textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Gusty winds on Saturday, creating choppy conditions for area lakes, especially across northwest Montana.

- Mild temperatures next week, with shower chances for most areas by Thursday and Friday.

- Confidence growing for colder temperatures by next weekend.

GOES Water Vapor imagery this morning shows a shortwave trough moving eastward along the Washington coast, with a shield of cirrus clouds moving over the Northern Rockies. This shortwave trough is projected to move along the Montana-Canada border this afternoon, leading to widespread gusty winds, with the strongest gusts in northwest Montana and along the Continental Divide. Winds will be felt first across the higher terrain, with valley winds picking up by early afternoon as inversions break and a dry cold front tracks through western Montana by late afternoon. Valley wind gusts of 20 to 35 mph are expected, while mountain areas experience gusts of 30 to 45 mph. Stronger gusts of 45 to 55 mph will impact the higher peaks of the Swan and Whitefish Ranges and Glacier Park. Winds will create choppy conditions on area lakes, especially between 200-600 pm.

Model guidance is in strong agreement for a split flow weather pattern Sunday into early next week. This pattern will be characterized by a low pressure system diving south along the west coast and settling along the central California coast, while a longwave trough and the Polar jet remains positioned in Alaska and northwest Canada. This pattern will provide mild Fall temperatures, with warm afternoons and colder morning temperatures, along with light winds. Isolated showers return to the forecast across Lemhi County, ID and southwest Montana by Tuesday and Wednesday as moisture begins to stream northward from the low near California.

Forecast uncertainty begins to increase Thursday into Friday. Global ensembles suggest the trough in Canada will begin to dig southward, with model guidance suggesting this trough phasing with the low over California as it begins to lift northward. The timing of these systems phasing remains the largest question mark. Around half of model ensemble members bring widespread shower activity across the Northern Rockies by Thursday, while the other remaining members suggest activity focused further south. By Friday into Saturday, around 90% of ensemble members suggest a trough passage will occur, with chances of precipitation increasing along with colder temperatures.

AVIATION

A ridge of high pressure remains over western Montana and north central Idaho this morning. Most areas will continue to experience VFR conditions, with valley fog forming once again in lower river valleys, including the Flathead Valley and KGPI. Surface observations suggest a south-easterly gradient will continue to strengthen along and south of I-90, helping mitigate fog development. A cold front will move through the region this Saturday bringing increased southwest-west winds, with gusts of 15-30kts.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Lake Wind Advisory from 2 PM this afternoon to 7 PM MDT this evening for Flathead/Mission Valleys.

ID...None.