Dense Fog Advisory 2, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1240 PM AKST MON JAN 10 2011

.ANALYSIS AND UPPER LEVELS...VERY STRONG UPPER RIDGE IS NOW CENTERED
OVER NORTHWEST ALASKA. WATER VAPOR IMAGERY SHOWS THE FIRST (OF WHAT
WILL BE A SERIES OF UPPER SHORT-WAVES TO MOVE THROUGH SOUTHCENTRAL
ALASKA THE NEXT FEW DAYS) DROPPING SOUTHWARD INTO THE NORTHERN
YUKON AND NORTHEAST CORNER OF ALASKA. ARCTIC AIR WILL ACCOMPANY
THIS SHORT-WAVE AND LEAD TO A CHANGE IN WEATHER ACROSS ALASKA.
RIGHT NOW CONDITIONS REMAIN CALM ACROSS THE SOUTHERN MAINLAND AND
GULF WITH JUST A FEW ISOLATED AREAS OF FOG UNDERNEATH SOME VERY
STEEP SURFACE BASED INVERSIONS. MOST OF ANCHORAGE CLEARED OUT
AGAIN THIS MORNING...BUT AS WAS THE CASE YESTERDAY EXPECT AREAS
OF FOG TO RE-FORM AND REMAIN IN THE VICINITY UNTIL THE COLDER AIR
AND WINDS ARRIVE LATE TONIGHT.

THE STRENGTHENING RIDGE HAS PUSHED THE SOUTHERLY JET OVER THE
BERING SEA WESTWARD. IT NOW EXTENDS FROM THE NORTH CENTRAL
PACIFIC WEST-NORTHWEST ACROSS THE CENTRAL ALEUTIANS AND ON UP
TO THE KAMCHATKA PENINSULA. AT THE SURFACE A VERY TIGHT PRESSURE
GRADIENT REMAINS PRETTY MUCH IN THE AREA RIGHT UNDERNEATH THE
UPPER JET. IR SATELLITE IMAGERY SHOWS A NORTH PACIFIC LOW TRACKING
TOWARD CENTRAL ALEUTIANS. IT IS SHOWING SIGNS OF WEAKENING...BUT
WILL STILL TIGHTEN UP THE PRESSURE GRADIENT FROM ATKA TO DUTCH
HARBOR AS IT TRACKS TOWARD ADAK. A MORE SIGNIFICANT LOW IS
DEVELOPING TO THE SOUTHWEST WITH SUPPORT FROM A STRONG WESTERLY
JET AND ARCTIC AIR FEEDING INTO THE SYSTEM. THIS LOW IS TRACKING
NORTHEASTWARD BUT WILL SOON BEGIN TO CURVE NORTHWARD AND EVENTUALLY
NORTHWESTWARD ALONG THE WESTERN ALEUTIANS AS IT ROUNDS THE UPPER
TROUGH AXIS. THIS SYSTEM WILL PRODUCE SOLID STORM FORCE WINDS
NORTH AND EAST OF THE TRACK FROM THE VICINITY OF ADAK AND UP
ACROSS THE WESTERN BERING SEA.

.MODEL DISCUSSION...MODELS REMAIN IN GOOD AGREEMENT WITH SYNOPTIC
SCALE FEATURES AND FORECAST CONFIDENCE IS ABOVE NORMAL. THERE ARE
SOME DIFFERENCES IN TRACK OF SYSTEMS ALONG AND TO THE SOUTH OF THE
ALEUTIANS. PLAN TO STICK WITH THE GFS WHICH HAS BEEN PERFORMING
BEST AS OF LATE.

.SHORT TERM FORECAST...

