465  
FXUS65 KPIH 080540  
AFDPIH  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE POCATELLO ID  
1040 PM MST WED DEC 7 2022  
   
UPDATE
 
 
HAD BEEN COVERING THE ONGOING FREEZING FOG SITUATION WITH AN SPS,  
BUT GIVEN SLIGHT EXPANSION OF THE FOG ON SATELLITE AND MULTIPLE  
SURFACE STATIONS NOW BELOW ONE-QUARTER MILE VISIBILITY INCLUDING  
ALONG THE I-86 AND I-84 INTERSTATE CORRIDORS, AND GIVEN LATEST NBM  
4.1 AND HRRR VISIBILITY PRODUCTS INSISTING FOG WILL REMAIN IN  
PLACE THROUGH THE NIGHT, HAVE UPGRADED TO A FREEZING FOG ADVISORY  
FOR THE EASTERN MAGIC VALLEY, LOWER SNAKE PLAIN, ADJACENT  
SOUTHERN HIGHLANDS, AND BEAR LAKE AREA THROUGH 11 AM THURSDAY.  
EVEN IF LARGE PORTIONS OF THESE ZONES DON'T CONSISTENTLY STAY  
BELOW ONE-QUARTER MILE, THE ADDITIONAL HAZARD OF SOME LIGHT  
FROST/ICE DEPOSITION ON ROADWAYS WARRANTS THE ADVISORY. SOME  
CONCERN THAT HIGH CLOUDS APPROACHING FROM THE SOUTH MAY HELP TO  
ERODE SOME OF THE FOG AT SOME POINT, BUT THOSE CLOUDS ARE REALLY  
TAKING THEIR TIME GETTING INTO OUR FORECAST AREA PER SATELLITE  
TRENDS, AND OVERALL CONFIDENCE ON THEIR IMPACT IS LOW. HIGH-RES  
MODELS ALSO ADVERTISE EXPANDING FOG AND LOW STRATUS OVERNIGHT  
FURTHER NORTH UP THE SNAKE PLAIN/ARCO DESERT INTO FREMONT COUNTY,  
BUT NO ISSUES THERE SO FAR SO WILL MONITOR TRENDS FOR ANY NEEDED  
ADJUSTMENTS IN SPS/ADVISORY MESSAGING OVERNIGHT. FORECAST GRIDS  
CURRENTLY COVER EXPECTED FREEZING FOG EVOLUTION FAIRLY WELL SO NO  
CHANGES MADE THERE. - KSMITH  
 

 
   
PREV DISCUSSION
 
/ISSUED 118 PM MST WED DEC 7 2022/  
 
SHORT TERM...TONIGHT AND THURSDAY. WE CONTINUE TO SEE AREAS OF  
STRATUS, FREEZING FOR AND/OR LIGHT SNOW TODAY ACROSS MAINLY THE  
SNAKE PLAIN, SOUTHERN AND EASTERN HIGHLANDS, AND STANLEY BASIN. WE  
HAVE SEEN SOME DISSIPATION ACROSS THE STANLEY BASIN, TETON VALLEY  
AND SNAKE PLAIN. HOWEVER, IN SOME CASES WHERE THE STRATUS CLEARED  
OUT, IT HAS REMAIN FOGGY PAST NOON. UNTIL THE NEXT STORM ARRIVES  
EARLY FRIDAY, EXPECT MORE OF THE SAME. WE SHOULD SEE SOME  
RETURN/EXPANSION OF STRATUS/FOG/LIGHT SNOW ACROSS THE SNAKE PLAIN,  
SOUTHERN AND EASTERN HIGHLANDS, AND STANLEY BASIN TONIGHT. THE  
IDEA OF LIGHT SNOW /FLURRIES OUT OF THE STRATUS DECK ACTUALLY  
LOOKS MORE PLAUSIBLE BY MORNING AS A WEAKENING LOW CLIPS SOUTHERN  
IDAHO. SNOW AMOUNTS LOOK LIKE, BUT STILL ENOUGH THAT IT COULD  
IMPACT TRAVEL WHERE IT DOES OCCUR. FREEZING FOG AGAIN WILL BE  
LOCALLY DENSE, AND POTENTIALLY CREATE ADDITIONAL SLICK SPOTS AND  
TRAVEL PROBLEMS DUE TO LOW VISIBILITY. BY TOMORROW AFTERNOON, WITH  
WINDS AND FLOW BECOMING SOUTH TO SOUTHEAST...WE SHOULD SEE ALL OF  
THIS ERODING SOUTH TO NORTH AND BY LATE AFTERNOON BE CONFINED TO  
THE EASTERN HIGHLANDS, THE ARCO DESERT AND UPPER SNAKE PLAIN.  
HEADING INTO FRIDAY MORNING, SNOW WILL BE SPREADING INTO THE  
CENTRAL MOUNTAINS, MAGIC VALLEY AND SOUTH HILLS/ALBION MOUNTAINS.  
AMOUNTS AT LEAST THROUGH SUNRISE WILL BE UNDER AN INCH, EXCEPT  
ACROSS PORTIONS OF THE WOOD RIVER VALLEY AND SAWTOOTHS. THIS IS  
PART OF THE EVENT THAT LASTS INTO FRIDAY EVENING AND WE HAVE MORE  
ON THAT IN OUR EXTENDED SECTION OF THIS DISCUSSION. TEMPERATURES  
WILL REMAIN A BIT BELOW AVERAGE, EVEN WHERE WE CAN GET SOME  
SUN...WITH MOST AREAS REMAIN AT OR BELOW FREEZING IN THE  
AFTERNOON. KEYES  
 
