Gale Warning 469, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
112 PM AKDT SAT AUG 24 2013

.ANALYSIS AND UPPER LEVELS...SATELLITE IMAGERY SHOWS A HIGHLY
AMPLIFIED BUT PROGRESSIVE PATTERN IN PLACE ACROSS THE ALASKA
REGION WITH A RIDGE CENTERED OVER THE NORTH CENTRAL PACIFIC AND
CENTRAL BERING SEA AND TROUGHS ON EITHER SIDE OF IT. THE SUBTROPICAL
JET EXITS ASIA AT 40N LATITUDE AND THEN CURVES NORTHWARD OVER THE
BERING RIDGE AND THEN DIVES SOUTHEASTWARD ACROSS SOUTHWEST ALASKA
INTO THE NORTHEAST PACIFIC. A STRONG SHORT-WAVE TRACKING INTO THE
SOUTHWEST BERING IS LEADING TO DEEPENING OF A SURFACE LOW WHICH IS
TRACKING NORTHWARD OVER THE WEST-CENTRAL BERING. A WARM FRONT IS
PROGRESSING NORTH AND EASTWARD RAPIDLY SPREADING RAIN AND FOG
ACROSS THE EASTERN BERING AND ALEUTIANS TOWARD SOUTHWEST ALASKA.

MEANWHILE...A COUPLE STRONG VORTICITY MAXIMA ARE RAPIDLY DIGGING
SOUTHEASTWARD ACROSS THE WESTERN GULF WITH A FEW WEAKER WAVES JUST
UPSTREAM. WATER VAPOR IMAGERY SHOWS STRONG SUBSIDENCE AND DRYING
FROM SOUTHWEST ALASKA TO THE WESTERN GULF. THIS IS CAUSING STRONGER
WINDS ALOFT TO MIX DOWN TO THE SURFACE ACROSS PORTIONS OF BRISTOL
BAY...THE WESTERN GULF AND COOK INLET AREAS. THERE IS ALSO A TIGHT
PRESSURE GRADIENT ACROSS MUCH OF SOUTHCENTRAL AS A SURFACE LOW OVER
THE NORTHERN GULF EXITS AND HIGH PRESSURE BUILDS IN FROM THE NORTH
AND WEST. THIS IS COMBINING WITH THE UPPER LEVEL SUBSIDENCE TO
PRODUCE STRONG GAP WINDS ALONG THE GULF COASTAL AREAS.

.MODEL DISCUSSION...MODELS HAVE BEEN STRUGGLING WITH CONSISTENCY
IN HANDLING OF SYSTEMS ORIGINATING IN THE NORTHWEST PACIFIC WHICH
IS LIKELY DUE TO A COMBINATION OF DATA SPARSITY AND DIFFICULTY IN
TIMING FEATURES IN SUCH PROGRESSIVE FLOW. THEY HAVE ALL INITIALIZED
WELL WITH THE STRONG FEATURES NOTED IN THE ANALYSIS SECTION ABOVE.
HOWEVER...DIFFERENCES DEVELOP WITH THE TRACK OF THE THE UPPER WAVE
OVER THE SOUTHWEST BERING AS IT REACHES SOUTHWEST ALASKA ALONG WITH
HANDLING OF WEAKER UPSTREAM WAVES WHICH CROSS A FLATTENED OUT RIDGE
AND THEN DIVE SOUTHEASTWARD AS THEY REACH SOUTHWEST ALASKA. THEY
ALL INDICATE THE SAME PRIMARY IMPACT...AN ELONGATING AND WEAKENING
FRONTAL SYSTEM OVER SOUTHWEST ALASKA. THE UNCERTAINTY LIES IN HOW
FAR EAST THE FRONTAL PRECIP AND CLOUDS WILL MAKE IT.

MODEL SPREAD AND UNCERTAINTY IS MUCH GREATER WITH TRACK OF NEXT
SYSTEM MOVING OVER TOP OF THE RIDGE SUNDAY NIGHT AND MONDAY. WITH
NEAR ZONAL FLOW IN THE WAKE OF THE CURRENT SYSTEM THE MODELS DO
SEEM TO BE TRENDING THE CORRECT WAY WITH A MORE SOUTHERLY TRACK
ACROSS THE BERING SEA. THUS...WILL ALSO TREND THE FORECAST HEAVILY
THAT DIRECTION.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...GUSTY WINDS WILL DEVELOP ACROSS MUCH OF
SOUTHCENTRAL THIS AFTERNOON DUE TO MIXING DOWN OF STRONGER WINDS
FROM ALOFT AS WELL AS TIGHT SURFACE PRESSURE GRADIENTS. THESE WINDS
WILL THEN QUICKLY DIE OFF DURING THE EVENING...ESPECIALLY INLAND...AS

