249  
FXAK69 PAFG 192349  
AFDAFG  
 
NORTHERN ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE FAIRBANKS AK  
349 PM AKDT SUN AUG 19 2018  
   
SYNOPSIS
 
 
ALOFT...  
THE LONG WAVE PATTERN CONSISTS OF A RIDGE OVER SOUTHEAST ALASKA  
AND MAINLAND ALASKA WITH A TROUGH OVER THE BERING SEA. THE LONG  
WAVE RIDGE PROGRESSES EAST LATE THIS WEEK AS THE LONG WAVE TROUGH  
OVER THE BERING EJECTS A SERIES OF SHORT WAVES EAST ACROSS  
MAINLAND ALASKA THROUGH THE WEEK. THIS EVENTUALLY PULLS THE LONG  
WAVE EAST OVER NORTHERN AK LATE IN THE WEEK. THIS MEANS THAT THE  
CURRENT PATTERN OF A WARM AND DRY EASTERN INTERIOR WILL  
TRANSITION TO A WET AND COOL PATTERN BY TUE AND REMAIN COOL AND  
WET THROUGH THE WEEKEND, WHILE THE WEST COAST AND WESTERN INTERIOR  
REMAINS WET THROUGH THE WEEK, AND THE NORTH SLOPE GOES FROM A DRY  
AND WARM PATTERN TO A COOL AND WET PATTERN BY TUE.  
 
MODERATE SOUTH FLOW ALOFT OVER THE ALASKA RANGE WILL KEEP CHINOOK  
CONDITIONS OVER THE SOUTHEAST INTERIOR THROUGH EARLY TUE, BEFORE  
WEAKENING ON TUE AND ALLOWING RAIN TO SPREAD OVER THE SOUTHEAST  
INTERIOR.  
 
A STRONG SHORT WAVE OVER SOUTHWEST ALASKA WILL MOVES EAST OVER  
THE ALASKA RANGE ON TUE CAUSING THE CHINOOK FLOW TO END AND  
PROVIDING INSTABILITY WHICH COULD CAUSE ISOLATED EMBEDDED  
THUNDERSTORMS IN THE SOUTHEAST INTERIOR TUE.  
 
SURFACE...  
A 1002 MB LOW SOUTHWEST OF WRANGEL ISLAND WILL PERSIST THROUGH  
MON THEN WEAKEN. A WEATHER FRONT STRETCHING EAST FROM THIS LOW TO  
100 NM NORTH OF DEMARCATION POINT, WILL MOVE TO DEMARCATION POINT  
TO UTQIAGVIK BY 4AM MON, AND THEN MOVE SOUTH OF KAKTOVIK TO POINT  
LAY BY 4PM TUE, THEN PERSIST INTO WED. HIGH PRESSURE OVER THE  
ARCTIC OCEAN NORTH OF THIS FRONT WILL BUILD SOUTH TO JUST NORTH OF  
THE ARCTIC COAST OF ALASKA BY TUE. THESE FEATURES WILL COMBINE TO  
CAUSE EAST WINDS AND FOG ALONG THE ARCTIC COAST BY MON THAT WILL  
PERSIST INTO WED. WINDS WILL INCREASE TO 20-30 KT BY MON NIGHT AND  
THEN PERSIST INTO WED.  
 
HIGH PRESSURE STRETCHING FROM SOUTHEAST ALASKA TO THE COPPER RIVER  
BASIN WILL PERSIST THROUGH MON NIGHT. THIS IS CAUSING GAP WINDS OF  
35G60 MPH THROUGH ALASKA RANGE PASSES THAT WILL PERSIST INTO EARLY  
TUE, WITH A LULL IN WINDS MON AS A FRONT MOVES OVER THE RANGE.  
 
