562
FXUS65 KMSO 201844
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1244 PM MDT MON JUL 20 2026
DISCUSSION
KEY MESSAGES:
- PERIODS OF HAZE AND SMOKE PERSIST ACROSS THE REGION INTO
TONIGHT. LOW RAIN SHOWER AND STORM CHANCES.
- MONSOON MOISTURE SURGE RETURNS TUESDAY THROUGH THURSDAY.
LOCALIZED FLASH FLOODING AND A FEW SEVERE THUNDERSTORMS
POSSIBLE.
- HOT TEMPERATURES ARE EXPECTED THIS WEEK, WITH HIGHS REACHING
THE 90S UP TO 106 DEGREES IN THE LOWER ELEVATIONS OF IDAHO.
THIS AFTERNOON THROUGH WEDNESDAY...UPPER LEVEL MONSOONAL MOISTURE
WILL CONTINUE TO STREAM ACROSS THE NORTHERN ROCKIES INTO TUESDAY
MORNING, BRINGING PERSISTENT HIGH AND MID-LEVEL CLOUD COVER AND
ISOLATED LIGHT SHOWERS. SMOKE AND HAZE FROM WILDFIRES IN OREGON
AND WASHINGTON WILL INTERMITTENTLY DEGRADE AIR QUALITY, THOUGH A
DEVELOPING EASTERLY PRESSURE GRADIENT TONIGHT MAY OFFER SOME
LOCALIZED CLEARING.
ATMOSPHERIC MOISTURE DEEPENS SIGNIFICANTLY ON TUESDAY, WITH
PRECIPITABLE WATER (PWAT) VALUES CLIMBING TO 200-250% OF NORMAL
FOR THE REGION. HOWEVER, ABUNDANT MORNING CLOUD COVER WILL LIKELY
LIMIT SURFACE INSTABILITY AND OVERALL THUNDERSTORM POTENTIAL. BY
TUESDAY AFTERNOON, HIGH-RESOLUTION GUIDANCE INDICATES SCATTERED
THUNDERSTORM DEVELOPMENT FROM LEMHI COUNTY INTO SOUTHWEST MONTANA,
WHERE BRIEF HEAVY RAINFALL AND ERRATIC WIND GUSTS EXCEEDING 40
MPH WILL BE THE PRIMARY THREATS.
BY WEDNESDAY AFTERNOON, THE THREAT SHIFTS SLIGHTLY NORTHWARD.
AREAS SOUTH OF U.S. HIGHWAY 12 WILL SEE AN INCREASED RISK OF
LOCALLY HEAVY RAINFALL CAPABLE OF TRIGGERING DEBRIS FLOWS OR FLASH
FLOODING. THE OVERALL MAGNITUDE OF THIS THREAT REMAINS HIGHLY
CONDITIONAL ON MORNING CLEARING AND THE RESULTING REALIZED
INSTABILITY.
IT WILL ALSO BE QUITE WARM TO HOT. NBM TEMPERATURES ARE ON THE
WARMER SIDE COMPARED TO MOST GUIDANCE AND WOULD BRING
TEMPERATURES NEAR HEAT ADVISORY LEVELS TO THE LOWER ELEVATIONS OF
NORTH-CENTRAL IDAHO. HOWEVER, THERE IS CONSIDERABLE UNCERTAINTY
REGARDING HOW MUCH CLOUDS AND SMOKE MAY IMPACT THE HIGH
TEMPERATURE FORECAST. STILL ADVISORIES MAY BE NEEDED FOR THE
WEDNESDAY/THURSDAY TIME PERIOD IF CONFIDENCE INCREASES.
THURSDAY THROUGH THE WEEKEND...THURSDAY PRESENTS A MORE DYNAMIC
SETUP AS THE REGION TRANSITIONS FROM DEEP MONSOONAL MOISTURE TO A
DRIER, MORE SHEARED SOUTHWESTERLY FLOW. THIS COMBINATION OF
ENHANCED VERTICAL WIND SHEAR AND INCREASED INSTABILITY COULD
SUPPORT STRONG TO SEVERE THUNDERSTORMS, MAKING THURSDAY A KEY
PERIOD TO MONITOR.
BY FRIDAY AND INTO THE WEEKEND, THE SYNOPTIC PATTERN SHIFTS
TOWARD NEAR-CRITICAL FIRE WEATHER CONDITIONS. INCREASING WESTERLY
WINDS, A DRYING AIR MASS, AND A SHARP DECLINE IN SHOWER ACTIVITY
WILL COMBINE TO ELEVATE FIRE DANGER ACROSS THE REGION.
AVIATION
VFR CONDITIONS WILL PREVAIL THROUGH TUESDAY MORNING.
MONSOONAL MOISTURE OVERSPREADING THE REGION WILL MAINTAIN
WIDESPREAD HIGH AND MID- LEVEL CLOUD COVER AND ISOLATED LIGHT
SHOWERS. BY TUESDAY AFTERNOON, SCATTERED THUNDERSTORMS ARE
POSSIBLE ACROSS LEMHI COUNTY AND SOUTHWEST MONTANA; HOWEVER,
CONVECTIVE DEVELOPMENT REMAINS HIGHLY CONDITIONAL ON THE CLEARING
OF MORNING CLOUD COVER. IF THESE STORMS MATERIALIZE, BRIEF MVFR
CEILINGS AND VISIBILITIES MAY IMPACT KSMN AND KBTM AFTER 21/2200Z.
WINDS WILL REMAIN RELATIVELY LIGHT AND DIURNALLY DRIVEN THROUGH
THIS AFTERNOON. AN EASTERLY PRESSURE GRADIENT WILL DEVELOP ACROSS
WESTERN MONTANA TONIGHT INTO TUESDAY MORNING, BUT PEAK GUSTS ARE
EXPECTED TO REMAIN UNDER 20 KNOTS.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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