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417
FXAK67 PAJK 211407
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
507 AM AKST FRI NOV 21 2014

.SHORT TERM...SHARP FRONTAL BOUNDARY APPROACHING FROM THE SOUTH CAUSING
STRONG WINDS AND INCREASED PRECIP IN SOUTHERN AND SOUTHWESTERN
AREAS AS EXPECTED. GUSTS UP TO 50KT OVER THE PAST COUPLE HOURS
HAVE OCCURRED AT A COUPLE LOCATIONS...HYDABURG AND METLAKATLA. THIS
BOUNDARY IS PRIMARILY FRONTAL AND NOT A DEVELOPING CLOSED LOW...SO
IMPACTS WILL BE BRIEF...WIND SHIFT WILL LIKELY BEGIN TO MAKE
LANDFALL OVER FAR SOUTHERN REACHES BY 16-18Z. THE IMPACTED ZONES
ARE CURRENTLY UNDER STRONG WIND WORDING IN ZONES. MEANWHILE WE ARE
STARTING OFF WITH GALES OFFSHORE IN 41-43 AND 51 THROUGH 15Z.
CLARENCE STRAIT ALSO IN GALE THROUGH 21Z. INSTABILITY IS CONFINED
TO WELL SOUTH OF OUR FORECAST AREA AS A FEW LIGHTNING HITS HAVE
OCCURRED AT 11Z SOUTH OF 50N. ON THE SHORT-RANGE MODELS INCLUDING
THE HIGH-RES VERSIONS...850MB SOUTHEASTERLY JET 35-50KT OVER THE
SOUTHERN/CENTRAL PANHANDLE UP INTO THE NORTHERN GULF IS ALREADY
WEAKENING BY 15Z AND DOWN TO 25-40 KT AT 18Z. WINDS SHOULD BEGIN
TO SUBSIDE BY LATE MORNING...BUT A SWITCH TO POSTFRONTAL
SOUTHWESTERLIES (10-15 KT WEAKER) FOR EXPOSED LOCATIONS IN OUR
SOUTHERNMOST ZONES 23, 25 AND 28 WILL LIKELY OCCUR PRIOR TO A
RELAXATION OF WINDS TO UNDER 20 KNOTS OR SO. WENT TO A POSTFRONTAL
SHOWERS SCENARIO FOR THE WESTERN PORTION OF THE SOUTHERN PANHANDLE
FROM 21Z ON. SOME NORTHERN AREAS WILL LIKELY SEE SOME BRIEF SNOW
AT THE BEGINNING OF THE PRECIP THIS MORNING AS PREEXISTING AIRMASS
IS DRY. HAINES IS THE CURRENT EXAMPLE. A SNOW/RAIN MIX IS LIKELY
FRIDAY NIGHT AT SEA LEVEL ON THE NORTHERN FRINGES AS WELL AS THE
HYDER VICINITY. MINOR ACCUMULATIONS EXPECTED. AFTER THE WEAKENING
SYSTEM MOVES ONSHORE, WE GO INTO A COUPLE DAYS OF MOIST SWLY
ONSHORE FLOW WITH CYCLONIC FLOW ALOFT AND GENERALLY WEAK WINDS.
WITH THE LACK OF AN ORGANIZED MARINE LOW...SNOWFALL MAY END UP A
BIT ENHANCED FOR THE NORTHERN AND EASTERN PORTIONS LATE TONIGHT
THAN WHAT MODEL GUIDANCE SUGGESTS AS CONTINENTAL AIR WONT BE
PUSHED INLAND AFTER A BRIEF PERIOD TODAY. ANOTHER POTENTIAL
SCENARIO IS SOME ISOLATED FOG POSSIBLE LATE TONIGHT AND EARLY
TOMORROW FOR ANY AREAS THAT HAVE PARTIAL CLEARING...NOT LIKELY BUT
WORTH KEEPING AN EYE ON.

