textproduct: Great Falls

KEY MESSAGES

- A few strong thunderstorms this afternoon and again Saturday afternoon.

- Cooler system begins moving in late Saturday, with some mountain snow and lower elevation rain through Monday.

- Generally unsettled conditions through much of next week.

DISCUSSION

The first larger disturbance ejecting from a broad scale trough and upper level low near the Pacific NW coast moves across the region through the remainder of the day today. Ample cloud cover has limited instability in western areas so far, but looks to at least briefly break through this afternoon, which will promote shower and thunderstorm development. The area of greatest concern for a stronger thunderstorm would be near Judith Basin and Fergus counties, where greater instability (conditional on cloud cover diminishing for long enough), and better shear would overlap. Large hail would be the greatest concern in these stronger thunderstorms. Regardless of magnitude of instability that develops, any thunderstorm today will be capable of producing at least briefly heavy rainfall rates given PWAT in place. Those with interests near areas susceptible to impacts from heavy rain, such as urban areas or areas on/around burn scars should be aware of this increased risk for flooding.

A final concern today will be for some gusty synoptic conditions near the Idaho border in Southwest Montana. Stronger gusts continue to look isolated so no High Wind Warnings are being considered at this time.

Upper level troughing and closed upper low begins to move across the region Saturday. Ahead of its arrival there appears to be enough of a window for daytime heating to result in another round of afternoon showers and thunderstorms in many areas. In fact, forcing from the approaching trough looks to result in elevated showers and perhaps a few thunderstorms across portions of the region late tonight into early Saturday morning. The area of greatest concern for a stronger thunderstorm continues to look to be in areas near/east of US-87 on the plains, under the assumption that the better instability is able to work in from eastern MT.

Colder temperatures aloft move in late Saturday afternoon across Southwest Montana, which will allow for snow levels to fall into Saturday night. Snow levels largely look to fall into the 6,500- 7,500 ft range under the core of the upper level low, but will briefly drop lower than this in heavier spurts of precipitation. The risk for snow in the mountains gradually expands through the remainder of the weekend, though at this time the mountain south of I-90 look to see the greatest impacts from the snow. Regardless of snow amounts or snow levels, the much cooler conditions with stretches of precipitation will result in difficult outdoor conditions in and near terrain this weekend.

Meanwhile at lower elevations there will be stretches of rain through Sunday into Monday. Given this precipitation will come over a longer stretch, and feature at least modest breaks in many areas, the concern for flooding remains low at this time.

Precipitation gradually diminishes later Monday into Monday night as the upper level disturbance gradually moves away from the region. Ensembles generally favor troughing lingering over the western CONUS through much of next week, which would keep afternoon and evening showers and thunderstorms in the cards in most areas. -AM

AVIATION

26/18Z TAF Period

Scattered showers and thunderstorms are expected to impact the CWA through this evening. The stronger storms are expected to occur over Central and North-Central MT. MVFR conditions and mountain obscuration may occur at times due to passing showers/thunderstorms. -Dzomba

CLIMATE

The Great Falls CWA has had 12 years with a winter statement issued during the month of June since 2008. That means around 60 percent of all June's since 2008 a winter weather statement was issued. Thus it is not uncommon for a winter statement to be issued in the Great Falls CWA during June. It does not snow in the same zones every year, but because the Great Falls CWA is quite large, it is not uncommon for a winter statement to be issued in June. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 51 70 48 58 / 90 50 80 80 CTB 48 69 48 60 / 50 30 70 80 HLN 51 66 46 56 / 80 90 90 90 BZN 48 64 42 57 / 60 90 90 70 WYS 40 55 32 50 / 40 90 80 70 DLN 46 60 38 54 / 60 90 90 60 HVR 52 75 50 65 / 80 30 80 90 LWT 48 66 44 59 / 90 90 70 80

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 6 PM Saturday to noon MDT Monday for Gallatin and Madison County Mountains and Centennial Mountains-Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains.