textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- The warmest temperatures continue today. There is an elevated heat risk for those sensitive to heat, especially those without cooling or hydration.

- A surge of monsoon moisture will bring clouds, showers, and thunderstorms late Monday into Tuesday.

- Chances for afternoon/evening thunderstorms will continue through Friday

The ridge of high pressure that brought hot, dry conditions to the Northern Rockies will continue east today. Moist southwesterly flow will replace the ridge. Although cloud cover and chances for precipitation will increase this week, the Northern Rockies will experience another day of temperatures about 10 degrees above normal today. The rest of the week will remain hot, about 5 degrees above normal. So, today expect more 90s for western Montana and 100s for the lower valleys of western Idaho. Daytime highs drop into the upper 80s on Tuesday and Wednesday for western Montana, upper 90s- 100s for western Idaho.

The biggest change this week will be the introduction of much more moisture to the atmosphere. As the upper levels of the atmosphere will moisten first, profiles show a dry lower atmosphere for this evening. This setup is ideal for thunderstorms producing dry, erratic outflow winds and will primarily affect southwest Montana and Lemhi County. Storms that do develop will be capable of 30-40 mph gusts. There will be a slight chance (5-10%) for some storms to become severe (about 60 mph gusts) along and just west of the Continental Divide including Silver Bow, Deer Lodge, and Powell counties.

By Tuesday afternoon and evening, the atmosphere will moisten enough for more rain to reach the ground. However, the erratic wind gusts will remain. The shower and thunderstorm coverage will become much more widespread, covering much of western Montana. Areas with the highest risk will be locations along I-90 and east of Highway 93 in west-central and southwest Montana, as well as Lemhi County.

The threat for severe thunderstorms increases on Wednesday and Thursday. If you have outdoor plans through mid-week, please plan accordingly.

AVIATION

A ridge of high-pressure sliding east will maintain predominantly VFR conditions across western Montana and north- central Idaho terminals through Monday morning. High density altitude remains a primary concern for all regional airports due to persistent unseasonably hot valley temperatures. There will be chances for thunderstorms producing gusty, erratic outflow winds (25-35 kts), primarily affecting KBTM and KSMN late this afternoon and early evening (after about 13/2200Z). There is about a 5-10% chance that KBTM could experience a severe storm where gusts exceed 50 kts.

MSO WATCHES/WARNINGS/ADVISORIES

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