Winter Storm in Alaska, January 29, 2013

SOUTHEAST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE JUNEAU AK
632 PM AKST MON JAN 28 2013

.SHORT TERM...SATELLITE IMAGERY THIS AFTERNOON SHOWING A 972 MB
LOW SOUTH OF THE ALEUTIAN TRACKING NORTHWARD TOWARD THE BERING
SEA. THE ASSOCIATED WARM FRONT IS TRACKING ACROSS THE EASTERN GULF
AND WILL REACH THE PANHANDLE MONDAY NIGHT. THIS FRONT WILL MOVE
OVER THE PANHANDLE THEN BEGIN TO SHEAR APART TUESDAY AFTERNOON.
COLD AIR FROM ARCTIC HIGH PRESSURE OVER THE YUKON HAS POURED INTO
THE PANHANDLE WITH TEMPERATURES IN THE SINGLE DIGITS TODAY FOR
THE NORTHERN PANHANDLE AND IN THE TEENS FOR THE CENTRAL. COLD AIR
WILL CONTINUE TO PUSH TO THE SOUTH WITH OVERNIGHT LOWS FOR THE
SOUTHERN REGIONS DROPPING INTO THE UPPER 20S. FOR THE CENTRAL
PANHANDLE OVERNIGHT TEMPS WILL BE IN THE LOW TEENS WITH TEMPS
BELOW ZERO FOR THE NORTHERN REGIONS. TEMPERATURES WILL BEGIN TO
RISE THROUGH THE DAY WITH WARM AIR ADVECTION FROM THE WARM FRONT
AND WILL CONTINUE TO RISE INTO THE UPPER 20S. SHORT WAVE OVER THE
SOUTHERN PANHANDLE IS EXITING INTO BRITISH COLUMBIA WITH ANY
LINGERING SHOWER ACTIVITY ENDING IN THE AFTERNOON. THE SUNNY
BREAKS SEEN THROUGH THE DAY WILL DIMINISH AS CLOUD COVER
INCREASES AND LOWERS WITH THE ADVANCING FRONT.

 AS THE FRONT PUSHES WARM MOIST AIR MOVING OVER THE ARCTIC AIR
MASS IN PLACE SNOW WILL BEGIN LATE TONIGHT AND CONTINUE INTO
TUESDAY MORNING. WHILE THIS SET UP IS IDEAL FOR AN OVER RUNNING
EVENT WITH THE COLD AIR PRODUCING HIGHER SNOW RATIOS WITH 90% OF
THE ATMOSPHERE WILL BE IN THE PRIME DENDRITIC SNOW GROWTH ZONE OF
-10 TO -20C. BUT THE NORTHERLY WINDS ADVECTING IN DRIER AIR MAY
LIMIT INITIAL SNOW FALL. AT THIS TIME LOOKING AT SNOW FALL
AMOUNTS RANGING 2 TO 6 INCHES TONIGHT WITH AN ADDITIONAL 2 TO
6 IN THE MORNING WITH A STORM TOTALS RANGING FROM 4 TO 12 FOR
AREAS NORTH OF FREDERICK SOUND. FOR THE SOUTHERN AREAS EXPECTING
1 TO 2 INCHES OVERNIGHT AND IN THE MORNING FOR STORM TOTAL OF
2 TO 4 INCHES. AS WARM AIR MASS MOVES IN AT MID LEVELS MAY SEE
ENOUGH MELTING AND A SHALLOW ENOUGH COLD SURFACE LAYER FOR
FREEZING RAIN TO DEVELOP. AS TEMPERATURES CONTINUE TO RISE WILL
SEE THE SOUTHERN AREAS TRANSITION TO RAIN IN THE AFTERNOON.
WINTER STORM WARNINGS FOR SNOW WILL REMAIN IN PLACE WITH
ADVISORIES ADDED FOR THE SOUTHERN PANHANDLE DUE TO SNOW AND
POSSIBLE FREEZING RAIN.

 TIGHT NORTHERLY GRADIENT WILL BEGIN TO SHIFT TO THE EAST AS THE
YUKON HIGH BEGINS TO TRACK INTO BRITISH COLUMBIA. STRONG
NORTHERLY WINDS WILL BEGIN TO SUBSIDE LATER TONIGHT. EASTERLY
OUTFLOW WINDS WILL INCREASE THROUGH THE EVENING WITH LOCALLY HIGH
GUSTS. FREEZING SPRAY WILL CONTINUE TO BE AN ISSUE THROUGH THE
MORNING DUE TO THE COLD AIR AND STRONG WINDS.

 MODELS WERE IN GOOD AGREEMENT WITH BEST AGREEMENT BETWEEN THE
ECMWF/NAM. AS THERE WAS LITTLE CHANGE BETWEEN THE NEW MODEL RUNS
AND INHERITED GIRDS ONLY MINOR CHANGES WERE MADE. OVERNIGHT
TEMPERATURES WERE DROPPED A FEW DEGREES OVERNIGHT DUE TO THE
CONTINUING ARCTIC OUTBREAK. FORECAST CONFIDENCE IS AVERAGE.

