Small Craft Advisory 765, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
607 AM AKST FRI NOV 25 2011

.SHORT TERM...SATELLITE IMAGERY THIS MORNING SHOWING A 987 MB
LOW IN THE NORTHERN AK GULF JUST SOUTH OF PRINCE WILLIAM SOUND
RETROGRADING WEST. RADAR REFLECTIVITY SHOWS FIRST FRONTAL BAND
ASSOCIATED WITH THE LOW HAS HIT THE PANHANDLE COAST AND WILL MOVE
ACROSS THE REGION THROUGH THE DAY. SNOW FROM THIS FIRST BAND HAS
STARTED WITH HEAVY SNOW REPORTED. SNOW ACCUMULATION SHOULD BE
JUST BELOW ADVISORY LEVELS FOR THE DAY AS THE LOW MOVES FAIRLY
QUICKLY EAST. SNOW RATIO WILL BE LOWER THAN THE PAST FEW DAYS AS
TEMPERATURES WARM THROUGH THE DAY. A SECOND SHORTWAVE CURRENTLY
SOUTH OF THE N GULF LOW WILL REACH THE PANHANDLE THIS AFTERNOON
AND INTO TONIGHT. A 986 MB LOW WILL MOVE UP FROM THE NORTH
PACIFIC TRACKING TOWARDS HAIDA GWAII LATE FRIDAY AFTERNOON THEN
MOVE TOWARDS THE SOUTHERN PANHANDLE OVER NIGHT. THE SECOND AK
GULF SHORTWAVE IS SHOWING HIGHER QPF VALUES AND ALON WITH
MOISTURE FEED FROM THE NORTH PACIFIC LOW EXPECTING HIGHER SNOW
TOTALS FRIDAY EVENING INTO EARLY SATURDAY. HAVE ISSUED WINTER
WEATHER ADVISORIES FOR AREAS NORTH OF FREDERICK SOUND AND A WATCH
FOR THE PETERSBURG ZONE INTO SATURDAY AFTER COORDINATION WITH THE
LONG TERM DESK. THE SOUTHERN ZONES WILL SEE HIGHER QPF VALUES
WITH THE NORTH PACIFIC LOW BUT WITH WARM AIR ADVECTION EXPECTING
A TRANSITION TO ALL RAIN OR A RAIN SNOW MIX. THE 530 DAM LINE AND
850MB -4C TEMP LINE MOVING JUST SOUTH OF SUMNER STRAIT SO EXPECT
LEST PRECIP MIX TO THE NORTH. STRONG WINDS WILL ACCOMPANY THE
SOUTHERN LOW WITH 40 MPH GUSTS AND GALE WARNINGS OVER THE
SOUTHERN AK PANHANDLE.

 MODELS WERE SHOWING SOME FAIR DIFFERENCES DEALING WITH THE SNOW
AMOUNTS FOR TODAY AND TONIGHT. 06Z NAM HAD THE HIGHEST QPF VALUES
FOR DAYTIME FRIDAY BUT STILL KEPT AVERAGE SNOW TOTALS JUST BELOW
ADVISORY CONDITIONS. THE 12Z NAM RUN NOW SHOWS LOWER QPF VALUES
FOR THE DAY SUPPORTING THE LOWER SNOW AMOUNT DECISION. OMEGA
VALUES DID NOT INTERSECT WITH THE SNOW GROWTH ZONE TODAY AS WELL
AS THEY DO TONIGHT. HOWEVER DEFORMATION BAND FORMING OVER THE
CENTRAL PANHANDLE THIS AFTERNOON MAY ENHANCE LIFT AND INCREASE
SNOW AMOUNTS. BUT SAW BETTER AGREEMENT WITH HIGHER QPF VALUES
BETWEEN THE MODELS FOR TONIGHT VS FRIDAY.

