246  
FXAK67 PAJK 252205  
AFDAJK  
 
SOUTHEAST ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE JUNEAU AK  
205 PM AKDT WED APR 25 2018  
   
SHORT TERM
 
LARGE UPPER LOW CONTINUES TO SPIN LATE THIS  
AFTERNOON OVER THE BERING SEA WHILE UPPER RIDGING IS BUILDING  
ALONG THE BC COAST. BETWEEN THESE TWO SYSTEMS IS THE REMNANTS OF  
THE FRONT THAT BROUGHT 1.5 TO 2 INCHES OF RAIN TO THE YAKUTAT AREA  
LAST NIGHT. THIS FRONT IS LITTLE MORE THAN A WEAK SURFACE TROUGH  
BUT SW FLOW ALOFT CONTINUES TO ADVECT A NARROW STREAM OF MOISTURE  
OVER THE NORTHERN/CENTRAL PANHANDLE AS EVIDENCED BY PW VALUES  
AROUND 1 INCH ON GOES BLENDED PW IMAGERY. SOUTHERN AREAS HAVE SEEN  
PARTLY TO MOSTLY SUNNY SKIES TODAY WITH TEMPERATURES WARMING INTO  
THE MID 50S WHILE THE CORRIDOR FROM SITKA TO GUSTAVUS/JUNEAU AS  
SEEN CHILLY LIGHT RAIN WITH TEMPERATURES IN THE MID 40S.  
 
GUIDANCE INDICATES THAT THE MID/UPPER RIDGE WILL CONTINUE TO BUILD  
THROUGH THURSDAY. THIS WILL PREVENT THE WEAK SURFACE FRONT FROM  
ADVANCING ANY FURTHER SOUTH. INSTEAD, ONE OR TWO WEAK WAVES WILL  
RUN ALONG THE FRONT THROUGH THURSDAY MORNING, KEEPING LIGHT  
PRECIPITATION GOING THROUGH MID DAY THURSDAY IN ROUGHLY THE SAME  
AREA AS TODAY. THE FRONT WILL EVENTUALLY WEAKEN AND DISSIPATE BY  
THURSDAY NIGHT AS SURFACE RIDGING BEGINS TO DEVELOP OVER THE GULF.  
WITH CONTINUED WEAK ONSHORE FLOW IN THE 925 TO 850 MB LAYER  
THROUGH THURSDAY, GOING TO BE HARD TO SCOUR OUT THE LOW LEVEL  
MOISTURE. EVEN THURSDAY NIGHT, AS THE FLOW TURNS NW'LY, WHILE WE  
MAY DRY OUT, CLOUDS WILL LIKELY HANG AROUND ESPECIALLY ALONG THE  
COAST AND THE NORTHERN/CENTRAL PANHANDLE.  
 
SW WINDS ARE CURRENTLY GUSTING TO 40 MPH IN THE SKAGWAY AREA WITH  
25 KT SOUTHERLY WINDS IN N LYNN CANAL. AS THE STRONGER SW FLOW  
ALOFT DIMINISHES THIS EVENING, EXPECT THESE WINDS TO DIMINISH. BY  
THURSDAY MORNING, LIGHT WINDS ARE EXPECTED IN MOST AREAS AS THE  
GRADIENT GOES TO ALMOST NIL. KEPT 15 KT SOUTHERLIES IN LYNN CANAL  
THURSDAY AFTERNOON DUE TO THERMAL GRADIENT BUT OTHERWISE WINDS  
SHOULD BECOME MORE NW'LY BY THURSDAY NIGHT AS SURFACE RIDGING  
BUILDS OVER THE GULF.  
 
OVERALL MODELS ARE IN GOOD AGREEMENT AND FORECAST CONFIDENCE IS  
ABOVE AVERAGE.  
   
LONG TERM.../FRIDAY THROUGH WEDNESDAY/
 
A LARGE SURFACE HIGH  
WILL BE CENTERED SOUTH OF THE ALEUTIANS AT THE START OF THIS LONG  
RANGE FORECAST PERIOD. PROMINENT RIDGE AXIS EXTENDS NORTHEAST  
DIAGONALLY ACROSS THE GULF. FARTHER NORTH, A LOW NEAR THE BERING  
STRAIT WILL BE PUSHING A FRONT EAST ACROSS THE SOUTHERN PORTION OF  
THE STATE AND ALONG THE NORTHERN PERIPHERY OF THE SURFACE RIDGE.  
MODELS ARE CURRENTLY IN SIGNIFICANTLY BETTER AGREEMENT WITH THIS  
SET-UP AND CHANGES WERE MADE IN THE EXTENDED FORECAST TO REFLECT  
THIS. MAIN CHANGE HAS BEEN TO INCREASE THE LIKELIHOOD OF RAIN FROM  
FRIDAY ONWARD. THE FRONT REFERENCED ABOVE WILL NOT MAKE MUCH  
EASTWARD PROGRESS BEYOND CAPE FAIRWEATHER. HOWEVER, A SECOND  
FRONTAL FEATURE WILL CROSS THE CENTRAL GULF BEGINNING SATURDAY AND  
ARRIVE ALONG THE CENTRAL/SOUTHERN OUTER COAST BY SUNDAY MORNING.  
A THIRD FRONT WILL CROSS THE GULF ON SUNDAY AND SPREAD RAIN ACROSS  
ALL OF THE PANHANDLE SUNDAY NIGHT.  
 
WITH THE INCREASES TO POP AND BASED ON MODEL SPECTRUM SPREADS,  
DECIDED TO DIMINISH DAYTIME HIGHS SLIGHTLY. OVERNIGHT LOWS WERE  
ADJUSTED UP EVEN LESS. NET EFFECT WILL BE A DIMINISHED DIURNAL  
RANGE OVER THE COMING WEEK.  
 
BLENDED GFS, ECMWF, AND THE CANADIAN NH FOR PRESSURE THROUGH  
SUNDAY NIGHT. USED CANADIAN NH WINDS AS A FOUNDATION THROUGH  
FRIDAY NIGHT, THEN PRIMARILY GFS. PREFERRED THE SREF POP FIELD  
EARLY ON, BUT THEN FAVORED THE UPPER LEVEL PATTERN DEPICTED IN GFS  
FOR THE SECOND AND THIRD FRONTS AND HOW THEY INTERACT WITH THE  
SURFACE RIDGE.  
 
FORECAST CONFIDENCE IN A CONTINUED WET PATTERN FOR THE UPCOMING  
WEEK REMAINS LOWER THAN AVERAGE BUT IS INCREASING.  
 

 
   
AJK WATCHES/WARNINGS/ADVISORIES
 
 
PUBLIC...STRONG WIND UNTIL 4 PM AKDT THIS AFTERNOON FOR AKZ018.  
STRONG WIND FROM 6 PM TO 10 PM AKDT THIS EVENING FOR AKZ018.  
MARINE...SMALL CRAFT ADVISORY FOR PKZ012.  
SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ022-041>043-051>053.  
 

 
 

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