Area Forecast Discussion
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FXAK67 PAJK 281351
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
551 AM AKDT TUE JUL 28 2015

.SHORT TERM...EARLY MORNING SATELLITE IMAGE SHOWS A WEAKENING
LOW...ABOUT 1005 MB...JUST OFF THE YAKUTAT BAY. A COLD FRONT
STRETCHING SOUTHEASTWARD FROM THE WEAKENING LOW SLOWLY MOVING EAST
ACROSS THE PANHANDLE. COOLER AIR ALOFT MOVES OVER SOUTHEAST ALASKA
AND RAIN TURNS TO SHOWERS. ALONG THE WEAK FRONTAL BOUNDARY...A BIT
OF GUSTY WINDS REPORTED. SMALL CRAFT LEVEL SOUTHERLY WINDS PERSIST
OVERNIGHT ACROSS THE NORTHERN AND CENTRAL INNER CHANNELS. LONG
PERIODS SOUTHWEST TO WEST SWELLS MAINTAIN ROUGH SMALL CRAFT LEVEL
SEAS ACROSS THE CENTRAL AND SOUTHERN OUTER WATERS. OVERNIGHT
TEMPERATURES MOSTLY IN THE LOWER TO MID 50S DUE TO EXTENSIVE
CLOUDS AND RAIN SHOWERS. NOT MUCH CHANGES OVER THE DIURNAL
TEMPERATURE FLUCTUATION DUE TO CONTINUED GLOOMY SKIES AND SHOWERS.

MODELS REMAIN IN GENERAL AGREEMENT FOR THE WEAKENING FRONTAL
PASSAGE OVER THE PANHANDLE SLOWLY DISSIPATES THROUGH LATE THIS
AFTERNOON AND A WEAK RIDGE OF HIGH PRESSURE REBUILDS OVER
SOUTHEAST ALASKA LATE TONIGHT INTO WEDNESDAY MORNING. REFRESHED
THE INHERITED FORECAST WITH THE 06Z RUN NAM12. OVERALL CHANGES
WERE SMALL AND MOSTLY COSMETIC TOUCHES FOR FINE TUNES.

AS THE FRONTAL PASSAGE WEAKENS AND DISSIPATES...RAIN SHOWERS WILL
GRADUALLY DECREASE IN COVERAGE THROUGH LATE THIS AFTERNOON. SMALL
CRAFT LEVEL WINDS OVER STEPHENS PASSAGE AND ACROSS THE NORTHERN
INNER CHANNELS WILL DECREASE THIS AFTERNOON...BUT NORTHERN LYNN
CANAL MAY EXPERIENCE A BIT LONGER TIME WITH NEAR SMALL CRAFT LEVEL
WINDS THROUGH THE LATE AFTERNOON HOURS. AS THE WEAK RIDGE OF HIGH
PRESSURE REBUILDS OVER SOUTHEAST ALASKA TONIGHT...SCATTERED TO
NUMEROUS SHOWERS WILL CONTINUE WITH NO SIGNIFICANT WINDS. THE
LONG PERIOD OF SWELLS WILL ALSO DISSIPATE WITH DECAYING OF FETCH
AREA OVER THE OPEN SEAS AND CONSEQUENTLY SUBSIDING SEAS ACROSS THE
OUTSIDE WATERS TONIGHT.

.LONG TERM...MOIST ONSHORE FLOW WILL CONTINUE WED OVER ALL OF THE
PANHANDLE AS SOUTHWESTERLY JET IS POSITIONED FROM THE SOUTHERN
GULF INTO THE SOUTHERN PANHANDLE. GENERAL WEAK FORCING ALOFT WILL
LIKELY LIMIT QPF VALUES TO 0.1-0.25 PER 6HR PERIOD. PRECIP MODE
WILL LIKELY BE MORE STRATIFORM THAN SHOWERY AS FORCING IS MOSTLY
OROGRAPHIC ALONG WITH WEAK ASCENT ALOFT. MODELS AGREE ON THIS
SCENARIO AND ONLY TWEAKS WERE NECESSARY IN THE WIND PATTERN
PROGGED WITH EC/NAM/GFS MODEL UPDATES ON THERMODYNAMICS PRODUCING
SMALL CHANGES. VERY WEAK GRADIENTS WILL LIKELY PREVENT ANY WIND
PROBLEMS WITH THE EXCEPTION OF NORTHERN LYNN CANAL WHERE 20KT IS
ANTICIPATED.

