textproduct: Glasgow

KEY MESSAGES

- The a warm frontal system will approach the area with more widespread thunderstorms late Monday night and continue 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 an isolated 100 possible Saturday.

DISCUSSION

WEATHER PATTERN OVERVIEW:

Today: Most morning showers and thunderstorms are expected to exit the area around 2 to 4AM leaving a partly cloudy day with increasing cloud cover from the southwest in the late afternoon as a warm front approaches.

A very aggressive shortwave will approach along a gradually sloped warm front on southwest flow aloft Monday night into Tuesday night. 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 watch may need to be considered under such sharp boundaries in such a high PW atmosphere.

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: Deviations include... Introduced a CAMS blend of NPoPs, Wind, and WindGusts, to match up with observations/radar/satellite where NBM was critically inaccurate for hourly data out to about 15Z in order to account for the cold front, shortwave, rain and thunder moving through this morning.

Confidence is MODERATE to HIGH through Thursday, but then fuzzes out to MODERATE to LOW Friday onward.

GAH

AVIATION

LAST UPDATED: 0500Z

FLIGHT CATEGORY: MVFR - VFR

DISCUSSION: Early morning showers and thunderstorms are expected to exit the area around 08 to 09Z leaving dry conditions and SCT mid to high clouds through most of the rest of the cycle. A new round of showers and thunderstorms are expected to enter from the southwest Monday night around 06-12Z and hang on till early Wednesday morning.

WIND: N at 10 to 15 kts through the day. Veering NE and E Monday evening and decreasing to around 10 kts through Monday night.

GAH

GGW WATCHES/WARNINGS/ADVISORIES

None.