Winter Storm in Alaska, January 17 to 18, 2011

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
1251 PM AKST MON JAN 17 2011

.SHORT TERM...A HIGH BUILDING OVER THE NORTH PACIFIC AND FAR
SOUTHERN GULF WILL PUSH OFF TO THE EAST TONIGHT. WEST WINDS HAVE
BEEN QUITE STRONG OVER THE TOP OF THE RIDGE IN COASTAL WATERS
WERE GALES WARNINGS CONTINUE TODAY BUT WILL EASE TONIGHT AS HIGH
MOVES OFF. A MARITIME AIR MASS IS SPREADING INTO THE PANHANDLE
AND OVERRUNNING AN ARCTIC AIR MASS THAT IS IN PLACE THROUGH THE
INNER CHANNELS. WARM AIR HAS PENETRATED COASTAL AREAS WERE RAIN
AND MIXED RAIN AND SNOW WAS FALLING WITH TEMPS IN THE UPPER 30S
AND WELL INTO E-W CHANNELS WHERE TEMPS HAVE RISEN ABOVE FREEZING.
OVERALL PRECIP AMOUNTS HAVE BEEN LIGHT AND LIMITED SNOW LESS THAN
2 INCHES TODAY.

 A 1012 MB LOW IN THE NORTHEAST GULF IS FORECAST TO MOVE ACROSS
THE NORTHERN PANHANDLE TONIGHT AND AS IT DOES IT WILL ROTATE A
COLD FRONT SE ACROSS NORTHERN PANHANDLE IN THE MORNING THEN
WEAKEN AS IT PUSHES FARTHER SOUTH THROUGH THE DAY. AHEAD OF THE
FRONT EXPECT OVERRUNNING PRECIP TO INCREASE THROUGH THE EVENING.
THIS WILL BE SNOW FOR INNER CHANNELS BUT WILL BE MIXED WITH RAIN
ALONG COAST AND EVEN INTO ICY STRAIT THIS EVENING. WILL SEE TEMPS
WARM THROUGH THE NIGHT BEFORE FALLING IN THE MORNING. WILL STILL
HAVE GOOD LIFT FOR SEVERAL HOURS BEHIND SHALLOW SLOPING FRONT AND
DO EXPECT A BURST OF MODERATE TO HEAVY SNOW LATE TONIGHT INTO
EARLY TUESDAY FOR NORTH CENTRAL PANHANDLE. THIS WILL RESULT IN
WARNING LEVELS SNOWS IN THE 5 TO 10 INCH RANGE FOR INLAND AREAS
BUT MUCH LESS ALONG IMMEDIATE COAST AND CHANNELS. HEAVIER PRECIP
WILL SPREAD TO SOUTH CENTRAL IN THE MORNING AND EXIT SOUTHERN
AREAS BY EVENING. AMOUNTS SHOULD STAY BELOW ADVISORY LEVELS FOR
SOUTHERN INNER CHANNELS AND COULD EVEN MIX WITH RAIN IN ZONE 26.

&&

.LONG TERM...NONE OF THE OPERATIONAL MODELS SHOWS FAIR AGREEMENT
ONE TO ANOTHER FOR THE TRANSITION TIME WITH A WARMING TREND. THE
GFS HAS SHOWN A BETTER CONSISTENCY THAN THE ECMWF AND NAM FOR
EARLIER PORTIONS OF THE LONG TERM. THE 00Z RUN ECMWF WAS CLOSER TO
THE 12Z RUN GFS BUT THE 12Z RUN NAM WAS TOO SLOW AND WEAK WITH THE
TREND. OPTED TO LEAN OVER THE GFS SOLUTIONS THROUGH THURSDAY THEN
PREFERRED TO GO WITH THE ENSEMBLE MEANS FORECAST FROM THE HPC
THROUGH THE END OF THE PERIOD. A WEAK UPPER LEVEL RIDGE WILL BUILD
ACROSS THE GULF AND MOVE EAST THROUGH WEDNESDAY THEN THE UPPER
FLOW WILL BECOME A LITTLE MORE ZONAL THROUGH LATE FRIDAY.

 BEHIND THE TRAILING EDGE OF THE FRONT...SNOW WILL DIMINISH
ACROSS THE FORECAST DOMAIN ON TUESDAY NIGHT INTO WEDNESDAY MORNING
WITH SUBSIDING WINDS/SEAS ACROSS THE COASTAL WATERS. THE NEXT
FRONTAL BOUNDARY WILL ARRIVE OVER THE OUTSIDE WATERS BY WEDNESDAY
EVENING WITH GALE FORCE WINDS AND BREEZY CONDITIONS ALONG THE
PANHANDLE COAST. THIS FRONT ACCOMPANIES WARM AIR MASS THAT
APPROACHES THE PANHANDLE COAST BY WEDNESDAY EVENING THEN OVER THE
ENTIRE FORECAST DOMAIN BY LATE WEDNESDAY NIGHT INTO EARLY THURSDAY
MORNING.

 EXPECT PRECIPITATION WILL BE MORE LIKELY SNOW ACROSS THE CENTRAL
AND NORTHERN PANHANDLE INITIALLY THEN CHANGING OVER RAIN OVERNIGHT
FOR THE MOST OF AREAS AND ALL RAIN ACROSS THE SOUTHERN AREAS
EXCEPT HYDER. THE FRONT WILL WEAKEN AS IT MOVES OVER INLAND WITH
SCATTERED RAIN SHOWERS ON THURSDAY AFTERNOON. NORTHERN MOST ZONES
AND HYDER WILL CONTINUE TO SEE SNOW THROUGH SATURDAY. AT LEAST
THREE MORE FRONTS WILL MOVE INTO THE AREA WITH PERSISTING ONSHORE
FLOW THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK. PRECIPITATION
SHOULD BE ALL RAIN WITH THE WARM AIR MASS OVER THE AREA...EXCEPT
AGAIN OVER THE NORTHERN MOST PANHANDLE AND HYDER WHERE COLDER AIR
FROM CANADA MAY BRING SOME SNOW OR AT LEAST SNOW/RAIN MIX.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WARNING UNTIL 9 AM AKST TUESDAY FOR AKZ019-021-
     024>026.
         WINTER STORM WARNING UNTIL 3 AM AKST TUESDAY FOR AKZ020-022.
MARINE...SMALL CRAFT ADVISORY FOR PKZ041>043-051-052.

&&

MM/AHN