Storm Warning 147, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 PM AKDT THU SEP 23 2010

.ANALYSIS AND UPPER LEVELS...
A PATTERN CHANGE CONTINUES TO TAKE PLACE ACROSS THE REGION...WITH THE
UPPER LEVEL HIGH WHICH ONCE DOMINATED THE MAINLAND WEATHER PATTERN
NOW SITUATED OVER FAR EASTERN RUSSIA. THIS RIDGE WAS PINCHED OFF OVER
THE PAST FEW DAYS BY LOW PRESSURE SYSTEMS OVER NORTHWESTERN
CANADA/EASTERN ALASKA AND SOUTH OF THE AKPEN. THE FLOW AROUND THE
CANADIAN LOW AND THE RUSSIAN HIGH IS HELPING TO CHANNEL COLD ARCTIC
AIR ACROSS MUCH OF THE ALASKAN MAINLAND. THE WESTERN LOW SITS UNDER
THE LEFT FRONT QUADRANT OF A 170 KT JET...WHICH WILL CONTINUE TO AID
IN THE INTENSIFICATION OF THE SYSTEM IN THE NEXT DAY OR TWO.

AT THE SURFACE...AN OCCLUDING 965 MB LOW PRESSURE SYSTEM IS SITUATED
350 MILES SOUTH OF SAND POINT AND SLOWLY TRACKING EASTWARD. THIS
LARGE LOW ENCOMPASSES MUCH OF THE NORTHEASTERN PACIFIC...WITH
EMBEDDED SHORTWAVES PROTRUDING EASTWARD ACROSS THE PANHANDLE AND
NORTHWESTWARD ACROSS THE WESTERN BERING SEA. GALE FORCE WINDS
ASSOCIATED WITH THIS SYSTEM ARE AFFECTING THE COASTAL WATERS OF THE
EASTERN ALEUTIANS AND THE ISLANDS JUST SOUTH OF THE AKEPN...SUCH AS
SAND POINT. MEANWHILE...LIGHT OFFSHORE WINDS ARE USHERING IN YET
ANOTHER COOL BUT PLEASANT FALL DAY ACROSS THE MAINLAND.

.MODEL DISCUSSION...
MODELS ARE IN DECENT AGREEMENT THIS AFTERNOON...BUT CONTINUE TO
STRUGGLE WITH THE EVOLUTION OF THE CURRENT EASTERN ALEUTIAN LOW. THE
PROBLEMS LIE IN THE EVENTUAL DEVELOPMENT OF ANOTHER TRIPLE POINT LOW
TONIGHT SEVERAL HUNDRED MILES EAST OF THE CURRENT LOW. THIS NEW LOW
WILL EVENTUALLY BECOME THE DOMINANT SYSTEM AND ABSORB THE CURRENT
LOW...AND IT IS THIS INTERACTION BETWEEN THE SYSTEMS THAT THE MODELS
STRUGGLE WITH. THE GENERAL TREND AFTER THIS POINT IS TO BRING THE LOW
INTO THE EASTERN GULF...WITH THE NAM BEING THE MOST AGGRESSIVE AND
THE GFS BRINGING UP THE REAR. THANKFULLY...THE NAM HAS FINALLY COME
INTO AGREEMENT WITH THE ECMWF AND GFS WITH REGARDS TO THE STRENGTH OF
THE SYSTEM. OUT WEST...THE MODELS SEEM TO HAVE GOOD GRASP ON THE
TRACK AND STRENGTH OF FORMER TYPHOON MALAKAS AS IT CHURNS THROUGH THE
ALEUTIANS EARLY NEXT WEEK.

.SHORT TERM FORECAST...
.SOUTHCENTRAL ALASKA...THE CURRENT 965 MB LOW SOUTH OF THE AKPEN WILL
SLOWLY TREK EASTWARD ALONG THE 50N PARALLEL TONIGHT AS A NEW TRIPLE
POINT LOW SPAWNS SEVERAL HUNDRED MILES TO ITS EAST AND BECOMES THE
DOMINANT SYSTEM BY TOMORROW MORNING. THIS NEW LOW MEANDERS SOUTH OF
THE GULF THROUGH SATURDAY MORNING AND DEEPENS TO 949 MB BEFORE
OCCLUDING AND WRAPPING INTO THE NORTHERN GULF AT 970 MB BY SATURDAY
NIGHT. DESPITE BRINGING STORM FORCE WINDS AND WET WEATHER TO THE
NORTHERN GULF...THIS LOW SHOULD HAVE LITTLE ADVERSE IMPACT ON INLAND
AREAS OF SOUTHCENTRAL. LIGHT NORTHERLY WINDS ON BACKSIDE OF THE LOW
SHOULD KEEP SKIES MOSTLY CLEAR ACROSS THE REGION AND HELP ADVECT
COLDER AIR SOUTHWARD. THE ONE EXCEPTION WILL BE THE COPPER RIVER
BASIN...WHICH COULD SEE SOME RAIN AND SNOW SHOWERS DUE TO THE PRESENT
UPPER LEVEL TROUGH TODAY AND TOMORROW AND FROM THIS LOW DURING THE
WEEKEND. WIDESPREAD FROST AND LOCAL HARD FREEZES ARE LIKELY ACROSS
THE MAT-SU VALLEY AND ANCHORAGE BOWL FOR THE REST OF THE WEEK.

