textproduct: Great Falls

KEY MESSAGES

- Remaining hot through the rest of the work week, with the hottest day of the upcoming week occurring on Saturday.

- Winds increase late Saturday and last into Sunday, with the strongest winds occurring along the Rocky Mountain Front.

- Brief reprieve from the heat early next week.

DISCUSSION

- Meteorological Overview:

Upper level ridging will dominate through much of the forecast period, with the ridge bringing continued hot temperatures to most locations from Southwest through North Central Montana until Saturday. By Sunday a potent longwave trough will breakdown the ridge and bring increasing winds and slightly cooler temperatures to the Northern Rockies, with temperatures falling below normal into the day on Monday in wake of a cold front. Monsoonal moisture lifting up and around the ridge will provide daily chances for isolated showers and storms; however, most locations will remain dry over the next week. - Moldan

- Forecast Confidence & Scenarios:

Return of Extreme Temperatures by Saturday...

While temperatures will remain hot through the remainder of the work week climate anomaly indicators have honed in on Saturday being the hottest day of the upcoming week, with values becoming unusual to very unusual with respect to late July/early August climatology. The fact that these climate anomaly indicators are suggesting another period of hot temperatures is remarkable considering that August 1st is (at most locations) only one day past the climatological peak for average high temperatures across Southwest through North Central Montana. The table below represents the potential high temperature scenarios for select cities across Southwest through North Central Montana, with the "Low End" scenario being the NBM10Pct (10% chance that temperatures are lower than the listed value), "Most Likely" scenario being the NBM50Pct, and the "High End" scenario being the NBM90Pct (10% chance that temperatures exceed the listed value).

Saturday's High Temperature Scenarios LOCATION Low End | Most Likely | High End Browning 88 | 93 | 98 Cut Bank 95 | 100 | 104 Havre 103 | 108 | 111 Great Falls 102 | 105 | 107 Lewistown 98 | 101 | 104 Helena 97 | 100 | 104 White Sulphur Springs 95 | 102 | 101 Bozeman 98 | 98 | 105 Dillon 95 | 98 | 100 Ennis 94 | 98 | 100 West Yellowstone 89 | 93 | 96

Given the presence of regional wildfires across the Northern Rockies the "High End" scenario will be tough to reach due to decreased solar insolation from the smoke, with dense smoke having the ability to hold temperatures back some 5 to 10 degrees.

Strong Winds from Saturday night through Sunday...

Confidence is increasing that a period of strong, nearing high, winds will impact the Rocky Mountain Front from Saturday night through the day on Sunday due to the combination of mountain wave activity (from the late evening hours on Saturday through Sunday morning) and deep mixing (during the daylight hourS on Sunday). H700 winds per NAEFS analysis are prog'd to reach 40-50kts from Saturday evening through Sunday morning across the aforementioned area, which is 2 to nearly 3 standard deviations above normal. The table below are the NBM5.0 probabilities for wind gusts to exceed 45 mph, 55 mph, and 65 mph for select locations along the Rocky Mountain Front for the previously mentioned timeframe.

Probabilities for Wind Gusts to Exceed LOCATION >45 mph | >55 mph | >65 mph Many Glacier Valley 55% | 15% | <5% Logan Pass 50% | 10% | 0% St Mary 80% | 40% | 10% Two Medicine Valley 70% | 30% | 10% East Glacier 75% | 25% | 10% Browning 70% | 25% | 5% Cut Bank 75% | 20% | 5% Heart Butte 80% | 30% | 20% Choteau 5% | 0% | 0% Augusta 20% | <5% | 0%

Those looking to travel or recreate along the Rocky Mountain Front should be prepared for strong winds; which could make driving and hiking difficult, lead to falling trees in the backcountry, and/or lead to the spread of existing/new wildfires. - Moldan

AVIATION

28/06Z TAF Period

Wildfire smoke from the Pacific Northwest will be the primary concern through the TAF period. Visibilities can drop down to MVFR at times in the morning due to the smoke across North-Central MT. Isolated showers and thunderstorms continue into the early morning for Southwest MT/Central MT. Another round of isolated to scattered showers and thunderstorms for Southwest MT Tuesday afternoon and early evening.

For KGTF: Winds will prevail out of the north into the early morning hours, becoming light and variable through the rest of the morning. By Tuesday afternoon, winds will prevail more out of the west. Probabilities for a 15kt crosswind remain low through the morning (10%), but it increases to 50% by 28/22 through 29/02z. -Wilson

PRELIMINARY POINT TEMPS/POPS

GTF 95 61 94 60 / 0 0 0 0 CTB 91 56 89 55 / 0 0 0 0 HLN 94 59 93 59 / 10 0 10 10 BZN 94 58 92 57 / 20 0 20 10 WYS 88 49 85 47 / 10 0 30 20 DLN 91 55 88 54 / 10 0 20 10 HVR 98 60 95 59 / 0 0 0 0 LWT 93 58 90 57 / 20 20 10 20

TFX WATCHES/WARNINGS/ADVISORIES

None.