507
FXUS65 KMSO 282017
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
217 PM MDT SAT JUN 28 2025
DISCUSSION
KEY MESSAGES:
- ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS ACROSS NORTHWEST
MONTANA THROUGH THIS EVENING.
- WARMING AND DRYING TREND SUNDAY INTO EARLY NEXT WEEK, WITH
TEMPERATURES 10-15F ABOVE NORMAL.
- MODERATE RISK OF HEAT IMPACTS ACROSS LOW ELEVATIONS OF IDAHO
AND CLEARWATER COUNTIES MONDAY AND TUESDAY.
- SHOWER AND THUNDERSTORM ACTIVITY RETURNS TUESDAY, BECOMING MORE
WIDESPREAD INTO WEDNESDAY.
GOES SATELLITE AND RADAR OBSERVATIONS THIS AFTERNOON SHOWS
SCATTERED SHOWERS DEVELOPING ACROSS NORTHWEST MONTANA, WITH
ISOLATED THUNDERSTORMS BEING OBSERVED ALONG THE USA-CANADA
BORDER. ACTIVITY WILL CONTINUE TO FOCUS ACROSS THESE AREAS THROUGH
THE EVENING HOURS, WITH DRIER AIR SOUTH OF THE I-90 CORRIDOR
BRINGING PLENTY OF SUNSHINE. CLOUD COVER WILL CLEAR LATER THIS
EVENING INTO THE OVERNIGHT AS HIGH PRESSURE BEGINS TO BUILD INTO
THE REGION.
MODEL GUIDANCE IS IN STRONG AGREEMENT FOR A RIDGE OF HIGH
PRESSURE ACROSS THE REGION SUNDAY INTO THE FIRST PART OF NEXT
WEEK CAUSING VERY WARM AND DRY CONDITIONS. TEMPERATURES WILL BE
RUNNING 10 TO 15 DEGREES ABOVE SEASONAL AVERAGES, AS THE VALLEYS
EXPERIENCE UPPER 80S TO MID 90S BY MONDAY AFTERNOON. THE LOWER
VALLEYS OF NORTH CENTRAL IDAHO ARE EXPECTED TO HAVE TEMPERATURES
BREAKING INTO THE TRIPLE DIGITS. THEREFORE, A HEAT ADVISORY HAS
BEEN ISSUED FOR MONDAY AFTERNOON THROUGH TUESDAY EVENING ACROSS
LOWER ELEVATIONS OF IDAHO AND CLEARWATER COUNTIES, WHERE WARM
OVERNIGHT TEMPERATURES (UPPER-50S TO LOW-60S) WILL CONTRIBUTE TO
HEAT STRESS.
SHOWERS AND THUNDERSTORMS RETURN TUESDAY NEXT WEEK SOUTH OF I-90,
WITH ACTIVITY EXPANDING NORTHWARD AND BECOMING MORE WIDESPREAD
WEDNESDAY. ENSEMBLE GUIDANCE HAS BEEN CONSISTENT THE LAST FEW DAYS
HIGHLIGHTING A SURGE OF SUBTROPICAL MOISTURE UNDER SOUTH-SOUTHWEST
FLOW ACROSS THE GREAT BASIN INTO THE NORTHERN ROCKIES, WITH
ATMOSPHERIC MOISTURE CLIMBING 125-150% OF NORMAL. THIS FLOW
PATTERN WILL BE AIDED BY A RIDGE OF HIGH PRESSURE CENTERED NEAR
THE FOUR CORNERS REGION AND A CLOSED LOW FORMING OVER CALIFORNIA.
WEDNESDAY STANDS OUT AS THE DAY TO WATCH FOR STRONG TO MARGINALLY
SEVERE THUNDERSTORMS. MODEL GUIDANCE SUGGESTS THE BEST COMBINATION
OF MOISTURE, INSTABILITY, AND WIND SHEAR, AND WITH A SHORTWAVE
TROUGH UPSTREAM, SYNOPTIC FORCING WILL BE PRESENT AIDING IN
CONVECTIVE INITIATION. THE LACK OF STRONG WIND SHEAR (>40KTS), AND
DEEPER MOISTURE IN PLACE, POINTS TOWARDS MULTI-CELLULAR CLUSTERS,
CAPABLE OF HEAVY RAIN, HAIL (MOSTLY UP TO NICKLE SIZE), AND
STRONG OUTFLOW WINDS WITH ANY STRONGER STORMS. THIS PERIOD WILL BE
MONITORED CLOSELY IN THE COMING DAYS!
AVIATION
GOES SATELLITE AND RADAR OBSERVATIONS THIS AFTERNOON
SHOW THE MAIN AREA OF SHOWER AND STORM ACTIVITY FOCUSED ACROSS
LINCOLN AND FLATHEAD COUNTIES. THIS WILL CONTINUE REMAIN THE THEME
THROUGH 29/0300Z THIS EVENING BEFORE ACTIVITY DIMINISHES THIS
EVENING AS HIGH PRESSURE BUILDS INTO THE REGION. MOSTLY SUNNY
SKIES ARE EXPECTED SOUTH OF I-90 WHERE DRIER AIR IS PRESENT.
BREEZY WEST-NORTHWEST WINDS WILL DEVELOP AREA WIDE WITH GUSTS NEAR
20-25KTS AS A SURFACE LOW DEEPENS IN SOUTHEAST IDAHO.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...HEAT ADVISORY FROM NOON MONDAY TO 9 PM PDT TUESDAY FOR LOWER
HELLS CANYON/SALMON RIVER REGION...OROFINO/GRANGEVILLE
REGION.
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