Blizzard in Alaska, April 12, 2010

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA...CORRECTED
550 AM AKDT SUN APR 11 2010

ADDED WATCHES/WARNINGS TO SUMMARY

.ANALYSIS AND UPPER LEVELS...UPPER LEVEL PATTERN THIS MORNING
DOMINATED BY LARGE UPPER LOW CENTERED OVER THE NORTHWEST BERING SEA.
A 175KT JET STREAK IS ROUNDING THE BASE OF THE LOW ACROSS THE
ALEUTIANS WHILE DOWNSTREAM THE UPPER LEVEL FLOW SPLITS AROUND A
CUTOFF HIGH OVER THE SOUTHERN YUKON/NW TERRITORIES WITH ONE BRANCH
MOVING NORTH ALONG THE ALCAN BORDER AND A SECOND BRANCH DIVING SOUTH
ALONG THE WEST COAST INTO CALIFORNIA. A SHARP UPPER TROUGH WITH
SURFACE REFLECTION IS WELL DEFINED ON IR IMAGERY MOVING ACROSS PRINCE
WILLIAM SOUND AND EXTENDING DEEP INTO THE MID-LATITUDES. OTHER
SURFACE FEATURES INCLUDE THE OCCLUDED 975 MB LOW CENTERED OVER THE
CENTRAL BERING WITH A COLD FRONT TRAILING ACROSS THE EASTERN
ALEUTIANS. AMPLE ISENTROPIC UPLIFT IN THE WARM SECTOR OF THE LOW IN
CONJUNCTION WITH A POWERFUL VORTMAX ALOFT IS GENERATING A BROAD AREA
OF SNOW MOVING INTO THE KUSKOKWIM DELTA AND BRISTOL BAY WHILE THE
TIGHT SURFACE PRESSURE GRADIENT IS CREATING STRONG SOUTHERLY
WINDS...LEADING TO POTENTIAL BLIZZARD CONDITIONS ALONG THE KUSKOKWIM
DELTA. A BLIZZARD WARNING IS CURRENTLY IN EFFECT FOR ZONE 155 AS A
RESULT.

.MODEL DISCUSSION...MODELS IN GREAT AGREEMENT IN THE FIRST 24
HOURS...THROUGH TUE MORNING. AFTER THAT THE SYNOPTIC AGREEMENT
REMAINS SOLID WITH THE MAIN ISSUE BEING THE TIMING OF FRONTAL WAVES
MOVING UP THE BOUNDARY ON THE LEE SIDE OF THE ALEUTIAN RANGE TUE
NIGHT INTO WED MORNING WITH THE NAM BEING THE FASTEST OF THE
SOLUTIONS WHILE THE GFS AND ECMWF WERE SLOWER. THE ECMWF HAS BEEN THE
MORE CONSISTENT MODEL IN TIMING THIS FEATURE AND THUS IS THE MODEL OF
CHOICE ON THE EAST DOMAIN. AFTER 84 HOURS...WED NIGHT...THE 12Z RUN
OF THE ECMWF WAS FAVORED BOTH EAST AND WEST GIVEN ITS CONSISTENCY.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...RAIN SHOWERS WILL GRADUALLY DIMINISH IN COVERAGE
THROUGH THE DAY ACROSS THE PRINCE WILLIAM SOUND REGION AS THE FRONT
MOVES EAST AND DISSIPATES. HOWEVER STRONG SOUTHWESTERLY FLOW IN THE
MID TO UPPER LEVELS ALONG WITH STRONG PVA AHEAD OF THE UPPER
LOW/VORTMAX IN THE EASTERN BERING SEA WILL RESULT IN SIGNIFICANT
SNOWFALL IN THE SUSITNA VALLEY...WITH STORM TOTALS OF 8-12 INCHES
POSSIBLE IN SOME LOCALES. THE SURGE OF WARM AIR AHEAD OF THE SURFACE
FRONT MAY CAUSE RAIN TO MIX IN DURING THE AFTERNOON...BUT PRECIP
SHOULD CHANGE BACK TO SNOW THIS EVENING AS COLD ADVECTION TAKES
PLACE. THIS COLD ADVECTION...IN COMBINATION WITH THE PREVIOUSLY
MENTIONED FACTORS SHOULD RESULT IN THE ANCHORAGE BOWL RECEIVING SNOW
TONIGHT AS WELL...THOUGH IN SMALLER QUANTITIES THAN THE SUSITNA
VALLEY...WITH HEAVIEST SNOWFALL ALONG THE MOUNTAINS. PRECIP SHOULD
STAY MAINLY AS LIQUID ACROSS KODIAK...THOUGH SNOW SHOWERS CANNOT BE
RULED OUT AS THE COLD FRONT PASSES THROUGH TONIGHT. SHOWERS LINGER
OVER THE REGION IN THE ONGOING SOUTHWESTERLY FLOW AS UPPER LOW
GRADUALLY SHIFTS INLAND. ANOTHER SHOT OF SNOW IS POSSIBLE FOR THE
ANCHORAGE BOWL AND MATSU ON WEDNESDAY AFTERNOON AS A FRONTAL WAVE
MOVES UP THE OLD FRONTAL BOUNDARY ACROSS KODIAK AND THE KENAI AND
INTO INLAND SOUTHCENTRAL WED EVENING.

