423
FXUS65 KMSO 202013
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
213 PM MDT WED MAY 20 2026
DISCUSSION
KEY MESSAGES:
- DISTURBANCE BRINGING WIDESPREAD SHOWERS AND THUNDERSTORMS
ACROSS WESTERN MONTANA THIS AFTERNOON AND TONIGHT.
- RIDGE OF HIGH PRESSURE CAUSING A WARMING AND DRYING TREND OVER
THE NORTHERN ROCKIES THIS WEEKEND.
- COLD FRONT EXPECTED MONDAY/TUESDAY TIME FRAME WITH SIGNIFICANT
LOW PRESSURE SYSTEM IMPACTING THE REGION THROUGH MUCH OF THE
WEEK.
A LOW PRESSURE SYSTEM WILL BE DROPPING SOUTHWARD OUT OF CENTRAL
CANADA THIS AFTERNOON THROUGH THE OVERNIGHT HOURS. THIS SYSTEM
WILL PUSH A BACKDOOR COLD FRONT ACROSS THE REGION. THE DYNAMICS
ASSOCIATED WITH THIS DISTURBANCE WILL CAUSE NUMEROUS SHOWERS ALONG
WITH SCATTERED THUNDERSTORMS THIS AFTERNOON ACROSS NORTHWEST
MONTANA. THEN THE SHOWER ACTIVITY WILL SHIFT SOUTHWARD ACROSS
WESTERN MONTANA THIS AFTERNOON THROUGH THE OVERNIGHT HOURS. THESE
SHOWERS WILL BE CAPABLE OF PRODUCING MODERATE TO HEAVY RAINFALL
WITH MOST LOCATIONS ACROSS WESTERN MONTANA RECEIVING BETWEEN 0.1
TO 0.5 INCH OF RAINFALL BY THURSDAY MORNING. NORTH CENTRAL IDAHO
AND LEMHI COUNTY IS ANTICIPATED TO MISS OUT OF THE MAJORITY OF
THIS PRECIPITATION. SNOW LEVELS ARE EXPECTED TO HOVER AROUND 6000
FEET DURING THE PASSAGE OF THIS FEATURE. MCDONALD AND HOMESTAKE
PASSES ALONG WITH AREAS AROUND GEORGETOWN LAKE COULD RECEIVE UP TO
2 INCHES OF NEW SNOW, BUT IMPACTS TO AREA ROADWAYS WILL BE
MINIMAL.
A RIDGE OF HIGH PRESSURE WILL BE BUILDING OVER THE REGION FRIDAY
INTO THE WEEKEND CAUSING A WARMING AND DRYING TREND. THE MAJORITY
OF THE VALLEYS WILL BE IN THE 70S BY SATURDAY WITH THE LOW
VALLEYS OF NORTH CENTRAL IDAHO APPROACHING THE 90 MARK.
THE LONG RANGE MODELS ARE SHOWING A SIGNIFICANT LOW PRESSURE
SYSTEM MOVING INTO THE PACIFIC NORTHWEST DURING THE FIRST PART OF
NEXT WEEK. THE GENERAL CONSENSUS HAS A COLD FRONT PUSHING ACROSS
THE NORTHERN ROCKIES SOMETIME BETWEEN MONDAY INTO TUESDAY. WARM
AND DRY CONDITIONS ALONG WITH GUSTY WINDS AHEAD OF THE FRONT COULD
CREATE CRITICAL FIRE WEATHER CONDITIONS ON MONDAY AFTERNOON FOR
SOUTHWEST MONTANA. THE LOW PRESSURE SYSTEM WILL CAUSE COOLER AND
ACTIVE WEATHER FOR THE REGION THROUGH MUCH OF NEXT WEEK.
AVIATION
RADAR RETURNS, ASOS OBSERVATIONS, AND SPOTTER REPORTS
THIS AFTERNOON INDICATE THUNDERSTORMS PRODUCING HALF-INCH HAIL,
GUSTY WINDS TO ABOUT 20 KNOTS, AND FREQUENT LIGHTNING OVER
NORTHWEST MONTANA INCLUDING KGPI. CONVECTION WILL CONTINUE
THROUGH THIS AFTERNOON, WITH INSTABILITY MIGRATING SOUTH TO
INCLUDE KMSO THROUGH ABOUT 21/0200Z. EXPECT NEWLY DEVELOPED STORMS
TO HAVE SIMILAR CHARACTERISTICS AS THOSE AFFECTING NORTHWEST
MONTANA. CONVECTIVE ACTIVITY WILL TAPER OFF THIS EVENING, BUT
CHANCES FOR RAIN WILL CONTINUE INTO EARLY THURSDAY MORNING.
SHOWERS WILL HAVE THE POTENTIAL TO DECREASE VISIBILITY AND OBSCURE
TERRAIN ACROSS THE NORTHERN ROCKIES AIRSPACE. A GRADUAL CLEARING
WILL TAKE PLACE ON THURSDAY, BUT NOT BEFORE THERE ARE SOME CHANCES
FOR FOG IN THE EARLY HOURS AT KGPI AND KMSO. CONFIDENCE ON FOG
WAS TOO LOW TO INCLUDE IN 20/1800Z TAF ISSUANCE.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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