textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Thunderstorms are in the forecast through the week for much of western Montana and portions of central Idaho. Storms will continue in southwest Montana through the weekend.

- Drying trend through the weekend

Satellite imagery early this morning indicates a broad ridge of high pressure over the central U.S. and a low pressure circulation off the coast of the Pacific Northwest. The Northern Rockies is stuck in the middle, under southwest flow aloft. Two visible moisture sources are also visible on satellite imagery, one feed of Pacific moisture from the southwest, and another feed of monsoonal moisture from the south. As a result, precipitable water stays above average for the entire forecast area going into the weekend. With little large-scale forcing for ascent, this moisture feed will remain in the form of clouds and increased relative humidity.

Smaller scale ascent in the form of convection will bring some chances for precipitation. While ample shear and moisture will be available, clearing skies early in the day could create enough instability to fuel afternoon/evening thunderstorms. A dry lower atmosphere still indicates that the biggest threat from thunderstorms will be erratic, gusty outflow winds. Lightning, brief heavy rain, and small hail will also be present with any storm that is able to form this afternoon.

The potential for afternoon thunderstorms will remain through at least Friday. On Saturday, the Pacific low pressure system moves north of our region and the flow flattens to a drier, westerly flow with decreased instability. The chances of afternoon showers and thunderstorms may be confined to southwest MT. Additionally, as the gradient between low pressure in Canada and high pressure ridge in the desert southwest increases, expect a breezy afternoon.

AVIATION

Expect mostly VFR flying conditions today with a couple exceptions. The first exception will be possible fog at KGPI this morning. Yesterdays rain introduced enough moisture for fog formation if skies clear before sunrise. Theres not enough confidence in clouds lifting, so no fog is mentioned in the 15/0600Z TAF. The second exception to VFR today will be chances for convection at KBTM, KSMN, and possibly KHRF. Keeping mention of thunderstorms in the TAFs this morning due to instability, moisture, and shear. If cloud cover persists all day, chances for convection will be diminished this afternoon.

MSO WATCHES/WARNINGS/ADVISORIES

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