Blizzard in Alaska, November 19, 2009

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
530 AM AKST THU NOV 19 2009

.MODEL DISCUSSION...ALL MAJOR MODELS ARE IN MODEST AGREEMENT THROUGH
SATURDAY AFTERNOON. THE BIGGEST DIFFERENCE IN THE UPPER LEVELS
REVOLVES AROUND A LOW OVER THE BERING. THESE DIFFERENCES ARISE BEYOND
SUNDAY AS THE LOW SHIFTS EAST AND BEGINS TO BREAK APART. AT THE
SURFACE...MODEL RUNS HAVE BEEN SOMEWHAT CONSISTENT THROUGH THE FIRST
FEW DAYS...BUT BEGIN TO FALL APART AS EARLY AS TOMORROW AFTERNOON. A
STRONG LOW OVER THE WESTERN BERING IS SET TO REMAIN NEARLY STATIONARY
WHILE WEAKENING. PROBLEMS ARISE AS ALL OF THE MODELS WHIP UP A TRIPLE
POINT LOW SOUTH OF SHEMYA AND SLINGSHOT IT NORTH. THE MODELS DO AGREE
TO THAT HAPPENING...BUT THERE IS A LARGE VARIABILITY IN WHERE THAT
LOW WILL GO. THE FORECAST PACKAGE TONIGHT WAS PRIMARILY BASED OFF OF
THE 19/00Z ECMWF.

.ANALYSIS AND UPPER LEVELS...
A STRONG SHORTWAVE TROUGH IS APPROACHING THE WESTERN ALEUTIANS. THIS
IS AMPLIFYING A TRANSIENT RIDGE OVER THE CENTRAL BERING SEA...WHICH
IS PUSHING ON THE LONGWAVE TROUGH SITUATION OVER THE GULF OF ALASKA.
A 135 KT JET RIDING UP THE BERING RIDGE IS SUPPORTING STRONG SURFACE
CYCLOGENESIS WEST OF SHEMYA. MEANWHILE...A 175 KT JET COMING DOWN THE
FRONT OF THE BERING RIDGE IS ENHANCING STRONG NORTHWESTERLY WINDS
OVER THE EASTERN ALEUTIANS AND PARTS OF SOUTHWEST ALASKA. A SERIES OF
WEAK LOWS IN THE NORTHERN GULF ARE PRODUCING PERIODS OF TIGHTENED
PRESSURE GRADIENTS AT THE USUAL OUTFLOW AREAS.

.SHORT TERM FORECAST...
.EAST OF THE ALASKA RANGE...COMPLEX AREA OF LOW PRESSURE IN THE GULF
CONTINUES TO SLIDE SOUTH...OTHERWISE CLEAR BUT COLD CONDITIONS WILL
CONTINUE FOR SOUTHCENTRAL. COASTAL AREAS WILL SEE THE WARMEST RANGE
IN TEMPERATURES WHILE INLAND AREAS IN THE NORTHERN SUSITNA VALLEY AND
COPPER RIVER WILL SEE DAYTIME TEMPERATURES IN THE NEGATIVE VALUES. A
WIND CHILL ADVISORY REMAINS IN EFFECT THIS MORNING FOR THOMPSON PASS
AND FOR AREAS NORTH OF TALKEETNA.

.WEST OF THE ALASKA RANGE...QUIKSCAT PASS THIS MORNING VERIFIES THE
FORECASTS FROM BEFORE...WITH STRONG WINDS WRAPPING AROUND THE DEEP
LOW IN THE WESTERN BERING. SHEMYA HAS MAINTAINED STRONG GALE TO STORM
FORCE WINDS AND PRESSURES CONTINUE TO FALL AT A RATE BEYOND 6 MB PER
3 HOURS AHEAD OF A FRONT THAT IS SWEEPING EAST. BEHIND THE FRONT
WINDS ARE ANTICIPATED TO REACH HURRICANE FORCE AS A SHORTWAVE DROPS
SOUTH AND IS AIDED A STRONG UPPER LEVEL JET. RAIN AND SNOW SHOWERS
WILL CONTINUE TO SHIFT EAST WITH THE FRONT. STRONG NORTHERLY WINDS
ACROSS THE AKPEN THIS MORNING SHOULD WEAKEN SOME AS THE RIDGE PASSES
OVERHEAD AND THEN SWITCH TO THE EAST AS WINDS GET PULLED TOWARDS THE
LOW.

.LONG TERM FORECAST...NO CHANGE TO THE INHERITED LONG RANGE FORECAST
TONIGHT DUE TO THE LARGE VARIABILITY AND LOW RELATIVE MEASURE OF
PREDICTABILITY BASED OFF OF ENSEMBLE GUIDANCE...STILL APPEARS THE
COLD AND RELATIVELY DRY WEATHER OVER SOUTHCENTRAL AND THE GULF WILL
COME TO AN END AS ACTIVE WEATHER FROM THE BERING SLIDES EASTWARD FOR
THE START OF NEXT WEEK. THIS WILL ALSO USHER IN A RETURN TO MUCH MORE
SEASONAL TEMPERATURES.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 191
MARINE...HURRICANE FORCE WIND WARNING 176
         STORM 175 185
         GALE 128 132 155 165 170 172 179
         HEAVY FREEZING SPRAY 121 127 129 138 140 150 160 180
FIRE WEATHER...NONE.

SSS NOV 09