Blizzard and High Wind in Alaska, February 5 to 6, 2010

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1200 PM AKST THU FEB 4 2010

.ANALYSIS AND UPPER LEVELS...UPPER TROUGH CONTINUES TO DIG SOUTHWARD
ACROSS SOUTHWEST ALASKA. ARCTIC AIR HAS SPREAD SOUTHWARD ACROSS
THE EASTERN BERING TO THE ALASKA PENINSULA. TEMPERATURES HAVE FALLEN
BELOW ZERO ACROSS MOST OF SOUTHWEST ALASKA AND NORTHERLY WINDS HAVE
INCREASED....WHICH IS PRODUCING WIND CHILLS TO AROUND 30 BELOW ZERO
ACROSS THE KUSKOKWIM DELTA. OVER SOUTHCENTRAL THE ARCTIC FRONT
REMAINS NORTH OF THE COASTAL RANGE. A SURFACE LOW NORTH OF MIDDLETON
ISLAND COMBINED WITH INCREASING SOUTHERLY FLOW AHEAD OF DIGGING
TROUGH IS SPREADING MOISTURE NORTHWARD OVER THE ARCTIC AIR PRODUCING
SNOW SHOWERS FROM PRINCE WILLIAM SOUND TO THE COPPER BASIN. OUT WEST
EASTERLY FLOW IS INCREASING ACROSS THE WESTERN BERING AND ALEUTIANS
AS PRESSURE GRADIENT TIGHTENS BETWEEN A 1045 MB SIBERIAN HIGH AND
A 982 MB LOW JUST SOUTHWEST OF THE WESTERN ALEUTIANS.

