Gale Warning 383, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
246 PM AKST TUE NOV 29 2011

.SHORT TERM...WEAK SHORTWAVE TROF WILL MOVE EWD ACROSS THE NRN
AREA THIS EVENING. UPPER RIDGE WILL BUILD IN STRONGLY OVER THE
FAR ERN GULF AND SE AK LATER TONIGHT INTO WED MORNING...THEN BE
JUST E OF THE AREA BY LATE WED AFTERNOON. OCCLUDED FRONT WILL
MOVE E INTO THE CENTRAL GULF BY WED AFTERNOON. USED A BLEND OF
THE 12Z NAM AND PREVIOUS GRIDS FOR TONIGHT AND WED...MAINLY TO
START A TREND OF SPEEDING UP THE EWD MOVEMENT OF THE FRONT.

 MAIN FORECAST CONCERNS WILL BE WIND...AND POSSIBLE DRAINAGE
FLOODING AND/OR SNOW LOAD ISSUES. AS FOR WINDS...AREA WILL BE
UNDER MODERATE WARM ADVECTION THRU A DEEP LAYER...SO STRONG WINDS
ALOFT WILL NOT TRANSLATE AS STRONGLY DOWNWARD AS THEY NORMALLY
DO. STILL...TERRAIN EFFECTS CAUSED BY CROSS MTN FLOW WILL ENHANCE
SLY WINDS IN LYNN CANAL AND PAGY AREA ESPECIALLY WED AFTERNOON.
THE 700 MB WINDS OF SW 70+KT WILL HELP AMPLIFY A LEE TROF NEAR
PAGY SO THEY WILL END UP WITH STRONGER WINDS THAN THE MODEL
GRADIENT SUGGESTS. PRESSURE GRADIENT FURTHER S WILL BE STRONG
ENOUGH FOR WINDS TO REACH STRONG WIND LEVELS DURING WED AFTERNOON
TO THE NW OF THE FREDERICK SOUND AREA EXCEPT PAGN.WILL PUT OUT
STRONG WIND HEADLINES FOR THE NRN ZONES...EXCEPT PAGN AND
PAHN...AND FOR THE PASI AND PAEL COASTAL ZONES STARTING AT 21Z
WED. WILL HAVE GALES FOR LYNN CANAL AND STEPHENS PASSAGE ON INNER
CHANNELS...WITH GALES FOR MUCH OF THE ERN GULF WATERS. ELSEWHERE
WILL HAVE SCA GOING.

 EXPECT PRECIP TO DEVELOP OVER THE PAYA AREA TONIGHT...THEN REACH
THE PAHN AREA AS OVERRUNNING DEVELOPS THERE BY DAYBREAK WED.
SHOULD SEE A SLOW EWD PROGRESSION OF PRECIP...AND BY LATE WED
AFTERNOON IT SHOULD NE NW OF A PAJN-PASI LINE. THE PRECIP WILL
GET RATHER HEAVY WED AFTERNOON OVER THE NE GULF COAST. THIS WATER
WILL BE ABSORBED BY A VERY DEEP SNOWPACK...SO THERE IS POTENTIAL
FOR SNOW LOAD PROBLEMS INCREASING ON ROOFTOPS ESPECIALLY IN THE
PAYA  AREA. PRECIP SHOULD START AS SNOW IN THE PAHN AREA...BUT
EXPECT ESE FLOW TO BECOME ESTABLISHED THERE LATER WED
MORNING...WORKING ITS WAY NW THRU THE CHILKAT VALLEY BY LATE
AFTERNOON...CHANGING PRECIP OVER TO RAIN. MAY SEE 1-4 INCHES OF
NEW SNOW BEFORE CHANGING OVER TO RAIN...WITH THE MOST SNOW
EXPECTED NEAR THE CANADIAN BORDER. THE SNOW IS VERY DEEP AROUND
PAHN (4+FT) SO THE ADDITIONAL SNOW AND RAIN WILL INCREASE SNOW
LOADS THERE AS WELL. IN ADDITION...WHERE STORM DRAINS ARE COVERED
BY THE SNOW...LOCALIZED DRAINAGE FLOODING IS POSSIBLE IN THE PAHN
AND PAYA AREAS.

 OTHERWISE...WITH A LOT OF BREAKS IN THE CLOUDS EXPECTED AND
WINDS BECOMING FAIRLY LIGHT TONIGHT...SOME FOG SHOULD DEVELOP
OVER MAINLY THE INNER CHANNEL AREAS. FOG COULD BE LOCALLY DENSE
WHERE THE LARGEST BREAKS IN THE CLOUDS REMAIN. THE FOG WILL
SLOWLY DISSIPATE WED AS A COMBINATION OF INCREASED CLOUD COVER
AND WINDS HELP TO MIX OUT THE FOG.

 .LONG TERM... CONCERN IS MAJOR UPR LOW CENTER JUST S OF DUTCH
HARBOR WITH COLD AIR COMING INTO THE BACK SIDE. THIS DEVELOPING
SYSTEM WILL BUILD A STRONG RIDGE AHEAD OF IT...BUT THIS RIDGE
WILL NOT BLOCK DURING THE LONG TERM. BIG HINT ARE THE JETS
@300 HPA COMING OFF JAPAN BOTH POLAR AND SUBTROPICAL BRANCHES AS
PER ALL ANALYSES. THIS WESTERLY PUSH WILL KEEP SYSTEMS
PROGRESSIVE THRU THU...SO THAT A SW BRANCH OF THE JET WILL BE
OVER THE NORTHERN PANHANDLE BY 12Z THU AS PER ALL 29/12Z OPS
MODELS.

