Small Craft Advisory 768, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
150 PM AKST FRI NOV 25 2011

.SHORT TERM...A COMPLES LOW PRESSURE AREA WILL REMAIN OVER THE
NW GULF AND SLOWLY WEAKEN THRU SAT. A TROF EXTENDS FROM THE NE
GULF SEWD ALONG THE CENTRAL COAST THE CURVES SSW OVER THE SE
GULF. THIS TROF WILL DRIFT JUST ONSHORE THIS EVENING THEN STALL
THERE. A DEVELOPING LOW OVER THE NE PAC WILL MOVE NNE TO THE FAR
SERN GULF BY LATE TONIGHT...THEN MOVE NE ACROSS THE S-CNTRL INNER
CHANNELS AND WEAKEN RAPIDLY SAT MORNING. USED A BLEND OF THE 12Z
NAM AND ECMWF FOR TONIGHT AND SAT.

 MAIN FORECAST ISSUE WILL BE SNOWFALL AMOUNTS. THE 2 MAIN AREAS
OF CONCERN ARE THE NRN THIRD OF THE INNER CHANNELS AND THE ERN
PARTS OF THE SRN INNER CHANNELS. OVER THE N...TROF MOVING ONSHORE
AND STALLING WILL FOCUS PRECIP IN THAT AREA THIS EVENING AND A
DEFORMATION BAND WILL ALSO SET UP OVER THE AREA MAINLY ALONG A
PAHN-PAEL LINE. THINK THIS AXIS WILL BE FOCUS FOR HEAVIEST
SNOWFALL EXCEPT THERE WILL BE SOME DOWNSLOPE DIMINISHING THE SNOW
IN THE PAGS ZONE LATER TONIGHT. THE PAOH ZONE WILL SEE INCREASING
ELY UPSLOPE FLOW SO THEIR SNOW SHOULD BE ENHANCED TONIGHT AS
WELL. THIS SAME FLOW WILL DIMINISH THE PRECIP IN THE PAJN AREA
OVERNIGHT. ATTM THINK MOST SNOW WILL BE AROUND PAHN AREA WHERE
GOOD ISENTROPIC UPGLIDE WILL ALSO OCCUR DUE TO PRESENCE OF COLDER
AIR IN LOWER LEVELS. THEY COULD GET AROUND 1 FOOT OF SNOW. THE
PAOH AND PAEL AREAS COULD SEE 6 TO 10 INCHES OF SNOW...WITH PAJN
AND PAGS GETTING 3 TO 6 INCHES BY 18Z SAT. WILL ISSUE WS WARNINGS
FOR THE PAHN/PAOH/PAEL ZONES...AND WW ADVYS FOR PAGS AND PAJN
ZONES. LOCALLY HIGHER AMOUNTS ARE POSSIBLE IN ANY OF THESE ZONES
THOUGH DUE TO POTENTIAL FOR TRAINING OF HEAVIER EMBEDDED SHOWERS
THIS EVENING...BUT IT IS NOT CERTAIN WHERE THIS WOULD SET UP
ATTM. WILL WATCH SATELLITE/RADAR TRENDS FOR THIS AND MAKE
ADJUSTMENTS IF NEEDED.

 OVER THE S...PRECIP WILL SPREAD INTO THE AREA AHEAD OF THE LOW
MOVING TOWARD THEM. LOOKS LIKE THE NE HALF OF ZONE 26 AND NERN
THIRD OF ZONE 29 WILL GET ENOUGH PRECIP AND REMAIN COLD ENOUGH
FOR SIGNIFICANT SNOW. HYDER LOOKS LIKE THEY COULD EASILY SEE
ANOTHER FOOT OF SNOW BY 18Z SAT...WITH NERN ZONE 26 GETTING 5 TO
8 INCHES FROM 06Z TO 18Z SAT. WILL ISSUE WS WARNINGS FOR BOTH
AREAS.