.MODEL DISCUSSION...GFS/ECMWF ARE VERY CONSISTENT IN HANDLING OF
MAJOR GULF STORM AND NAM/UKMET HAVE TRENDED HEAVILY TOWARD THIS
SOLUTION. THEREFORE...FORECAST CONFIDENCE IS ABOVE AVERAGE. THE
BIGGEST UNCERTAINTY IS THE TRACK OF THE SURFACE LOW OVER THE
NORTWHEST GULF AND INLAND. THE GFS IS THE MOST CONSISTENT SOLUTION
IN TAKING THE LOW OVER THE SOUTHERN TIP OF THE KENAI TO CENTRAL
COOK INLET AND INLAND. THE 12Z ECMWF HAS TRENDED TO THE NORTHEAST
OF THE GFS TRACK WHILE THE NAM/UKMET SOLUTIONS ARE IN BETWEEN.
THIS TRACK WILL GREATLY AFFECT PRECIP OVER THE KENAI PENINSULA
WHICH WILL CHANGE TO RAIN OVER THE EASTERN KENAI WITH THE GFS
TRACK...BUT WOULD SEE MORE SNOW WITH THE ECMWF TRACK. THAT IN
TURN WOULD RAISE THE POTENTIAL FOR A BLIZZARD THROUGH TURNAGAIN
ARM. SO...WILL STICK WITH GFS SOLUTION FOR NOW...BUT CLOSELY
MONITOR THE MODEL TRENDS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE CURRENT LOW NORTH OF MIDDLETON ISLAND WILL
DISSIPATE THIS EVENING AS ANOTHER LOW DEVELOPS SOUTH OF SEWARD (NEAR
THE ARCTIC FRONT) DUE TO FURTHER AMPLIFICATION OF TROUGH TO THE WEST.
FLOW WILL BECOME SOUTHERLY AND INCREASE...SPREADING MOISTURE OVER
THE KENAI PENINSULA TO ANCHORAGE AND THE MAT-SU. EXPECT LIGHT
SNOWFALL TO DEVELOP OVER THE REGION OVERNIGHT PRODUCING VERY
MINOR SNOW ACCUMULATION. CONDITIONS WILL RAPIDLY DETERIORATE FRIDAY
THROUGH FRIDAY NIGHT AS THE UPPER TROUGH BECOMES NEGATIVELY TILTED
AND A 970S MB LOW DEVELOPS OVER THE CENTRAL GULF WITH THE WARM FRONT
RAPIDLY MOVING THROUGH THE PRINCE WILLIAM SOUND REGION. IN ADDITION
TO STRONG DYNAMIC VERTICAL MOTION AHEAD OF THE TILTING TROUGH THE
WARM AIR WILL OVERRIDE THE ARCTIC AIR RESULTING IN MODERATE TO STRONG
THERMODYNAMIC LIFT. THE COMBINATION OF THESE WILL INITIALLY PRODUCE
AREAS OF MODERATE TO HEAVY SNOW ALONG THE COAST WITH LIGHTER AMOUNTS
NORTH OF THE COASTAL RANGE. HOWEVER...BASED ON THE CURRENT EXPECTED
LOW TRACK (WHICH THERE IS UNCERTAINTY IN) THE AIR MASS WILL QUICKLY
WARM UP ENOUGH TO CHANGE PRECIP TO MOSTLY RAIN OVER SOUTHEAST PRINCE
WILLIAM SOUND AND WESTERN PRINCE WILLIAM SOUND. AS THE LOW MOVES TO
THE SOUTHERN KENAI PENINSULA LATE FRIDAY NIGHT STRONG EASTERLIES
WILL MOVE TO THE COAST...BUT TEMPERATURES SHOULD WARM UP ENOUGH BY
THEN TO PREVENT BLIZZARD CONDITIONS. THESE STRONG WINDS WILL ALSO
RESULT IN DOWNSLOPING ALONG THE CHUGACH WHICH SHOULD DIMINISH OR
END SNOW IN ANCHORAGE AND OTHER LEE SIDE LOCATIONS. EVEN THOUGH
STRONG SOUTHEAST FLOW USUALLY LIMITS PRECIP IN VALDEZ....THIS IS
ONE OF THOSE EVENTS WHERE MOSTURE AND LIFT ARE SIGNIFICANT ENOUGH
TO OVERCOME THIS. IN FACT...PRESSURE PATTERN WILL BE FAVORABLE FOR
LOW LEVEL DRAINAGE FLOW TO CONTINUE...KEEPING TEMPS A BIT COOLER AT
THE SURFACE...SO THAT AS WARM AIR MOVES OVERHEAD LATE FRIDAY NIGHT
INTO SATURDAY PRECIP WILL LIKELY REMAIN MOSTLY SNOW. THOMPSON PASS
WILL EXPERIENCE STRONG EASTERLIES WITH THE SNOW. IT IS UNCERTAIN AT
THIS POINT HOW WARM THE TEMPERATURE THERE WILL GET...BUT THERE IS
GOOD POTENTIAL FOR A BLIZZARD. THEREFORE...WILL ISSUE A BLIZZARD
WATCH FOR FRIDAY NIGHT THROUGH SATURDAY MORNING. WITH MOSTLY SNOW
EXPECTED IN THE VALDEZ AREA SNOW TOTALS WILL BE SIGNIFICANT WITH ONE
TO TWO FEET STORM TOTAL ACCUMULATION. THE SURFACE LOW WILL QUICKLY
TRACK INLAND SATURDAY AS THE UPPER TROUGH BEGINS TO SWING BACK
NORTHWARD. ARCTIC AIR WILL RAPIDLY SPREAD ACROSS SOUTHCENTRAL
CHANGING ANY REMAINING PRECIP BACK TO SNOW. THE INFLUENCE OF THIS
TROUGH WILL CONTINUE ALL THE WAY INTO MONDAY WITH SHORT-WAVES
ROTATING ACROSS THE REGION...SO AREAS OF SNOW OR SNOW SHOWERS WILL
PERSIST.

