Heavy Snow in Alaska, December 3 to 4, 2005

SOUTHEAST ALASKA FORECAST DISCUSSION
630 AM AST SAT DEC 3 2005

.SHORT RANGE...LATEST GOES IR SATELLITE IMAGERY LOOP SHOWS
SMALL LOW SOUTH OF YAKUTAT BAY WITH A FRONTAL SYSTEM EXTENDING
FROM THE LOW TO STRETCH SOUTHEAST ALONG THE OUTER COAST OF
SOUTHEAST ALASKA. THE HEAVIEST SNOWFALL AT THE MOMENT IS
OCCURRING ALONG THE EASTERN GULF COAST WHERE THE VISIBILITY IS
REPORTED TO BE DOWN TO 1/2 MILE IN LIGHT SNOW AND FREEZING FOG.
ELSEWHERE OVER THE SOUTHEAST ALASKA PANHANDLE SNOWFALL IS LIGHTER
AND INTERMITTENT.

MODELS SHOW THE FRONTAL SYSTEM APPROACHING SOUTHEAST ALASKA
MOVING EAST OF NORTHERN AND CENTRAL SOUTHEAST ALASKA THIS
AFTERNOON WITH THE TRAILING END OF THE FRONT TURNING SOUTHWEST TO
STRETCH ACROSS SOUTHERN SOUTHEAST ALASKA. THIS PORTION OF THE
FRONT IS FORECAST TO REMAIN OVER SOUTHERN SOUTHEAST ALASKA
THROUGH TONIGHT.   A WAVE DEVELOPING ON THE FRONT IN THE
EASTERN GULF OF ALASKA TONIGHT WILL BECOME A LOW AS IT
PUSHES EAST ACROSS SOUTHERN SOUTHEAST ALASKA SUNDAY MORNING.
AS THE LOW EXITS THE REGION...THE FRONT ACROSS SOUTHERN
SOUTHEAST ALASKA WILL MOVE SOUTH TO BRITISH COLUMBIA.
LOW PRESSURE IN THE NORTHEAST GULF OF ALASKA WILL DISSIPATE
ALLOWING A NEW SURGE OF HIGH PRESSURE TO PUSH SOUTH FROM THE
YUKON OVER THE EASTERN GULF COAST SUNDAY MORNING  AND OVER THE
SOUTHEAST ALASKA PANHANDLE SUNDAY AFTERNOON.

SNOW OVER MUCH OF THE REGION TODAY...MIXING WITH RAIN ALONG
CENTRAL AND SOUTHERN OUTER COASTAL AREAS BY AFTERNOON.
SIGNIFICANT SNOWFALL AMOUNTS ARE FORECAST FOR MOST SECTIONS OF
SNOW ADVISORIES IN EFFECT FOR UP TO 4 INCHES OF SNOW  OVER MUCH
OF CENTRAL AND SOUTHERN SOUTHEAST ALASKA TODAY. ADDITIONALLY
A WIND ADVISORY IS IN EFFECT FOR 40 MPH  GUSTS IN NORTHERN
LYNN CANAL AND ALONG THE NORTHERN  OUTER COAST OF SOUTHEAST
ALASKA.

WITH THE STRONGEST DYNAMICS EAST OF THE REGION TONIGHT...
PRECIPITATION WILL BE LIGHTER OVERNIGHT...TAPERING OFF DURING THE
DAY SUNDAY AS HIGH PRESSURE BUILDS IN OVER THE REGION FROM THE
NORTH.

.LONG RANGE...MID RANGE MODELS GFS AND ETA ARE DIFFERENT BY LATE
SUN NIGHT. ETA HAS A BROAD UPPER RIDGE AND BRINGS A LARGE AREA OF
OVERRUNNING PRECIPITATION INTO THE ENTIRE EASTERN GULF POISED TO
SURGE INTO SOUTHEAST ALASKA MON MORNING.

OPERATIONAL GFS IS MUCH MORE CONSERVATIVE. IT HAS A NEGATIVE TILT
RIDGE PERSISTING OVER THE PANHANDLE...KEEPING ALL THE
PRECIPITATION IN THE YAKUTAT AREA FOR THAT FIRST SHOT. 06Z RUN
IS EVEN DRIER THAN THE 00Z RUN. HOWEVER THE GFS ENSEMBLE
SOLUTIONS FOR POPS MON RANGE FROM 5 PERCENT TO 95 PERCENT. WILL
GO WITH ETA SOLUTION BUT TONE THE POPS DOWN TO LIKELY. ETA TIME
SECTIONS SHOW A BREAK SUN NIGHT AND SNOW RETURNING MON
MORNING...CHANGING TO RAIN AT JUNEAU LATE MON NIGHT.

ECM IS SIMILAR TO THE ETA. THEY BOTH BRING ZERO CELSIUS AT 850 MB
TO THE OUTER COAST MON,,,WHEREAS GFS KEEPS THE COLD AIR AND
OFFSHORE FLOW OVER THE PANHANDLE...STALLED WITH THAT NEGATIVE
TILT RIDGE THOUGH TUE.

EVEN GFS HAS SOUTHEAST ALASKA UNDER SOUTHWEST FLOW ALOFT BY WED
NIGHT. THEN A WET AND RAINY SYSTEM WITH SUBTROPICAL ORIGINS MOVES
INTO THE AREA NEXT WED NIGHT AND ANOTHER FRI NIGHT.

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...SNOW ADVISORIES ZONES...20..21..22..25..26..28..28..29
         WIND ADVISORIES...ZONES..18..22
MARINE...GALE WARNING
          OUTSIDE WATERS...PKZ042-043-051
          INSIDE WATERS...PKZ021-022-034-035