 OTHERWISE...WINDS WILL PICK UP OVER THE SRN AREA LATE THIS
EVENING AND CONTINUE OVERNIGHT AS LOW MOVES PAST THEM JUST TO THE
W. WILL HEADLINE STRONG WINDS IN ZONES 27 AND 28 FOR MAINLY THE
LATE EVENING TO EARLY MORNING SAT PERIOD. PEAK WINDS SHOULD OCCUR
AROUND 12Z WITH GUSTS TO 50 MPH. WILL SEE RAIN OVER THE SRN ZONES
OUTSIDE THE WS WARNING AREA AND AS FAR N AS THE PASI AREA LATER
TONIGHT. TEMPS MAY RISE THRU THE NIGHT OVER THE SRN AREA AS THE
LOW BRINGS UP WARMER AIR FROM THE SSE...THEN COOLER AIR SHOULD
MOVE BACK IN ON SAT ONCE LOW MOVES INLAND.

 &&

.LONG TERM...MAIN CONCERN IN THE EXTENDED RANGE FORECAST REMAINS
THE FRONT THAT WILL BE IMPACTING THE PANHANDLE SUNDAY NIGHT AND
MONDAY BRINGING MORE PRECIP AND WIND. MODELS ARE IN DECENT
AGREEMENT ON THE TIMING OF THE SYSTEM, BUT SOME OF THE DETAILS ARE
SKETCHY AT BEST. THE MAIN PROBLEM IS HOW FAST WILL THE WARM AIR
GET ADVECTED INTO THE INNER CHANNELS AND AS A CONSEQUENCE HOW MUCH
SNOW WILL PLACES GET BEFORE THE SNOW CHANGES TO RAIN. IF IT
CHANGES OVER AT ALL. THE NAM IS TRENDING A BIT COLDER THEN THE EC
OR THE GFS WITH THE -6 DEGREES C AT 850 LINE NOT EVEN MAKING IT
NORTH OF FREDERICK SOUND MIDDAY MONDAY. GFS AND EC ON THE OTHER
HAND SEND THAT LINE A BIT FARTHER NORTH ALMOST TO TAKU INLET.
GENERALLY THOUGH BASED ON THE HIGH QPF AMOUNTS FORECAST FOR EARLY
MONDAY MOST INNER CHANNEL AREAS AND THE NORTHERN OUTER COAST MAY
GET A DECENT AMOUNT OF SNOW LATE SUNDAY NIGHT AND EARLY MONDAY
BEFORE THE SNOW CHANGES OVER TO RAIN. TENDED TO FAVOR THE EC AND
GFS OVER THE NAM BECAUSE OF BETTER AGREEMENT AND RUN TO RUN
CONSISTENCY BETWEEN THE TWO.

WIND WILL ALSO BE A PROBLEM AS GALE FORCE WINDS ARE EXPECTED FOR
THE OUTSIDE MARINE WATERS LATE SUNDAY NIGHT AND FOR CLARENCE
STRAIT EARLY MONDAY. STRONG WIND HEADLINES MAY BE NEEDED FOR THE
SOUTHERN ZONES AND OUTER COAST AS WINDS SHOULD BE GUSTING UP TO 40
KT AT TIMES.

AFTER THE EARLY WEEK SYSTEM, MODEL AGREEMENT FALLS APART AS
THE EXTENDED MODELS TRY TO RESOLVE SMALLER WEAKER FEATURES THAT
ARE MOVING ACROSS THE GULF. TIMING, PLACEMENT AS WELL AS STRENGTH
ARE OFF WITH EACH MODEL WANTING TO HANDLE THEM SOMEWHAT DIFFERENT.
TRENDED TOWARD THE HPC DATA TO TRY AND GET AN AVERAGE SOLUTION OUT
OF THE MESS.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WARNING FROM 9 PM THIS EVENING TO 9 AM AKST
     SATURDAY FOR AKZ026-029.
         STRONG WIND FROM 9 PM AKST THIS EVENING THROUGH LATE TONIGHT FOR
     AKZ027.
         WINTER WEATHER ADVISORY UNTIL 9 AM AKST SATURDAY FOR AKZ020-025.
         WINTER STORM WARNING UNTIL 9 AM AKST SATURDAY FOR AKZ019-021-022.
         STRONG WIND FROM MIDNIGHT AKST TONIGHT THROUGH LATE TONIGHT FOR
     AKZ028.
MARINE...GALE WARNING FOR PKZ012-036-041.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-022-031>035-042-043-051-
     052.

&&

RWT/EAL