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 022331
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
331 PM AKDT TUE SEP 2 2014

.SHORT TERM...A WEAK RIDGE EXTENDS FROM THE SURFACE ALOFT AND
COVERS THE EASTERN GULF AND PANHANDLE. AN UPPER TROUGH IS PUSHING
EAST ACROSS THE FAR NORTHERN GULF AND THE EFFECTS CAN BE SEEN IN
BOTH RADAR DATA AS WELL AS SATELLITE IMAGERY AS AN AREA OF
SHOWERS. CURRENTLY NO RAIN IS FALLING OVER LAND SITES, BUT
MOVEMENT OF THE CLOUDS SUGGESTS THAT SHOWERS WILL ARRIVE IN
YAKUTAT BY EARLY EVENING. A THIN BUT WELL DEFINED BAND OF PRECIP
ON THE RADAR OFF THE CENTRAL OUTER COAST SHOULD ARRIVE OVER LAND
AROUND THE SAME TIME, BUT MAY FALL AS VIRGA WITHOUT REGISTERING
AT THE SURFACE. AS THE TROUGH CONTINUES TO THE EAST, SCATTERED
SHOWERS WILL DEVELOP FROM NORTHWEST TO SOUTHEAST OVER MUCH OF
SOUTHEAST ALASKA THROUGH WEDNESDAY AFTERNOON.

NO MAJOR AIRMASS CHANGES EXPECTED TONIGHT AND THE LOWERS LEVELS OF
THE ATMOSPHERE REMAIN STABLE. GIVEN THAT, AM EXPECTING ANOTHER
NIGHT OF LOW CLOUDS AND FOG TO FORM OVER MOST OF THE PANHANDLE.
HAVE NOT ISSUED ANY DENSE FOG ADVISORIES WITH THE AFTERNOON
FORECAST, BUT CANNOT RULE THIS OUT BASED ON LAST NIGHT. CLEARING
EXPECTED BY LATE MORNING OR EARLY AFTERNOON.

WEAK PRESWURE GRADIENT OVER THE PANHANDLE...EXCEPT FOR THE FAR
NORTHERN INNER CHANNELS. WINDS OVER NORTHERN LYNN CANAL ARE AT
MARGINAL SMALL CRAFT LEVELS OUT OF THE SOUTH AND SKAGWAY WINDS
HAVE BEEN THE UPPER TEENS WITH GUSTS TO THE MID 20S. THESE WINDS
WILL DIMINISH BY LATE EVENING. NO SIGNIFICANT WINDS ELSEWHERE ON
TEH INSIDE. OFFSHORE, SOUTHWESTERLY WINDS 15 TO 20 KTS UP AND DOWN
THE ENTIRE COAST WILL PILE UP SEAS ALONG THE SHORE AND THERE ARE
SOME SMALL CRAFT SEAS IN THE FORECAST. SWELL OUT OF THE WEST OR
SOUTHWEST WITH PERIODS GENERALLY 8 SECONDS.

A VERY WEAK ONSHORE GRADIENT EXISTS FROM THE SURFACE UP TO 850 MB.
THERE WILL BE SOME VERY WEAK WARM AIR ADVECTION, SO OVERNIGHT LOWS
ALONG THE OUTER COAST SHOULD A DEGREE OR TWO HIGHER THAN LAST
NIGHT. WITH THE EXPECTED LOW CLOUDS AND FOG IN STORE FOR MUCH OF
TOMORROW, DAYTIME HIGHS SHOULD BE VERY MUCH LIKE TODAY.

USED A NAM/ECMWF BLEND FOR TONIGHT, THEN A NAM/GEM BLEND FOR
TOMORROW FOR PRESSURE AND WIND. POP AND QPF FROM NAM AND GEM.
TEMPS PER BIAS CORRECTED NAM AND ECMWF. FORECAST CONFIDENCE IS
AVERAGE.

.LONG TERM...REGION TO REMAIN GENERALLY QUIET UNDER WEAK FLAT
RIDGING ALOFT THURSDAY THROUGH EARLY FRIDAY EVENING BUT WILL BE
AFFECTED BY WAVES ALONG THE STORM TRACK FROM FRIDAY ONWARDS. ON
FRI WEAK MOISTURE ADVECTION AND SOME THERMAL FORCING SHOULD LEAD
TO SOME SCATTERED SHOWER ACTIVITY OVER THE AREA, CONCENTRATED ON
NORTHERN PORTIONS. NORTHWEST PORTIONS WILL LIKELY SEE SOME AREAS
OF MODERATE RAIN WITH THIS DISTURBANCE...AND SOME RAIN WILL SPREAD
SOUTHEASTWARD TO THE SOUTHERN PANHANDLE ON SATURDAY. DO NOT
ANTICIPATE SIGNIFICANT RAIN AMOUNTS WITH THIS SYSTEM EXCEPT FOR
SOME ISOLATED AREAS OF THE NORTHWEST. HOWEVER THE GFS SHOWS THIS
SYSTEM STALLING ON SATURDAY NIGHT WITH PERSISTENT AREAS OF RAIN ON
THE SOUTH SIDE AND SOME EVIDENCE OF A WEAK FRONTAL PASSAGE MOVING
SOUTH AND EAST ON SAT. GFS STRONGER THAN ECMWF WITH THIS SYSTEM. COASTAL
AREAS OF MOST OF CWA...AT LEAST...EXPECTED TO BE WET DURING THIS
TIME. GRADIENTS GENERALLY WEAK WITH THE SYSTEM OVERALL THOUGH SO
WINDS NOT EXPECTED TO BE A BIG PROBLEM.

A SECONDARY TROUGH DEVELOPING BEHIND THE WEEKEND WAVE WILL LIKELY REINFORCE
LIFT AND SHOWER PRODUCTION BY EARLY SUNDAY AS NEW CLOSED LOW SYSTEM
DEVELOPS AND PROGRESSES SOUTHEASTWARD THROUGH THE REGION LATE ON
SATURDAY AND SUNDAY. ECMWF IS WEAKER AND SLOWER WITH THIS NEW
UPPER TROUGH. GFS HAS THIS SYSTEM QUICKLY REPLACED BY UPPER
RIDGING ON MONDAY AS A NEW STRONGER TROUGH APPROACHES FROM THE
BERING SEA...MODELS DIVERGE AT THIS POINT. RIDGING WILL LIKELY BE
TRANSIENT AND MOISTURE FROM THE NEW SYSTEM APPEARS LIKELY TO GET
HERE LATE ON TUES. WENT WITH LIKELY POPS ON TUES FOR NOW BUT WE
WILL SEE HOW THE TIMING PLAYS OUT.

NAM/GFS GRIDS IN GENERAL AGREEMENT THROUGH 84H THEN SETTLED ON A
GFS/ECMWF BLEND AFTER THAT POINT...AS MODELS DIVERGE BY EARLY
WEEK...WITH GRIDS SELECTED IN LINE WITH WPC. FORECAST CONFIDENCE
LEVEL IS AVERAGE OVERALL WITH THIS PACKAGE.


&&

.AVIATION...VERY LOW CEILING AND AREAS OF FOG BELOW MINIMUMS
EXPECTED FOR PORTIONS OF THE PANHANDLE TONIGHT WILL IMPACT
AVIATION OPERATIONS OVERNIGHT AND THROUGH AT LEAST MID MORNING.
LITTLE TO NO TURBULENCE EXPECTED BELOW 10K FT.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043-051-052.

&&

$$

FRITSCH/WESLEY/AHN

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.