727
FXUS65 KMSO 160829
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
229 AM MDT THU JUL 16 2026
DISCUSSION
KEY MESSAGES:
- SCATTERED STRONG TO SEVERE THUNDERSTORMS THIS AFTERNOON AND
EVENING, WITH STRONG WINDS, LARGE HAIL, AND HEAVY RAIN.
- THUNDERSTORMS IN FORECAST THROUGH THE REST OF THE WEEK WITH
ACTIVE NORTH AMERICAN MONSOON FLOW PATTERN.
THE LARGE SCALE FLOW PATTERN WILL REMAIN NEAR STATIONARY FOR THE
NEXT 7-10 DAYS ACROSS THE WESTERN US. GLOBAL ENSEMBLES ARE IN
STRONG AGREEMENT FOR HIGH PRESSURE TO BE ANCHORED OVER THE
CENTRAL ROCKIES, WITH A TROUGH OF LOW PRESSURE OVER THE PACIFIC
NORTHWEST AND SOUTHERN BRITISH COLUMBIA. THIS PLACES THE NORTHERN
ROCKIES UNDER A SOUTH-SOUTHFLOW PATTERN, WITH ABUNDANT SUBTROPICAL
MOISTURE STREAMING NORTHWARD ASSOCIATED WITH THE NORTH AMERICAN
MONSOON. FURTHERMORE, THIS FLOW PATTERN WILL KEEP A WARM AIRMASS
OVERHEAD, WITH TEMPERATURES RUNNING ABOVE NORMAL THROUGH THIS
WEEKEND INTO NEXT WEEK.
THE THREAT FOR STRONG TO SEVERE THUNDERSTORMS IS THE PRIMARY
FOCUS TODAY AND TOMORROW. SATELLITE OBSERVATIONS THIS MORNING
SUGGEST SEVERAL HOURS OF SUNSHINE ON THE WAY THROUGH THE EARLY
AFTERNOON, WITH ATMOSPHERIC INSTABILITY PEAKING BY LATE AFTERNOON.
THE STORM PREDICTION CENTER HAS THE ENTIRE AREA UNDER A MARGINAL
TO A SLIGHT RISK OF SEVERE THUNDERSTORMS (5-15% PROBABILITY).
FORECAST MODELS SUGGEST MLCAPE OF 1000-2000 J/KG, ALONG WITH
30-40KTS OF VERTICAL WIND SHEAR, AS SOUTH-SOUTHWEST WINDS INCREASE
ALOFT AS PACIFIC DISTURBANCE MOVES INTO EASTERN OREGON AND
WASHINGTON. THIS COMBINATION OF INSTABILITY AND SHEAR WILL BRING
THE RISK FOR LARGE HAIL (>1 INCH IN DIAMETER), STRONG WINDS (60+
MPH OR GREATER), AND HEAVY RAINFALL. HIGH-RESOLUTION MODELS
SUGGEST A FEW SUPERCELLS MAY FORM, WHERE WIND SHEAR IS MAXIMIZED
ALONG THE DIVIDE IN WESTERN MONTANA AND ACROSS THE CAMAS PRAIRIE
IN IDAHO. THUNDERSTORMS WILL INITIATE ACROSS THE HIGHER TERRAIN IN
CENTRAL IDAHO AND NORTHEAST OREGON BY EARLY AFTERNOON, GRADUALLY
EXPANDING IN COVERAGE AND MOVING NORTHWARD THROUGH WESTERN MONTANA
THROUGH THE EVENING. PLEASE STAY WEATHER AWARE THIS EVENING,
ESPECIALLY IF YOU HAVE OUTDOOR PLANS!
ANOTHER ROUND OF STRONG TO SEVERE THUNDERSTORMS IS ON TAP FOR
FRIDAY, WITH THE STORM PREDICTION CENTER PLACING THE REGION UNDER
A MARGINAL THREAT. THIS THREAT WILL ONCE AGAIN BE DRIVEN BY HIGH
INSTABILITY FOR OUR AREA, WITH CAPE VALUES OF 1000-1500 J/KG.
LOOKING AHEAD TO THE WEEKEND, THE FOCUS FOR SHOWERS AND
THUNDERSTORMS SHIFT INTO LEMHI COUNTY, ID AND SOUTHWEST MONTANA.
THE REST OF THE AREA WILL REMAIN WARM AND DRY. THIS CHANGE WILL BE
DRIVEN BY A WESTERLY FLOW ALOFT, WITH ATMOSPHERIC INSTABILITY
DECREASING FOR MANY AREAS.
AVIATION
A MONSOON SURGE FROM THE SOUTH-SOUTHWEST HAS
ATMOSPHERIC MOISTURE RUNNING WELL ABOVE NORMAL ACROSS THE REGION.
CLEAR SKIES THIS MORNING INTO THE AFTERNOON, WILL SET THE STAGE
FOR PLENTY OF ATMOSPHERIC INSTABILITY. THUNDERSTORMS WILL
INITIATE OFF THE TERRAIN OF CENTRAL IDAHO AND NORTHEAST OREGON
BETWEEN 16/1800-2000Z, WITH STORMS MOVING NORTHWARD THROUGH THE
EVENING. INCREASING SOUTH-SOUTHWEST WINDS ALOFT WILL PROVIDE
SUFFICIENT WIND SHEAR TO ORGANIZE THUNDERSTORMS, WITH A 5-15%
CHANCE FOR SEVERE THUNDERSTORMS ACROSS THE REGION. PRIMARY STORM
THREATS INCLUDE LARGE HAIL (1 INCH IN DIAMETER OR GREATER), STRONG
WINDS (50-60KTS), AND HEAVY RAIN.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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