815  
FXAK67 PAJK 251347  
AFDAJK  
 
SOUTHEAST ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE JUNEAU AK  
547 AM AKDT SUN AUG 25 2019  
   
SYNOPSIS
 
LOW PRESSURE IN THE NORTHWEST GULF DISSIPATES AS MORE  
LOW PRESSURE DEVELOPS IN THE SOUTHWEST GULF THIS AFTERNOON. THE  
LOW IN THE SOUTHWEST GULF THEN TRACKS INTO THE EASTERN GULF  
THROUGH TUESDAY EVENING. A FRONT LIFTS ACROSS THE EASTERN GULF  
MONDAY AND INTO SOUTHEAST ALASKA MONDAY NIGHT. A RIDGE OF HIGH  
PRESSURE OVER THE INNER CHANNELS SHIFTS EAST INTO WESTERN CANADA  
SUNDAY NIGHT.  
 

 
   
SHORT TERM
 
NUMEROUS SHOWERS OCCURRED OVER MOST PORTIONS OF  
SOUTHEAST ALASKA OVERNIGHT. SOME OF THE SHOWERS PRODUCED HEAVY  
RATES OF RAINFALL OVERNIGHT; HOWEVER, ACTUAL 12-HOUR RAINFALL  
AMOUNTS, ALTHOUGH NOT INSIGNIFICANT, MAINLY WERE UNDER A HALF  
INCH. AN INTENSE SHORT-WAVE YESTERDAY EVENING DEPICTED IN WV  
IMAGERY SHOT ACROSS THE NORTHERN GULF SATURDAY AND THE NORTH-  
CENTRAL PANHANDLE SATURDAY EVENING. THIS FEATURE CLEARLY ENHANCED  
SHOWERS. BUT UPON APPROACHING THE COAST MOUNTAINS, A THUNDERSTORM  
ERUPTED IN THE HOLKHAM BAY, TRACY ARM, AND ENDICOTT ARM AREA.  
FOLLOWING THE SHORT-WAVE'S CROSSING INTO BC, LIGHTNING ENDED OVER  
OUR REGION.  
 
A WEAK RIDGE OF HIGH PRESSURE OVER THE PANHANDLE WILL STRENGTHEN  
THROUGH THIS EVENING. OROGRAPHICALLY ENHANCED SHOWERS WILL TEND  
TOWARD WEAKENING THROUGH TONIGHT AS THE RIDGE SHARPENS AHEAD OF  
A BIG STORM APPROACHING SOUTHEAST ON MONDAY. SO FAR, CONSENSUS IS  
ONLY MARGINALLY BETTER, BUT CHANGES WERE MADE WITH THE ECMWF AND  
06Z NAM AND CANADIAN THROUGH MONDAY NIGHT TO ELEVATE QPF, AND SOME  
POP ADJUSTMENTS WERE MADE TO REFLECT THIS. AS BEST WE CAN TELL  
RAIN WILL BEGIN ALONG THE IMMEDIATE COAST EARLY MONDAY MORNING AND  
QUICKLY SPREAD INLAND THROUGH THE DAY. AT THIS POINT MOST ALL  
POINTS WITHIN THE PANHANDLE LOOK TO RECEIVE 1 TO 2 INCHES MONDAY  
AND MONDAY NIGHT. THE ONE EXCEPTION BEING YAKUTAT WHO LOOKS TO  
RECEIVE LESS THAN AN INCH. BUT EVEN AS THE WEATHER FRONT PRESSES  
NORTHWARD AND HANGS UP ACROSS THE NORTHERN PANHANDLE, A  
DEFORMATION BAND LOOKS TO SET UP SOMEWHERE AHEAD OF THE MAIN LOW  
CENTER. SHOULD THE DEFORMATION BAND SET UP OVER THE PANHANDLE, THE  
NORTH-CENTRAL PANHANDLE FROM SITKA TO JUNEAU MAY SEE HEAVY RAIN  
PERSIST WELL INTO MONDAY NIGHT.  
 
WINDS WILL LIKELY BE A FACTOR AS MUCH AS HEAVY RAIN. WE INCREASED  
THEM ONCE AGAIN OVER THE OUTER GULF TO AROUND 30 KT. AS GUIDANCE  
NARROWS ON THE POSITION OF THE LOW, WE MAY INCREASE THEM FURTHER  
TO GALES. SOME WORK WAS ALSO DONE THROUGH THE INNER CHANNELS WITH  
HIGHER INCREASES OF EASTERLIES THROUGH CROSS SOUND. STRONG WIND  
GUSTS OF 45 MPH OR SO ARE POSSIBLE FROM SITKA SOUTHEAST TO  
KETCHIKAN AND ALL POINTS BETWEEN. WHILE ONLY HINTED AT IN THE  
FORECAST, WE HOPE TO BETTER DEFINE REGIONS OF STRONG WIND GUSTS  
IN THE NEAR FUTURE.  
 
FORECAST CONFIDENCE IS MEDIUM HIGH, WITH SOME DETAILS YET TO  
COMPLETELY IRON OUT.  
   
