Gale Warning 972, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
100 PM AKST WED NOV 24 2010

.ANALYSIS AND UPPER LEVELS...HEMISPHERIC FLOW IS PROGRESSIVE WITH
A SERIES OF WAVES MOVING EASTWARD ACROSS ALASKA AND THE NORTH
PACIFIC. THE STRONGEST OF THESE IS AN UPPER TROUGH AND SURFACE
LOW OVER SOUTHWEST ALASKA. THESE FEATURES ARE TRACKING EAST-NORTHEAST
TOWARD SOUTHCENTRAL ALASKA BRINGING ANOTHER ROUND OF PRECIPITATION.
TEMPERATURES HAVE RISEN TO ABOVE FREEZING ACROSS NEARLY ALL OF
LOWLAND SOUTHCENTRAL SO THE PREDOMINANT PRECIP-TYPE IS RAIN. ANOTHER
WEAKER TROUGH IS OVER THE EASTERN BERING SOUTHERN ALASKA PENINSULA
AND ACCOMPANIED BY ARCTIC AIR. THIS COLDER AIR IS FILTERING INTO
THE BACK SIDE OF THE LOW AND CHANGED PRECIP TO SNOW ACROSS THE
KUSKOKWIM DELTA. THE COLD ADVECTION IS ALSO CONTRIBUTING TO GALE
FORCE WINDS OVER THE EASTERN BERING/ALEUTIANS AND SOUTHERN ALASKA
PENINSULA. LOOKING UPSTREAM...THERE IS A LOW OVER THE NORTHERN
BERING RIDING OVER TOP OF A SHORT-WAVE RIDGE AND SUPPORTED BY A
100 KT JET STREAK. FINALLY...SATELLITE IMAGERY SHOWS AN IMPRESSIVE
LOW SOUTH OF THE KAMCHATKA PENINSULA TRACKING TOWARD THE BERING SEA.

.MODEL DISCUSSION...MODELS GENERALLY IN GOOD AGREEMENT THROUGH THE
NEXT FEW DAYS. THE NAM DEPICTS A SHARPER UPPER TROUGH MOVING UP COOK
INLET TOWARD ANCHORAGE TONIGHT WHICH IS REFLECTED BY THE HIGHER QPF
AMOUNTS. 18Z NAM SHOWS CONTINUITY IN THIS SOLUTION. FOR NOW...WILL
TAKE A MIDDLE GROUND SOLUTION AND MONITOR RADAR AND MODEL TRENDS.
ELSEWHERE...GFS IS THE ODD SOLUTION OUT WITH FASTER TRACK OF LOW
ACROSS BERING SEA THURSDAY NIGHT AND FRIDAY. GFS ENSEMBLE MEMBERS
ALSO SUPPORT THE SLOWER SOLUTION INDICATED BY OTHER MODELS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...FIRST UPPER TROUGH WILL SLOW AND PERHAPS
EVEN STALL AS IT REACHES ANCHORAGE LATE TONIGHT. SIMILARLY...THE
SURFACE LOW WILL TRACK TO THE KENAI PENINSULA AND THEN OVER THE
NORTHERN GULF ON THURSDAY. THIS WILL RESULT IN PERSISTENT AREAS
OF PRECIPITATION ACROSS MUCH OF SOUTHCENTRAL. PRECIP-TYPE WILL
INITIALLY BE PREDOMINANTLY RAIN TONIGHT AS FIRST UPPER TROUGH
APPROACHES. COLDER AIR WILL THEN FILTER INTO THE REGION FROM THE
WEST ON THURSDAY...SWITCHING PRECIP OVER TO SNOW. HOWEVER...THE
SURFACE LOW WILL BEGIN TO TRACK OFF ACROSS THE GULF. THE SECONDARY
UPPER TROUGH CURRENTLY OVER THE EASTERN BERING WILL PROVIDE SOME
SYNOPTIC LIFT...BUT THIS DOES NOT LOOK LIKE A BIG EVENT.
THEREFORE...EXPECT GENERALLY LIGHT SNOWFALL ACCUMULATION. A SMALL
CHANGE IN THE DETAILS OF THIS SYSTEM COULD CHANGE THAT...SO WILL
NEED TO CLOSELY MONITOR THE LATEST TRENDS AND MODEL FORECASTS.