.LONG TERM...THE WINTER STORM MENTIONED IN THE SHORT TERM
DISCUSSION ABOVE WILL WIND DOWN TUESDAY EVENING. WARMER MARINE
AIR WILL BE WORKING ITS WAY FROM THE OUTER COAST INTO THE INNER
CHANNELS. TEMPERATURE-WISE, THE NIGHTTIME LOW TEMPERATURES ARE
EXPECTED TO OCCUR EARLY ON TUESDAY EVENING. TEMPERATURES ARE THEN
EXPECTED TO RISE OVERNIGHT AS LOW-LEVEL ARCTIC AIR CONTINUES TO BE
ERODED OVERNIGHT.

 PRECIPITATION TYPE ON TUESDAY NIGHT IS ONE OF THE TRICKY THING
FOR THIS FORECAST PACKAGE. SNOW ARE EXPECTED TO CHANGEOVER TO RAIN
ALONG THE OUTER COASTS OF BARANOF ISLAND AND PRINCE OF WALES
ISLAND. THE CHANGEOVER WILL WORK ITS WAY INTO THE INNER CHANNELS.
SNOW ACCUMULATION FOR TUESDAY NIGHT WILL BE AROUND 1 TO 2 INCHES.
WITH
LOW LEVEL WARM AIR ADVECTION, THERE WILL BE A SMALL LAYER OF
ABOVE- FREEZING AIR ABOVE SUBFREEZING GROUND SURFACE. THERE IS A
POSSIBILITY OF SNOW MELTING IN THE WARM LAYER, THEN REFREEZING
UPON CONTACT WITH GROUND. THUS, KEEPS THE MENTION OF SLIGHT CHANCE
OF LIGHT FREEZING RAIN FOR CENTRAL AND SOUTHERN PANHANDLE. THE
HIGHEST THREAT WILL BE DURING TUESDAY NIGHT INTO EARLY WEDNESDAY
MORNING. FOR CENTRAL AND SOUTHERN PANHANDLE, PRECIPITATION SHOULD
BECOME PRIMARILY RAIN BY WEDNESDAY AFTERNOON.

AFTER THIS WINTER STORM DISSIPATES, SOUTHEAST ALASKA WILL RETURN
TO A WARM AND WET REGIME. LOW PRESSURE OVER THE BERING SEA IS
GOING TO ERODE THE ARCTIC HIGH OVER THE INTERIOR. WITH PRESSURE
FALL IN THE INTERIOR AND A PERSISTENT HIGH PRESSURE OVER
NORTHEAST PACIFIC, UPPER AIR FLOW WILL TURN MORE SOUTHERLY. KEPT
POPS TO THE LIKELY CATEGORY FOR THE REST OF THE LONG TERM TO
ACCOUNT FOR THE SOUTHERLY FLOW REGIME. THERE WILL BE SHORTWAVE
DISTURBANCES MAKING LANDFALL OVER THE PANHANDLE. WITH THIS FLOW
PATTERN, IT IS TOUGH TO PINPOINT THE POSITION AND STRENGTH OF
THESE SHORTWAVE FEATURES. TEMPERATURES WILL BE ABOVE AVERAGE, AND
PRECIPITATION SHOULD REMAIN MOSTLY RAIN. THIS WARM AND WET PATTERN
WILL CONTINUE INTO EARLY NEXT WEEK.

 FORECAST CONFIDENCE IS AVERAGE. DECIDES TO UTILIZE ECMWF/NAM FOR
THE BEGINNING OF THE LONG RANGE. THEN SHIFTS TOWARDS HPC GUIDANCE
BEYOND DAY 4. MINOR CHANGES ARE MADE TO SHOWCASE THE RETURN OF
WARM AND WET REGIME TO SOUTHEAST ALASKA.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO NOON AKST
TUESDAY
     FOR AKZ017-020>024-026.
         WINTER WEATHER ADVISORY FROM 3 AM TO NOON AKST TUESDAY FOR
     AKZ027-028.
         WINTER STORM WARNING FROM 3 AM TO 3 PM AKST TUESDAY FOR
AKZ025.
         WINTER WEATHER ADVISORY UNTIL MIDNIGHT AKST TONIGHT FOR
AKZ019.
         WINTER WEATHER ADVISORY UNTIL 9 AM AKST TUESDAY FOR
AKZ018.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ051.
         HEAVY FREEZING SPRAY WARNING FOR PKZ011.
         HEAVY FREEZING SPRAY WARNING FOR PKZ013-031.
         HEAVY FREEZING SPRAY WARNING FOR PKZ012.
         STORM WARNING FOR PKZ012.
         GALE WARNING FOR PKZ011-013-021-022-031-034-043-051>053.
         SMALL CRAFT ADVISORY FOR PKZ032-033-035-036-041-042.

&&

PRB/RCL