textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Near-normal with the weather pattern during upcoming week, with dry conditions

- Increasing winds Tuesday, especially across northwest Montana and the higher terrain.

- A few rain showers on Wednesday then warming trend into the remainder of the week.

- Confidence increasing for a warm, dry early October beyond the 7 day forecast.

Satellite imagery shows a very large upper low over northern California which is pushing a lot moisture (in the form of thick middle clouds) into the Northern Rockies this afternoon. These clouds combined with the cold morning that we had has resulted in temperatures climbing slower. High temperatures could be a few degrees cooler than expected due the clouds today. Showers are seen on the radar extending from Lemhi County and points eastwards. Also showers are poised to move over Idaho County. Later today, weak instability could result in a few weak thunderstorms from Lemhi County to southwest Montana. Precipitation may struggle to make it to the ground in some places due to dry air in place.

A weak shortwave will move across the region on Monday. This will help the sun to come out and provide warming again. Also it will bring some breezy afternoon westerly winds, generally staying below 20 mph across northwest Montana.

On Tuesday, a weakening moisture plume that will have brought rain to southern British Columbia and northwest Washington State will begin to impact northwest Montana. Increasing clouds, and westerly winds will be felt. General west to southwest winds of 10 to 20 mph with gusts to 30 mph can be expected. There's a 50% chance that the US-2 corridor between Happy's Inn and Kalispell could experience gusts exceeding 30 mph. Over the Divide in the Glacier Region, there is a 80% chance for wind gusts exceeding 45 mph. For Flathead Lake the probabilities suggest that only a few places could experience sustained 15 mph winds from Wild Horse Island to the center of the lake, and also across southern Polson Bay. Expect choppy conditions.

The main moisture plume moves over northwest Montana later Tuesday night into Wednesday morning. Expect periods of light rain mainly in the mountains. A few valley locations from Lowell, Idaho north and east to the Seeley/Swan Valley, to Glacier National Park have a 40 to 50% chance of receiving measurable moisture in the morning.

A gradual warming trend will begin to end the week!

Confidence is increasing for a warm, dry early October beyond the 7 day forecast. The large scale weather pattern is being influenced by upstream tropical activity. With 2 hurricanes and 1 tropical cyclone in the central and east Pacific Ocean from Hawaii to Baja and a typhoon approaching the eastern periphery of Japan, it's been a difficult forecast for models. However, they're starting to coalesce around higher chances for a potent ridge over the northern Rockies into the first third of October. Ensemble mean temperature forecasts are coming in 15 degrees above seasonal averages at about 9-12 days out. Those are large anomalies for that long of a lead time! Add in that the signal is coming from multiple ensemble systems including both dynamical (physics based) and AI modeling systems, this provides above normal levels of confidence for such a long lead time forecast. Looking back, the last time this kind of warm ridge set up over the northwestern US in early October was october 9-11 and 14, 1991. Eureka, Montana hit 86 degrees, Grangeville, Idaho 87 degrees, and Butte 81 degrees! The Center for Climate Prediction has issued forecasts for the Northern Rockies region with a 70-80% chance of above average temperatures and precipitation forecasts are leaning below average for that time period as well.

AVIATION

VFR conditions are expected across the airspace over the next 24 hours. Satellite imagery shows a cloud shield moving towards the Northern Rockies. This trend will continue through the afternoon, with cloud ceilings trending towards 10,000-15,000 feet AGL. Scattered showers will develop across the higher terrain of Lemhi County, ID into southwest Montana, perhaps leading to isolated terrain obscurations over the highest peaks. Precipitation will struggle to reach the ground with drier air in the low levels of the atmosphere. Winds will be primarily light and terrain-driven today.

MSO WATCHES/WARNINGS/ADVISORIES

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