AN OCCLUDED FRONT FROM DUTCH HARBOR TO THE KUSKOKWIM DELTA WITH A  
WARM FRONT THE KUSKOKWIM DELTA TO EAGLE AND A COLD FRONT FROM THE  
KUSKOKWIM DELTA TO THE KENAI PEN. THE OCCLUDED FRONT WILL MOVE O  
THE YUKON DELTA TO KOTZEBUE TO AMBLER BY 4AM MON WITH A WARM FRONT  
FROM AMBLER TO EAGLE AND A COLD FRONT FROM AMBLER TO ANCHORAGE. BY  
4PM MON OCCLUDED FRONT WILL LIE FROM THE YUKON DELTA TO A TRIPLE  
POINT NEAR ANAKTUVUK PASS, WITH A WARM FRONT FROM ANAKTUVUK PASS  
TO OLD CROW AND COLD FRONT FROM ANAKTUVUK PASS TO DENALI PARK. THE  
FRONT WILL THEN WEAKEN IN PLACE THROUGH TUE AM. EXPECT RAIN ALONG  
AND JUST NORTH OF THE OCCLUDED AND WARM FRONTS, AND ALONG THE COLD  
FRONT THROUGH TUE AM, EXCEPT IN CHINOOK SHADOW IN THE SOUTHEAST  
INTERIOR. EXPECT BETWEEN .25-.50 INCH OF RAIN IN THE WESTERN  
INTERIOR AND WEST COAST WITH THIS SYSTEM.  
 
THE COLD FRONT WILL MOVE EAST ACROSS THE EASTERN INTERIOR TUE WITH  
A 999 MB LOW DEVELOPING BY 4PM TUE NEAR TANANA, AND THEN INTO THE  
YUKON OF CANADA ON WED. THIS WILL BRING RAIN TO ALL OF THE EASTERN  
INTERIOR ON TUE WITH THE RAIN TAPERING OFF FROM THE NORTH ON WED.  
EXPECT 1-2 INCHES OF RAIN FROM TUE PM THROUGH WED WITH THE  
HEAVIEST RAIN ALONG THE ALASKA RANGE. THIS WILL CAUSE RAPID RISES  
ON SOUTHEAST INTERIOR RIVERS IN THE SECOND HALF OF THIS WEEK BUT  
NO FLOODING IS EXPECTED AT THIS TIME.  
 
A 988 MB LOW OVER KAMCHATKA WILL MOVE TO THE CENTRAL BERING SEA AS  
A 995 MB LOW BY 4PM WED. THIS WILL CAUSE WINDS TO INCREASE OVER  
THE EASTERN BERING SEA TUE NIGHT AND WED.  
 

 
   
DISCUSSION
 
 
MODELS INITIALIZE WELL AND SHOW SIMILAR SOLUTIONS ALOFT AND AT  
THE SURFACE THROUGH WED. PRECIPITATION SHOWS SIMILAR AREAS OF  
OCCURRENCE ON GFS/ECMF THROUGH WED, WITH NAM SLIGHTLY DIFFERENT  
LOCATIONS. PREFER THE GFS PRECIP FIELD THROUGH WED.  
 
MODELS BEGIN TO DIFFER ON SHORT WAVE DETAILS ON THU, WITH  
SIGNIFICANT DIFFERENCE BY NEXT WEEKEND. WILL FOLLOW WPC IDEA OF  
GOING PRIMARILY WITH ENSEMBLES FROM FRI INTO NEXT WEEKEND.  
 
COASTAL HAZARD POTENTIAL DAYS 3 AND 4...NONE.  
 

 
   
FIRE WEATHER
 
 
STRONG WINDS ALONG THE ALASKA RANGE THROUGH EARLY TUE, BUT RH  
GENERALLY ABOVE 40%.  
 

 
   
HYDROLOGY
 
 
EXPECT BETWEEN .25-.50 INCH OF RAIN IN THE WESTERN INTERIOR AND  
WEST COAST TONIGHT THROUGH MON. THIS WILL CAUSE SLIGHT RISE ON  
WESTERN ALASKA RIVERS THIS WEEK.  
 
RAIN WILL DEVELOP OVER ALL OF THE EASTERN INTERIOR ON TUE WITH  
THE RAIN TAPERING OFF FROM THE NORTH ON WED. EXPECT 1-2 INCHES OF  
RAIN FROM TUE PM THROUGH WED WITH THE HEAVIEST RAIN ALONG THE  
ALASKA RANGE. THIS WILL CAUSE RAPID RISES ON SOUTHEAST INTERIOR  
RIVERS IN THE SECOND HALF OF THIS WEEK BUT NO FLOODING IS EXPECTED  
AT THIS TIME.  
 

 
   
AFG WATCHES/WARNINGS/ADVISORIES
 
 
WIND ADVISORY FOR AKZ223-AKZ226.  
 
SMALL CRAFT ADVISORY FOR PKZ225.  

 
 

 
 
JB AUG 18  
 
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