textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- A brief cooling trend today before an amplified upper ridge drives temperatures back above normal

- A surge of monsoonal moisture Friday night into Saturday may bring thunderstorms capable of heavy rain and gusty winds to southwest Montana and Lemhi County

High confidence exists among deterministic and ensemble guidance for a highly amplified upper-level ridge building across the Northern Rockies today and Friday. This synoptic setup will facilitate rapid warming, driving afternoon high temperatures into the mid-to-upper 80s across western Montana and the mid-90s within the lower elevations of central Idaho. High resolution models show an increased potential for showers to develop across western Montana this afternoon, with a few thunderstorms possible along the Continental Divide in northwest Montana.

By late Friday night, a surge of anomalous monsoonal moisture will advect northward from the Great Basin, phasing with a weak shortwave trough. This combined moisture and forcing will yield widespread showers and thunderstorms, primarily impacting Lemhi County and southwest Montana through Saturday, with primary hazards including torrential rainfall and gusty, erratic outflow winds. Uncertainty remains regarding the northern extent of this convective activity, with some guidance projecting the precipitation shield advancing as far north as Missoula. In the wake of this trough, ensemble clusters indicate upper-level ridging will rapidly re-establish over the region, initiating another period of above-normal temperatures.

AVIATION

Predominantly VFR conditions will prevail across western Montana and north central Idaho today and Friday under the influence of a building upper-level ridge. The primary operational concern will be isolated to scattered shower development across western Montana, with a few thunderstorms possible along the Continental Divide in northwest Montana near Glacier National Park after 17/2100Z. There is a 20 percent probability they could develop far enough west to impact KGPI. Gusty erratic winds and perhaps small hail will be the main threats. While widespread flight restrictions are not anticipated, terminal sites near the Divide may experience brief, localized MVFR conditions and gusty, erratic outflow winds from passing convection. Winds will once again be breezy from the west or northwest area wide this afternoon, with gusts up to 25 kts.

MSO WATCHES/WARNINGS/ADVISORIES

MT...None. ID...None.