textproduct: Glasgow

KEY MESSAGES

- Dangerous heat and humidity are expected across northeast Montana today. Highs will be in the 100s. An Extreme Heat Warning has been issued through early Monday morning.

- Hot and dry weather and breezy conditions will lead to near critical fire weather concerns for this afternoon. While recent precipitation and green fuels may limit some risk, increased dry thunderstorm downdraft gust chances this afternoon will put it over the top for Red Flag in the SW. - Temperatures will moderate early this work week, but are expected to remain above normal. Precip chances return Tuesday night into Wednesday morning.

DISCUSSION

WEATHER PATTERN OVERVIEW: An upper ridge is over the area, and the peak heat is expected to build in today before the ridge breaks down slightly Monday. The base NBM indicates lows staying above 65 degrees for this morning, and Monday morning. So, it will be difficult to stay cool enough to sleep comfortably. There is an extreme heat warning in place for the heat from now through Sunday evening.

There are small shortwave wiggles in the upper level flow for various CAMs this afternoon, especially in the western half of the CWA. Any forcing over the south central Montana would be enough to generate a dry thunderstorm or showers and move it north into our west by the afternoon hours. Cloud bases will be very high based on hot surface temperatures with evaporation leading to dry thunder potential. a couple CAMs suggest a severe gust or two with the passage of these cells. With near inverted Vs on Fcst soundings can not rule this out due to high DCAPE (1500 to 2500 J/kg).

The latest GFS and ECMWF ensemble suggests a toppling of the ridge crest to the east by late Monday evening, so central Montana is expected to start to see precipitation chances rise again into a weak Tuesday night/wednesday morning event. The base NBM suggests these shower and storm chances will then continue on though slightly diminished through the early weekend.

FORECAST CONFIDENCE & DEVIATIONS: NO deviations to NBM.

There is HIGH confidence on temperatures exceeding 100 degrees for high temperatures and low temperatures struggling to drop below 65 degrees for Sunday, and for highs exceeding 90 on Monday.

There is MODERATE confidence that fire weather will hold off for at least the next week. Recent rains are keeping the vegetation pretty green, so fire concerns are low.

There is LOW to MODERATE confidence of an isolated dry thunderstorm producing a 60 to 65 mph wind gust from 2 PM to 8 PM Sunday in the western half of the CWA.

There is HIGH confidence of precipitation chances returning by Tuesday evening.

/GAH

AVIATION

UPDATED: 0430Z

FLIGHT CATEGORY: VFR

DISCUSSION: Mainly dry weather and mostly clear skies are expected over the TAF cycle. A few model runs suggest isolated dry thunderstorms may impact KGGW this afternoon.

There is low confidence(5-10%) in isolated gusts as high as 65 mph from 21-02Z. Gust signatures are showing up in HREF CAMs which look to lack thunder. So, a gust of wind may simply come out of an otherwise innocuous looking dying rain shower as they move from SSW to NNE in the late afternoon and early evening.

DENSITY ALTITUDE: Hot temperatures near and above 100 degrees will lead to needs for increased length of runway and increased power for take off. Worst times will be in the afternoon and evening from 18Z to 03Z.

WIND: Light and variable through the morning. Veering from E to S and increasing to 10 to 20 kts this afternoon. Further veering NW to N in the evening behind a front and reducing to 15 kts or less after midnight/06Z. Gusty erratic wind is possible near any storm or shower.

GAH

GGW WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 6 AM MDT Monday for Central and Southeast Phillips-Central and Southern Valley-Daniels-Dawson- Eastern Roosevelt-Garfield-McCone-Northern Phillips-Northern Valley-Petroleum-Prairie-Richland-Sheridan-Southwest Phillips- Western Roosevelt-Wibaux.

Red Flag Warning from noon today to 9 PM MDT this evening for Southern Petroleum and Southern Garfield Counties-The Lower Missouri River Breaks including the Charles M Russell National Wildlife Refuge.