SOUTHCENTRAL...UPPER SHORT-WAVE OVER THE YUKON WILL CROSS
SOUTHCENTRAL TONIGHT AND MOVE INTO THE GULF TUESDAY MORNING WITH
ARCTIC AIR ADVECTING IN BEHIND IT. MEANWHILE THE SURFACE PRESSURE
GRADIENT WILL TIGHTEN AS PRESSURE RISES OVER INTERIOR ALASKA AND
FALL OVER THE GULF. THE COLD AIR ADVECTION COMBINED WITH TIGHT
PRESSURE GRADIENT WILL KICK UP WINDS ACROSS THE REGION...ESPECIALLY
FOR CHANNELED AREAS SUCH AS THE MATANUSKA VALLEY AND VALDEZ/THOMPSON
PASS. ANY REMAINING FOG WILL RAPIDLY DISSIPATE AS THE WINDS ARRIVE.
ANOTHER UPPER WAVE WILL MOVE THROUGH TUESDAY NIGHT AND WEDNESDAY
BRINGING ANOTHER SURGE OF EVEN COLDER AIR WHICH MEANS WINDS WILL
BE STRONGER. PLAN TO ISSUE A HIGH WIND WATCH FOR THE VALDEZ ZONE
WITH THE AFTERNOON FORECAST PACKAGE. DON'T HAVE THE CONFIDENCE TO
ISSUE A WATCH AT THIS TIME...BUT WILL ALSO NEED TO KEEP AN EYE
ON WARNING LEVEL WIND POTENTIAL IN THE MATANUSKA VALLEY. A MUCH
STRONGER SHORT-WAVE LOOKS LIKE IT WILL MOVE THROUGH THURSDAY.
HOWEVER...THERE WON'T MUCH ADDITIONAL COLD ADVECTION WITH THAT
ONE...SO IMPACT ON WINDS LIKELY WON'T BE THAT SIGNIFICANT. IN
ADDITION TO ALL THE WINDS...TEMPERATURES WILL GRADUALLY FALL AS
WE HEAD THROUGH THE WEEK.

SOUTHWEST ALASKA...UPPER LEVEL SHORT-WAVES WILL PASS MOSTLY TO
THE EAST OF SOUTHWEST ALASKA THROUGH WEDNESDAY NIGHT AND SURFACE
PRESSURE GRADIENT WON'T BE NEARLY AS TIGHT AS OVER SOUTHCENTRAL.
THERE WILL STILL BE SOME COLD AIR ADVECTION WHICH WILL CONTRIBUTE
TO LOCALIZED GUSTY WINDS...ESPECIALLY ACROSS THE KUSKOKWIM DELTA.
THE SHORT-WAVE ON THURSDAY LOOKS LIKE IT WILL TRACK ACROSS SOUTHWEST
ALASKA SO MAY SEE SOME STRONGER COLD AIR ADVECTION AND WIND AT
THAT POINT.

BERING SEA/ALEUTIANS...THE UPPER RIDGE WILL RETROGRADE WESTWARD THE
NEXT COUPLE DAYS PUSHING THE STORM TRACK OFF TO THE SOUTH AND WEST.
THERE WILL BE TWO MORE LOWS WHICH WILL AFFECT THE ALEUTIANS AND
BERING SEA...ONE POWERFUL STORM PASSING BY TONIGHT AND THEN A
WEAKER STORM PASSING SOUTH OF THE ALEUTIANS WEDNESDAY. AFTER THAT
CONDITIONS WILL CALM DOWN A BIT FOR AT LEAST THE REST OF THE WEEK.

.LONG TERM FORECAST...UPPER RIDGE OVER THE ARCTIC WILL GRADUALLY
WEAKEN LATE THIS WEEK THROUGH EARLY NEXT WEEK. THERE IS POOR MODEL
RUN-TO-RUN CONSISTENCY IN THIS TIME FRAME WITH HANDLING OF ENERGY
MOVING UNDERNEATH THIS RIDGE ACROSS THE SOUTHERN MAINLAND/GULF
OVER TO THE BERING SEA. CHANCES ARE THOUGH THAT MOSTLY DRY AND
COLD CONDITIONS WILL PERSIST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WATCH ZONE 131.
MARINE...STORM WARNING...127 170 172 175.
         GALE WARNING...120 121 126 128 130 132 138 140 150 155
                        171 176 179 185.
FIRE WEATHER...NONE.

SEB JAN 11