textproduct: Glasgow

KEY MESSAGES

- Isolated showers will drift across northeast Montana today as winds begin to pick up ahead of a major pattern shift.

- Thursday and Friday will see the manifestation of that pattern shift with cooler and potentially significantly wetter conditions. Over a 48 hour period, many locations could see over of an inch of accumulated rainfall.

- Precipitation chances don't completely go away this weekend and into early next week, but overall conditions will trend towards drier and warmer.

DISCUSSION

WEATHER PATTERN OVERVIEW:

Today and tonight, the flow aloft will transition from an upper ridge to SW flow aloft across Montana. Meanwhile, an upper trough move into the Canadian Rockies and Pacific NW. The pattern change will lead to increasing daily chances for showers and thunderstorms, with heavy rain potential as some southwestern monsoonal moisture does transport its way this far north.

There will be chances for showers and thunderstorms at times today. Chances for showers and thunderstorms increase tonight with widespread rain expected between Thursday, Thursday night and Friday morning with heavy rain possible at times. The current probability for one inch or more rain between tonight and Friday is 60 to 80 percent across NE Montana. The probability for 2 or more inches of rain between tonight and Friday is between 10 and 40 percent. If more than 2 inches of rain occurs, flooding could become a possibility depending on how quickly the rain falls in a given location. WPC currently has a slight risk of excessive rainfall for NE Montana Thursday and Friday at this time. Will hold off on any Flood Watches for now given that the ground is dry and rainfall has been light over the last 4 weeks.

Flow aloft Friday night and Saturday turns into a drier WSW aloft as the upper trough moves east across the Canadian Prairies. Rain chances diminish Friday afternoon and Friday night and Saturday look mainly dry with isolated showers possible.

Frequent waves moving across eastern Montana will bring shower and thunderstorm chances at times early next week.

FORECAST CONFIDENCE & DEVIATIONS:

Generally tweaked pops tonight and Thursday to provide better hour to hour consistency in rain chances.

Low confidence in shower and thunderstorm chances today. Confidence in precipitation chances increase tonight and Thursday and are high Thursday night and Friday morning. High confidence in many areas getting an inch or more rain overall but low confidence possibility of amounts higher than an inch.

AVIATION

Updated: Wednesday, August 12, 0700Z

Expected Flight Category: VFR most of time, areas of MVFR after 09z Thursday.

Synopsis: Skies will vary from clear to broken mid and high clouds today with isolated showers and thunderstorms possible. Mid level clouds and chances for showers and thunderstorms will increase tonight with low clouds moving in from the west after 09z Thursday.

Winds: NE 5 to 15 knots this morning and 10 to 15 knots this afternoon and evening becoming east to NE 5 to 10 knots late tonight.

GGW WATCHES/WARNINGS/ADVISORIES

None.