textproduct: Great Falls

KEY MESSAGES

- Strong winds over the plains continue through the evening, particularly in areas west of Interstate 15.

- Mild conditions persist this week, warmest Thursday and Friday.

- Additional breezy stretches over the plains this week.

DISCUSSION

- Meteorological Overview:

Strong zonal flow aloft is in place across the region this afternoon. Daytime mixing and a potent mountain wave setup is allowing for some of the stronger winds and gusts aloft to be translated to the surface across the plains, particularly west of I- 15. Mid-level flow in excess of 70 kts near the Rocky Mountain Front in and below the stable layer gives confidence in gusts greater than 80 mph materializing in and around Browning as mountain waves ebb and flow east/west. Locally stronger gusts approaching 100 mph cannot be ruled out in wind prone locations near the immediate eastern slopes of the Rocky Mountain Front through late afternoon. Stronger surface winds decrease this evening across the plains.

Zonal flow aloft persists early this upcoming week, which will keep the plains on the breezy side. A wave progressing through this flow aloft will bring some light mountain precipitation late Monday night into Tuesday, though snow levels largely look to remain above 6,000ft. Cross barrier flow does increase with this wave, but by Tuesday afternoon it trends a bit north of west, which is a less favorable direction for resulting in High Wind criteria gusts. Trends will be monitored with this system.

Ridging builds in toward the latter portion of the week, which will allow for already mild temperatures to trend even warmer. Uncertainty arises toward the weekend with respect to just how quickly the ridge is broken down. Additional windy stretches with light mountain precipitation along the Continental Divide will be favored when the ridge breakdown occurs. -AM

- Forecast Confidence & Scenarios:

Winds Today:

Latest high resolution guidance has been consistent with the strongest mountain wave retreating westward from the Cut Bank area late this morning to the Browning area this afternoon. So far observations support this trend, as areas near Browning have gusted up to 60 mph, while areas around Cut Bank have been gusting closer to 70 mph. The expectation is for the area of stronger gusts to shift westward this afternoon, with the overall magnitude of the winds and gusts also increasing. A several hour stretch of sustained winds in the 50 mph range, with frequent gusts between 75 and 85 mph is forecast in and around Browning this afternoon once the mountain wave retreats westward and becomes stationary.

Late Monday night and Tuesday winds:

As mentioned prior, cross barrier flow increases once again as the next wave progresses through the region. Orientation of the stronger flow aloft (southwesterly) is more favorable late Monday evening, though ridgetop stability will be weaker compared to Tuesday. This raises doubts that stronger winds will materialize at the surface near the Rocky Mountain Front Monday evening/night. As better ridgetop stability develops into Tuesday the stronger winds aloft trend more northwesterly. This orientation is less conducive to mixing stronger winds to the surface, but it will bear monitoring. At this point the probability of a 65 mph gust in Browning is 50% Tuesday. -AM

AVIATION

08/18Z TAF Period

VFR conditions will prevail at all terminals during this TAF Period. During this TAF Period it will be very windy at the KCTB terminal with gusts in excess of 60 kts expected through 08/21Z. It will also be windy at the KGTF and KHVR terminals with gusts in excess of 45 kts expected through 09/00Z. Mountain wave turbulence is expected across North-central Montana through 09/06Z. There will be instances of low-level wind shear across North-central Montana through 09/12Z. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 40 56 42 58 / 0 10 10 0 CTB 31 51 37 53 / 0 0 0 0 HLN 34 55 37 56 / 0 10 10 0 BZN 33 55 35 54 / 0 0 10 10 WYS 25 49 26 46 / 0 0 0 0 DLN 31 55 34 54 / 0 0 0 0 HVR 34 53 35 60 / 0 0 10 10 LWT 36 57 39 55 / 0 0 10 10

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Warning until 8 PM MST this evening for Bears Paw Mountains and Southern Blaine-Cascade County below 5000ft-East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Eastern Pondera and Eastern Teton-Eastern Toole and Liberty-Hill County-Judith Basin County and Judith Gap-Northern Blaine County-Northern High Plains-Southern High Plains-Western and Central Chouteau County.