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Ramsay, Montana Weather Forecast Discussion

406
FXUS65 KMSO 111916
AFDMSO

Area Forecast Discussion National Weather Service Missoula MT 116 PM MDT Thu Sep 11 2025

.DISCUSSION...

KEY MESSAGES:

- Afternoon and evening showers and thunderstorms are expected today and Friday, bringing threats of gusty outflow winds up to 45 mph, localized heavy downpours, small hail, and frequent lightning.

- A low-end debris flow threat continues for sensitive burn scars due to the potential for localized heavy rain.

- An unsettled, cooler pattern persists through the weekend and into early next week, with another storm system expected to bring widespread showers and potentially much cooler temperatures by Monday.

An upper-level low continues to spin slowly eastward across the Northern Rockies, keeping our region under a moist and unstable airmass. Convection allowing models agree on showers and thunderstorms developing by late this afternoon and continue into the evening.

The primary concerns with today`s storms will be gusty outflow winds, brief heavy rain, and lightning. With precipitable water values remaining high, some storms could produce localized rainfall rates that elevate the debris flow risk over susceptible burn scars, such as the Daly Burn scar. The potential for small hail also exists, particularly across north-central Idaho and southwest Montana, where instability in the hail growth zone is slightly higher, with CAPE values approaching 500J/kg. The HRRR model suggests some of the stronger cells could produce hail up to penny size (0.75 inches). Storms will diminish by late in the evening. patchy fog may develop overnight in valleys that received significant rainfall.

The slow-moving low will keep the region unsettled on Friday, with another round of scattered showers and thunderstorms expected. Model guidance suggests the focus for heavier showers may shift to northwest Montana and toward the mountains of Glacier National Park and the Salish Mountains. This could bring periods of heavy rain to the Going to the Sun Road. Threats of gusty winds and lightning will persist. By Friday night and into Saturday morning, partial clearing combined with moist ground could once again lead to patchy valley fog.

By Saturday, the upper low finally shifts into eastern Montana. Our region will remain under cyclonic flow, supporting scattered showers and a few isolated thunderstorms, primarily across western Montana. Sunday may offer a brief lull with some morning sun before clouds increase ahead of our next approaching weather system.

Confidence is increasing on another Pacific trough will move into the region Sunday afternoon into Monday, ushering in another round of widespread showers and cooler temperatures, and increased westerly winds.

Ensemble model guidance presents two primary scenarios:

A "cut-off" low (around a 70% probability): The trough deepens and slows down over the region. This would result in a wetter and colder period, with prolonged rainfall and valley high temperatures potentially struggling to get out of the 50s and low 60s on Monday.

A progressive trough (around 30% probability): The system moves through more quickly without cutting off from the main jet stream. This would lead to a drier and breezier outcome with less overall precipitation.

We will continue to monitor this system closely as it develops. For now, plan on a cool and wet start to the work week.

&&

.AVIATION...Convective showers and thundershowers possible again this afternoon and evening between 11/2000z and 12/0400z. Spotty IFR/LIFR weather conditions expected with reduced visibilities and ceilings. Isolated areas of strong gusty outflow winds to 40 knots, heavy rainfall intensities that may cause ponding on runways and airfields, and small hail possible. The highest risk areas are most likely near KMSO, KHRF, and to a lesser extent KBTM and KGPI. Overnight patchy valley fog and lingering lowered ceilings/stratus are possible through about 12/1400z.

&&

.MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. &&

$$

NWS MSO Office Area Forecast Discussion

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