 FELL PRETTY GOOD ABOUT THE MODEL AGREEMENT SO FAR ON THIS SHIFT.
ALL OPS MODELS SHOW RAPIDLY MOVING UPR SHORTWAVE TROF ALG 147W AT
12Z THU AND THIS SCENARIO ACCEPTED. THIS TROF WILL HAVE MOVED
PAST THE PANHANDLE BY 00Z FRI HEADED EAST...AS THE NEXT UPR RIDGE
BUILDS OVR THE CENTRAL GULF. EXPECT UPR RIDGE AXIS ALG 140W BY
12Z FRI FOR DRY FRI DAYTIME. ALL MODELS REVIEWED AGREE THAT
ANOTHER COLD UPR LOW WILL DEVELOP OVR THE CENTRAL ALEUTIANS SAT
WHICH SLOWS DOWN OUR UPR RIDGE AND ALL THIS W TO E PROGRESSION.
BY 12Z SAT LOOK FOR A SECONDARY UPR LOW TO DEVELOP NEAR 41N 155W
WHICH WILL EVENTUALLY PUSH THE UPR RIDGE E. IT TAKES UNTIL 12Z
MON FOR THE UPR RIDGE TO GET PUSHED FAR ENUF E TO GET THE SSW UPR
LVL WIND OVR THE NORTHERN PANHANDLE FOR WET WARM ONSHORE FLOW.

 STARTED OUT WITH LITTLE CHANGE ON WED NIGHT THEN USED 12Z
AK-GFS-40 AND SREF FOR MOST OF THE EARLY GRIDS THIS SHIFT. HPC
GUIDANCE NOT USED ON SAT BUT ACCEPTED SUN & BEYOND. CONFIDENCE
HIGH THRU SAT AND MODERATE SUN & BEYOND.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM WEDNESDAY AFTERNOON THROUGH LATE
WEDNESDAY
     NIGHT FOR AKZ018-020>023-025.
MARINE...GALE WARNING FOR PKZ012-013-031-042-043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011-021-022-032>036-041.
&&

RWT/JC

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE JUNEAU AK
240 PM AKST TUE NOV 29 2011

AKZ018>022-024>026-029-301500-
TAIYA INLET AND KLONDIKE HIGHWAY-HAINES BOROUGH AND LYNN CANAL-
GLACIER BAY-EASTERN CHICHAGOF ISLAND-
SALISBURY SOUND TO CAPE FAIRWEATHER COASTAL AREA-
EASTERN BARANOF ISLAND AND SOUTHERN ADMIRALTY ISLAND-
JUNEAU BOROUGH AND NORTHERN ADMIRALTY ISLAND-
INNER CHANNELS FROM KUPREANOF ISLAND TO ETOLIN ISLAND-
MISTY FJORDS-
INCLUDING THE CITIES OF...SKAGWAY...HAINES...GUSTAVUS...HOONAH...
ELFIN COVE...PELICAN...ANGOON...JUNEAU...PETERSBURG...WRANGELL...
KAKE...HYDER
240 PM AKST TUE NOV 29 2011

...CHANGING WEATHER PATTERN FOR SOUTHEAST ALASKA MID WEEK...

WARMER TEMPERATURES, SNOW LEVELS AS HIGH AS 3000 FEET, AND RAIN
THAT WILL BE HEAVY AT TIMES WILL MOVE TO SOUTHEAST ALASKA WEDNESDAY
NIGHT AND THURSDAY. 1 TO 2 INCHES OF RAIN IS POSSIBLE ACROSS THE
AREA.

THE RAIN WILL FALL ON DEEP SNOW PACK THAT RANGES FROM 8 TO 13
INCHES IN THE JUNEAU AND PETERSBURG AREAS, AROUND 45 INCHES AT
ANNEX CREEK AND SNETTISHAM, TO 53 INCHES IN HAINES. INITIALLY THE
SNOW WILL ABSORB THE RAIN AND WILL LEAD TO LOCALLY VERY HIGH SNOW
LOADS ON ROOF TOPS, BOATS AND OTHER STRUCTURES.

AS TEMPERATURES CONTINUE TO RISE, SNOW MELT AND HEAVY RAIN WILL
CAUSE INCREASED RUNOFF. WITH STORM DRAINS AND DITCHES COVERED BY
SNOW AND LARGE SNOW BERMS ALONG ROADS, THERE IS THE POTENTIAL FOR
PONDING OF WATER IN LOW LYING AREAS WEDNESDAY NIGHT AND THURSDAY.
STANDING WATER ON ICY SURFACES WILL MAKE ROADS AND SIDEWALKS
EXTREMELY SLIPPERY.

ALSO, AS THE FREEZING LEVELS RISE, AVALANCHE DANGER WILL INCREASE
ALONG MOUNTAIN SLOPES UP TO AT LEAST 3000 FEET.

PERSONS IN SOUTHEAST ALASKA CAN PREPARE FOR THIS EVENT BY REMOVING
SNOW FROM STRUCTURES, BOATS, AND OTHER OBJECTS THAN CAN BE DAMAGED
BY THE EXCESSIVE WEIGHT OF WET SNOW. CLEAR STORM DRAINS AND BREACH
SNOW BERMS TO ALLOW FOR BETTER DRAINAGE.