Heavy Snow in Alaska, December 22, 2002

SOUTHEAST ALASKA FORECAST DISCUSSION
245 AM AST SUN DEC 22 2002

.SYNOPSIS...
.SHORT RANGE...FIRST WEAK OCFNT MOVING THROUGH THE PANHANDLE THIS
MORNING AND GRADUALLY ERODING AWAY THE ARCTIC FRONT BACK TO NEAR
CAPE SPENCER-FIVE FINGER LINE. LIGHT SNOW OCCURRING OVER THE
INNER CHANNELS NORTH OF ARCTIC FRONT BUT NO SIGNIFICANT
ACCUMULATIONS EXPECTED WITH THIS FIRST SYSTEM. SOME LIGHT RAIN
STILL OCCURRING SOUTH OF ARCTIC FRONT.

STRONGER PUSH OF WARM AIR COMING WITH NEXT FRONT OVER THE CENTRAL
GLFAK. THIS SYSTEM MOVING RAPIDLY TOWARD THE PANHANDLE AND SHOULD
PICK UP THE PRECIP 15Z-18Z. THIS ONE WEAKENING ALSO AS IT MOVES
ONSHORE AS NEW LOW DEVELOPS ON THE FRONT AND MOVES NORTH ALONG
140W. SO WINDS AND PRECIP CONTINUE TO INCREASE THROUGH THE
EVENING. GALE FORCE WINDS DEVELOPING OVER ALL COASTAL WATERS 1B
AND 2A TODAY. MAIN FORECAST PROBLEM WILL BE RAIN/SNOW BOUNDARY.
ZONES 24 AND 25 THE ONLY ONES THAT SHOULD SEE ANY SIGNIFICANT
SNOWFALL. REMAINDER OF THE ZONES ALREADY ABOVE FREEZING. MOST OF
ZONE 25 SHOULD BE RAIN BY NOON ALTHOUGH INLAND VALLEYS AROUND
JUNEAU COULD SEE A COUPLE OF INCHES BEFORE FINALLY CHANGING OVER
LATE IN THE DAY. PAHN/PAGY AREA WILL STAY SNOW ALL DAY BUT
HEAVIER PRECIP WILL NOT START UNTIL THIS EVENING. EASTERN GULF
COAST WILL SEE SOME LIGHT SNOW EARLY THIS MORNING...BUT 00Z
SOUNDING SHOWED COLD AIR ONLY A VERY SHALLOW LAYER NEAR THE
SURFACE SO PRECIP SHOULD CHANGE TO RAIN BY MID MORNING.

.LONG RANGE...MODELS SHOW FNTL SYS OVR THE ERN GLFALSK EARLY
SUN NIGHT MOVG E TO BCM QSTNRY OVR THE INNER CHNLS OF CNTRL AND
SRN SE AK LATER SUN NIGHT. THIS WL PUSH ARCTIC FNTL BNDRY OVR
NRN SE AK EARLY SUN NIGHT NWD INTO THE YUKON LATE SUN NIGHT.
STG JET OVERLYING AND  PARALLEL TO THE SFC FNT WL CAUSE WVS TO
DVLP ALG THE FNT AND MOV NE THRU THE INNER CHNLS OF SE AK DURG
MON.

RAIN CONTG ALG THE ERN GLF CST AND OVR CNTRL AND SRN SE AK.
SNOW OVR NRN SE AK CHGG TO RAIN AFTER MIDNIGHT AND CONTG MON.
SNOWFALL AMTS OVR NRN SE AK MAY RANGE OVER 6 INCHES PRIOR TO
MIDNIGHT. WL CONSIDER A WINTER STORM WARNING FOR HEAVY SNOW
FOR ZONE 24 SUN NIGHT. WINDY CONDS WL PREVAIL MOST SXNS SUN
NIGHT AND MON.

EXTDD RANGE CHARTS SHOW FNTL BNDRY OVR THE INNER CHNLS OF SE AK
MOVG E TO B.C. IN RESPONSE TO A DVLPG LOW PRES SYS OVR THE
ERN PACIFIC MOVG NE TWD THE QUEEN CHARLOTTE ISLANDS. THIS WL
ALLOW COOLER UNSTBL AIR TO MOV OVR THE RGN FM THE GLFALSK
CHGG STDY RAIN TO RAIN SHWRS.

CHRISTMAS DAY MODELS CONT TREND OF MOVG MDT 980 MB LOW TO
THE QUEEN CHARLOTTE ISLANDS BY WED AFTN. WINDY WITH RAIN SPRDG
TO THE S HLF OF SE AK...MOSTLY CLDY AND WINDY N HLF OF SE AK AND
ERN GLF CST.

ON THU...MODELS SHOW LOW PRES EXITING THE RGN VIA B.C. ALLOWING
AN UPR LVL TROF TO MOV OVR SE AK AND THE ERN GLF CST. RSTLG
CHG TO A MORE ZONAL FLOW ALF WL ALLOW COOLER UNSTBL AIR TO MOV
IN FM THE W. THEREFORE...RAIN SHWRS OVR THE S HLF OF SE AK...
RAIN AND SNOW SHWRS OVR THE N HLF OF SE AK AND ERN GLF CST.

FRI AND SAT...COOLING TREND IS FCST TO CONT AS A LONG WV HI
PRES RDG ALF BGNS TO BLD OVR THE BERING SEA. LOW PRES DVLPG
DOWNSTREAM FM THE HI OVR THE CNTRL GLFALSK WL CONT TO TRIGGER
RAIN AND SNOW SHWRS FOR THE ENTR RGN FRI AND SAT.

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...WINTER STORM WARNING FOR HEAVY SNOW ZONE 24 THIS
         EVENING.
MARINE...GALE 1B 2A 1A2 SRN 1A3.
         SCA REMAINDER 1A2.

PES/DED