Area Forecast Discussion

DISCUSSION

KEY MESSAGES:

- Warming and drying trend through the weekend and into early next week.

- Showers and isolated thunderstorms possible Tuesday evening, with potential for gusty winds.

- Widespread rain and much cooler temperatures arrive Wednesday through Friday.

A strong ridge of high pressure will build over the Northern Rockies today and Monday, starting a significant warming trend. Temperatures across the region will peak on Tuesday, with valley highs reaching the 70s and 80sabout 20 degrees warmer than average for this time of year. Record-breaking high temperatures are likely for several locations. By Tuesday afternoon, increasing instability will support the development of thunderstorms with high cloud bases, primarily across north-central Idaho. The primary threats from these storms will be frequent lightning and gusty winds.

A cold front will move through the region Wednesday ahead of a large area of low pressure aloft, bringing widespread rain, snow, and breezy conditions. While the precise path of the following low-pressure system remains uncertain for late next week, we have high confidence in a transition to much cooler and more unsettled weather. Moderate to heavy rain is expected Wednesday through Thursday, with the highest chances for over 1.00 inch of total rainfall focused over the Clearwater Mountains and the Continental Divide. There is a 20 percent probability of an alternate scenario where a surge of deep moisture moves into the area, potentially producing 2.00 to 3.00 inches of rain and melted snow along the Divide.

Impacts will include rising water levels in local rivers and streams, though flooding is currently not expected. People should remain alert for water ponding in areas with poor drainage and small rockslides or debris flows on steep terrain. Additionally, the potential for snow increases by Thursday for the higher valleys and mountain passes of southwest Montana, including the Butte area and Homestake/MacDonald passes. Travel impacts from snow will depend heavily on the eventual path of the low-pressure system.

As the low exits to the east, 40 percent of the ensemble models show a north to northeast flow developing, bringing much lower snow-levels, potentially bringing several inches of snow to the region. Stay tuned!

AVIATION

Clear skies and excellent visibility (VFR) will continue through the next 24 hours as a strengthening ridge of high pressure stays over the region. Expect light winds that follow local terrain patterns. Some patchy fog is possible near river bottoms early Sunday morning, but no impacts to local airports are expected.

MSO WATCHES / WARNINGS / ADVISORIES

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