textproduct: Glasgow

KEY MESSAGES

- Widespread thunderstorms beginning late tonight and continuing through Tuesday night. Isolated severe storms are possible but heavy focused rainfall is the main concern.

- Unsettled weather will likely continue through Thursday.

- Expect highs to begin reaching the 90s Friday through the weekend with isolated tipple digits possible Saturday.

DISCUSSION

WEATHER PATTERN OVERVIEW:

Tonight: A very aggressive shortwave will approach along a gradually sloped warm front on southwest flow aloft beginning just before midnight tonight. This will provide dynamic forcing for ascent in a moisture rich environment. Precipitable water amounts will range from 1.0" to 1.5" during these periods which ranks in the top 90th percentile. Scattered thunderstorms and widespread rain showers are expected. Given the flash flooding that has occurred in June/earlier this week across area, the ground is closing in on saturated. Thus, this period will need to be monitored for not only an isolated severe risk, but the potential impacts compounding from additional heavy rainfall.

Main concerns to watch for will be any sharp frontal gradients that provide focus to lift and training thunderstorms. Currently with the warm front's gradual slope this does not look to be the case. But, mesoscale boundaries could begin to form up where not previously anticipated... in which case a flash flood warnings may be issued during isolated bouts of heavy rainfall.

Ensembles show a continuing progressive weather pattern unfolding with a shortwave Wednesday into Thursday.

Thursday night into the weekend main ridge across the Intermountain west begins to strengthen and drags 90s for highs into the region and some suppression for showers and thunderstorms. However northeast Montana remains on the periphery of this ridge which could reintroduce a new shortwave rather than clear skies at any time washing out some of the drier condition confidence in the ensembles.

FORECAST CONFIDENCE & DEVIATIONS: Blended SREF for PoPs through day 2, and put a greater emphasis on the HRRR for short term heavier rainfall tonight. No changes to NBM otherwise.

AVIATION

LAST UPDATED: 2000Z

FLIGHT CATEGORY: MVFR - VFR

DISCUSSION: Late evening showers and thunderstorms are expected to enter from the southwest into TAF cites beginning 6Z. Periods of moderate to heavy rainfall will bring intermittent MVFR conditions through late Tuesday night.

WIND: E at 10 to 15 kts decreasing to around 10 kts through tonight.

GGW WATCHES/WARNINGS/ADVISORIES

Flood Watch from 10 PM MDT this evening through late Tuesday night for Central and Southern Valley-Dawson-Garfield-McCone- Prairie-Richland-Western Roosevelt-Wibaux.