATTERED SNOW SHOWERS TO
MAINLY COASTAL LOCATIONS.

&&

.MODEL DISCUSSION...

THE MODELS HAVE COME INTO BETTER AGREEMENT THROUGH EARLY THIS
WEEK WITH RESPECT TO THE OVERALL SYNOPTIC PATTERN. A BROAD TROUGH
WILL CONTINUE TO ASSERT ITS INFLUENCE OVER THE MAINLAND AND
PROVIDE FOR COLD WEATHER TO CONTINUE THROUGH EARLY IN THE WEEK.
WITH THE JET STREAM SOUTH OF THE GULF...THE PRIMARY STORM TRACK IN
THIS REGION WILL REMAIN SOUTH OF OUR AREA BUT IMPACT THE SOUTHERN
PANHANDLE BY MONDAY.

MEANWHILE...THE WELL-DEFINED LOW IN THE CENTRAL BERING WILL TRACK
QUICKLY SOUTHEAST INTO THE NORTH PACIFIC SOUTH OF THE ALASKA
PENINSULA AND THEN DISSIPATE MONDAY AFTERNOON...WITH STRONG YET
TRANSITORY RIDGING BEHIND IT TO QUICKLY MOVE THROUGH THE SOUTHERN
BERING AND ALEUTIANS TONIGHT INTO MONDAY. THE NEXT WEATHER SYSTEM
QUICKLY FOLLOWS LATE MONDAY IN THE WESTERN ALEUTIANS. THIS GALE-
FORCE FRONTAL SYSTEM LOOKS TO REPRESENT THE LEADING EDGE OF A
MUCH WARMER AIR MASS TO IMPACT THE ENTIRE REGION FROM WEST TO EAST
BY THE WEEKEND.

THE MODELS ARE IN GOOD AGREEMENT WITH THE QPF ALONG THE BERING
SEA COAST AND THE SECONDARY WRAP THAT ROTATES AROUND THE MAIN LOW
ACROSS THE BERING SEA THROUGH TOMORROW EVENING.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
SOUTHCENTRAL IS FIRMLY ENTRENCHED IN AN ARCTIC AIR MASS WITH VERY
COLD AND DRY CONDITIONS ACROSS MOST OF THE REGION. THERE IS STILL
SOME LIGHT SNOW FALLING OVER PORTIONS OF THE COPPER RIVER
BASIN...BUT THIS WILL TAPER OFF AS AN UPPER LEVEL SHORT-WAVE EXITS
TO THE NORTHEAST THIS AFTERNOON. THE SURFACE LOW WHICH HAS BEEN
SITTING OVER THE NORTHEAST GULF THE PAST COUPLE DAYS WILL FINALLY
EXIT TO THE EAST TODAY WITH THE UPPER TROUGH. AS A RESULT PRESSURE
GRADIENTS AND GAP WINDS ALONG THE NORTH GULF COAST/PRINCE WILLIAM
SOUND WILL CONTINUE TO SLACKEN TODAY INTO TONIGHT. TEMPERATURES
HAVE REMAINED QUITE A BIT WARMER ALONG THE IMMEDIATE COAST DUE TO
THE PRESENCE OF THE WIND...BUT AS WINDS LIGHTEN TEMPERATURES WILL
DROP MORE SIGNIFICANTLY IN THESE AREAS.

THE GENERAL FORECAST FOR THE NEXT COUPLE DAYS REMAINS ON TRACK
WITH CONTINUED COLD AND DRY CONDITIONS. HOWEVER...THERE HAS BEEN
A KEY CHANGE IN THE LATEST MODEL GUIDANCE. INSTEAD OF SIMPLY
HAVING A BROAD TROUGH ALOFT...ALL GUIDANCE NOW INDICATES AN UPPER
LOW CURRENTLY OVER THE WESTERN INTERIOR WILL TRACK ACROSS INTERIOR
SOUTHCENTRAL OVERNIGHT TONIGHT THROUGH MONDAY. IN ADDITION...A
SEPARATE SHORT-WAVE TROUGH WILL DROP OUT OF THE BERING SEA AND
INTO THE WESTERN GULF MONDAY AFTERNOON AND EVENING. THESE FEATURES
WILL USHER IN A RESUPPLY OF ARCTIC AIR. MEANWHILE...A STRONG
SURFACE LOW WILL TRACK TO SOUTHEAST ALASKA MONDAY WITH A RESIDUAL
TROUGH/LOW SETTING UP OVER THE NORTHERN GULF. WHEN YOU PUT THIS
ALL TOGETHER THE END RESULT WILL BE ANOTHER FAIRLY STRONG WIND
EVENT FOR THE GULF COAST. WIND OVER INLAND AREAS OF SOUTHCENTRAL
WILL BE MUCH LIGHTER AND MORE ISOLATED IN NATURE. AREAS WHICH DO
OBSERVE A LITTLE WIND WILL SEE MILDER TEMPERATURES THAN AREAS WITH
NO WIND. IN ANY CASE THE AIR MASS WILL BE AS COLD IF NOT COLDER
THAN THE AIR MASS IN PLACE. SO EXPECT CONTINUED VERY COLD
TEMPERATURES THROUGH THE BEGINNING OF THE WORK WEEK.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
DRY AND COLD CONDITIONS ARE EXPECTED FOR THE SOUTHWEST THROUGH
MONDAY AS WEAK NORTHEAST FLOW CONTINUES TO BRING DOWN COLDER AIR
FROM THE NORTH. LATE ON MONDAY A WEAK TROUGH SWINGS IN OVER THE
COAST BRINGING SOME SNOW SHOWERS TO THE AREA BUT WILL HAVE LITTLE
IMPACT FURTHER INLAND.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE LOW OVER THE CENTRAL BERING IS TRACKING SOUTHEAST AND WILL
PASS OVER THE PRIBILOF ISLANDS BRINGING SNOW AND SEVERAL CHANGES
IN WIND DIRECTIONS EVENTUALLY BECOMING NORTHEASTERLY. EVEN THROUGH
THERE IS NOT MUCH COLD AIR ADVECTION WITH THE LOW THE WINDS ARE
STILL EXPECTED TO BE STRONG. THE SNOW AND STRONG WINDS WILL ALSO
IMPACT THE EASTERN ALEUTIANS AND ALASKA PENINSULA AS THE LOW MOVES
ACROSS THE PENINSULA THIS EVENING. MEANWHILE RIDGING IS BUILDING
IN OVER THE WESTERN ALEUTIANS WHICH IS CLEARING OUT SOME OF THE
PRECIPITATION. FOLLOWING CLOSE BEHIND THE RIDGE IS A WARMER SYSTEM
THAT WILL BRING RAIN TO THE WESTERN ALEUTIANS MONDAY AS IT TRACKS
TO THE EAST.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

