422  
FXAK67 PAJK 191445  
AFDAJK  
 
SOUTHEAST ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE JUNEAU AK  
545 AM AKST SUN NOV 19 2017  
   
SHORT TERM.../THROUGH MONDAY NIGHT/
 
SIGNIFICANT SHIFT IN THE  
NAM WITH THE 06Z MODEL PUTS THAT MODEL IN VERY CLOSE ALIGNMENT  
WITH THE GFS AND THE CANADIAN NH WITH RESPECT TO A FRONT THAT  
WILL AFFECT SOUTHEAST ALASKA ON MONDAY. CHANGES MADE OVERNIGHT  
BASED ON INCREASED CONFIDENCE IN THE AGREEMENT OF THESE MODELS,  
BUT THE 19/00Z ECMWF REMAINS AN OUTLIER. AS IT IS, THE FRONT IS  
NOW DEPICTED AS MAKING FURTHER PROGRESS TO THE NORTH AND WITH A  
NOTABLE INCREASE IN QPF. LOW LEVEL WARM AIR ADVECTION FROM THE  
SOUTH IS ALSO EVIDENT, BUT THIS FRONT LOOKS LIKE IT WILL BE A SNOW  
EVENT FOR PANHANDLE LOCATIONS BETWEEN CAPE FAIRWEATHER AND SUMNER  
STRAIT, MINUS THE CENTRAL OUTER COAST. AT PRESENT, 24-HOUR SNOW  
TOTALS MAX OUT ALONG THE ICY STRAIT CORRIDOR AT 3 TO 4 INCHES,  
WHICH WOULD BE LESS THAN ADVISORY LEVELS.  
 
GALE FORCE WINDS ASSOCIATED WITH THE FRONT ARE EXPECTED OVER THE  
CENTRAL GULF BY THIS EVENING, PROGRESSING EASTWARD THROUGH THE  
NIGHT WITH SMALL CRAFT WINDS DOWN TO THE DIXON ENTRANCE BY EARLY  
MONDAY MORNING. STRONG NORTHEAST PRESSURE GRADIENT THAT HAS BEEN  
THE NORM FOR SEVERAL WEEKS NOW CONTINUES. AS THE FRONT DRAWS  
NEAR, WINDS ON THE INSIDE WILL ONCE AGAIN INCREASE WITH GALES  
EXPECTED OVER THE INNER CHANNELS FROM STEPHENS PASSAGE NORTH BY  
LATE TONIGHT. STRONG WINDS IN SKAGWAY NOT PANNING OUT AS  
ORIGINALLY FORECAST, SO THE STRONG WIND HEADLINE WAS DROPPED FOR  
THAT ZONE. STILL, NORTHERLY GUSTS AROUND 30 MPH ARE EXPECTED BOTH  
IN TOWN AND ALONG THE KLONDIKE HIGHWAY. MOUNTAIN WAVE MODEL  
GUIDANCE FOR THE DOWNTOWN JUNEAU AREA NOT INDICATING VERY GOOD  
POTENTIAL FOR A TRUE TAKU WIND, BUT CROSS BARRIER FLOW INCREASES  
TONIGHT, SO GUSTS TO 30 MPH ARE POSSIBLE TONIGHT AND TOMORROW.  
 
CLEARING SKIES OVERNIGHT ALLOWED TEMPERATURES TO FALL ABRUPTLY IN  
SOME SPOTS. YAKUTAT, THE MENDENHALL VALLEY, AND GUSTAVUS ALL GOT  
DOWN TO 5-7 DEGREES BY VERY EARLY SUNDAY MORNING. INCREASING CLOUD  
COVER ASSOCIATED WITH THE FRONT SHOULD PREVENT ANOTHER SINGLE-  
DIGIT NIGHT SUNDAY NIGHT. HIGH TODAY SHOULD RANGE FROM THE LOW 20S  
IN THE NORTH TO THE MID/UPPER 30S FOR THE SOUTHERN ZONES.  
 
