Wind Chill Advisory 16, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1250 PM AKST FRI JAN 2 2009

.ANALYSIS AND UPPER LEVELS...BLOCKING RIDGE OVER EASTERN BERING IS
BEGINNING TO BE PINCHED NEAR ITS BASE AS ENERGY ROTATES NORTHEASTWARD
FROM MAJOR CLOSED LOW SOUTHWEST OF THE ALEUTIANS AND ENERGY ROTATES
SOUTHWARD ACROSS WESTERN MAINLAND ALASKA. THE SHORT-WAVE THAT DROPPED
SOUTHWARD ACROSS ALASKA ON THURSDAY HAS NOW DEVELOPED INTO AN UPPER
LOW CENTERED OVER SOUTHCENTRAL ALASKA. THE COLD ADVECTION HAS HELPED
DEEPEN THE SURFACE LOW OVER THE NORTHEAST GULF AND SOUTHERLY FLOW ON
THE EAST SIDE OF THE NEWLY FORMED UPPER LOW HAS PULLED THIS LOW TO
NEAR CAPE SUCKLING. CLOUDS AND SOME LIGHT SNOW ASSOCIATED WITH THIS
LOW HAVE MOVED ONSHORE OVER PORTIONS OF EASTERN PRINCE WILLIAM SOUND
AND THE SOUTHEASTERN COPPER BASIN. THIS HAS HELPED TO MODERATE
TEMPERATURES SOMEWHAT...BUT IT IS STILL VERY COLD. ELSEWHERE ACROSS
MAINLAND ALASKA ARCTIC AIR IS FIRMLY ENTRENCHED WITH WIDESPREAD
READINGS OF 20 BELOW TO 40 BELOW THIS MORNING...AND A RECENT READING
OF 50 BELOW IN MCGRATH. COLD ADVECTION ACROSS SOUTHCENTRAL ALONG
WITH THE TIGHTER PRESSURE GRADIENT IS PRODUCING THE USUAL GUSTY
WINDS THROUGH MOUNTAIN PASSES AND BAYS. OUT WEST...THE ELONGATED
THAT PUSHED ACROSS THE ALEUTIANS THURSDAY IS NOW ORIENTED EAST-WEST
OVER THE SOUTHERN BERING. NEW LOWS CONTINUE TO DEVELOP ON THE EAST
SIDE OF THE MAJOR LOW SOUTHWEST OF THE ALEUTIANS WITH ONE SUCH LOW
CURRENTLY ROTATING NORTHWESTWARD SOUTH OF THE WESTERN ALEUTIANS.
THIS IS CAUSING STRONGER WINDS WEST OF ADAK. DEVELOPMENTS FURTHER
EAST OF THE MAIN LOW ARE BING DRIVEN EASTWARD BY THE UPPER JET WITH
LITTLE OR NO IMPACT ON THE ALEUTIANS.

.MODEL DISCUSSION...MODELS INITIALIZATION WAS GENERALLY GOOD. THERE
WERE SOME SMALL ERRORS IN PLACEMENT OF DEVELOPING LOW SOUTH OF
SHEMYA AS WELL AS THE GULF LOW. NAM HAS THE BEST POSITION ON THE
GULF LOW WHILE GFS IS BEST ON THE ALEUTIAN LOW. DISAGREEMENTS
CONTINUE WITH TRACK OF LOWS SOUTH OF THE ALEUTIANS...BUT SOLUTIONS
ARE ALL GROUPED IN THE SAME GENERAL AREA. ECMWF IS THE ODD MAN OUT
WITH TRACK OF LOW SOUTH OF SHEMYA SO PREFER THE CONSENSUS OF
GFS/NAM/UKMET. GFS IS ODD MAN OUT WITH TRACK OF A WEAKER LOW
DEVELOPING FARTHER EAST TO THE CENTRAL ALEUTIANS TONIGHT. ALL
OTHER SOLUTIONS KEEP LOW FARTHER SOUTH AND WEAKEN IT AS YET ANOTHER
LOW DEVELOPS TO THE SOUTH. WILL STICK WITH THE CONSENSUS HERE AS
WELL AND GRADUALLY INCREASE WINDS ALONG CENTRAL ALEUTIANS WITH NO
INDICATION OF AN ACTUAL LOW IN THE FORECAST AREA. THE NEXT LOW
DEVELOPING IS DRIVEN QUICKLY EASTWARD ALONG THE UPPER JET...FAR
ENOUGH SOUTH OF THE ALEUTIANS AND ALASKA PENINSULA THAT MODEL
DIFFERENCES ARE INSIGNIFICANT TO THE FORECAST. MODEL CONSENSUS IS
TAKES THIS LOW SOUTH OF THE GULF AS WELL. ACROSS THE REST OF THE
FORECAST AREA MODELS ARE VERY CONSISTENT AND FORECASTS WILL ONLY
REQUIRE FINE-TUNING.

