273  
FXUS65 KBOI 182112  
AFDBOI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOISE ID  
312 PM MDT FRI SEP 18 2020  
   
SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT
 
UPPER LEVEL TROUGH  
AND ASSOCIATED COLD FRONT IS MOVING ONTO THE OREGON COAST THIS  
AFTERNOON. A LINE OF SHOWERS AND ISOLATED THUNDERSTORMS IS  
FORMING ACROSS FAR EASTERN OR AND SOUTHWEST IDAHO THIS AFTERNOON.  
SOME OF THE THUNDERSTORMS WILL BE ACCOMPANIED BY HEAVY RAIN,  
GUSTY WINDS AND SMALL HAIL. SHOWER COVERAGE WILL CONTINUE TO  
INCREASE THIS EVENING AND THE LINE WILL EVENTUALLY SHIFT NORTHEAST  
OF THE AREA OVERNIGHT WITH THE PASSAGE OF THE COLD FRONT. WITH  
UPPER LEVEL JET RIGHT OVER SOUTHERN IDAHO, A THREAT OF STRONG  
DOWNSLOPING WINDS IS POSSIBLE ACROSS OWYHEE COUNTY THIS AFTERNOON  
AND EVENING WITH THE SHOWERS AND THUNDERSTORMS. THE TROUGH WILL  
MOVE THROUGH OUR AREA LATE TONIGHT THROUGH SATURDAY FOR MORE  
SHOWERS AND A SLIGHT CHANCE OF THUNDERSTORMS. MOST OF THE SHOWER  
ACTIVITY IS EXPECTED IN THE CENTRAL IDAHO MOUNTAINS. THE SHOWERS  
WILL TAPER OFF BY SATURDAY NIGHT AS THE SYSTEM MOVES EAST. DRY  
CONDITIONS EXPECTED ON SUNDAY UNDER WESTERLY FLOW ALOFT. THE  
WILDFIRE SMOKE IS EXPECTED TO IMPROVE SLIGHTLY BUT RETURN LATE  
SUNDAY. TEMPERATURES WILL TREND COOLER THROUGH SATURDAY WITH  
WARMER TEMPERATURES RETURNING ON SUNDAY.  
   
LONG TERM...MONDAY THROUGH FRIDAY
 
AN UPPER LEVEL RIDGE  
WILL SLOWLY BUILD OVER THE AREA WITH DRY WEATHER AND A WARMING  
TREND. THE UPPER LEVEL WINDS WILL ALSO SHIFT BACK TO A SOUTHWESTERLY  
FLOW WHICH WILL LIKELY ALLOW WILDFIRE SMOKE FROM CALIFORNIA TO FLOW  
BACK INTO OUR AREA. A SERIES OF SHORTWAVE TROUGHS WILL RIPPLE OVER  
THE TOP OF THE RIDGE DURING THIS TIME BUT WILL NOT HAVE MUCH AFFECT  
ON THE OVER ALL DRY WEATHER PATTERN.  
 

 
   
AVIATION
 
MVFR VISIBILITIES DUE TO WILDFIRE SMOKE ARE SLOWLY  
IMPROVING WITH MOST AIRPORT LOCATIONS NOW REPORTING VISIBILITY  
GREATER THAN 3 STATUTE MILES. A COLD FRONT WILL MOVE FROM WEST TO  
EAST THROUGH THE AREA THIS EVENING. EXPECT LIGHT AND VARIABLE  
SURFACE WINDS AHEAD OF THE FRONT, SHIFTING TO WESTERLY AT 15 TO 20  
KTS BEHIND THE FRONT LATER THIS EVENING. SCATTERED THUNDERSTORMS ARE  
ALSO EXPECTED ALONG THE FRONT WITH GUSTS TO 40 KTS POSSIBLE. THE  
FRONT SHOULD REACH THE OREGON/IDAHO BORDER AROUND 00Z AND SWEEP  
EASTWARD THROUGH IDAHO OVERNIGHT.  
 
WEEKEND OUTLOOK...SURFACE WINDS WILL SHIFT TO NW BEHIND THE FRONT BY  
SATURDAY MORNING WHICH MAY CLEAR SOME OF THE SMOKE AND ALLOW  
VISIBILITIES TO IMPROVE A BIT BY SATURDAY AFTERNOON. RAIN SHOWERS  
WITH MVFR CEILINGS WILL LINGER IN THE CENTRAL IDAHO MOUNTAINS  
THROUGH SATURDAY AND DIMINISH BY SATURDAY NIGHT. WINDS ALOFT AT 10 K  
FEET WILL BE WESTERLY AT 15 TO 20 KTS.  
 

 
   
BOI WATCHES/WARNINGS/ADVISORIES
 
 
ID...RED FLAG WARNING UNTIL 9 PM MDT THIS EVENING  
IDZ401>403-421-423-426.  
OR...NONE.  
 

 
 

 
 
WWW.WEATHER.GOV/BOISE  
WWW.FACEBOOK.COM/NWSBOISE  
WWW.TWITTER.COM/NWSBOISE  
 
SHORT TERM...KA  
LONG TERM....JB  
AVIATION.....JB  
 
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