111  
FXUS65 KPIH 221951  
AFDPIH  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE POCATELLO ID  
151 PM MDT FRI SEP 22 2017  
   
DISCUSSION
 
A LOW PRESSURE SYSTEM POSITIONED OVER BOISE EARLY THIS  
AFTERNOON WILL GRADUALLY FILL AND WEAKEN AS IT SHIFTS SLOWLY SE INTO  
NRN UTAH SATURDAY AND THEN EJECTS SLOWLY NE INTO WYOMING SUNDAY. THE  
NAM AND GFS MODELS DIFFER ON THE EXACT TRACK OF THE EJECTING LOW,  
PARTICULARLY SUNDAY, WHICH WILL HAVE A FAIRLY DRAMATIC IMPACT ON THE  
FORECAST ACROSS THE SE HIGHLANDS DURING THAT TIME FRAME. FOR NOW,  
HAVE EXTENDED THE WINTER WEATHER ADVISORY FOR THE CENTRAL MOUNTAINS  
UNTIL 11 PM THIS EVENING WHERE THE MODELS INDICATE THAT WE MAY PICK  
UP AN ADDITIONAL 1 TO 3 INCHES ABOVE 6000 FT MSL. AS THE LOW DRIFTS  
SE INTO NE NEVADA LATE TONIGHT WE EXPECT TO SEE AT LEAST PARTIAL  
CLEARING WHILE COLDER AIR INFILTRATES THE REGION FROM THE NORTH.  
STATISTICAL MODEL GUIDANCE IS INDICATING FREEZING TEMPERATURES  
THROUGHOUT THE SNAKE RIVER PLAIN AND EASTERN MAGIC VALLEY BY MORNING  
AND HAVE THUS ISSUED A FREEZE WARNING FOR THOSE AREAS. DUE TO THE  
DISCREPANCY IN THE TRACK OF THE LOW EJECTING NE INTO WYOMING  
SATURDAY NIGHT AND SUNDAY, WE HAVE MAINTAINED THE HIGHER  
PRECIPITATION PROBABILITY AND POTENTIAL ACCUMULATIONS ACROSS THE SE  
HIGHLANDS. WE WILL HAVE TO TAKE A LOOK AT A POTENTIAL WINTER WEATHER  
ADVISORY FOR THAT REGION IF WE SEE THE MODELS CONSOLIDATE TOWARD THE  
NORTHERLY AND WETTER TRACK OF THE NAM. MORE ON THAT LATER. BEYOND  
SUNDAY, THE MODELS SHOW A RIDGE BUILDING ALONG THE COAST AS A WEAK  
PACIFIC DISTURBANCE TOPS THE RIDGE AND DIGS SE ALONG THE CONTINENTAL  
DIVIDE MONDAY NIGHT/TUESDAY PRODUCING A LOW END CHANCE OF SHOWERS  
ALONG THE MONTANA DIVIDE THROUGH THAT TIME FRAME. BY WEDNESDAY, THE  
GFS HAS THE RIDGE BUILDING INLAND WITH WARMER AND DRIER CONDITIONS  
INTO THE WEEKEND. THE ECMWF ON THE OTHER HAND WANTS TO DEVELOP A  
RETROGRADING CUT-OFF LOW FROM THE PASSING WAVE TUESDAY THAT SINKS  
INTO NEVADA AND LATER EJECTS NE INTO WYOMING SATURDAY PROVIDING AT  
LEAST A LOW END CHANCE OF SHOWERS ACROSS THE SE HIGHLANDS. WE ARE  
NOT GIVING THE ECMWF MUCH WEIGHT AT THIS TIME BUT WILL MAINTAIN SOME  
"CHICKEN-POPS" ACROSS THE SE MOUNTAINS UNTIL WE SEE SOME RESOLUTION  
AMONG THE MODELS EITHER WAY. DAYTIME HIGHS REMAIN COOL-ISH THROUGH  
MONDAY AND THEN BEGIN TO GRADUALLY WARM THROUGH THE WEEK. HUSTON  

 
   
AVIATION
 
EXPECT RAIN TO CONTINUE TO TAPER OFF THIS AFTERNOON AT  
ALL SITES WITH DIJ THE MOST LIKELY TO CONTINUE THIS EVENING. EXPECT  
THE MVFR CEILINGS TO IMPROVE AT SUN...PIH AND IDA WHILE CONTINUE THE  
MARGINAL CEILINGS AT DIJ. BYI SHOULD REMAIN VFR. EXPECT MAINLY  
DRY CONDITIONS AT ALL SITES AND REMAINING VFR BUT COULD SEE  
AFTERNOON SHOWERS AND MARGINAL CEILINGS AT SUN AND DIJ SATURDAY  
AFTERNOON. WINDS NOT EXPECTED TO BE STRONG BUT UP VALLEY 10 TO 15  
KNOT WINDS POSSIBLE AT IDA AND PIH AGAIN ON SATURDAY AFTERNOON. GK  

 
   
FIRE WEATHER
 
NO FIRE WEATHER CONCERNS FOR SEVERAL DAYS WITH FUELS  
NOW NON CRITICAL AFTER SEVERAL DAYS OF COLD TEMPERATURES, HIGH  
HUMIDITY AND ABUNDANT PRECIPITATION. COULD SEE A FEW SHOWERS  
CONTINUING THROUGH SUNDAY MAINLY IN HIGH ELEVATIONS WITH A DRYING  
AND WARMING TREND EXPECTED NEXT WEEK. HIGH TEMPERATURES WILL WARM  
TO SEASONAL NORMAL FOR LATE SEPTEMBER BY TUESDAY AND ARE EXPECTED TO  
RISE TO WELL ABOVE NORMAL BY NEXT THURSDAY. EXPECT MAINLY DRY  
CONDITIONS MONDAY THROUGH NEXT WEEK. GK  

 
   
PIH WATCHES/WARNINGS/ADVISORIES
 
 
WINTER WEATHER ADVISORY UNTIL 11 PM MDT THIS EVENING FOR IDZ018-019-  
031-032.  
 
FREEZE WARNING LATE TONIGHT THROUGH 9 AM MDT SATURDAY FOR IDZ017-020-  
021.  

 
 

 
 
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