Gale Warning 66, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1230 PM AKST MON JAN 18 2010

.ANALYSIS AND UPPER LEVELS...
THE AXIS OF A BROAD UPPER LEVEL TROUGH EXTENDS SOUTHWARD FROM THE
ARCTIC THROUGH THE BERING STRAIT AND THEN CURVES SOUTHEASTWARD OVER
THE ALASKA PENINSULA AND FINALLY CRESTS OFF THE COAST OF OREGON.
THIS TROUGH ENCOMPASSES MUCH OF ALASKA AND THE BERING SEA...WITH A
WEAK SHORT-WAVE RIDGE SLOWLY MOVING IN FROM THE WEST OVER THE FAR
WESTERN ALEUTIANS. THE AXIS OF A SECOND RIDGE LIES ACROSS CENTRAL
BRITISH COLUMBIA AND NUDGES INTO THE FART EASTERN REGIONS OF THE
STATE. A 190 KT SUBTROPICAL JET IS RIDING ALONG THE 40N PARALLEL
SOUTH OF THE ALEUTIANS.

AT THE SURFACE...A RAPIDLY DETERIORATING TROUGH OF LOW PRESSURE OVER
COOK INLET IS ALL THAT REMAINS OF A LOW PRESSURE SYSTEM THAT MOVED
ONSHORE YESTERDAY NEAR SELDOVIA. A NEARLY STATIONARY 970 MB LOW
CENTERED 300 MILES SOUTH OF CHIGNIK IS SPREADING CLOUDS AND SHOWERS
ACROSS THE AKPEN...KODIAK ISLAND...AND EASTERN ALEUTIANS. A SECOND
977 MB LOW IS RACING NORTHWARD INTO THE EASTERN GULF. OUT WEST ACROSS
THE BERING SEA AND ALEUTIANS...COLD ADVECTION SNOW SHOWERS AND STRONG
NORTHERLY WINDS DOMINATE. THE COMBINATION OF ARCTIC AIR AND STRONG
WINDS IS ALSO PRODUCING A LARGE AREA OF HEAVY FREEZING SPRAY FROM
THE CENTRAL TO EASTERN BERING AND ALL THE WAY SOUTH TO THE EASTERN
ALEUTIANS AND ALASKA PENINSULA.

.MODEL DISCUSSION...
MODELS ALL INITIALIZED WELL THIS MORNING AND ARE IN DECENT AGREEMENT
THROUGH THE NEAR SHORT TERM. THE COOK INLET TROUGH AND ASSOCIATED
PRECIPITATION WILL DISSIPATE BY THIS EVENING. THE LOW SOUTH OF THE
AKPEN SHOULD DRIFT EASTWARD AND BE 300 MILES SOUTH OF KODIAK ISLAND
BY TUESDAY AFTERNOON. THE EASTERN GULF LOW SHOULD CONTINUE TRACKING
NORTHWARD AND WRAP INTO THE MUCH BROADER CIRCULATION OF THE AKPEN
LOW JUST SOUTH OF THE KENAI PENINSULA BY TUESDAY MORNING.

AS THIS INTERACTION OCCURS...THE NAM TRANSFORMS THE MAIN LOW INTO A
BROAD COMPLEX LOW PRESSURE CENTER WITH UP TO THREE SEPARATE EMBEDDED
VORTICIES. MEANWHILE...THE EUROPEAN AND GFS MAINTAIN A SINGLE CORE
LOW WITH MULTIPLE EMBEDDED SHORTWAVES. YET ANOTHER LOW CREEPS UP THE
ALASKA PANHANDLE ON WEDNESDAY AND SHOULD ABSORB THIS SYSTEM IN THE
WESTERN GULF LATE IN THE WEEK. HOWEVER...SIGNIFICANT DIFFERENCES
EXIST AS IT THE PROJECTED TRACK OF THIS NEW SYSTEM.

OUT WEST...A RIDGE OF HIGH PRESSURE BUILDS OVER THE ALEUTIANS EARLY
IN THE WEEK. THIS RIDGE BREAKS DOWN LATER IN THE WEEK AS A STORM
SYSTEM TAKES AIM AT THE ISLAND CHAIN. WITH THE MODELS ONCE AGAIN IN
GOOD AGREEMENT...FEW CHANGES WERE MADE TO THE FORECAST PACKAGE. A
BLEND OF THE MODELS WAS USED ACROSS THE BOARD...WITH A SLIGHT NUDGE
TOWARDS THE NAM SOLUTION.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THERE WILL BE A BRIEF BREAK ACROSS SOUTHCENTRAL
TONIGHT AS CURRENT WEAK FEATURES CAUSING SHOWERS AND CLOUDS EXIT
THE REGION. THIS WILL CLEAR OUT THE MID TO UPPER LEVELS...LEAVING
LOW LEVEL MOISTURE IN PLACE...TRAPPED BENEATH A SURFACE BASED
INVERSION. THEREFORE...THERE IS GOOD POTENTIAL FOR AREAS OF FOG.
THE ONE LIMITING FACTOR IS THAT THE PRESSURE GRADIENT WILL TIGHTEN
SLIGHTLY AND BECOME FAVORABLE FOR A WEAK OFFSHORE FLOW. SO...THERE
SHOULD BE JUST ENOUGH LOW LEVEL FLOW THROUGH GAPS ALONG THE COASTAL
RANGE AS WELL AS DOWN COOK INLET TO INHIBIT FOG FORMATION. AREAS NOT
EXPOSED TO THIS GAP FLOW...SUCH AS ANCHORAGE/KNIK ARM AND PORTIONS
OF THE SUSITNA VALLEY SHOULD SEE SOME FOG. THE REMNANTS OF A LOW
CROSSING THE EASTERN GULF TONIGHT WILL MOVE TO COASTAL SOUTHCENTRAL
DURING THE DAY TUESDAY IN THE FORM OF A SURFACE TROUGH WITH AN
ACCOMPANYING UPPER SHORT-WAVE. UNLIKE THE FEATURE WHICH CAUSED SNOW
THIS MORNING FROM THE KENAI PENINSULA TO SUSITNA VALLEY WHICH MOVED
NORTHWARD THROUGH THE REGION...THIS TROUGH WILL TRACK WESTWARD
TOWARD SOUTHWEST ALASKA TUESDAY NIGHT AND DISSIPATE WEDNESDAY AS
A TROUGH MOVING IN FROM THE WEST STOPS IT IN ITS TRACKS. THIS
MOVEMENT COMBINED WITH THE FACT THAT CONVERGENCE AND LIFT
ASSOCIATED WITH THIS TROUGH WILL BE WEAK MEANS INLAND AREAS WILL
SEE NO MORE THAN A FEW SHOWERS AS IT MOVES THROUGH...AND THE REGION
WILL DRY OUT ONCE AGAIN ON WEDNESDAY BEHIND THE TROUGH.

