Small Craft Advisory 718, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
552 AM AKST MON NOV 26 2012

.SHORT TERM...SATELLITE IMAGERY THIS MORNING SHOWING DOUBLE LOBE
LOW PRESSURE SYSTEM WITH CENTERS LOCATED NEAR 56N 148W AND 50N
150W. WEATHER FRONT EXTENDING FROM THIS SYSTEM EXTENDS ACROSS THE
AK GULF OVER THE PANHANDLE ALONG A CORRIDOR FROM ELFIN COVE TO
JUNEAU. ARCTIC HIGH PRESSURE SYSTEM REMAINS OVER THE YUKON WITH A
WEAK LOW OVER BRITISH COLUMBIA. AS THE DAY PROGRESSES THE DOUBLE
CENTER LOW WILL BE ABSORBED BY A LOW MOVING INTO THE NORTH PACIFIC.
THE ASSOCIATED WEATHER FRONT WILL DISSIPATE THROUGH THE MORNING
WHILE THE HIGH OVER THE YUKON WILL WEAKEN AS IT TRACKS TO THE EAST.

PRECIPITATION OVER THE PANHANDLE THROUGH MONDAY MORNING COULD BE
BROKEN DOWN TO RAIN EVENT OVER THE SOUTHERN AND COASTAL
PANHANDLE...HEAVY SNOW EVENT FOR THE CENTRAL PANHANDLE AND LIMITED
SNOW FOR THE FAR NORTHERN PANHANDLE. THE RAIN SNOW LINE DRAWN FROM
SITKA AND ALONG FREDERICK SOUND WITH WARM AIR ADVECTION FROM THE
FRONT STACKED AGAINST THE ARCTIC AIR FROM THE YUKON HIGH. DAY TIME
HIGHS NORTH OF THIS LINE WILL BE IN THE UPPER 20S TO LOW 30S WITH
TEMPS IN THE UPPER 30S TO LOW 40S TO THE SOUTH. EXPECTING
OVERNIGHT LOWS TO BE A BIT COOLER TONIGHT WITHOUT THE WAA OVER
THE SOUTHERN PANHANDLE. PRECIPITATION OVER THE ENTIRE PANHANDLE
WILL DIMINISH THROUGH THE AFTERNOON WITH LINGERING SHOWER ACTIVITY
IN THE EVENING THEN DRY WEATHER OVERNIGHT. THIS DRYING TREND WITH
CLEARING SKIES COULD DROP OVERNIGHT LOWS A BIT MORE DUE TO
RADIATIONAL COOLING.

TWO SEPARATE FEATURES WERE INVOLVED IN THE SNOW EVENT THAT
STARTED SUNDAY MORNING. FIRST HEAVY SNOW SHOWERS ASSOCIATED WITH A
500 MB VORT MAX MOVING OVER THE CENTRAL PANHANDLE SUNDAY MORNING
THEN DIMINISHED IN THE AFTERNOON. STEADY SNOW CONTINUED THROUGH
THE EVENING AND OVERNIGHT AS DEFORMATION BAND MOVED OVER THE AREA.
THROUGH THE MORNING EXPECTING SNOW TO INTENSIFY AT TIMES BEFORE
DIMINISHING THROUGH NOON. KEPT WINTER WEATHER ADVISORIES FOR THE
GUSTAVUS AND JUNEAU AREAS THROUGH NOON. THE JUNEAU FORECAST OFFICE
RECEIVED 5.5 INCHES OF SNOW THROUGH MIDNIGHT WITH THE JUNEAU
AIRPORT RECEIVING 5.2 INCHES. EXPECTING AN ADDITIONAL 1 TO 3
INCHES FOR THESE AREAS UNDER THE DEFORMATION BAND FOR STORM TOTAL
ACCUMULATION OF 5 TO 8 INCHES. HOWEVER SOME INDICATION OF THE
DEFORMATION BAND WEAKENING A BIT EARLIER SO ADDITIONAL SNOW TOTALS
MAY BE A BIT LESS.

WITH THE WEAKENING FRONT WINDS OVER THE AK GULF WILL DIMINISH
THROUGH THE DAY WITH EASTERLY SMALL CRAFT WINDS OVER THE NORTHERN
COASTAL WATERS DROPPING TO 15 TO 20 KT. FOR THE NORTHERN INNER
CHANNELS THE PRESSURE GRADIENT CAUSING STRONGER WINDS WILL WEAKEN
AS THE YUKON HIGH MOVES EAST. STRONGEST WINDS ARE OCCURRING OVER
NORTHERN LYNN CANAL WITH GALE FORCE THIS MORNING WHICH WILL
SUBSIDE TO SMALL CRAFT THIS AFTERNOON. FOR THE REST OF THE
PANHANDLE EAST TO NORTHEAST WINDS WILL SUBSIDE THROUGH THE DAY
WITH LIGHTER WINDS EXPECTED TONIGHT.

