textproduct: Glasgow

KEY MESSAGES

- Lingering hot afternoon temperatures and scattered thunderstorms through this evening.

- There's a marginal risk (1/5) for strong thunderstorms with hail and erratic gusty winds upwards of 60 mph. - Periods of heavy rain and widespread precipitation begin Saturday lasting through early next week, with a slight risk (2/5) for excessive rainfall across portions of Montana from 6 AM Saturday through 6 AM Sunday.

- A return to closer to seasonably average temperatures looks to be next week.

DISCUSSION

WEATHER PATTERN OVERVIEW: The upper ridge over the northern plains with a cut off low in California will continue to keep hot temperatures through this afternoon over eastern Montana. Scattered showers and strong thunderstorms are possible this afternoon with a marginal risk for severe thunderstorms this afternoon. Increasing mid to upper level moisture but very dry low levels suggest inverted V soundings and the primary threat as strong, erratic winds produced by outflow or gust front boundaries. Strong winds may not follow the path of thunderstorms this afternoon, and may not be accompanied by storm clouds with precipitation or lighting.

By Saturday, a more significant change is expected with increasing moisture with widespread precipitation and chances for thunderstorms. More seasonably average temperatures and wetter conditions are expected through early next week, with continued chances for lighter showers as the upper low moves away. Temperatures next week return to near normal. FORECAST CONFIDENCE & DEVIATIONS: Lowered max temperature for tomorrow using 33% NBM10. Increased day 1 (23Z - 6Z) PoPs using GFS 1hr/HiRes ARW and SREF based on HREF ensemble max wind gusts and model SBCAPE, assuming afternoon convection.

Increasing confidence in some thunderstorms this afternoon becoming marginally severe. I have the most concern for wind, as RH values remain low today and PWAT values approaching 1.3 ahead of the main push of moisture.

12Z HREF QPF continues to increase - while the highest totals remain over western and central Montana, western zones (Phillips, Petroleum, SW Garfield) may see in excess of 1" of rain on Saturday alone - confidence is low for +2", but totals in counties bordering North Dakota continue to trend upwards.

AVIATION

Updated: 2000Z

FLIGHT CATEGORY: VFR, MVFR after 12Z

DENSITY ALTITUDE: Upper ridge across the region will keep temperatures high, potentially resulting in density altitude issues at area airports.

WIND: Southeast at 10 to 15 gust 25 kts becoming east 15 to 25 kts tomorrow.

GGW WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 6 PM MDT this evening for Central and Southeast Phillips-Central and Southern Valley-Daniels-Dawson- Eastern Roosevelt-Garfield-McCone-Northern Phillips-Northern Valley-Prairie-Richland-Sheridan-Western Roosevelt-Wibaux.