USED A GFS/NAM BLEND FOR UPDATES TO PRESSURE AND WIND TONIGHT. POP  
AND QPF FROM SREF, NAM, AND GFS. OVERALL SHORT RANGE FORECAST  
CONFIDENCE IS AVERAGE, TRENDING ABOVE AVERAGE.  
 
   
LONG TERM
 
/TUESDAY THROUGH SUNDAY/MODELS HAVE A REASONABLE  
AGREEMENT TUESDAY IN REGARDS TO A LOW THAT DROPS DOWN FROM THE  
WESTERN GULF INTO THE NORTH PACIFIC. IT WILL NOT BE THE LAST TIME  
SE ALASKA WILL SEE THIS LOW PRESSURE, AS IT DOES A SWEEPING  
CONCAVE TURN TOWARDS HAIDA GWAII. THIS IS ABOUT THE TIME THAT THE  
MODELS START TO DIVERGE IN THEIR SOLUTIONS. THE GFS IS THE MOST  
AGGRESSIVE BRINGING A CLOSED LOW TO NEAR HAIDA GWAII, WHILE THE  
NAM HAS THE SLOWEST APPROACH WITH THE EC TAKING THE MIDDLE ROAD.  
BY THANKSGIVING THE GFS HAS BROUGHT THE LOW TO NEAR YAKUTAT,  
WHILE THE ECMWF SOLUTIONS DAWDLES IN THE SOUTHEAST GULF AND  
EVENTUALLY FILLS THE LOW. THE ECMWF HAS ALSO BECOME THE ROGUE  
MODEL SOLUTION WITH MAJOR SOLUTIONS BETWEEN THE LAST TWO RUNS,  
THIS LEAVES THE GFS A REASONABLE MODEL TO DO BLENDING TO AS  
NEEDED. OVERALL USING AN ENSEMBLE APPROACH WILL BE THE MOST  
PRUDENT SOLUTION FOR THE LATER PART OF THE UPCOMING WEEK. USED WPC  
TO EXTEND OUT THROUGH SUNDAY, WITH A SMALL NUDGE USING THE GFS.  
 
A SLOW TREND TO WARMER WEATHER BY MID WEEK FOR THE SOUTHERN  
PANHANDLE AND THEN SPREADING INTO THE CENTRAL PANHANDLE AS FAR  
NORTH OF JUNEAU OVER THE WEEKEND. AREAS IN THE SOUTH AND ALONG  
THE OUTER COASTAL WATERS FROM SITKA SOUTH WITH BE PREDOMINATELY  
RAIN, WHILE A MIX OF PRECIPITATION WILL BE THE NORM FOR THE  
CENTRAL AREAS. BY SATURDAY THE WARMER AIR SHOULD REACH YAKUTAT AND  
HAINES AREAS MAKING FOR A MIX OF RAIN AND SNOW DURING THE WARMER  
PART OF THE DAY. SNOW WILL CONTINUE IN THE SKAGWAY.  
 
STRONG OUTFLOWS WILL BE DIMINISHING AS THE SOUTHERLY WINDS ADVANCE  
NORTHWARD, LYNN CANAL AREA AND NORTHERN AREAS OF GLACIER BAY WILL  
BE THE HOLD OUTS WITH NORTHERLY WINDS PERSISTING BUT DIMINISHING  
INTO THE WEEKEND.  
 
FORECAST CONFIDENCE IN THE MID RANGE /TUESDAY-WEDNESDAY/ IS  
AVERAGE AND THEN SLIPS LOWER. WITH THE MEAGER MODEL AGREEMENT AND  
MODEL RUN DISPARITIES WITH THE ECMWF, CONFIDENCE REMAINS LOW FOR  
THE DETAILS LATE WEEK AND INTO THE WEEKEND.  
 

 
   
AJK WATCHES/WARNINGS/ADVISORIES
 
 
PUBLIC...NONE.  
MARINE...GALE WARNING FOR PKZ012-013-021-022-031-034-043-051-052.  
SMALL CRAFT ADVISORY FOR PKZ011-032-033-035-036-041-042-053.  
 

 
 

 
 
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