SOUTHWEST ALASKA...WIND CHILL ADVISORIES FOR THE SOUTHERN KUSKOKWIM
VALLEY AND KUSKOKWIM DELTA REGIONS LOOK TO BE ON TRACK FOR TONIGHT
AS TEMPERATURES CONTINUE TO DROP. WIND SPEEDS WILL BE MARGINAL FOR
THE KUSKOKWIM VALLEY...BUT CLOSE ENOUGH TO ADVISE OF THE THREAT.
WILL LIKELY EXTEND THE ADVISORY FOR THE DELTA THROUGH SATURDAY AS
THE NORTHERLIES WILL CONTINUE TO BLOW. WHEN THE UPPER TROUGH/LOW
BECOME NEGATIVELY TILTED FRIDAY AND FRIDAY NIGHT MOISTURE WILL
SPREAD WESTWARD ACROSS EASTERN PORTIONS OF SOUTHWEST ALASKA WHICH
WILL BRING AND END TO THE STRONG NORTHERLIES...RAISE TEMPS
SLIGHTLY...AND PRODUCE AREAS OF LIGHT SNOW. THE UPPER LOW WILL
LIFT NORTHWARD ACROSS THE REGION SUNDAY WITH REFLECTION OF THIS
LOW AT THE SURFACE. THIS WILL FINALLY BRING AN END TO THE COLD
ADVECTION AND STRONG NORTHERLIES ALONG THE KUSKOKWIM DELTA...BUT
SNOW SHOWERS WILL CONTINUE ACROSS THE REGION UNTIL THE LOW EXITS
TO THE NORTH ON MONDAY.

BERING SEA/ALEUTIANS...ARCTIC AIR MOVING OFF OF THE ICE EDGE HAS
BEGUN TO PRODUCE LONG CLOUD STREETS AND SNOW SHOWERS...WHICH WILL
INTENSIFY AS EVEN COLDER AIR ADVECTS SOUTHWARD TONIGHT THROUGH
FRIDAY...ESPECIALLY OVER THE EASTERN BERING. STRONG NORTHERLIES
AND SNOW SHOWERS WILL PERSIST THROUGH SATURDAY AND THEN GRADUALLY
COME TO AN END SUNDAY AS THE UPPER TROUGH LIFTS BACK NORTHWARD AND
COLD ADVECTION ENDS. MEANWHILE...THE AMPLIFYING TROUGH WILL CAUSE
THE RIDGE OVER THE BERING TO RETROGRADE BACK TOWARD RUSSIA SO THAT
THE PRESSURE GRADIENT ACROSS THE WESTERN BERING WILL SLACKEN HEADING
INTO THE WEEKEND AND WINDS WILL LIGHTEN UP. MODELS THEN INDICATE
A MAJOR PACIFIC LOW TRACKING TOWARD THE REGION LATE IN THE
WEEKEND...BUT UNCERTAINTY IN WHERE THIS LOW WILL TRACK IS LOW.

.LONG TERM FORECAST...MODELS INDICATE A MORE AMPLIFIED LONG-WAVE
TROUGH FROM THE BERING SEA TO THE NORTHWEST PACIFIC. THIS WILL
ALLOW PACIFIC STORMS TO TRACK A LITTLE CLOSER TO MAINLAND ALASKA.
THE FIRST OF THESE LOOKS LIKE IT WILL AFFECT MUCH OF THE REGION THE
FIRST HALF OF NEXT WEEK. IT IS TOO SOON TO TALK ABOUT THE DETAILS
OF THIS...BUT IT DOES LOOK LIKE A SAFE BET FOR THE SOUTHERN MAINLAND
TO WARM UP THROUGH THE WEEK UNDER SOUTHERLY FLOW.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WATCH ZONE 131.
MARINE...GALE WARNING...120 127 128 160 165 172 175 176 179 180
         HEAVY FREEZING SPRAY WARNING...121 127 128 130 140 150 155
                                        160 165 170 179 185.
FIRE WEATHER...NONE.

SEB FEB 10