Area Forecast Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
000
FXAK67 PAJK 181300
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
5 AM AKDT THU SEP 18 2014

.SHORT TERM...THE COMPLEX GALE-FORCE DEEPENING LOW CONTINUES TO
CRANK UP OVER THE CENTRAL GULF AT THE MOMENT...WITH IR IMAGERY
INDICATING STRONG ROTATION AND SOON TARGETING THE PANHANDLE, A
STRENGTHENING FRONTAL BAND IS APPROACHING THE SE AK COASTLINE AND
SOME CONVECTION EVIDENT OVER WATER ON ITS WEST SIDE. THE GFS 00Z
RUN WAS A BIT STRONGER ON THE SURFACE LOW THROUGH FRIDAY MORNING
THAN THE 00Z NAM BUT THE 06Z NAM HAS NOW COME AROUND TO THE CURRENT
MODEL CONSENSUS. THE FIRST SURFACE LOW IN THE SYSTEM IS OVER THE
NORTHWEST MOVING SLOWLY NORTHWARD AND IS SPREADING STRONG WINDS AND
RAIN THURSDAY INTO THE ENTIRE PANHANDLE AS ASSOCIATED FRONT
APPROACHES THE COAST. A 60+ KT WSW ORIENTED 850 JET IS ON THE SOUTH
SIDE OF THE LOW MOVING EASTWARD WHILE ANOTHER COMPACT JET IS
OFFSHORE NEAR YAKUTAT...MOVING SLOWLY NORTHWARD. THE ORGANIZED 850
LOW STRENGTHENS EARLY IN THE PERIOD OVER THE CENTRAL GULF AND IS
GENERALLY STRONGER ON THE 06Z NAM/GFS THAN PREVIOUS RUNS. THE
SOUTHERN JET IMPACTS LAND ABOUT 09Z FRI OVER THE CENTRAL/SOUTHERN
PANHANDLE AND THAT IS WHEN VERY STRONG WINDS WILL INITIATE INLAND
FOR EXPOSED AND WELL-ORIENTED AREAS FOR THE SOUTH AND CENTRAL
PANHANDLE PORTIONS. MEANWHILE APPEARS THAT RAIN TOTALS WILL BE
1-2.5 INCHES OVER PORTIONS OF THE NORTHERN COAST BY FRIDAY
MIDDAY...WITH SIGNIFICANT BUT LESSER AMOUNTS ELSEWHERE. THERE IS
SOME CONCERN WITH RIVERS IN THE CENTRAL/NORTHERN PANHANDLE BUT FEEL
THAT RAIN RATES WILL NOT OVERCOME THE CURRENT RELATIVELY LOW STAGE
IN THE DRAINAGES. APPEARS THAT THIS SYSTEM IS MORE FALL-LIKE AND
DOES NOT HAVE A SUBTROPICAL CONNECTION. THE LOW WEAKENS AFTER ABOUT
12Z FRI BUT MOIST STRONG SW FLOW ALOFT CONTINUES. THE SECOND MAJOR
LOW MOVES IN FROM THE SOUTH AFTER THIS PERIOD AND IS JUST OFFSHORE
OF THE SOUTHERN PANHANDLE 12Z SAT...ADDRESSED BY LONG TERM
FORECASTER BELOW.

GALES COVER MOST OF THE ENTIRE OUTER WATERS REGION THROUGH EARLY
FRI WITH SOME ZONES DECREASING TO ADVISORIES LATE THU NIGHT.
INLAND...CHANNELS BEGIN WITH WIDESPREAD ADVISORIES GOING TO GALES
IN CLARENCE STRAIT LATER TODAY. MEANWHILE PUBLIC ZONES HAVE STRONG
WIND WORDING FOR THE SOUTHERN PANHANDLE AND THE SITKA ZONE LATER
TODAY AND FOR STEPHENS PASSAGE/JUNEAU AREA TONIGHT. WE MADE MINOR
CHANGES TO PREVIOUS FORECAST FOR LOCAL WIND INCREASES AND A FEW
TEMPERATURE ADJUSTMENTS AS WELL AS ADD HIGHLIGHTS FOR THE APPROPO
AREAS IN MARINE AND PUBLIC ZONES THROUGH TONIGHT. FORECAST
CONFIDENCE A BIT ABOVE AVERAGE FOR THE PERIOD WITH A GENERAL BLEND
MOSTLY TO THE LATEST GFS/ECMWF/NAM CONTINUING.

.LONG TERM...UPPER SW JET MAKES LANDFALL AROUND PRINCE RUPERT B.C.
ON FRI MORNING. AFTER THAT ALL 18/00Z OPS MODELS AGREE THAT THE JET
WILL BACK OVER THE PANHANDLE BECOMING SSW OVER YAKUTAT BY 12Z SAT.
NATURALLY THIS IS A WET PATTERN...BUT THE FORECAST PROBLEM WILL BE
A SERIES OF WAVES (SECONDARY LOW PRESSURE CENTERS UP TO GALE FORCE)
THAT DEVELOP TO THE SW AND ROLL UP TO THE PANHANDLE COAST. CLEARLY
THE MEAN POSITION OF THE UPPER TROUGH WILL BE ALONG 155W BY SAT
MORNING THEN LOOK FOR THE UPPER TROF TO SLOWLY NEGATIVELY TILT
(AXIS ANGLE TOWARD THE SE) AROUND 145W BY SUN. THAT PATTERN
SUGGESTS THAT ALL WAVES THAT DEVELOP AND MOVE INTO THE EASTERN GULF
WILL RECURVE BACK INTO THE CENTRAL GULF WITH TIME. OUR WIND
FORECASTS WILL HAVE TO DEAL WITH TIMING AND STRENGTH OF THESE LOWS
AND YOU CAN REALLY SEE THE OPS MODELS INCLUDING THE 06Z RUNS
DIVERGE ON THESE WAVES BY SUNDAY. SO BANK ON WET WITH MODERATE
TEMPS BUT CONFIDENCE LOW ON THE WINDS SUNDAY AND BEYOND. RAINFALL
AMOUNTS DO NOT APPEAR EXTREME FOR THE LONG RANGE AT THIS TIME.
FORECASTS FOR DAYS 5-8 REMAIN UNCHANGED AND WPC GUIDANCE WAS USED
BY THE DAY SHIFT ON THESE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM 10 AM THIS MORNING TO 4 PM AKDT THIS
AFTERNOON FOR AKZ023-027. STRONG WIND FROM LATE TONIGHT THROUGH
FRIDAY MORNING FOR AKZ025. STRONG WIND FROM 10 AM AKDT THIS MORNING
THROUGH THIS EVENING FOR AKZ028.

MARINE...GALE WARNING PKZ022-033-036-041>043-051-052.
         SMALL CRAFT ADVISORY PKZ011>013-021-031-032-034-035-053.
&&
$$
DAW/JC

VISIT US AT HTTP://WWW.WEATHER.GOV/JUNEAU




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.