025  
FXAK67 PAJK 202300  
AFDAJK  
 
SOUTHEAST ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE JUNEAU AK  
300 PM AKDT WED SEP 20 2017  
   
SYNOPSIS
 
A SURFACE RIDGE WILL SHIFT EAST ACROSS THE GULF AND  
PRODUCE FOG OVER THE OUTER COAST AND INNER CHANNELS WEDNESDAY  
NIGHT AND THURSDAY MORNING. A FRONT WILL ENTER THE EASTERN GULF  
THURSDAY NIGHT AND SPREAD RAIN ACROSS THE PANHANDLE BY FRIDAY  
MORNING.  
 

 
   
SHORT TERM...WEDNESDAY EVENING THROUGH THURSDAY NIGHT/
 
LIGHT  
WINDS, A RIDGE TO THE WEST, AND LOW TIDE NEAR DAYBREAK AIDED IN  
THE FORMATION OF LOCALLY DENSE FOG THIS MORNING. PERSISTENT LIGHT  
WINDS THROUGH MUCH OF THE DAY ALLOWED PATCHES OF FOG TO LINGER  
OVER PORTIONS OF THE INNER CHANNELS INTO THE AFTERNOON. LITTLE  
CHANGE IN THE SHORT TERM FORECAST ISSUES THIS AFTERNOON WITH NO  
CHANGE IN AIRMASS, SO A RETURN OF THE FOG IS EXPECTED AGAIN  
TONIGHT WITH SIMILAR IMPACTS TO AVIATION OPERATIONS.  
 
WHEN THE FOG DID FINALLY LIFT, GENTLE SEA BREEZES SET UP IN THE  
USUAL SPOTS OVER THE INNER CHANNELS AND A SMALL CRAFT  
NORTHWESTERLY WIND HAS FORMED IN CROSS SOUND. THESE WINDS WILL  
DIMINISH WITH SUNDOWN AND AM EXPECTING DRAINAGE WINDS TO FORM LATE  
TONIGHT OVER THE FAR NORTHERN INNER CHANNELS. AN APPROACHING  
FRONT HAS BEGUN TO DISPLACE THE RIDGE OVER THE FAR EASTERN GULF TO  
THE EAST. THE RIDGE IN TURN IS PRESSING UP AGAINST THE REMAINS OF  
AN INVERTED TROUGH AND IS PRODUCING SMALL CRAFT NORTHWESTERLIES  
OVER THE COASTAL MARINE ZONES FROM CAPE EDGECUMBE SOUTH TO THE  
DIXON ENTRANCE. THESE WINDS ARE EXPECTED TO RELAX TOMORROW AS THE  
RIDGE AXIS MOVES EAST.  
 
THE FRONT REFERENCED ABOVE WILL PUSH EAST ACROSS THE GULF THURSDAY  
AND SPREAD RAIN ACROSS THE PANHANDLE FROM NORTH TO SOUTH AND WEST  
TO EAST WILL ALL LOCATIONS IN RAIN BY LATE THURSDAY NIGHT.  
 
LITTLE CHANGE IN THE SHORT TERM FORECAST WITH UPDATES MADE USING  
BOTH NAM AND GFS. TEMPS ADJUSTED USING BIAS CORRECTED MOS AND  
ECMWF. OVERALL FORECAST CONFIDENCE IS ABOVE AVERAGE.  
 
   
LONG TERM
 
/ FRIDAY TO TUESDAY / UPPER LEVEL RIDGE AXIS WILL  
SHIFT EAST OF THE PANHANDLE DURING THE DAY FRIDAY, AND THE REST  
OF THE RIDGE WILL SLOWLY MOVE EASTWARD TO THE WESTERN CONUS INTO  
WESTERN CANADA REGION BY THE FOLLOWING MID WEEK. WHICH MEANS ANY  
PROTECTION FROM THE RAIN MOVING INTO THE WESTERN GULF AT THE END  
OF THE WEEK IS ENDING AS WELL. ONCE THE ONSHORE FLOW AND RAINS  
BEGIN EARLY FRIDAY FOR SOUTHEAST ALASKA PANHANDLE, RAIN IS  
EXPECTED FOR THE REMAINDER OF THE FORECAST WEEK.  
 
FIRST FRONT SPREADS IN LATE THURSDAY NIGHT EARLY FRIDAY WITH A  
GOOD BURST OF RAIN. A TRAILING WAVE LIFTING ACROSS THE CENTRAL  
AND SOUTHERN PANHANDLE IS EXPECTED LATE FRIDAY NIGHT. FOLLOWING  
THAT, OUT OF THE CENTRAL PACIFIC, IS ANOTHER DEVELOPING SYSTEM AT  
THE HEAD OF WHAT MAY BE THE START OF AN ATMOSPHERIC RIVER AIMED  
TOWARDS HAIDA GWAII BY SUNDAY. SIGNIFICANT AMOUNTS OF RAINFALL  
COULD BE EXPECTED FOR THE SOUTHERN ZONES SATURDAY NIGHT INTO  
SUNDAY. THE PRESENT WIND FORECAST FOR THE EVENT IS AROUND 25 KT,  
BUT THIS COULD BE BUMPED UP IF THE LOW CONTINUES TO DEVELOP.  
 
FRIDAY'S FORECAST WAS ADJUSTED SLIGHTLY WITH INFLUENCE FROM THE  
NAM AND ECMWF WHILE THE LATER PORTIONS WERE WPC AND SOME ECMWF.  
MAY SEE THE TRACK ON THIS SHIFT MORE BY WEDNESDAY AFTERNOON IF THE  
NEW GFS RUNS ARE LEADING THE CHANGE IN PATTERN, AS THE GFS  
SOLUTION MAY HAVE MORE OF THE ENERGY CONCENTRATED OVER THE  
SOUTHEAST PORTION OF THE GULF.  
 

 
   
AJK WATCHES/WARNINGS/ADVISORIES
 
 
PUBLIC...NONE.  
MARINE...SMALL CRAFT ADVISORY FOR PKZ022-041-042.  
 

 
 

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