FOR THE GRIDS, UPDATED QPF FIELDS WITH SLIGHT ADJUSTMENTS PER
NAM/EC GUIDANCE FOR LATER TODAY AND TONIGHT AND TWEAKED THE
PREDICTED WIND FIELDS ALONG THE COASTLINE FOR BETTER CONTINUITY
ACCORDING TO THE PRESSURE FIELD. MODEL CONSISTENCY HAS LED TO VERY
GOOD AGREEMENT IN THE FIELDS FOR SATURDAY MORNING WITH ONLY MINOR
ADJUSTMENTS TO PREVIOUS FORECASTS.

.LONG TERM...UPPER LOW CURRENTLY POSITIONED OVER THE SWRN TIP OF
THE AK PENINSULA IS FORECAST TO REMAIN QUASI-STATIONARY THROUGH
MON...AND THEN MOVE EWD ACROSS THE NRN GULF ON TUE BEFORE SHEARING
APART/WEAKENING OVER THE PANHANDLE TUE NIGHT INTO WED. IN THE
MEANTIME...COLD MIDLEVEL AIRMASS /H5 TEMPERATURES AROUND -33C/
WILL BE PRESENT FROM THE GULF NWWD ACROSS THE PANHANDLE. THIS
AIRMASS COMBINED WITH PERSISTENT SWLY FLOW ALOFT WILL FAVOR
SHOWERS THROUGH THE WEEKEND.

THERE WILL ALSO BE A NON-ZERO THREAT FOR AN ISOLATED THUNDERSTORM
OVER MARINE ZONES 310...41...42...AND 43 SAT AFTERNOON/EVENING.
DID NOT INCLUDE THIS POSSIBILITY IN CURRENT FORECAST DUE TO THE
OVERALL LOW PROBABILITY...BUT WILL CONTINUE TO EVALUATE IN FUTURE
FORECASTS. NO SIGNIFICANT FRONTAL SYSTEMS ARE EXPECTED TO IMPACT
THE REGION THROUGH EARLY NEXT WEEK...AND PRESSURE GRADIENT OVER
THE INSIDE CHANNELS WILL GENERALLY BE WEAK. THUS...MARINE HAZARDS
WILL BE LIMITED TO SMALL CRAFT SEAS OVER THE OUTSIDE WATERS.

BY THE MIDDLE OF NEXT WEEK...SPREAD AMONGST DETERMINISTIC MODEL
SOLUTIONS BECOMES VERY LARGE...AS THE ECMWF DEVELOPS A STRONG LOW
OVER THE NERN PAC/SERN GULF...WHILE THE GFS FAVORS A DOMINANT
RIDGE CENTERED OVER THE GULF. AS A RESULT...FORECAST UNCERTAINTY
IS CONSIDERABLE. PATTERN DOES APPEAR TO SUPPORT A GENERAL COOLING
TREND GOING INTO NEXT WEEK...WHICH WILL YIELD INCREASING
POTENTIAL FOR LIGHT SNOW OVER THE NRN HALF OF THE PANHANDLE...AS
WELL AS HYDER.

INHERITED PRESSURE GRIDS WERE LEFT UNCHANGED THROUGH 18Z
SUN...THEN ECMWF WAS BLENDED IN WITH PREVIOUS FORECAST THROUGH 12Z
MON...AFTER WHICH WPC WAS COMBINED WITH THE 00Z GFS IN ORDER TO
MAINTAIN CONSISTENCY WITH AFC BORDER. COMBINATION OF GFS AND
ECMWF WAS USED TO REFRESH POP/QPF...THROUGH MAGNITUDE OF BOTH
FIELDS WAS DECREASED BY THE MIDDLE OF NEXT WEEK DUE TO PREVIOUSLY
MENTIONED MODEL SPREAD. WEATHER GRIDS WERE UPDATED TO REFLECT
UNSTABLE SHOWER REGIME THROUGH MON.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 9 AM AKST THIS MORNING FOR AKZ027-028.
         STRONG WIND UNTIL 6 AM AKST EARLY THIS MORNING FOR AKZ023.
MARINE...GALE WARNING FOR PKZ036-041>043-051.
         SMALL CRAFT ADVISORY FOR PKZ012-021-022-031>035-052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ053.

&&

$$

WESLEY/GARNER

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