textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Unseasonably cold temperatures will bring frost to high- elevation valleys Monday morning, marking some of the coldest temperatures seen so far this year.

- A brief warm-up with dry conditions and low relative humidities in the teens to low 20s is expected early next week.

- A shortwave disturbance on Wednesday will increase thunderstorm activity and winds, posing a near-critical fire weather risk in southwest Montana before precipitation arrives.

- An active, cooler weather pattern with above-normal precipitation probabilities returns late next week.

Today through Tuesday:

Clearing skies and drying air tonight will promote strong radiational cooling, leading to quite chilly Monday morning low temperatures. These morning lows will be some of the coldest temperatures we have seen so far this year. Widespread frost is expected in high-elevation locations, including Seeley Lake, Georgetown, Drummond to Butte, and Dixie Idaho, where temperatures will drop into the upper 20s to low 30s. Localized light frost may also reach lower elevation spots like Stevensville and the western Missoula Valley.

Transitory ridging will bring warm, dry conditions Monday into Tuesday, pushing valley highs back into the 80s. With this ridge, a drier airmass will spread across the region, dropping afternoon relative humidities into the widespread teens to low 20 percent range on Monday. By Tuesday afternoon and evening, the ridge will begin to break down, yielding a slight increase in winds, scattered showers, and isolated thunderstorms. High cloud bases showers on Tuesday afternoon elevating the potential for strong, gusty outflow winds.

Wednesday through Late Week:

A notable shortwave disturbance will move through the area on Wednesday, bringing a definite uptick in winds and more widespread thunderstorm activity, particularly across southwest Montana. Before the precipitation arrives Wednesday afternoon, these stronger winds combined with the dry conditions could create near- critical fire weather conditions in southwest Montana. As the system fully moves in, the showers and thunderstorms will carry the potential to produce moderate to heavy rainfall. Wetting rain probabilities will increase to 50-70% across much of the Northern Rockies during this timeframe.

Lingering showers and elevated winds will persist into Thursday and Friday before winds taper off for the weekend. Looking into the weekend, ensemble guidance shows strong confidence that a trough of low pressure will sit over the Pacific Northwest. This will maintain southwesterly flow over the Northern Rockies, keeping temperatures slightly below seasonal averages and favoring an active regime with above-normal precipitation probabilities due to daily shower and thunderstorm activity.

AVIATION

Showers and lowered ceilings will continue to impact northwest Montana especially between KGPI and Glacier National park, that will obscured mountains at times. Gusty westerly winds will steadily decrease throughout the afternoon into the evening. A ridge of high pressure will be building over the region tonight into Monday. This ridge will allow for the development of patchy fog and low stratus. KGPI will have the best potential of experiencing fog.

MSO WATCHES/WARNINGS/ADVISORIES

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