.SHORT TERM FORECAST...A SHORT-WAVE TROUGH EXTENDING FROM THE UPPER
LOW OVER SOUTHCENTRAL TO NORTHWEST ALASKA WILL DROP SOUTHWARD ACROSS
WESTWARD ALASKA TONIGHT AND SATURDAY WHILE THE RIDGE BECOMES FULLY
CUT-OFF AND RETROGRADES INTO EASTERN RUSSIA. THIS WILL THEN ALLOW
THE SHORT-WAVE TO AMPLIFY AND MOVE SOUTHWARD ACROSS THE CENTRAL AND
EASTERN BERING SEA SATURDAY NIGHT AND SUNDAY. THEREFORE...ARCTIC
AIR THAT HAS RECENTLY BEEN CONDIFNED TO MAINLAND ALASKA WILL SPREAD
SOUTHWARD ACROSS THE BERING SEA TO NEAR THE ALEUTIANS SUNDAY. COLD
ADVECTION SNOW SHOWERS WILL SET UP OFF THE ICE EDGE ALONG THE
NORTHERN TO EASTERN BERING. MEANWHILE...DEEP ARCTIC AIRMASS WILL
REMAIN FIRMLY ENTRENCHED OVER MAINLAND ALASKA. GUSTY WINDS WILL
ACCOMPANY THE COLD ADVECTION OVER SOUTHWEST ALASKA...ESPECIALLY
ALONG THE KUSKOKWIM DELTA...SO WILL ISSUE A WIND CHILL ADVISORY
BEGINNING TONIGHT AND CONTINUING THROUGH SUNDAY.

THE GULF LOW WILL SLOWLY WEAKEN TONIGHT AND SUNDAY AND THEN WILL
BE ABSORBED INTO THE NORTH PACIFIC LOW TRACKING TO SOUTHEAST ALASKA
SUNDAY. THUS...THE PRESSURE GRADIENT ACROSS SOUTHCENTRAL WILL RELAX
A BIT TONIGHT BUT TIGHTEN RIGHT BACK UP ON SATURDAY NIGHT AND SUNDAY.
GUSTY WINDS WILL PERSIST AND WIND CHILL ADVISORIES WILL LIKELY
REMAIN IN EFFECT FOR MOST OF THIS PERIOD FOR THOMPSON PASS AND FOR
THE NORTHERN SUSITNA VALLEY. WINDS WILL BECOME MORE WIDESPREAD
SUNDAY NIGHT AND MONDAY AS THE TORUGH THAT DROPPED SOUTHWARD ACROSS
THE EASTERN BERING SWINGS SOUTHEASTWARD AND THE TROUGH AND EMBEDDED
LOW OVER SOUTHCENTRAL TRACKS EASTWARD TO CANADA. THIS WILL ALLOW
STRONG NORTHERLY WINDS ALOFT TO SHIFT TO SOUTHCENTRAL WHICH WILL
AID IN MIXING DOWN MORE WIND TO THE SURFACE.

THE LOW COMPLEX SOUTHWEST OF THE ALEUTIANS WILL REMAIN IN PLACE
THROUGH AT LEAST EARLY NEXT WEEK. UPPER WAVES AND ASSOCIATED SURFACE
FEATURES EMBEDDED IN THE CYCLONIC FLOW WILL REMAIN MAINLY SOUTH OF
THE ALEUTIANS. GENERALLY...STRONG EASTERLY FLOW WILL PERSIST NORTH
OF THESE SYSTEMS AND ASSOCIATED PRECIPITATION WILL NOT MAKE IT MUCH
FARTHER NORTH THAN THE ALEUTIANS.

.LONG TERM FORECAST...MODELS ARE VERY CONSISTENT IN INDICATING A
CHANGE IN THE LONG-WAVE PATTERN BY THE END OF NEXT WEEK...WITH AN
AMPLIFYING TROUGH BECOMING CENTERED OVER THE BERING/NORTH PACIFIC
AND A RIDGE BUILDING OVER THE EAST PACIFIC/WESTERN NORTH AMERICA.
THIS WILL SET UP A STORM TRACK FROM THE NORTH PACIFIC NORTHWARD TO
THE GULF OF ALASKA. IT IS TOO EARLY TO PINPOINT PARTICULAR
STORMS...BUT EXPECT MODERATING TEMPERATURES ALONG WITH A CHANCE
OF SNOW OVER THE SOUTHERN MAINLAND (ESPECIALLY COASTAL AREAS) BY
THE END OF NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...130 155 165 170 172 175 176 179 185.
         HEAVY FREEZING SPRAY WARNING...121 129 130 138 140 141 150
                                        160 165 179 185.
FIRE WEATHER...NONE.

SEB JAN 09