AS ARCTIC AIR FEED IN BEHIND THE SYSTEM EXPECT WINDS TO STRENGTHEN
ACROSS THE GULF COASTAL WATERS WITH THE TYPICAL MUCH STRONGER WINDS
THROUGH BAYS AND PASSES. A DRYING AND COOLING TREND WILL CONTINUE
ACROSS THE REGION THROUGH FRIDAY. LOOKS LIKE THE REMNANTS OF A
BERING SEA LOW WILL THEN MOVE THROUGH OVER THE WEEKEND...LIKELY
BRINGING A QUICK SHOT OF SNOW.

SOUTHWEST ALASKA...FIRST TROUGH AND SURFACE LOW WILL EXIT SOUTHWEST
ALASKA LATER TODAY...BUT SECONDARY TROUGH WILL CROSS THE REGION
TONIGHT THROUGH THURSDAY MORNING. COLD ADVECTION WITH THIS TROUGH
WILL SWITCH PRECIP OVER TO ALL SNOW BY LATE THIS EVENING. LOCALLY
GUSTY WINDS WILL ALSO ACCOMPANY THE COLD ADVECTION...ESPECIALLY
ALONG THE COAST. DRY AND COLD CONDITIONS WILL DOMINATE THROUGH
THURSDAY BEFORE A BERING LOW MOVES IN FRIDAY. THIS WILL BRING
ANOTHER SHOT OF SNOW FOLLOWED BY A SHOT OF EVEN COLDER AIR AS
WE HEAD THROUGH THE WEEKEND.

BERING SEA/ALEUTIANS...LOW CURRENTLY OVER THE NORTHERN BERING WILL
DIVE SOUTHEASTWARD ALONG EAST SIDE OF NORTH-CENTRAL PACIFIC RIDGE.
WATER VAPOR IMAGERY INDICATES STRONG SUBSIDENCE WITH THE UPPER
LEVEL SHORT-WAVE SUPPORTED BY THE 100 KT JET STREAK. COMBINATION
OF UPPER LEVEL SUPPORT WITH LOW LEVEL COLD ADVECTION WILL PRODUCE
VERY STRONG WINDS FROM THE BERING DOWN ACROSS THE EASTERN ALEUTIANS
AND ALASKA PENINSULA TONIGHT THROUGH THURSDAY. SNOW WILL ACCOMPANY
THESE WINDS AND RESULT IN REDUCED VISIBILITIES IN BLOWING SNOW...BUT
SURFACE TEMPERATURES LOOK TOO WARM TO PRODUCE BLIZZARD CONDITIONS.
THE SYSTEM SOUTH OF KAMCHATKA WILL FLATTEN OUT THE RIDGE AS IT
TRACKS QUICKLY ACROSS THE BERING THURSDAY AND TO SOUTHWEST ALASKA
FRIDAY. THIS SYSTEM WILL BRING WARMER AIR WITH IT...BUT COLDER AIR
WILL MOVE RIGHT BACK IN ON THE BACK SIDE.

.LONG TERM FORECAST...MODELS ARE IN VERY GOOD AGREEMENT LATE THIS
WEEKEND INTO EARLY NEXT WEEK WITH DEPICTION OF A BUILDING RIDGE
OVER THE BERING SEA AND AMPLIFYING TROUGH OVER MAINLAND ALASKA
AND THE GULF. THIS WILL SET UP A STRONG COLD ADVECTION WIND EVENT
ACROSS THE SOUTHERN MAINLAND. THE HEMISPHERIC PATTERN DOES LOOK LIKE
IT WILL REMAIN PROGRESSIVE...SO THIS SHOULD NOT LAST LONGER THAN A
FEW DAYS BEFORE THE BERING RIDGE BUILDS EASTWARD OVER THE MAINLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...170 179.
         GALE WARNING...121 130 132 138 150 155 160 165 171 172 175
                        176 185.
FIRE WEATHER...NONE.

SEB NOV 10