textproduct: Glasgow

KEY MESSAGES

- Dangerous heat and humidity are expected to cause impacts to northeast Montana this weekend. Highs will be in the 90s and 100s with lows in the mid 60s to mid 70s. An Extreme Heat Warning has been issued for Saturday through Sunday night.

- Hot and dry weather and breezy conditions will lead to near critical fire weather concerns for Sunday afternoon, but recent precipitation and green fuels may limit the extent of this risk. - Temperatures will moderate early next week, but are expected to remain above normal. Precip chances begin to return Tuesday night.

DISCUSSION

WEATHER PATTERN OVERVIEW:

A large upper ridge is slowly building over the area. Southeast winds at low levels will help transport warm air northward into our area. The peak in intensity of the ridge is likely to be Sunday, with almost the entire area expected to be from around 98 to 110 degrees for a high temperature. The base NBM indicates lows staying above 65 degrees for Saturday night, Sunday night, and Monday night, so it will be difficult to stay cool enough to sleep comfortably. There are small wiggles in the upper level flow for various CAMs tomorrow afternoon and Sunday afternoon. Any forcing over the area would be enough to generate an intense storm since recent rainfall has helped keep high dewpoint air in place, especially in the east. We will keep an eye on this potential, but storm coverage is expected to be low at the very least. There is an extreme heat warning in place for Saturday and Sunday.

There is a low (10 percent) chance of a shortwave moving through and using the sfc boundaries near or after peak heating to generate a strong thunderstorm or two today. There is a similar event expected on Sunday, with this low chance starting mostly in central Montana and moving into our CWA. One CAM suggests a severe gust or two with the passage. With near inverted Vs on Fcst soundings can not rule this out due to high DCAPE(1500 to 2000J/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 again. A push into the northwest is likely to occur by Tuesday evening, so shower and thunderstorms will need to be monitored for severe weather chances again from then onward.

FORECAST CONFIDENCE & DEVIATIONS: Deviations to NBM include... using a CAMs blend of RAP, HRRR, NAMNest, FV3, ARW to produce an NPoP blend for PoPs and then shrink_stretch all hourly grids up for the final PoP product through 18Z. NBM ensemble was not accounting at all for showers and thunderstorms on radar developing over south central Montana last evening and making it's way into our southwest CWA during the early morning hours. NDFD Wind and WindGust also used the same blend. Increased Sky with a 2x PoP layered on top of NBM Sky in attempt to keep the old NBM field in place under the hood. Sky needed to be improved beyond this, but both NBM10 and NBM90 hourly data is no longer produced to fix it. Did all this through 18Z/Noon today.

There is HIGH confidence on temperatures exceeding 95 degrees for high temperatures and low temperatures struggling to drop below 65 degrees this weekend.

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 HIGH confidence of precipitation chances returning by Tuesday evening.

/GAH

AVIATION

UPDATED: 0520Z

FLIGHT CATEGORY: VFR

DISCUSSION: Mainly dry weather and mostly clear skies are expected over the TAF cycle as an upper ridge begins to gain an influence.

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

WIND: Light and variable or E at 10 kts or less this morning. Varying from E to S at 5 to 15 kts this afternoon and evening. Becoming light and variable overnight.

GAH

GGW WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning from 6 AM Saturday to 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.