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000
FXAK67 PAJK 312327
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
327 PM AKDT TUE MAR 31 2015

.SHORT TERM...AFTERNOON SATELLITE IMAGE REVEALS A WEAKENING
LOW...ABOUT 1001 MB...OVER THE EASTERN GULF WITH A TROUGH
STRETCHING SOUTHEASTWARD FROM THE LOW CENTER TO NEAR HAIDA GWAII AND
A WEAK RIDGE OF HIGH PRESSURE BUILDS ACROSS THE SOUTHERN
PANHANDLE. LARGE AREA OF RAIN SHOWERS WRAPPING AROUND THE LOW
OVER THE OPEN OCEAN. BETWEEN THE RIDGE AND THE LOW...SOUTHERLY
ONSHORE FLOW 10 TO 15 MPH PREVAIL OVER THE PANHANDLE WITH SMALL
CRAFT LEVEL WINDS ACROSS NORTHERN LYNN CANAL. ACROSS THE OUTER
WATERS...SOUTH TO SOUTHWEST WINDS AROUND 15 KNOTS PREVAIL WITH
ROUGH SMALL CRAFT LEVEL SEAS 8 TO 12 FEET DUE TO LONG PERIOD
SOUTHWEST SWELLS. AFTERNOON TEMPERATURES RANGE IN THE LOWER TO MID
40S.

MODELS REMAIN IN GENERAL AGREEMENT FOR THE WEAKENING LOW IN THE
EASTERN GULF THIS EVENING DISSIPATES BY EARLY WEDNESDAY MORNING AS
THE RIDGE OF HIGH PRESSURE CONTINUES TO BUILD OVER THE PANHANDLE
THROUGH LATE WEDNESDAY. A DEVELOPING LOW IN THE WESTERN GULF ON
WEDNESDAY AFTERNOON WILL MOVE EASTWARD AND PUSH THE RIDGE A LITTLE
TO THE EAST. REFRESHED THE INHERITED FORECAST WITH THE GFS AND NAM
FOR THEIR GOOD CONSENSUS.

AS THE RIDGE CONTINUES TO BUILD...THE SMALL CRAFT LEVEL SOUTHERLY
WINDS LATE THIS AFTERNOON OVER NORTHERN LYNN CANAL WILL DIMINISH
THIS EVENING. EXPECT NO SMALL CRAFT LEVEL WINDS ACROSS THE OUTER
WATERS...BUT THE ROUGH SEAS WILL REMAIN THROUGH WEDNESDAY DUE TO
SWELLS. A WEAK UPPER LEVEL SHORTWAVE TROUGH ACROSS SOUTHEAST
ALASKA WILL CONTINUE TO PRODUCE SCATTERED TO NUMEROUS RAIN SHOWERS
ON AND OFF BASES TONIGHT AND WEDNESDAY. DUE TO ONGOING RAIN
SHOWERS AND CLOUD COVER...EXPECT SMALL DIURNAL TEMPERATURE
FLUCTUATIONS WITH OVERNIGHT LOWS MOSTLY IN THE MID TO UPPER 30S
AND WEDNESDAY HIGHS IN THE MID 40S.