.SOUTHWEST ALASKA...A RELATIVELY BENIGN WEATHER PATTERN IS IN STORE
FOR SOUTHWEST ALASKA THROUGH THE WEEKEND. THE ONE EXCEPTION WILL BE
ALONG THE AKPEN SOUTH OF KING SALMON...WHERE RAIN SHOWERS ARE
POSSIBLE TODAY AND FRIDAY AS THE LOW SOUTH OF COLD BAY MEANDERS SOUTH
OF KODIAK. AS THE AFOREMENTIONED LOW WRAPS UP INTO THE GULF...A
TIGHTENING PRESSURE GRADIENT BETWEEN THIS SYSTEM AND A SURFACE RIDGE
IN SIBERIA WILL PRODUCE LOCALLY STRONG WINDS ALONG THE ALASKA RANGE
AND THE KUSKOKWIM DELTA COASTLINE STARTING TOMORROW AND LASTING
THROUGH SUNDAY. SUSTAINED WINDS OF 35 MPH WITH LOCAL GUSTS TO 55 MPH
ARE POSSIBLE IN THESE AREAS. ANTICYCLONIC FLOW AROUND THE UPPER LEVEL
CUTOFF HIGH OVER THE BERING STRAIT WILL CONTINUE TO ADVECT COOLER AND
DRIER AIR FROM THE INTERIOR TO THE COAST THROUGH THE WEEKEND.

.ALEUTIANS AND BERING SEA...RAIN SHOWERS WILL END ACROSS THE EASTERN
ALEUTIANS TODAY AS THE LOW SOUTH OF COLD BAY TRACKS EASTWARD. A LOW
EMBEDDED IN THE WESTERLY JET SKIRTS THE WESTERN ISLANDS ON FRIDAY
AFTERNOON AND EVENING...BRINGING SCATTERED SHOWERS BUT NO SIGNIFICANT
WINDS. COOLER AND DRIER MAINLAND AIR WILL FILTER ACROSS THE EASTERN
BERING ON FRIDAY...COURTESY OF SURFACE AND UPPER LEVEL RIDGING OVER
FAR EASTERN RUSSIA. A TIGHTENING PRESSURE GRADIENT BETWEEN THIS RIDGE
AND THE GULF LOW WILL GENERATE NEAR GALE FORCE WINDS ACROSS THE
EASTERN BERING TODAY THROUGH SUNDAY.

.LONG TERM FORECAST...
AN ACTIVE WEATHER PATTERN CONTINUES INTO THE NEXT WEEK. A POWERFUL
EXTRATROPICAL LOW...THE REMNANTS OF TYPHOON MALAKAS...ENTER THE
WESTERN BERING SEA ON SUNDAY. THE LOW SHOULD TRACK ALONG THE ALEUTIAN
ISLAND CHAIN AND REACH THE AKPEN BY TUESDAY MORNING. FURTHER
EAST...ANOTHER LOW RACES INTO THE EASTERN GULF ON SUNDAY NIGHT AND
PARKS ITSELF ALONG THE NORTH COAST OF THE PANHANDLE BEFORE
DISSIPATING ON TUESDAY MORNING.

THE REMNANTS OF MALAKAS TRACK INTO THE GULF TUESDAY AFTERNOON AND
PERSIST THROUGH THE LATTER HALF OF THE WEEK. WHILE THE NORTH GULF
COAST WILL SEE LARGE AMOUNTS OF WIND AND PRECIPITATION FROM THESE
STORMS...THE PLACEMENT OF THESE SYSTEMS (IN THE EASTERN GULF) WILL
ALLOW FOR CONTINUED OFFSHORE FLOW ACROSS SOUTHWEST AND SOUTHCENTRAL
ALASKA. THUS EXPECT CONTINUED CALM WEATHER AND SEASONABLY COOL FALL
TEMPERATURES ACROSS THE INTERIOR MAINLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...120 130 132 138 150.
         GALE WARNING...127 140 155 170 180.
FIRE WEATHER...NONE.

KS SEP 10