PATTERN DOESN`T CHANGE MUCH AT ALL FOR THU BUT A SOMEWHAT STRONGER WAVE
IS FORECAST TO TRACK INTO THE SOUTHERN PANHANDLE BY THU NIGHT,
INDUCING A WEAK SURFACE FEATURE OVER THE SOUTHEASTERN GULF. THIS
WILL INCREASE RAINFALL OVER THE CENTRAL AND SOUTHERN
PANHANDLE...WHILE OVER THE NORTH THE LIGHT RAIN PERIOD WILL CONTINUE.
SOME MODERATE RAINFALL IS LIKELY FOR SOUTHERN PORTIONS INTO THU
PM.

FOR THE FRI/SAT PERIOD RAIN CHANCES WILL GRADUALLY LESSEN FROM NORTH
TO SOUTH AS WEAKER ONSHORE FLOW PREVAILS BEHIND THE THU
WAVE...WITH OFFSHORE FLOW DEVELOPING OVER THE NORTHERN PANHANDLE
BY SAT AND THE MOIST JET SWLY FLOW FINALLY SAGGING SOUTH OF THE
REGION. BOTH GFS/EC MODELS SHOW THE WEAK UPPER FLOW SCENARIO IN
CONTROL ON SUNDAY...STILL WIDESPREAD CLOUDINESS BUT NO FORCING FOR
PRECIP EVIDENT AS THE DYNAMIC LIFT CONTINUES TO RETROGRADE TO THE
ALEUTIAN REGION. THE GEM MODEL SUPPORTS THIS EVOLUTION ON SUNDAY
WITH THE STRONG CLOSED ALEUTIAN LOW AND STRONG RIDGING BECOMING
DOMINANT OVER THE CENTRAL GULF... WITH TROUGHING PRESENT ON THE
EAST SIDE OVER BC. CONFIDENT ENOUGH IN THIS SCENARIO TO REMOVE
PRECIP FROM FORECASTS FOR SUN/MON BUT AT THIS POINT LEFT THE
MOSTLY CLOUDY WORDING FOR THAT TIME.

THE FLOW AMPLIFIES ON MON ON BOTH MODELS WITH WEAK NWLY FLOW
ALOFT PERSISTING OVER MUCH OF THE PANHANDLE WITH LITTLE EVIDENCE OF
ANY PRECIPITATING FEATURES. AT THIS POINT THIS SCENARIO APPEARS
LIKELY TO PERSIST THROUGH TUE ALTHOUGH THIS WILL DEPEND ON THE
EVOLUTION OF THE PRIMARY TROUGHS ON BOTH SIDES OF SOUTHEAST AK AT
THAT TIME.

UPDATES TO GRIDS WERE MINOR AND STUCK WITH THE EVOLUTION TO WPC
GUIDANCE FROM SAT ONWARDS AS THIS WAS GENERALLY CONSISTENT WITH
THE 00Z/06Z MODEL UPDATES MENTIONED ABOVE. CONFIDENCE IS ABOVE
AVERAGE IN THE MEDIUM AND EXTENDED RANGE FOR THIS ROUND.

&&

.HYDROLOGY...TAIYA RIVER RESPONDED TO MODERATE RAINFALL MONDAY
EVENING AND CRESTED TO 16.1 FEET AT 8:45 PM. THE WATER LEVEL
RECEDED TO 15.9 FEET BY 10 PM AND CONTINUED DECREASING OVERNIGHT.
HOWEVER...ANOTHER RAINBAND PASSING ACROSS THE NORTHERN PANHANDLE
CAUSED THE WATER LEVEL RISING BACK TO 16.2 FEET AROUND 4 AM EARLY
THIS MORNING...THEN SLIGHTLY DROP DOWN TO 16.1 FEET AT 5 AM. EXPECT
THE WATER LEVEL TO DROP TO NEAR 15.5 FEET BY 10 AM.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-013-031.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-013-031.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043.

&&

$$

AHN/WESLEY

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