 PRESSURE AND WIND FIELD INITIALIZATION SHOWED GFS AS A BIT OF AN
OUTLIER WITH NAM/EC HANDLING THE POSITION OF THE N GULF LOW
FAIRLY WELL. DID SEE SOME TIMING ISSUES WITH THE LOW
RETROGRADING. EC HAD THE LOW FARTHEST TO THE EAST AND WAS A BIT
SLOWER MOVING THE LOW BACK EAST WITH NAM BEING THE FASTEST.
GEM/UKMET HAD A PRETTY GOOD COMPROMISE AND IN THE END MADE FEW
CHANGES TO THE PRESSURE AND WIND GRIDS AS THEY ALREADY HAD A
REASONABLE ENSEMBLE SOLUTION. BLENDED NAM/EC FOR QPF WITH SOME
SREF FOR POP AND NUDGED SNOW AMOUNTS UP ABOUT 1 INCH TO ADVY
LEVELS FOR FRIDAY NIGHT. OVERALL CHANGES WERE FAIRLY SMALL.
FORECAST CONFIDENCE IS ABOUT AVERAGE.

 &&

 .LONG TERM...MAJOR FOCUS IN THE EXTENDED RANGE FORECAST
CONTINUES TO BE HOW MUCH OF A WARM UP WE CAN EXPECT OVER THE NEXT
WEEK. THIS WILL HAVE TREMENDOUS IMPACT ON SNOW VERSUS RAIN AND,
IF SNOW, HOW MUCH. QPF VALUES STILL QUITE HIGH, WHICH IS
CONSISTENT FROM LAST NIGHT, SO HAVE FAIRLY HIGH CONFIDENCE THAT
PRECIP WILL BE HEAVY AT TIMES DURING THE UPCOMING WEEK. THE MAJOR
SOURCE OF UNCERTAINTY CONTINUES TO BE TEMPERATURES. MODEL
GUIDANCE STILL SIGNIFICANTLY COLDER THAN WHAT WOULD BE EXPECTED
WITH A WARM FRONT THAT APPROACHES SOUTHEAST ALASKA FROM THE SOUTH
ON FRIDAY NIGHT, AND THEN ANOTHER THAT APPROACHES FROM THE WEST
ON SUNDAY NIGHT. BELIEVE THE FRONT APPROACHING FROM THE SOUTH
FRIDAY NIGHT WILL POSSIBLY PRODUCE ADVISORY LEVEL, IF NOT WARNING
LEVEL, SNOWFALL BEFORE CHANGING TO RAIN THAT HAVE ISSUED A WINTER
STORM WATCH FOR ZONE 26. THINK ZONE 27 WILL ALSO SEE SNOW
SATURDAY MORNING BEFORE CHANGING TO RAIN, BUT SNOW TOTALS
ASSOCIATED WITH THE FRONT DO NOT LOOK LARGE ENOUGH AT THIS TIME
TO INCLUDE THAT ZONE IN THE WATCH. LIKEWISE FOR ZONE 29. COLDER
AIR ASSOCIATED WITH A THICKNESS TROUGH WILL ADVECT IN FROM THE
WEST ON SUNDAY, DRIVING OVERNIGHT TEMPS BACK DOWN TO FREEZING OR
BELOW AND SET THE STAGE THE STAGE FOR THE FRONT APPROACHING FROM
THE WEST SUNDAY NIGHT. BELIEVE OVERNIGHT TEMPS WILL BE A LITTLE
WARMER SUNDAY NIGHT, BUT STILL COLD ENOUGH TO PRODUCE ANOTHER
ADVISORY OR WARNING SNOW EVENT SUNDAY NIGHT THROUGH MONDAY
MORNING FOR ALL LOCATIONS EXCEPT THE SOUTHERN 3 ZONES.

 SHOULD SEE SOME SIGNIFICANT MELTING, HOWEVER, LATER THIS WEEK
TUESDAY THROUGH THURSDAY AS DAYTIME HIGHS GET INTO THE UPPER 30S
OR LOW 40S WITH OVERNIGHT LOWS REMAINING ABOVE FREEZING FOR MUCH
OF SOUTHEAST ALASKA. SO ENJOY THE SNOW WHILE YOU CAN.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WATCH FROM LATE TONIGHT THROUGH SATURDAY MORNING
     FOR AKZ026.
         STRONG WIND FROM 6 PM AKST THIS EVENING THROUGH LATE TONIGHT FOR
     AKZ027-028.
         WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 5 AM AKST
     SATURDAY FOR AKZ019>021-025.
MARINE...GALE WARNING FOR PKZ035-036-041-051.
         SMALL CRAFT ADVISORY FOR PKZ012-013-021-022-031>034-042-043-052.

&&

PRB/FRITSCH