SOUTHWEST ALASKA...AN UPPER LEVEL LOW/TROUGH OVER THE BERING
STRAIT/NORTHERN BERING WILL DROP DUE SOUTH ACROSS THE EASTERN
BERING TONIGHT AND TUESDAY HELPING TO PULL MOISTURE (ASSOCIATED
WITH WEAK UPPER FEATURES OVER BRISTOL BAY) NORTHWARD TOWARD THE
KUSKOKWIM DELTA. THIS WILL KEEP INLAND AREAS MOSTLY CLOUDY...WHICH
MEANS TEMPERATURES WILL REMAIN FAIRLY STEADY...PERHAPS RISING A
LITTLE BIT. HOWEVER...THE COAST WILL REMAIN MOSTLY CLEAR...ESPECIALLY
AS YOU HEAD NORTH AND WEST TOWARD HOOPER BAY...SO THAT TEMPERATURES
WILL REMAIN COLDER. WITH WINDS EXPECTED TO REMAIN FAIRLY STEADY AS
WELL...WIND CHILLS TO 40 BELOW WILL PERSIST THROUGH AT LEAST
TUESDAY MORNING. WINDS WILL THEN SLOWLY DIMINISH AND WIND CHILLS
SHOULD BEGIN TO MODERATE. ELSEWHERE ACROSS SOUTHWEST ALASKA...WEAK
UPPER WAVES WILL CONTINUE TO ROTATE THROUGH THE REGION FROM THE EAST
THROUGH WEDNESDAY. SNOWFALL WITH THESE WILL BE LIGHT AND SHORT-LIVED.

BERING SEA/ALEUTIANS/SOUTHERN ALASKA PENINSULA...UPPER TROUGH
DROPPING DOWN OVER EASTERN BERING WILL HELP ENHANCE SNOW SHOWERS
AND WINDS AS IT SWINGS SOUTHEASTWARD TUESDAY AND WEDNESDAY. BEHIND
THE TROUGH...SNOW SHOWERS AND WINDS WILL BOTH DIMINISH AS A
SHORT-WAVE RIDGE MOVES IN FROM THE WEST.

.LONG TERM FORECAST...A STRONG TROUGH MOVING ACROSS ASIA THE NEXT
COUPLE DAYS WILL RAPIDLY AMPLIFY AS IT MOVES INTO THE FAR NORTHWEST
PACIFIC MID WEEK...WITH POLAR AIR PLUMMETING SOUTHWARD ACROSS
EASTERN ASIA. THIS WILL CAUSE DOWNSTREAM AMPLIFICATION OF THE
BERING RIDGE...PRODUCING AN EXTREMELY LONG N/S ORIENTED FRONTAL
BOUNDARY FROM THE ARCTIC SOUTHWARD ACROSS THE CENTRAL BERING AND
ON DOWN TO AROUND 30N BY FRIDAY. THE PORTION OF THE FRONT OVER THE
ALEUTIANS AND BERING WILL BE OCCLUDED...SO DON'T EXPECT AN EXTREME
WARM UP OF THE AIR MASS. HOWEVER...GALE FORCE SOUTHERLIES WILL
PUSH SURFACE TEMPS ACROSS THE CENTRAL BERING ABOVE FREEZING.

MEANWHILE...THE TROUGH WHICH MOVES ACROSS THE EASTERN BERING EARLY
THIS WEEK WILL MOVE ACROSS WESTERN ALASKA WEDNESDAY AND WEDNESDAY
NIGHT AND QUICKLY WEAKEN HEADING TO THE END OF THE WEEK AS THE BERING
RIDGE AND RIDGE OVER CANADA SQUEEZE IT FROM BOTH SIDES. ARCTIC AIR
WILL ACCOMPANY THE EASTWARD PROGRESSION OF THE TROUGH AND A STRONG
SURFACE HIGH WILL SET UP OVER THE MAINLAND...SO EXPECT DRY AND COLD
CONDITIONS TO DOMINATE. A REMNANT LOW DOWN OVER THE NORTHEAST
PACIFIC AND GULF WILL RESULT IN A MINOR WIND EVENT THROUGH
CHANNELED AREAS ALONG THE GULF COAST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...155 160 165 170 171 172 179 180.
         HEAVY FREEZING SPRAY WARNING...155 160 165 170 171 179 185.
FIRE WEATHER...NONE.

KS/SEB JAN 10