Heavy Snow in Alaska, March 6, 2009

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
238 PM AKST THU MAR 5 2009

.SHORT TERM...SATELLITE TODAY IS REVEALING A SHIELD OF MID TO
LOW LEVEL CLOUDS OVER MOST OF THE PANHANDLE. THE EXCEPTION TO
THIS ARE THE MOSTLY CLEAR SKIES OVER THE SOUTHEASTERN PANHANDLE.
SURFACE OBSERVATIONS CONFIRM THIS WITH A LOW MARINE LAYER OF ONLY
A FEW THOUSAND FEET PRESENT OVER GUSTAVUS AND SITKA AND SOME
LIGHT SNOW FALLING IN ELFIN COVE. WINDS ACROSS THE PANHANDLE ARE
MAINLY LIGHT WITH THE EXCEPTION OF SKAGWAY WHERE SOUTHERLY WINDS
ARE STARTING TO PICK UP.

 IN THE UPPER LEVELS A RIDGE AXIS IS POSITIONED OVER THE NORTHERN
GULF WHILE A TROUGH SITS IN THE BERING SEA. THE RIDGE AXIS WILL
START TILTING TO THE EAST TONIGHT AS THE TROUGH IN THE BERING
BEGINS TO MOVE IN.

 MAIN CONCERN FOR THE SHORT TERM FORECAST TODAY IS HOW MUCH SNOW
THE NORTHERN PANHANDLE WILL GET ON FRIDAY BEFORE IT STARTS TO MIX
WITH RAIN LATE FRIDAY MORNING. CURRENT THINKING IS THAT THE
PRECIP WILL START OUT AS LIGHT SNOW FOR MOST OF THE NORTHERN AND
CENTRAL PANHANDLE THURSDAY NIGHT BEFORE CHANGING OVER TO A MIX OR
ALL RAIN FRIDAY MORNING AS TEMPS RISE IN THE SOUTHERLY FLOW AHEAD
OF THE FRONT. WE WILL REACH OUR HIGH EARLY FRIDAY BEFORE THE
FRONT PUSHES THROUGH MIDDAY FRIDAY AND BEGINS TO COOL US DOWN
ONCE AGAIN. THE HIGHEST QPFS FOR THIS SYSTEM COME IN FRIDAY
MORNING BUT BY THAT POINT IT SHOULD BE JUST A LITTLE TO WARM TO
BRING ANY SIGNIFICANT ACCUMULATIONS OF SNOW. ANY REMAINING PRECIP
SHOULD SWITCH BACK OVER TO SNOW FOR THE NORTHERN PANHANDLE BY
FRIDAY NIGHT. THE EXCEPTION TO THIS IS THE HAINES ZONE WHERE
PRECIP COULD TAKE A WHILE TO INITIALLY CHANGE OVER TO RAIN. AS
SUCH HAVE ISSUED A WINTER WEATHER ADVISORY FOR HAINES FOR TONIGHT
INTO TOMORROW MORNING. KEPT THE WIND ADVISORY FOR SKAGWAY AS THE
PRESSURE GRADIENT BETWEEN WHITEHORSE AND JUNEAU IS FORECAST TO BE
AROUND 10 MB FRIDAY

 MOST OF THE MAJOR MODELS AGREE ON THE TIMING OF THE FRONTAL
PASSAGE OVER THE PANHANDLE. THE EXCEPTION IS THE THE NAM THAT
BRINGS THE FRONT IN A LITTLE SLOWER THEN THE OTHER MODELS. IT IS
ALSO THE COLDER OF THE MODELS. MODEL OF CHOICE FOR THE SHORT TERM
WAS THE GFS AS I THOUGHT THE NAM WAS TOO SLOW AND COLD AND THAT
THE GFS HAD THE SUPPORT OF SEVERAL OF THE OTHER MODELS INCLUDING
THE GEM AND EC.

