FXUS65 KBYZ 262001 AFDBYZ

Area Forecast Discussion National Weather Service Billings MT 201 PM MDT Fri Jul 26 2024

DISCUSSION
Today through Saturday night...

The rest of today will see temperatures in the 80s to low 90sF. A surface low and associated cold front will move across the state later this evening and into the early morning hours. Along with this front, an increased chance (15-50%, best chance in the southwestern mountains) for showers and thunderstorms is forecast. While storms are not expected to be severe, some could be strong with dewpoint depressions of 30-40F which could help amplify downdraft winds in the 50s mph. Locally heavy rainfall is possible with some storms but widespread accumulations are not expected. In the wake of the passing front, winds will shift from the WSW to the NW, with some gusts in the 20-30 mph range for a few hours.

Saturday and Sunday will be fairly similar in nature to today, with temperatures in the 80s to low 90sF, as well as the chance for showers and thunderstorms. Saturday evening and into Sunday morning, another shortwave disturbance will move across the Northern Rockies. The chance for showers and thunderstorms will again be in the 15-50% range, with the best chance in the mountains.

One last note is that wildfire smoke from the western US is sifting back into the Northern Rockies and will bring hazy conditions for much of the weekend. Heavier concentrations of smoke are expected in the southwestern mountains, as the mid-level flow pattern is trapping much of the smoke.

Matos

Sunday through Friday...

Another shortwave in zonal flow w/ below normal heights should bring another round of scattered showers & t-storms on Sunday, though must stress that there is model disagreement in timing of this energy. Precip will be spotty and most locations will remain dry. Look for seasonable temps (mid 80s to lower 90s).

Heights will build and pwats will drop on Monday. This will allow temps to climb back to the lower-mid 90s, w/ deep mixing into drier air bringing RHs to the teens most areas. Mid level winds to ~25 knots should mix to the surface, especially along our western foothills. Overall, this is a day to monitor for increased fire weather concerns...though there is no frontal passage or risk of t-storms.

Next Pacific trof moves to the northern Rockies on Tuesday. This feature has trended a bit sharper w/ today's model runs, and the pre-frontal warming for our east is a bit more pronounced. Areas from Sheridan to Miles City eastward could push 100F, while most locations will be in the 90s. The falling heights and increasing pwats will lead to the next chance of t-storms in the afternoon and evening. We expect a cold frontal passage late Tuesday night and a cooler day Wednesday. Timing of the fropa (at night)
suggests a reduced post-frontal wind risk but this is still something to watch.

Consensus is strong for a building ridge and and more heat to end the week. Heights are expected to rise to ~595dam, and some ensembles show heights to 600dam by Friday or next weekend. There is a greater than 50% chance that we will see a return of triple digit temps. Thursday & Friday should be dry, but at some point next weekend we will probably see a return of monsoon moisture and a risk of high-based t-storms.

JKL
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