textproduct: Missoula

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.