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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