MODELS WERE IN GOOD CONSENSUS WITH THE SYNOPTIC PRESSURE PATTERN.
HAD SOME BETTER AGREEMENT BETWEEN THE NAM AND ECMWF COMPARED TO
THE GFS. MOST NEW MODEL RUNS DID DROP WINDS IN THE AK GULF OFF A
BIT FASTER THAN PREVIOUS RUNS. LIKED THE ECMWF BIT MORE THAN THE
NAM COMPARING UPPER LEVEL RH TO WATER VAPOR SATELLITE. USED A
BLEND OF NAM/ECMWF WITH INHERITED GRIDS. MAIN FORECAST ISSUE IS
THE ADDITIONAL SNOW AMOUNTS FROM THE DEFORMATION BAND AND
NORTHERLY AND SOUTHERLY EXTENT OF PRECIP FROM THIS FEATURE.
EXPECTING SNOW SHOWERS OVER YAKUTAT TO SUBSIDE BUT IF 500 MB VORT
MAX TO THE SOUTH DOES NOT EXIT AS EXPECTED SHOWER ACTIVITY MAY
LINGER A BIT LONGER. WHILE EXPECTING SNOW TO INTENSIFY THIS
MORNING UNDER THE DEFORMATION BAND...IF THE FEATURE SHEARS APART
FASTER MAY ONLY SEE AN ADDITIONAL INCH OF SNOW. AS WITH PREVIOUS
NIGHTS FORECAST CONFIDENCE IS HIGH FOR THE OVERALL SYNOPTIC
PATTERN BUT LOW FOR SMALL SCALE FEATURES AND ESPECIALLY SNOW
AMOUNTS.

&&

.LONG TERM.../TUESDAY THROUGH SUNDAY/...
MAIN FOCUS FOR THE EXTENDED RANGE FORECAST WAS ON THE WINDS
EXPECTED. HIGH PRESSURE OVER THE YUKON AND NORTHERN B.C. ALONG WITH
A LOW MOVING INTO THE FAR SE GULF WILL CAUSE NORTH WINDS TO INCREASE
TUESDAY NIGHT THROUGH WEDNESDAY. THE SET UP BECOMES VERY FAVORABLE
FOR A TAKU WIND EVENT DURING THIS TIME FRAME. THE NORTH WINDS
THROUGH LYNN CANAL WILL CAUSE COLDER AIR AT THE SURFACE AND AN
INVERSION TO DEVELOP AND STRENGTHEN. CROSS BARRIER FLOW OVER SALISBURY RIDGE
INCREASES OUT OF THE NE WHILE A CRITICAL LEVEL IS APPARENT AT ABOUT
600MB WITH REVERSE FLOW ABOVE. HAVE OPTED TO NOT ISSUE A HIGH WIND
WATCH AT THIS TIME AS IT IS MORE THAN 36HRS AWAY AND THERE IS
ALREADY AN ADVISORY IN EFFECT FOR THE JUNEAU AREA. CURRENTLY HAVE
GUSTS OF 40MPH MENTIONED FOR TUESDAY NIGHT AND GUSTS OF 50MPH FOR
WEDNESDAY FOR DOWNTOWN JUNEAU AND DOUGLAS.

ELSEWHERE THE WINDS WILL ALSO BE STRONG SIMPLY DUE TO THE TIGHT
PRESSURE GRADIENT. HAVE CONTINUED THE STORM FORCE WINDS FOR NORTHERN
LYNN CANAL WEDNESDAY AND THURSDAY. AS A RESULT CAN EXPECT EQUALLY
GUSTY WINDS OUT OF  THE NORTH IN SKAGWAY AND DOWNTOWN HAINES NEAR LYNN
CANAL PRETTY MUCH ALL WEEK.

AS THE LOW DRAWS NEAR CHANCES OF PRECIP WILL INCREASE...MAINLY OVER
THE SOUTHERN HALF OF THE PANHANDLE. THE OFFSHORE COMPONENT OF THE
MID LEVEL FLOW AND THE DRY NORTH WINDS WILL KEEP QPF TO A MINIMUM
OVER THE NORTHERN HALF OF THE AREA WITH PARTLY CLOUDY SKIES FOR A
GOOD PORTION OF THE FORECAST PERIOD.

OVERALL MODELS WERE AND GOOD AGREEMENT AND MINOR TWEAKS MADE TO THE
FORECAST OR INCORPORATING NEW MODELS DID NOT MAKE BIG CHANGES FROM
THE INHERITED FORECAST. CONFIDENCE IS AVERAGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY UNTIL NOON AKST TODAY FOR AKZ020-025.
MARINE...GALE WARNING FOR PKZ012.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-022-043-051>053.

&&

PRB/HANNON

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
1219 PM AKST MON NOV 26 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0900 AM     SNOW             GUSTAVUS                58.41N 135.80W
11/26/2012  M3.4 INCH                           AK   CO-OP OBSERVER

            GUSTAVUS-SNOWFALL FROM 5 AM SUNDAY TO 530 AM MONDAY

0900 AM     SNOW             JUNEAU                  58.30N 134.41W
11/26/2012  M4.0 INCH                           AK   CO-OP OBSERVER

            JUNEAU-DOUGLAS WWTP-SNOWFALL FROM 8 AM SUNDAY TO 8 AM
            MONDAY.

0900 AM     SNOW             JUNEAU                  58.30N 134.41W
11/26/2012  M3.9 INCH                           AK   OFFICIAL NWS OBS

            JUNEAU AIRPORT-SNOWFALL FROM 9 AM SUNDAY TO 9 AM MONDAY.

0900 AM     SNOW             JUNEAU                  58.30N 134.41W
11/26/2012  M4.3 INCH                           AK   NWS EMPLOYEE

            WFO JUNEAU-SNOWFALL FROM 9 AM SUNDAY TO 9 AM MONDAY.

&&

KAV