Gale Warning 645, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT FRI OCT 25 2013

.ANALYSIS AND UPPER LEVELS...
A LONGWAVE TROUGH CONTINUES OVER THE BERING SEA WITH THE MASSIVE
LONGWAVE RIDGE OVER WESTERN NORTH AMERICA HOLDING STRONG. THIS
PATTERN IS NOW SEVERAL WEEKS OLD ACROSS THE ALASKAN DOMAIN...AND
ASSOCIATED WARM AIR MOVING INTO THE STATE HAS KEPT TYPICAL FREEZE-UP
ON HOLD ACROSS MANY AREAS OF THE MAINLAND. YESTERDAYS WEATHER-MAKING
LOW OVER THE BERING SEA IS NOW RAPIDLY WEAKENING...WITH THE
ASSOCIATED FRONT NOW BARELY RECOGNIZABLE ACROSS THE FAR NORTHERN
INTERIOR AND THE PANHANDLE. ONSHORE FLOW ACROSS THE SOUTHWEST
MAINLAND IS WEAKENING AS THE ENTIRE CIRCULATION AROUND THE LOW FALLS
APART. SOME LIGHT RAIN IS LINGERING ACROSS THE NORTH GULF
COAST...WHILE SUN HAS BROKEN OUT FURTHER WEST ACROSS MUCH OF COOK
INLET AND THE MAT-SU VALLEY IN RESPONSE TO HIGH PRESSURE BEGINNING TO
SPREAD INTO THE AREA.

.MODEL DISCUSSION...
THE ATMOSPHERIC MODELS ARE SLOWLY COMING INTO SOME BETTER
AGREEMENT...BUT ARE BY NO MEANS IN EXCELLENT AGREEMENT. THE FIRST
FEATURE OF NOTE IS A SHORTWAVE OVER THE WESTERN GULF THAT WILL
AMPLIFY AS STRONG MIDLEVEL RIDGING MOVES INTO THE GULF TONIGHT. ALL
MODELS DEPICT THIS SHORTWAVE MOVING INTO THE FAR NORTHERN
PANHANDLE...CLIPPING THE FAR EASTERN COPPER RIVER BASIN WITH SOME
FAIRLY LIGHT PRECIPITATION THIS EVENING. THE MORE SIGNIFICANT IMPACTS
OVER THE COMING DAYS WILL BE FROM A DRAMATIC NORTHWARD EXPANSION OF
THE WESTERN NORTH AMERICAN RIDGE TO INCLUDE MAINLAND ALASKA. THIS
WILL ONCE AGAIN PLUNGE THE REGION INTO WARM...WET...AND WINDY
SOUTHERLY FLOW AS A SERIES OF IMPULSES MOVE UP THE FRONT OF THE RIDGE
ON SUNDAY AND MONDAY. THE FIRST FEATURE WILL BE A VERY STRONG WARM
FRONT THAT BEGINS TO AFFECT THE SOUTHWEST MAINLAND SATURDAY EVENING
AND MOVES ON TO SOUTHCENTRAL ON SUNDAY. THE GFS IS A BIT SLOW WITH
THE TIMING OF THE WARM FRONT...BUT IS IN THE SAME BALLPARK AS THE
OTHER MODELS. BASED ON THE STRENGTH OF THE HIGH PRESSURE THAT WILL BE
IN PLACE AHEAD OF THIS FRONT...THINK PRESSURE GRADIENTS WILL TIGHTEN
IN A HURRY SUNDAY MORNING. THUS WILL BE ISSUING A HIGH WIND WATCH FOR
TURNAGAIN ARM WITH THE AFTERNOON PACKAGE. ON MONDAY...THE BULK OF THE
BERING LONGWAVE TROUGH EJECTS NORTHWARD AND LIFTS INTO INTERIOR
ALASKA. WHILE ALL MODELS ARE SHOWING THIS SAME BASIC TREND...THE
STRENGTH AND TIMING OF ASSOCIATED SURFACE LOWS ARE STILL VERY MUCH IN
DOUBT. THE GEM/UKMET ARE BOTH TRYING TO DEVELOP A FAIRLY STRONG LOW
SOMEWHERE OVER THE AKPEN/KODIAK ISLAND REGION...WHILE THE NAM/EC HAVE
BEEN MORE CONSISTENT WITH A WEAKER AND FURTHER WEST TRACK. SINCE THE
GFS IS TRENDING TOWARD THE WEAKER SOLUTION...HIGHEST CONFIDENCE AT
THIS POINT IS IN THE AFOREMENTIONED NAM/EC SOLUTION...AND WILL BE THE
BASIS FOR THE FORECAST TODAY. OF NOTE...EVEN THE WEAKER PRESSURE
GRADIENTS ASSOCIATED WITH THE NAM/EC SOLUTION WOULD BE ENOUGH TO
GENERATE VERY STRONG WINDS THROUGH TERRAIN GAPS AROUND SOUTHCENTRAL
ALASKA ON MONDAY. THIS SITUATION WILL BE WATCHED VERY CLOSELY WITH
EACH SUBSEQUENT MODEL CYCLE.