THE GULF LOW RE-FORMS OVER THE SOUTHEAST GULF ALLOWING GRADIENTS AND
WINDS AT ALL LEVELS TO WEAKEN ACROSS SOUTHCENTRAL. WITH CLEAR SKIES
AND DRY AIR SETTLING IN ACROSS THE REGION RADIATIONAL COOLING WILL
LEAD TO DECOUPLING OF THE BOUNDARY LAYER WHICH IN TURN WILL LEAD
TO THE COLDEST NIGHT-TIME TEMPERATURES IN QUITE A WHILE. EXPECT
THE COPPER RIVER BASIN TO DROP DOWN TO FREEZING OR BELOW WITH
WIDESPREAD LOWER TO MID 40S ACROSS MUCH OF THE REST OF SOUTHCENTRAL.

ON SUNDAY SOME MID TO HIGH CLOUDS ASSOCIATED WITH THE SYSTEM
CROSSING THE BERING SEA WILL LIKELY MOVE THROUGH...BUT ANY PRECIP
CHANCES WILL BE CONFINED TO PORTIONS OF KODIAK ISLAND. UNCERTAINTY
GROWS WITH TRACK OF THE NEXT BERING SYSTEM BUT CURRENT INDICATIONS
ARE THAT IT WILL REMAIN SOUTH OF THE REGION AND DRY WEATHER MAY
HOLD FOR SOUTHCENTRAL ALL THE WAY THROUGH TUESDAY.

SOUTHWEST ALASKA...THOSE LOCATIONS EXPERIENCING GUSTY WIND TODAY
WILL SEE THE WINDS QUICKLY LIGHTEN UP THIS EVENING AS HIGH PRESSURE
MOVES OVERHEAD. THE FRONTAL SYSTEM CROSS THE BERING SEA WILL ARRIVE
ALONG THE KUSKOKWIM DELTA LATE TONIGHT AND SPREAD INLAND DURING THE
DAY SUNDAY. THE FRONT WILL ELONGATE AND WEAKEN AS IT MOVES INLAND...
SO THE SOUTHERN KUSKOKWIM VALLEY AND INTERIOR BRISTOL BAY WILL
LIKELY SEE LIGHTER RAIN THAN COASTAL AREAS. ANOTHER SYSTEM WILL
RAPIDLY CROSS THE BERING SEA MONDAY...ALTHOUGH FORECAST CONFIDENCE
IN THE TRACK IS BELOW AVERAGE. BASED ON A MODEL TREND TOWARD A MORE
SOUTHERLY TRACK BRISTOL BAY WILL HAVE THE BEST SHOT OF RECEIVING
ANOTHER ROUND OF RAIN MONDAY AFTERNOON THROUGH MONDAY NIGHT.

BERING SEA/ALEUTIANS...MARGINALLY COOLER LOW LEVEL AIR MOVING IN
THE BACK SIDE OF THE CURRENT STORM WILL ERODE SOME OF THE STEEP
TEMPERATURE INVERSIONS CURRENTLY IN PLACE ACROSS THE BERING SEA
AND ALEUTIANS...HELPING BRING AN END TO WIDESPREAD DENSE FOG. THE
UPPER LEVEL RIDGE WILL FLATTEN OUT WHICH MEANS THE NEXT SYSTEM WILL
TAKE A FARTHER SOUTH TRACK ON SUNDAY AND MONDAY WITH RAIN AND FOG
PRIMARILY CONFINED TO THE ALEUTIANS AND SOUTHERN ALASKA PENINSULA.

.LONG TERM FORECAST...AT THE BEGINNING OF THE EXTENDED PERIOD MODELS
ARE LOCKED ON TO AN UPPER LOW/SHORT-WAVE MOVING OUT OF RUSSIA AND
AMPLIFYING OVER THE WESTERN MAINLAND ON WEDNESDAY...LIKELY BRINGING
RAIN AND COOLER TEMPERATURES TO THE SOUTHWEST AND SOUTHCENTRAL
ALASKA. THERE IS MUCH LARGER UNCERTAINTY WITH THE SOUTHERN STREAM
FLOW OVER THE FLATTENED NORTH CENTRAL PACIFIC RIDGE. LATEST MODELS
ARE COMPLETELY OUT OF PHASE WITH NEXT SYSTEM TRACKING ALONG THE
ALEUTIANS MID TO LATE NEXT WEEK. THUS...WILL HOLD TIGHT UNTIL
MODELS GAIN SOME SORT OF HOLD ON THE PROGRESSION OF SHORT-WAVES.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...172 175 176 179 185.
FIRE WEATHER...NONE.

SEB AUG 13