Area Forecast Discussion
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FXAK67 PAJK 080018
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
318 PM AKST SUN FEB 7 2016

.SHORT TERM...PROMINENT UPPER-LEVEL RIDGE IS POSITIONED OVER THE W
COAST OF N AMERICA SUN AFTERNOON...WHILE AN ELONGATED TROUGH
RESIDES FROM THE ALEUTIANS S OVER THE NCNTRL PAC. IN BETWEEN THESE
TWO FEATURES...A LONG NARROW RIVER OF SUBTROPICAL MOISTURE WAS
SPREADING N WITHIN A ZONE OF DEEP-LAYER SSWLY FLOW. MODEL GUIDANCE
SHOWS A MIDLEVEL IMPULSE EMBEDDED WITHIN THE MERIDIONAL FLOW
REGIME PROGRESSING N ACROSS THE GULF MON AFTERNOON/EVENING. THIS
FEATURE IS FORECAST TO BE ACCOMPANIED BY A SURFACE
WAVE...HOWEVER...DETERMINISTIC SOLUTIONS ARE DRAMATICALLY
DIFFERENT IN HOW THE WAVE EVOLVES. THE ECMWF AND CANADIAN MODELS
SPIN UP A RELATIVELY DEEP LOW OVER THE ERN GULF THAT TRACKS
TOWARD THE NERN GULF COAST BY MON EVENING. ON THE OTHER HAND...THE
NAM AND GFS DEPICT A SIGNIFICANTLY WEAKER WAVE THAT GENERALLY
REMAINS WELL OFFSHORE. GIVEN THE LARGE MODEL SPREAD...TOOK AN
ENSEMBLE APPROACH THAT WAS WEIGHTED SLIGHTLY HEAVIER TOWARD THE
ECMWF/CANADIAN...WHICH YIELDS SMALL CRAFT TO LOCALIZED GALE FORCE
SSELYS MON AFTERNOON OVER THE SERN GULF AND SRN INNER CHANNELS.
STAY TUNED...AS MAJOR ADJUSTMENTS TO THE WIND FORECAST ARE
POSSIBLE AS CONFIDENCE IN SURFACE LOW EVOLUTION BECOMES MORE
CLEAR DURING THE NEXT 24 HRS.

IN THE MEAN TIME...DEEP-LAYER ASCENT IS FORECAST TO WEAKEN THIS
AFTERNOON INTO TONIGHT FROM ROUGHLY KLAWOCK NWD TO
JUNEAU...HAINES...AND SKAGWAY. THIS WILL CAUSE LINGERING SHOWERS
TO DISSIPATE...AND PERHAPS AID IN PATCHY FOG OVER THE CNTRL
PANHANDLE AS WINDS WEAKEN AND SOME BREAKS IN MIDLEVEL CLOUDS
DEVELOP. ELSEWHERE...SNOW/RAIN SHOWERS WILL CONTINUE TO BE
FOCUSED OVER AKZ017/YAKUTAT DUE TO PERSISTENT SLY FLOW IMPINGING
ON THE SAINT ELIAS MOUNTAINS. SLIGHT CHANCE OF THUNDERSTORMS WILL
ALSO EXIST OVER THE WRN AND NRN GULF SUN EVENING DUE TO THE
PRESENCE OF MODEST BUOYANCY AND LOCALLY AUGMENTED ASCENT
ASSOCIATED WITH THE PASSAGE OF WEAK UPPER IMPULSES.

FARTHER S...MOIST SLY STREAM OF AIR WILL IMPACT THE SRN PANHANDLE
THROUGHOUT THE SHORT TERM PERIOD. MODEL GUIDANCE SHOWS PW VALUES
NEAR 0.95 INCH /3 STANDARD DEVIATIONS ABOVE CLIMO/ REMAINING
STATIONARY OVER THE FAR SRN PANHANDLE FROM 06Z MON THROUGH 06Z
TUE. THIS MOISTURE COMBINED WITH ENHANCED FLUX VIA A 30-50 KT LOW-
LEVEL SSWLY JET WILL MAKE LOCALLY HEAVY RAIN PROBABLE FOR
COMMUNITIES SUCH AS KETCHIKAN...HYDABURG...AND KLAWOCK. IN
ADDITION...3 TO 7 INCHES OF SNOW WILL BE POSSIBLE FOR HYDER...WITH
AMOUNTS FALLING SHORT OF ADVISORY LEVEL DUE TO RELATIVELY WARM
SURFACE TEMPERATURES/DEWPOINTS.

FINALLY...A WARM AIRMASS /CHARACTERIZED BY 925 MB TEMPERATURES
NEAR 5 C OVER THE SRN PANHANDLE...TO AROUND 0 C OVER THE NRN
PANHANDLE/ WILL SPREAD NWD ON MON AS PREVIOUSLY MENTIONED WAVE
MOVES ACROSS THE GULF. THIS SHOULD YIELD HIGH TEMPERATURES
MODERATING THROUGH THE 30S AND INTO THE LOW TO MID 40S. INHERITED
TEMPERATURE GRIDS CAPTURED THIS SCENARIO WELL...FEW CHANGES WERE
NECESSARY. PRESSURE GRIDS WERE NUDGED TOWARD AN ECMWF/CANADIAN/NAM
BLEND...WITH AN ENSEMBLE APPROACH UTILIZED FOR UPDATES TO THE
REMAINDER OF THE GRIDS AS WELL.

.LONG TERM...MAJOR UPPER LOW S OF THE EASTERN ALEUTIANS ON MON
NITE AS THE WEST COAST RIDGE MENTIONED ABOVE PERSISTS...AND THE
AXIS OF THAT RIDGE IS TOO FAR INLAND FOR A HOPE OF DRYING. THIS
ALLOWS WARM MOIST ONSHORE FLOW ALOFT. A SECONDARY SYSTEM DEVELOPS
OVER THE OFFSHORE WATERS AS A WAVE ON THE FRONT BY MONDAY NIGHT AS
MENTIONED ABOVE AND THE CENTER MOVES TO YAKUTAT NO LATER THAN
EARLY TUE. TIMING IS DIFFICULT ON THIS LOW CENTER. NEXT WE HAVE
ANOTHER LOW THAT DEVELOPS NEAR 48N 142W TUE AFTERNOON WHICH
ALLOWS A WEAK UPPER RIDGE TO MOVE OVER THE PANHANDLE...BUT THERE
IS STILL MOISTURE IN THE UPPER RIDGE. USED THE 07/12Z ECMWF FOR
THE FORECASTS UP TO WED BUT AM SKEPTICAL OF THE TIMING. HIGH
CONFIDENCE IN WET AND WARM BUT TIMING OF WIND IS SKETCHY. USED WPC
FORECASTS FOR DAYS 4-8 WHICH SEEMED REASONABLE, BUT NOT GOOD NEWS
FOR DRYING. ONSHORE FLOW ALOFT OVER AND OVER AND OVER AND OVER DAY
BY DAY. CONFIDENCE IN THE 4-8 FORECAST MODERATE TO HIGH BECAUSE
IT REPEATS THE AWFUL PATTERN THAT WE`VE BEEN STUCK IN.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ036.
     SMALL CRAFT ADVISORY FOR PKZ022-031-033>035-041>043-051>053.
&&

$$

GARNER/JC

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