.SHORT TERM FORECAST...
SOUTHCENTRAL...A FEW SHOWERS ARE POSSIBLE AROUND COOK INLET THIS
EVENING BEFORE THE UPPER TROUGH PASSES THROUGH. AS WARM ADVECTION
BEGINS AND HIGH PRESSURE BUILDS...SOME FOG AROUND THE AREA IS
POSSIBLE AFTER MIDNIGHT BUT IS NOT EXPECTED TO BE A MAJOR IMPACT AT
THIS TIME. SATURDAY SHOULD BE A BEAUTIFUL FALL DAY BEFORE AN ABRUPT
TRANSITION BACK TO VERY ACTIVE WEATHER FOR THE LATTER HALF OF THE
WEEKEND AND START OF NEXT WEEK. AS MENTIONED ABOVE...A HIGH WIND
WATCH WILL BE POSTED WITH THE AFTERNOON FORECAST PACKAGE FOR
TURNAGAIN ARM AS WINDS SPIKE QUICKLY ON SUNDAY. THE LULL BETWEEN THE
SUNDAY AND MONDAY STORMS WILL BE WEAK AND SHORT-LIVED AS WIDESPREAD
RAIN OVERSPREADS THE AREA. WHILE CONFIDENCE IS INCREASING IN A REPEAT
HIGH-WIND EVENT THROUGH TURNAGAIN ARM ON MONDAY...LESS CLEAR IS THE
POTENTIAL FOR WINDS TO IMPACT THE LOWER ELEVATIONS OF THE ANCHORAGE
BOWL WITH THIS SECOND STORM. WILL NOT DRAMATICALLY ALTER THE FORECAST
AT THIS TIME AS THE EXPECTED SURFACE PRESSURE PATTERN REMAINS A BIT
UNCLEAR...BUT WILL BE WATCHING FUTURE MODEL RUNS CLOSELY.

SOUTHWEST...STRONG SOUTHERLY ONSHORE FLOW WILL DIMINISH THIS EVENING
AS HIGH PRESSURE CLIPS THE AREA THROUGH MIDDAY SATURDAY. CONDITIONS
WILL RAPIDLY DETERIORATE SATURDAY NIGHT AS WIND AND RAIN
ARRIVE...ESPECIALLY OVER THE BRISTOL BAY ZONE. NOT EXPECTING WINDS TO
REACH WARNING-LEVEL AT THIS TIME...BUT GUSTS IN EXCESS OF 60 MPH ARE
LIKELY THROUGH GAPS IN THE ALEUTIAN RANGE. THE STORM ON MONDAY WILL
BE FAR ENOUGH EAST THAT A REPEAT HIGH-WIND EVENT IS UNLIKELY ACROSS
THE AREA...THOUGH ANOTHER ROUND OF WIDESPREAD MODERATE RAIN IS
EXTREMELY LIKELY.

BERING SEA AND ALEUTIANS...THE CYCLE CONTINUES AS ONE LOW WEAKENS
TONIGHT OVER THE NORTHERN BERING AND ANOTHER STORM MOVES INTO THE
CENTRAL ALEUTIANS AND SOUTHERN BERING WITH WIND AND RAIN. THE LOW
CENTER...CURRENTLY AROUND 982 MB...WILL REMAIN NEARLY STATIONARY AND
AT THE SAME STRENGTH THROUGH SUNDAY AS THE LONGWAVE PATTERN UNDERGOES
SIGNIFICANT AMPLIFICATION IMMEDIATELY DOWNSTREAM OVER THE GULF. GALE
FORCE WINDS AND RAIN OVER THE SOUTHERN BERING WILL GIVE WAY TO MORE
SHOWERY CONDITIONS AND DIMINISHING WINDS BY SATURDAY EVENING AS THE
MOST ACTIVE WEATHER SHIFTS TO THE EAST FOR THE START OF THE WEEK.

.LONG TERM FORECAST...
LONG-RANGE MODELS HAD BEEN SUGGESTING A RETURN TO MORE SEASONAL
CONDITIONS ACROSS THE DOMAIN BY THE MIDDLE OF NEXT WEEK...BUT ARE NOW
SHOWING SIGNS THAT THE MORE PROGRESSIVE PARADE OF FORMER TROPICAL
SYSTEMS MAY CONTINUE THROUGH NEXT WEEKEND ACROSS MUCH OF THE REGION.
WHILE THE EXTREME WARMTH AND RAINFALL OF THIS UPCOMING WEEKEND ARE
NOT CURRENTLY EXPECTED TO REPEAT...A CONTINUED PATTERN OF ABOVE
NORMAL TEMPERATURES AND WETTER THAN NORMAL CONDITIONS IS LIKELY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WATCH 101
MARINE...GALE 120 130 131 132 138 150 155 160 165 170 172 173 174 175
177 178 180 181
FIRE WEATHER...NONE

AMD OCT 13