textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Strong to severe thunderstorms this afternoon and evening, bringing the threat of strong winds, large hail, and heavy rain.

- Trending drier and breezy this weekend. Elevated fire weather by Sunday from hot, dry, and breezy conditions.

- Thunderstorms return by Tuesday next week with next Monsoon moisture surge.

Subtropical moisture associated with the North American Monsoon continues to stream northward as seen in GOES Water Vapor imagery this morning. This surge of moisture will peak this afternoon, with precipitable water values ranging from 1.00-1.25 inches, or 200-225% of normal. With abundant moisture in place and a warm airmass overhead, modest instability (1000-1500 J/kg) will fuel another round of shower and thunderstorm activity this afternoon and evening. High-resolution models point towards convection initiating across the higher terrain of central Idaho by early afternoon, with storms moving south to north through the evening.

The Storm Prediction Center has placed the region under a marginal threat for severe thunderstorms, with any location having a 5% chance for large hail (1.00-1.50 inch in diameter) and damaging winds (60 mph or greater). Atmospheric instability and wind shear profiles suggest multicellular storm clusters, with discrete storms growing upscale into storm complexes by the evening hours as they track north into west-central and northwest Montana. Storms will also be capable of producing heavy rainfall. Our region is under a marginal risk (5% chance for any given location) for excessive rainfall across flood prone areas, including recent burn scars.

Looking ahead to the weekend, the focus for showers and thunderstorms shifts into Lemhi County, ID and southwest Montana. By Sunday, drier air will move overhead, with most locations seeing warm and dry conditions. Hot, dry, and breezy conditions on Sunday will lead to elevated fire weather conditions.

Global ensembles suggest the next surge of monsoon moisture will arrive by the middle of next week (Tuesday into Thursday). Chances for showers and thunderstorms will trend higher each day as precipitable water values reach over one inch.

AVIATION

Nocturnal thunderstorms continue to move northward across the higher terrain of the Idaho/Montana border. Distant lightning will be seen from KMSO through 17/1000Z, with thunderstorm activity moving through far northwest Montana into 17/1200Z. Another round strong to isolated severe thunderstorms will impact the region this afternoon and evening as monsoon moisture continues to surge northward into the airspace. High- resolution models point towards convection initiation across mountain areas of north-central Idaho by 17/1900Z, with storms tracking northward near KSMN/KBTM/KHRF between 17/2100-2300. Atmospheric instability and wind shear profiles suggest storms will grow upscale into large complexes, especially as they track northward into west-central and northwest Montana. These storms will bring a higher risk of strong winds, particularly for KMSO and KGPI during the evening hours.