.SOUTHWEST...THE LOW IN THE BERING WILL TRACK NORTHWEST INTO NORTON
SOUND TONIGHT...PUSHING THE FRONT ONSHORE THIS MORNING AND INTO THE
INTERIOR BY THIS EVENING. THIS WILL RESULT IN A WIDESPREAD AREA OF
PRECIPITATION SPREADING INLAND ACROSS THE KUSKOWIM VALLEY AND BRISTOL
BAY. PRECIP WILL INITIALLY FALL AS SNOW ACROSS THE REGION WITH RAIN
MIXING IN BY THE AFTERNOON AND INTO THE EVENING AS THE WARM SECTOR
MOEVS NORTH AND EAST. PRECIP SHOULD CHANGE BACK TO ALL SNOW BY THIS
EVENING THOUGH AS COLD ADVECTION KICKS BACK IN BEHIND THE FRONT. THE
WARMING TEMPS SHOULD BRING AN END TO BLIZZARD CONDITIONS IN THE
KUSKOKWIM DELTA BY THIS AFTERNOON AS THE SNOW MIXES IN...ALTHOUGH
WINDS WILL CONTINUE TO BE STRONG AT TIMES. STRONG SOUTHWESTERLY FLOW
ALOFT AND AT THE SURFACE WILL CONTINUE TO BRING SNOW SHOWERS TO
SOUTHWEST ALASKA INTO WED MORNING THOUGH COVERAGE SHOULD START TO
DIMINISH ON WED AS THE UPPER TROUGH SHIFTS EAST INTO THE
INTERIOR...THOUGH SHOWERS WILL CONTINUE INTO WED NIGHT AS THE TROUGH
PASSES.

.BERING SEA/ALEUTIANS...THE AFOREMENTIONED LOW IN THE CENTRAL BERING
MARCHES NORTHEAST AND ITS ATTENDANT FRONT MOVES ACROSS THE EASTERN
ALEUTIANS AND AKPEN TODAY. RAIN IN THESE AREAS WILL SWITCH TO SNOW
TONIGHT AS THE COLD FRONT MOVES THROUGH AND COLD ADVECTION BRINGS THE
UBIQUITOUS SNOW SHOWERS TO MUCH OF THE BERING AND ALEUTIANS THROUGH
TUE NIGHT. A BRIEF PERIOD OF CALMER WEATHER AS A RIDGE MOVES ACROSS
THE WESTERN ALEUTIANS TUE NIGHT AND TO THE AKPEN BY WED NIGHT.
ANOTHER STRONG FRONT MOVES INTO THE WESTERN ALEUTIANS WED BRINGING
RAIN AND SNOW ALONG WITH STRONG SOUTHERLY WINDS WITH WEST WINDS
BEHIND THE FRONT. THE FRONT MOVES TO THE AKPEN BY THU AFTERNOON AS
THE PARENT LOW MOVES INTO THE CENTRAL BERING.

.LONG TERM FORECAST...EXPECT UNSETTLED WEATHER TO CONTINUE INTO NEXT
WEEKEND AS THE LONGWAVE TROUGH REMAINS IN PLACE OVER ALASKA AND THE
BERING. AS THE FIRST MAJOR LOW DEPARTS THE FORECAST AREA TUE
AFTERNOON...ANOTHER MAJOR LOW AND FRONTAL SYSTEM MOVES INTO THE
BERING THU. THE FRONT ACCOMPANYING THIS SYSTEM MOVES INTO THE GULF OF
ALASKA BY FRIDAY BRINGING ANOTHER SOLID CHANCE OF PRECIP TO MUCH OF
SOUTHCENTRAL BY FRI/SAT. THE UPPER LOW STALLS IN BRISTOL BAY BY THE
WEEKEND...KEEPING SOUTHCENTRAL GENERALLY WET WITH SEASONABLE
TEMPERATURES WHILE THE BERING AND ALEUTIANS REMAIN COOLER AND WINDIER
WITH WIDESPREAD SNOW SHOWERS ON THE BACK SIDE OF THE LOW THROUGH THE
WEEKEND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING...155
MARINE...GALE 120 130 132 138 140 150 155 160 165 170 172 175 176 180
              185
FIRE WEATHER...NONE

WOOD APR 10