.LONG TERM...THE FORECAST MODELS THIS MORNING ARE IN VERY GOOD
AGREEMENT THROUGH THE WEEKEND AND THEY HAVE BEEN STABLE FOR THE
PAST COUPLE OF DAYS WITH VERY GOOD RUN TO RUN CONTINUITY. SO WITH THAT SAID
THERE IS HIGH FORECASTER CONFIDENCE THROUGH THE WEEKEND. INTO
NEXT WEEK THERE SPREAD IN THE ENSEMBLES INCREASE SOME IN THE UPPER
LEVELS WITH A TROF MOVING SOUTH OF THE CHAIN. THE EC IS DIGGING
THIS FEATURE INTO THE NORTH PACIFIC BUT THE GFS IS KEEPING MORE OF
A ZONAL FLOW. AFTER TALKING OVER WITH HPC THE CONSENSUS WAS TO GO
WITH A BLEND OF THE GFS/EC AND HPC GRIDS. THIS DID NOT CHANGE THE
OVER ALL FORECAST THAT MUCH AS ONCE THE COLD FRONT LIFTS OVER THE
PANHANDLE THROUGH FRIDAY NIGHT THE AREA WILL BE ON THE DRY AND
COLD SIDE THROUGH EARLY NEXT WEEK.

THE STRONG UPPER LEVEL TROF OVER THE PANHANDLE EARLY FRIDAY
EVENING WILL CONTINUE TO PRODUCE SNOW SHOWERS ACROSS THE AREA FROM
PAJN/PAOH LINE SOUTH. THERE WILL BE MINOR ACCUMULATIONS OVER THE
NORTHERN AREAS WITH UP TO 1 INCH AND UP TO 2 INCHES WITH LOCALLY
HIGHER AMOUNTS NEAR STRONGER SHOWERS FROM PAPG SOUTHWARD. AS THE
UPPER TROF CONTINUES TO SLIDE SE A RIDGE WILL BUILD OVER GULF TO
INCREASE NW FLOW. THIS OFFSHORE FLOW WILL DECREASE THE CLOUD COVER
AND INCREASE CAA. THE COLD AIR AND CLEAR SKIES WILL ALLOW TEMPS TO
FALL INTO THE SINGLE DIGITS OVER THE FAR NORTHER AREAS AND LOWER
TEENS OVER THE NORTHERN INNER CHANNELS AND LOWER 20 OVER THE FAR
SOUTHERN AREA THIS WEEKEND. THE WINDS OUT OF THE NORTH WILL
INCREASE AS 1040MB HIGH BUILDS OVER THE YUKON. SO HAVE EXTENDED
THE END TIME OF THE PAGY ADVY TO FRI MORNING. THE WINDS WILL RELAX
FROM THE SOUTH EARLY FRI EVENING AND SWITCH THE NORTH WITH GUSTS
TO 45KT. THIS ADVY MAY NEED TO GET EXTENDED AGAIN INTO SAT. THE
WINDS OVER THE MARINE AREAS WILL ALSO INCREASE FROM THE NORTH SO
SMALL CRAFT WINDS WILL INCREASE IN N/S CHANNELS THROUGH FRI NIGHT
WITH GALES IN NORTHERN LYNN.

THE RIDGE WILL PERSIST THROUGH THE WEEKEND AND WILL SLOWLY BREAK
DOWN THROUGH THE EARLY WEEK AS A TROF MOVES INTO THE GULF BUT
THERE IS LOW CONFIDENCE IN THIS. THE NEXT TIME THE PANHANDLE MAY
SEE SOME SIGNIFICANT PRECIP WOULD TUE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 3 PM AKST
     FRIDAY FOR AKZ019.
         WIND ADVISORY FROM MIDNIGHT TONIGHT TO 5 AM AKST SATURDAY FOR
     AKZ018.
MARINE...GALE WARNING FOR PKZ012-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-022-031>036.

&&

EAL/ABJ