TEMPERATURES WILL REMAIN WELL BELOW NORMAL ACROSS THE SOUTHERN
MAINLAND THROUGH TUESDAY BEFORE BEGINNING TO REBOUND DURING THE
MIDDLE OF THE WEEK AS THE LONGWAVE TROUGH SHIFTS TO THE EAST.
HOWEVER...MODELS CONTINUE TO STRUGGLE GREATLY WITH THE EVOLUTION
OF THE PATTERN DURING THE LATTER HALF OF THE WEEK AS THE TROUGH IS
REPLACED BY WEAK SHORTWAVE RIDGING. THE GFS QUICKLY MOVES THIS
FEATURE OFF TO THE EAST AND TRANSITIONS TO ZONAL FLOW WITH SEVERAL
EMBEDDED WAVES TRAVERSING THE INTERIOR. MEANWHILE...EUROPEAN
GUIDANCE CONTINUES TO AMPLIFY THE RIDGE OVER THE EASTERN HALF OF
THE MAINLAND AND HOLD BACK MOST OF THE ENERGY OVER THE WESTERN
HALF OF THE STATE THROUGH THE END OF THE WEEK. THIS LENDS BELOW
AVERAGE CONFIDENCE TO THE FORECAST...WITH PRECIPITATION CHANCES
GRADUALLY INCREASING FROM WEST TO EAST AND TEMPERATURES RETURNING
TO NEAR NORMAL TO ABOVE NORMAL VALUES BY THE END OF THE WEEK IN
WEST TO SOUTHWEST FLOW. MODELS ARE ALSO HAVING TROUBLE PINNING
DOWN THE DETAILS OVER THE BERING NEXT WEEK...BUT ARE GENERALLY
ADVERTISING A PROGRESSIVE PATTERN FEATURING UNSETTLED CONDITIONS
AS A NUMBER OF SYSTEMS TRACK THROUGH THE REGION.

WITH THE UPCOMING WEATHER CHANGE LATE THIS WEEK...IT APPEARS THE
POTENTIAL FOR AN IMPACTFUL STORM SYSTEM TO AFFECT SOUTHWEST ALASKA
WEDNESDAY AND SOUTHCENTRAL ALASKA BY THURSDAY IS EVER PRESENT.
THERE IS SOME DISCREPANCY AMONGST THE GUIDANCE ON THE STRENGTH OF
THE UPPER LEVEL JET AND A SERIES OF VORT MAXES EXPECTED TO MOVE
ACROSS THE STATE. THE GFS AND ECMWF SOLUTIONS VARY QUITE
DRASTICALLY BY LATE WEDNESDAY IN THE DEGREE OF WAA FROM THE
SOUTHWEST. THE ECMWF IS BY FAR THE COLDER SOLUTION THAT FAVORS A
SNOWY PATTERN THAT MAY MIX WITH RAIN AT SOME LOCATIONS.
HOWEVER...THE GFS PAINTS THE COMPLETE OPPOSITE PICTURE WITH VERY
STRONG WAA AND A CHANGE OF PRECIPITATION TO RAIN. IF THE GFS WERE
TO PAN OUT...IT WOULD APPEAR THAT SURFACE TEMPERATURES WOULD BE
SLOW TO REACT TO THE WARMER AIR ALOFT WHICH COULD POTENTIALLY LEAD
TO A WIDESPREAD FREEZING RAIN EVENT. WEDNESDAY AND THURSDAY ARE
STILL A WAYS OFF AND WITH THIS UNCERTAIN PATTERN NO DETAILS CAN
REALLY BE IRONED OUT AT THIS TIME. DETAILS SHOULD BECOME CLEARER
IN THE COMING DAYS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...HEAVY FREEZING SPRAY...160 180 181
         GALE...150 170 172 173 174 175 176 177 179 185

&&

SYNOPSIS AND MODEL DISCUSSION...CC
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...CB/MMC