Area Forecast Discussion

DISCUSSION

KEY MESSAGES:

- Warming and drying trend through Tuesday, with valley temperatures reaching the upper 70s to 80s.

- Rain showers and a few thunderstorms are possible Tuesday evening, bringing a risk of gusty winds, especially in north- central Idaho and NW Montana.

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

Prepare for a major weather shift this week, beginning with unseasonably warm temperatures followed by a dramatic cool-down. Monday and Tuesday will be the warmest two days of the week with Tuesday peaking in the 70s and 80s. This is approximately 25 degrees warmer than average for April and may break several local daily records. By late Tuesday afternoon and evening, increased mid-level moisture and an unstable atmosphere will allow for isolated showers and thunderstorms. lightning and gusty outflows will be the main threat for any convection that develops. Meanwhile, southwest Montana will see elevated fire danger through Tuesday evening due to very dry air and gusty winds.

The warm weather will end abruptly Tuesday night as a cold front moves through the region. We are highly confident this shift will bring much cooler temperatures, breezy conditions, and widespread rain and snow. Temperatures will be as much as 30 to 40 degrees cooler by Friday, around 10 degrees below normal. Expect moderate to heavy rain Wednesday through Thursday, particularly over the Clearwater Mountains and the Continental Divide, where over an inch of rain is likely (75 percent probability). There is a 10 to 20 percent chance that a heavier surge of moisture could drop two to three inches of total water (from rain and melted snow) along the Divide. While local rivers and streams will rise, widespread flooding is unlikely at this time. Please stay alert for water pooling on roadways and the potential for small rockslides or debris flows in steep terrain.

As temperatures continue to drop, the chance for snow will increase by Thursday for higher valleys and mountain passes along the Continental Divide and in southwest Montanaincluding Butte and the Homestake and MacDonald passes. If you are traveling through these areas, be prepared for winter driving conditions. The exact impact on travel will depend on the storm's final path. Looking ahead to the weekend, the weather will remain unusually cool and showery. There is also a 40 percent chance that a second blast of cold air from Canada could arrive over the weekend, potentially bringing snow down to the valley floors in western Montana.

AVIATION

VFR weather conditions are anticipated through the forecast period with generally light and terrain driven winds.

MSO WATCHES / WARNINGS / ADVISORIES

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