textproduct: Glasgow

KEY MESSAGES

- Dangerous heat is again expected across northeast Montana today. Near 100 Highs will be possible in the Yellowstone Valley again. For these locations an Extreme Heat Warning is still out thourgh Monday evening. For all other locations a Heat Advisory is in effect. - Temperatures will reduce to 80s and 90s for highs through the work week.

- There is an isolated chance for showers along Phillips and northern Valley tonight which could bring a sudden wind burst gust. Next significant chance for rain will be Tuesday night and Wednesday in the west.

DISCUSSION

WEATHER PATTERN OVERVIEW: An upper ridge breaks down today and topples over slowly to the east. There is an extreme heat warning in place today across the SE and the Yellowstone Valley where temps will still close in on 100 degrees. All other locations that run 90 to 95 for max temps of heat index have been downgraded to a heat Advisory for the same amount of time.

Repeated CAM runs have suggested that thunderstorms over central Montana will drift into our northwest during the evening hours. Most downdraft CAPE seems confined to the west before it passes the Phillips border with only about 500 to 1000 J/kg left over as it moves through Phillips and northern Valley county.

With the ridge toppled over a few shortwave troughs move through the flow across the region. The first shortwave is supposed to move through in late Tuesday afternoon and generate showers and thunderstorms across the northwest through the night and spread them a bit farther SW into Wednesday morning. Highest totals will be confined to the west with 1 to 2 tenths of an inch in Phillips county with areas along the Yellowstone Valley receiving nothing in the SE.

The next couple wiggles in the upper level flow are more subtle and may not carry enough lift or moisture to bring a wetting rain Thursday or Friday. In addition warm temperatures and low RH may inhibit accumulating rain for most locations as they pass. But, any precipitation remains welcome.

FORECAST CONFIDENCE & DEVIATIONS: Deviations from NBM include... An early CAMs blend for hourly PoPs, WindGusts, and Wind fields through 12Z this morning. And a second CAMs PoP blend for thunderstorms moving through Valley and Phillips county for Tuesday night which were un-resolved in NBM.

There is MODERATE to LOW confidence of a few locations reaching 100 today along the Yellowstone Valley.

There is MODERATE confidence of showers and thunderstorms tonight in the northwest during the evening.

There is MODERATE confidence of precipitation across the west Tuesday night to Wednesday. And HIGH confidence of none in the Yellowstone.

GAH

AVIATION

UPDATED: 0530Z

FLIGHT CATEGORY: VFR

LLWS: Any current low level wind shear should give out around 14Z with the passage of the morning front over all terminals.

DENSITY ALTITUDE: Hot temperatures from 95-100 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 19Z to 02Z today and possibly Tuesday and Wednesday as well.

DISCUSSION: Mainly dry weather and mostly clear skies are expected over the TAF cycle. A few Convective Models suggest isolated dry thunderstorms just northwest of KGGW in the evening hours. Roughly 01 to 05Z.

SFC WIND: S wind of 10 to 15 kts will flip north behind a front this morning. Veering further N to NE and increasing to 10 to 20 kts in the afternoon. Veering furthern NE to E in the evening thorugh TUesday morning.

GGW WATCHES/WARNINGS/ADVISORIES

Lake Wind Advisory until 6 AM MDT early this morning for Central and Southeast Phillips-Central and Southern Valley-Garfield- McCone-Petroleum.

Heat Advisory until 2 AM MDT Tuesday for Central and Southeast Phillips-Central and Southern Valley-Daniels-Garfield-McCone- Northern Phillips-Northern Valley-Petroleum-Sheridan-Southwest Phillips-Western Roosevelt.

High Wind Warning until 4 AM MDT early this morning for Dawson- Eastern Roosevelt-McCone-Prairie-Richland-Sheridan-Wibaux.

Extreme Heat Warning until 2 AM MDT Tuesday for Dawson-Eastern Roosevelt-Prairie-Richland-Wibaux.