899  
FXAK67 PAJK 222236  
AFDAJK  
 
SOUTHEAST ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE JUNEAU AK  
236 PM AKDT SAT JUL 22 2017  
   
SYNOPSIS
 
A LOW IN THE SE GULF WILL GRADUALLY WEAKEN THROUGH  
EARLY SUNDAY AS AN AREA OF HIGH PRESSURE BUILDS OVER THE GULF. AN  
ASSOCIATED FRONTAL BAND MOVING OVER THE PANHANDLE WILL TRACK EAST  
AND WEAKEN SATURDAY NIGHT.  
 

 
   
SHORT TERM
 
/SATURDAY NIGHT THROUGH MONDAY/ AS OF 230PM  
SATURDAY...UPPER LOW OVER THE SE GULF CONTINUES ITS EASTWARD  
TRACK THIS EVENING WITH THE ASSOCIATED SURFACE LOW FOLLOWING  
SUIT. MODERATE SHOWERS THIS AFTERNOON ARE EXPECTED WITH DISSIPATE  
QUICKLY AS THE VORTICITY BANDS PUSH INTO BRITISH COLUMBIA. THREE  
HOUR RAIN RATES UPWARDS OF 0.25 INCHES WERE MEASURED ACROSS THE  
SOUTHER PANHANDLE OVERNIGHT AND OVER THE CENTRAL PANHANDLE THIS  
AFTERNOON ALONG THE TRACK OF THE FRONT. SO FAR ONLY MINOR RISES  
IN LOCAL STREAMS AND RIVERS. WHAT WAS LOOKING TO BE A DRYING AND  
CLEARING TREND THROUGH THE START OF NEXT WEEK IS NOW LOOKING LIKE  
A DEVELOPING MARINE LAYER AND DIRTY RIDGE. MODEL SOUNDINGS KEEPING  
SHALLOW LAYER OF MOISTURE IN PLACE AND HIGHER BOUNDARY LAYER RH  
INDICATIVE OF A MARINE CLOUD DECK. SO HAVE CONTINUED THE TREND OF  
KEEPING IN MOSTLY CLOUDY SKIES, WILL LIKELY BUMP TO CLOUDY WHEN  
THE LAYER BEGIN TO FORM OVER THE GULF. HAVE ISOLATED SHOWERS  
RIDING OVER THE RIDGE, MAINLY OVER THE NORTHEAST GULF COAST AND  
CENTRAL PANHANDLE, BUT EXPECT LITTLE IN THE WAY OF QPF. STILL HAVE  
MAX TEMPS RISING INTO THE MID 60S BUT IF LITTLE MIXING OCCUR MAY  
BE ON THE HIGH SIDE. WITH SHOWERS EXITING THE REGION AND COOLER  
TEMPS INCLUDED PATCHY FOG FOR TYPICAL LOCATIONS TONIGHT AND SOME  
MARINE FOR ALONG THE COAST TOMORROW NIGHT. ALL REGIONAL WINDS HAVE  
SHIFTED TO THE SOUTH THIS AFTERNOON AS THE LOW WEAKENS AND A  
RIDGE BUILDS OVER THE PANHANDLE. WITH DECREASING GRADIENT OVER  
MOST OF THE PANHANDLE WIND SPEEDS WILL SUBSIDE BY LATE TONIGHT AND  
BE LESS THAN 10 KT THROUGH MONDAY. AFTERNOON SEA BREEZE MAY  
DEVELOP DUE TO THERMAL GRADIENT. EXCEPTION BEING N LYNN CANAL  
WHERE JUST ENOUGH SOUTHERLY GRADIENT IN THE AFTERNOON TO PICK UP  
TO NEAR SMALL CRAFT LEVELS. WATCHING A LOW TACKING ACROSS THE N  
PACIFIC MONDAY NIGHT NEARING HAIDA GWAII, WITH CURRENT TRACK NO  
IMPACTS EXPECTED.  
 