LONG TERM...FRIDAY THROUGH NEXT WEDNESDAY. TWO PACIFIC STORM  
SYSTEMS WILL IMPACT THE REGION THROUGH THIS FORECAST PERIOD. THE  
FIRST FAIRLY PROGRESSIVE WAVE SWEEPS THROUGH THE REGION FRIDAY AND  
EXITS EAST OF THE AREA LATE FRIDAY NIGHT DEPOSITING 2 TO 5 INCHES OF  
SNOW ACROSS THE SAWTOOTH, ISLAND PARK, AND BEAR LAKE MOUNTAIN  
REGIONS WITH VARYING AMOUNTS IN THE VALLEY LOCALES WITH THE HARDEST  
HIT REGION BEING THE SHOSHONE-ARCO-HAILEY AREA WITH UPWARDS OF 0.5  
TO 3 INCHES POSSIBLE. WE GET A QUICK BREAK IN THE WAKE OF THAT  
SYSTEM BEFORE THE LEADING EDGE OF THE NEXT INCOMING STORM SPREADS  
INTO THE CNTRL MOUNTAINS SATURDAY MORNING. HERE THE MODELS CONTINUE  
TO SHOW THE PARENT STORM SPREADING SSE INTO CALIFORNIA BY SUNDAY  
WITH A BROADENING ENVELOP OF POSSIBILITIES ON THE TRACK AND SPEED OF  
THE SYSTEM AS IT WORKS THROUGH THE INTERMOUNTAIN WEST SUNDAY NIGHT  
AND MONDAY. THANKFULLY, THE BULK OF THE PRECIPITATION IS EXPECTED TO  
FALL SATURDAY THROUGH SUNDAY WITH THE LEADING EDGE OF THE STORM  
SYSTEM. WATCH/WARNING HEADLINES FOR THE CNTRL MOUNTAINS AND CRATERS  
AREA WILL LIKELY FOLLOW AS THE EVENT DRAWS NEAR AND STARTING  
SATURDAY MORNING AND CONTINUING INTO SUNDAY MORNING. NEAR ADVISORY  
LEVEL SNOWFALL WILL SPREAD EAST INTO THE REMAINDER OF SE IDAHO  
SATURDAY NIGHT THROUGH SUNDAY NIGHT, MAINLY IMPACTING THE SRN AND  
ERN MOUNTAIN AREAS. HEADLINES FOR THOSE AREAS ARE UNCERTAIN AT THIS  
TIME. DRIER CONDITIONS WILL SPREAD FROM WEST TO EAST ACROSS THE  
REGION MONDAY NIGHT THROUGH TUESDAY AS THE STORM SYSTEM GRADUALLY  
EXITS EAST OF THE REGION. LOOK FOR A RETURN TO MUCH BELOW NORMAL  
TEMPERATURES MONDAY AND PARTICULARLY TUESDAY AND WEDNESDAY. HUSTON  
 
AVIATION...WE CONTINUE WITH ISSUES RELATED TO STRATUS, FREEZING  
FOG AND/OR LIGHT SNOW FALLING OUT OF THE LOW CLOUD DECK. WE HAVE  
SEEN THAT ERODE AT IDA AND DIJ TODAY. SUN HASN'T BEEN A PROBLEM  
AND SHOULDN'T BE AT LEAST FOR TONIGHT AND TOMORROW MORNING. FOG  
HAS BEEN VERY LOW TO ERODE AT PIH, AND LOW CLOUDS/FOG ARE PUSHING  
WEST INTO BYI. WHERE CONDITIONS REMAIN POOR, EXPECT IFR/LIFR  
WEATHER. WE EXPECT ALL OF THIS TO EXPAND OVERNIGHT AND TOMORROW  
MORNING, IMPACT ALL TAF SITES EXCEPT SUN. IFR TO VLIFR WEATHER DUE  
TO LOW CLOUDS, VISIBILITY AND/OR LIGHT SNOW ARE POSSIBLE. BY  
TOMORROW AFTERNOON, WE SEE SOUTH TO SOUTHEAST FLOW PICKING UP  
AHEAD OF THE NEXT LOW FOR FRIDAY. THAT SHOULD HELP ERODE THE  
STRATUS AND FOG FROM SOUTH TO NORTH. LOOK FOR IMPROVING CONDITIONS  
EARLY IN THE AFTERNOON FOR BYI AND PIH. IT LOOKS LIKE MID TO LATE  
AFTERNOON FOR IMPROVEMENT AT DIJ AND IDA. ADMITTEDLY, CONFIDENCE  
FOR SUN IS FAIRLY LOW. WE DID INCREASE LOW AND MID CLOUD COVER  
IN THE AFTERNOON BASED ON THE IDEA SOUTHERLY WINDS WILL PUSH  
ANYTHING REMAINING IN MAGIC VALLEY INTO THE WOOD RIVER VALLEY.  
HOWEVER, THE LATEST PROBABILISTIC FORECAST SAYS THAT CHANCE IS  
LESS THAN 20% WE DON'T THINK FOG WILL BE AN ISSUE AT ALL. THE  
LATEST TAF IS BORDERING ON MVFR DURING THAT PERIOD. KEYES  
 

 
   
PIH WATCHES/WARNINGS/ADVISORIES
 
 
FREEZING FOG ADVISORY UNTIL 11 AM MST THURSDAY FOR IDZ054-055-  
057>059-061.  
 

 
 

 
 
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