textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Near-normal temperatures with the weather pattern during this week, along with mostly dry conditions.

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

- Scattered rain showers Tuesday night into early Wednesday then slight warming trend into the remainder of the week.

- Confidence increasing for a warmer and drier than normal early October beyond the 7 day forecast.

Valley inversions in September today started with weak valley inversions which may keep realization of peak warming subdued and hold off afternoon breezes until late afternoon.

Tuesday as a weak wave moves through the region, breezy conditions are expected to develop. Strongest winds will be north of I-90 and in the mountains but valleys of northwest MT could easily see gusts into the 20s on Tuesday. Due to winds developing early lake recreationalists will be less likely to be surprised during the afternoon. That said, prepare for choppy conditions on area lakes.

Overnight into Wednesday a few showers develop, mainly along the Idaho/ Montana border and in Glacier National Park. These showers will be light in nature and the probability of a wetting rain, or greater than 1/10 of an inch, is 40 to 60% in the highest terrain. Most valleys, with the elevated winds even overnight, will see increased effects of downsloping.

Longer term the models have been very consistent is demonstrating a building ridge of high pressure. This outcome is common in the fall but temperatures in the National Blend of Models are forecast to be 10 to 15 degrees above normal. The reason this discussion began with 'valley inversions' is because, depending if valley inversions develop and their strength, high temperature forecasts may be difficult for the start to October. Current models predict for the ridge axis to be west of the Rockies, which would assist in the development of valley inversions. Additionally, Pacific tropical activity could throw a wrench into longer term forecasts, causing more variation in the pattern or exciting ridge breakdowns, more to come.

AVIATION

VFR conditions will dominate into Tuesday with light, diurnally driven winds. Westerly winds will pick up on Tuesday late morning/early afternoon, and a weakening moisture plume will bring some showers to the terrain of northwest Montana late in the day.

MSO WATCHES/WARNINGS/ADVISORIES

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