.LONG TERM...AFTER A DAY OF RELATIVE AGREEMENT IN THE LONG RANGE
IN YESTERDAY`S AM PACKAGE...WE RETURN TO GENERAL MODEL
DISAGREEMENT AFTER 4-5 DAYS IN TODAY`S PACKAGE. MODERATE FRONT
APPROACHING THE COASTLINE AT 03Z THURS IS BEING PUSHED BY UPPER
CLOSED LOW BARGING INTO THE CENTRAL GULF WITH 1000 MB LOW SURFACE
REFLECTION. THE SURFACE LOW...A TWEAK FASTER ON THE NEW MODEL
UPDATES...SLOWS RAPIDLY AFTER ABOUT 09Z AND THEN TAKES A TURN TO
THE SOUTHEAST AS IT BEGINS TO SLOWLY WEAKEN LATE ON THU. FRONT`S
MAIN IMPACT WILL BE A MODERATE EAST-WEST PRESSURE GRADIENT AND SCA-
LEVEL SE WINDS OVER MOSTLY THE SOUTHERN INNER CHANNELS DURING THE
DAY ON FRI WHILE MUCH OF THE ADJACENT OUTER WATERS WILL HAVE WINDS
IN VICINITY OF 30KT SUSTAINED FOR A PERIOD EARLY ON THURSDAY
BEFORE THE WEAKENING TAKES OVER. THIS INCLUDES A BRIEF BARRIER JET
ENHANCEMENT OVER THE NORTHWESTERN MARINE AREA. INLAND/COASTAL WINDS
WILL LIKELY BE SUB- STRONG WIND LEVEL THROUGH THE EVENT. MEANWHILE ON
THU MODERATE RAIN WILL SPREAD INTO THE SOUTHERN HALF OF THE
PANHANDLE WHILE LIGHTER PRECIP WILL COVER MUCH OF THE NORTH. WITH
THE NAM AMOUNTS APPEARING TO BE OVERDONE STILL HAVE TOTAL VALUES
WELL OVER AN INCH TO 2 INCHES OVER FAVORABLE AREAS OF THE SOUTH.
EC/NAM COMBO UTILIZED FOR MUCH OF THESE EARLY UPDATES THOUGH MODEL
DIFFERENCES WERE MINOR. THESE INCLUDED BUMPING HI TEMPS UPWARDS ON
THU BY A COUPLE DEGREES F. THE LOW IS SLOW TO MOVE OUT TO THE
SOUTHEAST ON FRI AND SHOWERS APPEAR LIKELY TO LINGER OVER MOSTLY
THE SOUTHERN HALF OF THE PANHANDLE...ESPECIALLY IF THE PERSISTENT
RETENTION OF ENERGY TO THE SOUTH ADVERTISED BY THE GFS VERIFIES.

SATURDAY APPEARS TO BE POTENTIALLY MOSTLY DRY FOR ALL BUT SOUTHERN
AREAS ON THE CURRENT GUIDANCE AS UPPER RIDGING GENERALLY TAKES
OVER THE GULF...HOWEVER THIS IS WHERE MODEL GUIDANCE BEGINS TO
DIVERGE  SIGNIFICANTLY. THE EC BRINGS A MODERATE WAVE
SOUTHEASTWARD THROUGH THE PANHANDLE WITHIN THE NW FLOW
ALOFT SUN/SUN PM...ALTHOUGH WEAKER THAN PREVIOUS RUNS. THE GEM
SOLUTION IS FOR A TRACK SOUTHEASTWARD THROUGH THE CENTRAL GULF
WITH A STRONGER WAVE. YET ANOTHER SOLUTION IS THE GFS...WHICH
SHOWS A WEAKENING WAVE AND FRONT MOVING INTO THE PANHANDLE FROM
THE WNW BY SUNDAY NIGHT AS STRONG TROUGHING BUILDS INTO THE
ALEUTIANS. THE LATTER IS THE ONE COMMON GENERAL THREAD AMONGST ALL
OF THE GUIDANCE... THE TIMING IS MODEL DEPENDENT BUT GENERALLY
FASTER THAN PREVIOUS RUNS. AN ENTRENCHED TROUGH SEEMS LIKELY BY
MON PM/TUES. ANYWAYS, THE DETAILS OF THE LATE WEEKEND/MONDAY WAVE
ARE THUS STILL UP IN THE AIR. GIVEN THE MODEL TEMPS PREDICTED FOR
LATE WEEKEND...SNOW IS STILL A THREAT OVER THE NORTHERN 1/3 OF THE
PANHANDLE OR SO ALTHOUGH THE POTENTIAL OF AN INTERIOR AIR SOURCE
SEEMS TO BE WANING AT THIS POINT. THUS ANY SNOW THAT DOES OCCUR
WOULD LIKELY BE BRIEF, ESPECIALLY WITH THE CONTINUING LACK OF SNOW
COVER INLAND BELOW A COUPLE THOUSAND FEET IN ELEVATION. WENT WITH
WPC GRIDS FROM DAY 5 ONWARDS WITH THE AMOUNT OF UNCERTAINTY
PRESENT. THESE GRIDS WERE BASED ON A NAEFS/GEM COMBO WITH NO INPUT
FROM THE EC UPDATES.


&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043.

&&

$$

AHN/WESLEY

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