LONG TERM.../TUESDAY THROUGH SUNDAY NIGHT/
 
AN UPPER LOW WILL  
BE MOVING ASHORE NEAR CAPE FAIRWEATHER AT THE START OF THIS LONG  
RANGE FORECAST PERIOD. A SHORT WAVE TROUGH WITH A 100KT JET MAX  
WILL BE LOCATED OVER THE SOUTHERN PANHANDLE. A MUCH LARGER AND  
POSITIVELY TILTED UPPER TROUGH WILL EXTEND FROM THE UPPER LOW WSW  
TO THE FAR SOUTHWEST GULF. THIS LARGER TROUGH WILL PINCH OFF AN  
UPPER LOW AND BECOME MORE NORTH-SOUTH ORIENTED BY WEDNESDAY  
MORNING. THE CAPE FAIRWEATHER LOW WILL HAVE TRACKED WELL TO THE  
EAST - TO THE NWT - BY THAT TIME AND THE JET CORE WILL HAVE  
SHIFTED NORTH TO THE CENTRAL PANHANDLE AS A BROAD UPPER RIDGE  
BUILDS NORTH OVER THE EASTERN GULF AND SOUTHEAST ALASKA.  
 
AT THE SURFACE, THE LOW ASSOCIATED WITH THE UPPER LOW WILL BE  
LOCATED WEST OF CROSS SOUND, SOUTH OF YAKUTAT, AND WEAKENING AS IT  
MOVES SLOWLY TO THE SOUTHEAST. SHOWERS WILL BE DIMINISHING THROUGH  
TUESDAY AND BY WEDNESDAY MORNING ALL OF SOUTHEAST ALASKA SHOULD BE  
DRY, IF NOT SUNNY. THE DRY WEATHER SHOULD RELIABLY LAST THROUGH  
THURSDAY NIGHT. BY FRIDAY MORNING, WPC AND THE NATIONAL BLEND ARE  
TRYING TO BUILD IN PRECIPITATION FROM THE WEST. ECMWF IS PUSHING A  
FRONT OVER THE NORTHERN PANHANDLE FROM THE SOUTHWEST AT THAT  
TIME, AND THE GFS IS TOTALLY DRY. AS A RESULT, CONFIDENCE IN A DRY  
WEEKEND IS BELOW AVERAGE.  
 
MODELS ARE STILL TRYING TO BRING DOWN DAYTIME HIGHS FOR THE SECOND  
HALF OF THIS WEEK. WE ARE NOW LOOKING AT HIGHS IN THE SECOND HALF  
OF THE WEEK IN THE MID TO UPPER 60S. NOT THE 70S WE WERE  
ORIGINALLY EXPECTING, BUT STILL SOLIDLY ABOVE NORMAL FOR THIS TIME  
OF THE YEAR.  
 

 
   
AVIATION
 
IF TAF WRITING WERE A VIDEO GAME, THIS WOULD BE LEVEL  
FIVE DIFFICULTY, GIVEN SHOWERS AND THEIR INHERENT CEILING AND  
VISIBILITY VARIABILITY, POTENTIAL CLEARING, AND FOG FORMATION. OUR  
SYNOPTIC SKILL LEVEL CAN ONLY HOPE TO NEGATE THE NOISE OF VOLATILE  
CHANGEABILITY AT THE CONVECTIVE MESOSCALE LEVEL. THEREFORE, 12Z  
TAFS STROVE TO MAINTAIN MEAN CONDITIONS AND NOT TO GAMBLE ON  
EXTREMED OUT THERE. BECAUSE OF ATMOSPHERIC INSTABILITY, WE FEEL  
THAT ANY FOG THAT FORMS WILL BE FAIRLY TEMPORARY, AND THAT LOW  
STRATUS WILL BE MORE LIKELY TO OCCUR. WE DO EXPECT SOME MODEST  
IMPROVEMENTS TO OCCUR INTO THE AFTERNOON, BUT CONFIDENCE IN NOT  
GREAT. WE ANTICIPATE A SLIGHT DETERIORATION OVERALL TONIGHT WITH  
BOUNDARY LAYER COOLING. WINDS WILL NOT BE FACTOR DURING THIS TAF  
PERIOD WITH SHEER FROM THE NEXT STORM LIKELY HOLDING OFF UNTIL  
AFTER 12Z MONDAY.  
 

 
   
MARINE
 
CONDITIONS WILL BE BENIGN TODAY AND TONIGHT ACROSS MOST  
OF THE AREA (LESS THAN 25 KT WINDS); HOWEVER, A BARRIER JET IN THE  
NORTHERN GULF TIPS MARINE ZONE 52 INTO SMALL CRAFT EARLY MONDAY  
MORNING. WINDS AND SEAS ONLY GROW INTO TUESDAY. WE LOWERED SEAS  
OVER THE NEXT 12 TO 18 HOURS OR SO TO BETTER REFLECT BUOY  
INDICATED SEA-STATES.  
 

 
   
AJK WATCHES/WARNINGS/ADVISORIES
 
 
PUBLIC...NONE.  
MARINE...SMALL CRAFT ADVISORY FOR PKZ052.  
 

 
 

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