textproduct: Great Falls

KEY MESSAGES

- Warming trend through Saturday with temperatures peaking Saturday afternoon.

- Showers and a few isolated weak thunderstorms move through the area Saturday afternoon and evening.

- Slightly cooler and wetter weather later Sunday through Monday with mainly high elevation snow.

- Potential for a cooler and windier system mid-late next week.

DISCUSSION

- Meteorological Overview:

Westerly flow aloft turns to the southwest by this afternoon as upper level ridging shifts east across the State. Temperatures warm to above seasonal averages today with overall dry and pleasant conditions expected. Clouds begin to increase from south to north this afternoon and evening as moisture begins to move in ahead of an upper trough moving onshore across CA/NV. Enough moisture is present across far SW MT by late this afternoon to support the development of a few widely scattered showers and perhaps an isolated/weak thunderstorm, mainly across the mountains near the ID border.

Southwesterly mid-level flow increases Saturday, pushing temperatures further above seasonal averages (afternoon max temps in the 70s) with breezy to windy conditions likely across southwest MT, where deeper atmospheric mixing may tap 30-40kt mid level winds. Additional moisture and an embedded shortwave disturbance lifting out of the western trough will spread showers and few isolated thunderstorms across the area Saturday afternoon and evening. A period of cooler and more unsettled weather follows as the western upper level trough shifts further inland Sunday across across the region Monday. The bulk of the upper level energy with this system largely tracks south of the area, keeping precipitation somewhat disorganized and showery with a period of more widespread precipitation likely late Sunday through Monday morning.

A break between systems is most likely on Tuesday between the initial trough exiting and the next one dropping south out of the Gulf of AK into the NW US by Wednesday. Trajectory of the Wednesday system would support a risk for strong winds followed by stronger cooling as it moves through the region later next week.

- Forecast Confidence & Scenarios:

Precipitation amounts in the Sun-Mon period have decreased some, though central MT remains favored for highest amounts with a 30-40% probability for QPF in excess of 0.50" from Helena to Great Falls and Lewistown with A 50-60% probability for these amounts in the the adjacent mountain ranges. Enough cooling is expected by Monday morning to push snow levels as low as around 6000 Ft, though impactful snow looks to mainly be limited to elevations above most mountain passes. Hoenisch

AVIATION

10/06Z TAF Period

VFR conditions will largely prevail throughout the duration of the 1006/1106 TAF period; however, isolated to widely scattered showers and thunderstorms will be possible from the mid-afternoon through early evening hours on Friday across Southwest Montana. While the probability of any one shower directly impacting the KBZN and KEKS terminals is low there is still around a 30% chance of said precipitation moving over the terminals. Main impact would be a reduction in CIGS to MVFR/low-VFR. Otherwise residual smoke/haze from local prescribed burns on Thursday will continue to impact the KHLN terminal through the overnight hours, with VIS temporarily falling to MVFR through 09z Friday. - Moldan

PRELIMINARY POINT TEMPS/POPS

GTF 29 66 40 72 / 0 0 10 50 CTB 24 63 33 66 / 0 0 10 30 HLN 30 69 41 70 / 0 0 20 60 BZN 28 69 39 70 / 0 10 10 30 WYS 27 64 33 58 / 0 20 20 60 DLN 32 69 40 67 / 0 10 20 40 HVR 26 67 36 73 / 0 0 10 10 LWT 27 65 41 73 / 0 0 10 40

TFX WATCHES/WARNINGS/ADVISORIES

None.