WITH SUCH A LIGHT GRADIENT MODELS HAD SLIGHT DIFFERENCES ON  
SURFACE PRESSURE BUT OVERALL WERE IN LINE FOR WIND AND POP FIELDS.  
REFRESHED GRIDS WITH A BLEND OF NAM WITH SOME ECMWF. MAIN CHANGE  
WAS BUMPING UP POP ON MONDAY AND TONE DOWN SOME OF THE THERMAL  
WINDS. FORECAST CONFIDENCE IS AVERAGE.  
 
   
LONG TERM.../MONDAY THROUGH SATURDAY/ AS OF 1030PM FRIDAY
 
AN  
UPPER LEVEL LOW TRAVERSING SOUTH OF HAIDA GWAII WILL ASSIST IN  
PROVIDING OFFSHORE FLOW ALOFT OVER MOST OF THE PANHANDLE DURING  
THE MONDAY TO TUESDAY TIMEFRAME. THIS PATTERN SHOULD ALLUDE TO  
CLOUDY SKIES WITH SOME SHOWERS POSSIBLE, MAINLY OVER THE SOUTHERN  
PANHANDLE. BY WEDNESDAY, MODELS SEEM TO SHOW THE LOW LIFTING  
NORTH, BUT GENERALLY, IT APPEARS TO DEEPEN AND REMAIN OVER THE  
AREA THROUGH THE REST OF THE TIME PERIOD. IF THIS SOLUTION COMES  
TO FRUITION, WE COULD SEE BANDS OF SHOWERS EXPAND TO INCLUDE  
PORTIONS OF THE NORTHERN PANHANDLE. THE FORECAST KEEPS A CHANCE OR  
SLIGHT CHANCE OF SHOWERS OVER MANY AREAS THROUGH THE REST OF NEXT  
WEEK. AS HAS BEEN THE CASE ALL SUMMER, OUR WEATHER HAS BEEN  
INFLUENCED MAINLY BY UPPER LEVEL FEATURES, RATHER THAN SURFACE-  
BASED, SO THIS SYSTEM WARRANTS WATCHING.  
 
AT THE SURFACE, ANTICYCLONIC FLOW DOMINATES THROUGH MUCH OF THE  
WEEK, AS A WEAK RIDGE DEVELOPS OVER THE EASTERN GULF AND PERSISTS  
THROUGH THE PERIOD OF INTEREST. LOW LEVEL WINDS WILL BE WEST-  
NORTHWESTERLY, BUT THEY WILL BE RELATIVELY WEAK, DUE TO A  
GENERALLY STABLE AIRMASS IN THE LOW LEVELS. HOWEVER, SINCE THE  
RIDGE IS SOMEWHAT FLAT, THERE MAY BE PLENTY OF OPPORTUNITY FOR  
CLOUDS TO MOVE IN WITH SOME ISOLATED SHOWERS, AS MENTIONED  
PREVIOUSLY.  
 
MODEL DIFFERENCES PERTAINING TO THE UPPER LEVEL PATTERN INCREASE  
THROUGH AS EARLY AS MID WEEK, INDICATING THAT THE SURFACE PATTERN  
MAY BE EVEN MORE DIFFERENT BETWEEN MODELS. THE 12Z CANADIAN AND  
18Z GFS WERE IN BETTER AGREEMENT, WITH THE 12Z ECMWF BEING THE  
OUTLIER, BUT THE 00Z GFS FELL BACK IN LINE WITH THE ECMWF. THIS  
INDECISIVENESS OF THE MODELS MAKES FOR EVEN GREATER FORECAST  
UNCERTAINTY THROUGH THE NEXT WEEK.  
 

 
   
AJK WATCHES/WARNINGS/ADVISORIES
 
 
PUBLIC...NONE.  
MARINE...NONE.  
 

 
 

 
 
PRB/VOVERIS  
 
VISIT US AT HTTP://WWW.WEATHER.GOV/JUNEAU  
 
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