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KEY MESSAGES

- Extreme Heat Warning from Saturday afternoon through Saturday night.

- Tomrrow's high temperatures reach or exceeding 100 in many places. Overnight temperatures are not expected to drop below the low to mid 70s.

- Hot, dry, and windy conditions Saturday and Sunday will create critical fire weather conditions.

- A stark cooldown across the region by the beginning of next week.

DISCUSSION

WEATHER PATTERN OVERVIEW: Upper ridging will remain in place over most of the country, with a very strong upper low over the Gulf of Alaska, will continue to bring very hot, dangerous heat through Sunday. Temperatures will peak tomorrow as the ridge begins to breakdown and southwest flow increases. As a dry cold front approaches the region, prefrontal compressional heating looks to counteract the influences of wildfire smoke. Tomorrow will be one of the hottest days of this summer with temperatures reaching or exceeding 100. Overnight lows will provide little relief as temperatures are expected to remain warm. Low relative humidity and an increase in 700 mb winds through Sunday bring elevated to critical fire weather concerns for the weekend. Sustained surface winds 15 to 25 mph are forecast to overlap with the lowest RH values, as well as ERCs above the 90th percentile mean that any fires that start will spread rapidly and quickly become out of control. Issued a Red Flag Warning, which is in effect from 2 PM Saturday to 9 PM MDT Sunday.

The strong upper low over the Gulf of Alaska will move east translating to an upper trough over west-central Canada by Tuesday. This will send a couple of cool fronts across the area, the first one arriving early Sunday morning with the second pushing through Monday morning. Wind will signal their arrival as only small chances of brief showers are expected Sunday night. The wind with the leftover warm air late Saturday and Sunday could result in Fire Weather issues. A Fire Weather Watch remains in effect for this period. Windy conditions Saturday night through Monday will also likely need a Lake Wind Advisory.

After Monday, the upper trough moves east and a zonal flow succumbs a bit to a Desert southwest ridge by the end of the forecast cycle. Expect dry conditions with temperatures warming to near normal. Winds generally look light so Fire Weather issues should be minimal.

FORECAST CONFIDENCE & DEVIATIONS:

Lowered min RH day 2 and 3 using a blend of HiRes models. Increased winds day 2 night though day 3 using FV3 and manual increases to further collaboration with neighbors.

AVIATION

FLIGHT CATEGORY: VFR

DISCUSSION: Clear skies are expected into tonight. Periods of mid level cumulus clouds will linger over eastern terminals.

WINDS: Southeast at 10 - 20 kts becoming west during the afternoon. Light and variable winds during the night.

DENSITY ALTITUDE: Will be a concern especially Saturday with temperatures near or over 100. Extra power and longer runway will be needed for takeoffs.

FIRE WEATHER

A Red Flag Warning, which is in effect from 2 PM Saturday to 9 PM MDT Sunday. On Saturday sustained surface winds 15 to 25 mph are forecast to overlap with widespread very low RH values, between 10 to 20% and as low as 7%, as well as ERCs above the 90th percentile. Both temperatures and RH are not expected to recover much overnight. There is a low chance of dry lightning on Sunday, which would only work to add to the fire weather concerns.

Windy but cooler conditions are expected Monday, then another warm-up into mid-week.

GGW WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning from noon Saturday to noon MDT Sunday for Central and Southeast Phillips-Central and Southern Valley- Garfield-Northern Phillips-Northern Valley-Petroleum-Southwest Phillips.

Red Flag Warning from 2 PM Saturday to 9 PM MDT Sunday for Dawson/McCone/Prairie/Richland/Wibaux Counties-Fort Peck Reservation and Daniels/Roosevelt/Sheridan Counties-Northern Valley and Northern Phillips Counties-Southern Petroleum and Southern Garfield Counties-The Little Rockies-The Lower Missouri River Breaks including the Charles M Russell National Wildlife Refuge.

Lake Wind Advisory from 6 PM Saturday to 6 PM MDT Sunday for Central and Southeast Phillips-Central and Southern Valley- Garfield-McCone-Petroleum.

Extreme Heat Warning from noon Saturday to 6 PM MDT Sunday for Daniels-Dawson-Eastern Roosevelt-McCone-Prairie-Richland- Sheridan-Western Roosevelt-Wibaux.