textproduct: Glasgow

KEY MESSAGES

- Shower and thunderstorm chances at times today with some becoming strong to severe. Hazards include large hail, strong erratic winds, and brief torrential rainfall. - Widespread rain is expected tonight through Monday night as the upper low moves through Montana. - Strong west winds develop Monday afternoon and continue through Tuesday night.

- Cooler start and end to the week, with a brief warm up around mid week.

DISCUSSION

WEATHER PATTERN OVERVIEW: Montana will be in SW flow aloft today with upper low over the Pacific NW and upper ridge to the east. A humid airmass will combine with the moist SW flow aloft today to create an unstable atmosphere which will allow for chances for showers and thunderstorms at times. A few storms could become severe with large hail and damaging winds. PWATs measuring near the daily max, and well above the 90th percentile, provide stronger storms ample moisture for high rainfall rates. HREF guidance suggests 1hr QPF greater than 0.25", and a 3hr QPF maximum of greater than 4". While meeting this is unlikely, storms will be able to produce torrential rainfall. Any storm that stalls or moves slowly may lead to localized flooding. NAM forecast soundings suggest very high MUCAPE and strong deep layer shear after 3Z. Given the isolated updraft helicity tracks during the same window values between 150-300 m^2/s^2 supports an isolated supercell or two.

The upper low moves into Montana on Monday as the surface low moves north into Saskatchewan. Rain is expected to continue most of the time in the north while the models differ on how much the dry slot will limit rain in the south. The upper low moves to Saskatchewan and Manitoba tomorrow night and becomes stacked with the surface low. Gusty west winds will develop during the day on tomorrow and continue through Tuesday with gusts to 40 to 50 mph possible. Wrap around rain is likely Monday night and Tuesday over the NW half of the forecast area while the SE will be dry most of the time.

Rainfall totals 1 to 2 inches are likely in the NW between tonight and Tuesday while some areas in the SE could end up with less than a tenth of an inch.

The system exits the region Tuesday night and Wednesday and Thursday are expected to be dry.

FORECAST CONFIDENCE & DEVIATIONS:

Upped day 1-2 PoPs to further collaboration. Did not touch winds or wind gusts, but given how often we surpass NBM winds during strong lows and 60kt 700mb winds, that will need to be a conversation with neighbors soon.

AVIATION

LAST UPDATED: 1830Z

FLIGHT CAT RANGE: VFR, diminishing MVFR CIGS. MVFR in any strong storms tonight.

DISCUSSION: Low level clouds causing MVFR/IFR CIGS continue to lift and clear, but return and again after 12Z Monday. Widespread rain with scattered thunderstorms will develop late tonight and continue on Monday.

WINDS: North to northeast at 5 - 15 knots today becoming east to NE tonight. Winds begin to shift after 14Z following a surface low. Strong west winds 20 - 25 kts begin in the afternoon tomorrow and last through Tuesday night.

GGW WATCHES/WARNINGS/ADVISORIES

None.