textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Widespread frost possible tonight into Monday morning.

- Cool and wet conditions Tuesday through Wednesday

Unstable conditions under a cool upper level trough will allow for fairly widespread showers this afternoon, with a few thunderstorms, primarily across northwest Montana. These will quickly dissipate this evening as drier air moves into the region. As skies clear tonight, valley temperatures across western Montana and north-central Idaho will drop into the low to mid 30s. A brief period of near freezing temperatures is possible early tomorrow morning, so please take precautions to protect sensitive outdoor plants. Frost advisories have been issued. Monday will be a mostly dry transition day with increasing clouds ahead of our next major weather system.

Widespread rain and scattered thunderstorms will push into north- central Idaho Monday night, spreading across western Montana throughout Tuesday and continuing into Wednesday as the next low pressure system moves through the region. The heaviest rainfall is expected across north-central Idaho and along the Continental Divide in northwest Montana, where a half inch or more is likely (70 to 90 percent chance). Broad western Montana valleys will see lighter rainfall amounts due to downsloping effects. In addition to the rain, breezy winds and noticeably cooler temperatures will create raw, cold conditions in the high country. Backcountry recreationists should prepare for winter-like weather, as snow levels will drop to roughly 6,500 to 7,000 feet by Wednesday morning with light accumulations of an inch or two possible.

Forecast models trended drier for Thursday as the majority expect the upper level trough to move through quicker than previously depicted. However, it is worth noting that around 30 percent of model runs continue to maintain a slower moving trough into Thursday. If these models are correct, precipitation could linger across western Montana.

Looking further ahead, a general trough remains over the Northern Rockies from Friday into next weekend with high pressure building along the west coast. Temperatures return to seasonable levels but the pattern is left open for daily shower chances.

AVIATION

Unstable conditions associated with a cool upper level trough will generate widespread showers and isolated thunderstorms across the airspace this afternoon, primarily impacting northwest Montana and in the vicinity of KGPI. Localized MVFR conditions and mountain obscurations near precipitation cores are anticipated. Breezy westerly winds are anticipated this afternoon, with gusts approaching 20 kts at times. Convective activity and winds will dissipate rapidly this evening as drier air advects into the region, leading to clearing skies and prevailing VFR conditions overnight. Widespread VFR conditions are expected to persist through Monday, though mid and high level cloud cover will gradually increase throughout the day ahead of the next approaching frontal system.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Frost Advisory from midnight tonight to 9 AM MDT Monday for Flathead/Mission Valleys...Kootenai/Cabinet Region...Lower Clark Fork Region...Missoula/Bitterroot Valleys.

ID...Frost Advisory from midnight MDT /11 PM PDT/ tonight to 9 AM MDT /8 AM PDT/ Monday for Eastern Lemhi County...Northern Clearwater Mountains...Orofino/Grangeville Region... Southern Clearwater Mountains.