Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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636 FXUS65 KTFX 112040 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 240 PM MDT Sat May 11 2024 .SYNOPSIS... The ongoing warm weekend will continue into Monday. Showers and a few thunderstorms will develop along the Hi-Line tonight, with additional afternoon and evening showers and thunderstorms likely across the plains Sunday and Monday. A cooler and more unsettled pattern will arrive for mid-week. && .DISCUSSION... Through Monday... Upper level ridging, with axis over the west coast, is slowly building eastward. With ridge axis off to the west, flow aloft is out of the northwest. A weak wave diving southeastward through this flow will result in showers and a couple thunderstorms tonight, mainly across eastern portions of the Hi-Line. This activity moves east of the area by 7AM Sunday. Additional instability will develop across Central and North-central Montana Sunday, resulting in a round of isolated afternoon and evening showers and thunderstorms. Concerns with thunderstorms that form will be for gusty winds, given relatively deep mixing and inverted-V soundings. Expect more of the same on Monday, though the opportunity for showers and perhaps a thunderstorm or two will spread further southwest into Southwest Montana. Additionally, breezy westerly winds look to develop over the plains as a passing wave moves overhead. -AM Tuesday through next Saturday... Expect periods of rainfall to continue through the day on Tuesday as moisture continues to work into the area from the north and west. For the most part, precipitation will be rainfall except at the highest elevations even as cooler air from Canada pours into the region behind a surface cold front that will work in with the rain. Beyond Tuesday, a ridge will develop to our southwest, but with a northwesterly flow aloft in place, expect near to perhaps a bit cooler than average temperatures, with opportunities for showers. Ludwig/AM && .AVIATION... 1126 AM MDT Sat May 11 2024 (11/18Z TAF Period) The main concern this TAF period will be for showers and perhaps a thunderstorm or two across eastern portions of the Hi-Line (KHVR) late tonight. Confidence in thunder at the KHVR terminal was too low to mention in the TAF at this time. The only other concern will be for lower clouds across the plains of North-central and Central Montana tomorrow morning, though confidence in sub-VFR conditions being realized is less than 40% a this time. -AM Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .HYDROLOGY... A Flood Warning remains in effect for Clear Creek in North Central Montana through this evening, with water levels expected to slowly fall from minor flood stage to action stage tonight. Additionally, a Flood Watch remains in effect for the nearby Bears Paw Mountains through the weekend as warming temperatures and subsequent snowmelt runoff, and remaining runoff from rainwater, could push creeks and streams out of their banks. While some rainfall is expected this evening, rainfall amounts should not be high enough to significantly worsen any flooding of streams and creeks. Further south across the Island Ranges of Central Montana (i.e. Highwood, Moccasin, Judith, Little Belt, and Snowy), increased snowmelt and subsequent runoff into creeks and streams is expected through Monday as overnight temperatures and dewpoint temperatures remain above freezing. This runoff could result in waterways nearing bankful by Saturday night/Sunday morning. Hence, a Flood Watch has been issued for the Little Belts eastward toward the Lewistown area. - Moldan/AM/Ludwig && .PRELIMINARY POINT TEMPS/POPS... GTF 48 78 49 76 / 20 20 10 20 CTB 47 78 49 73 / 20 20 0 20 HLN 50 80 51 77 / 0 10 0 20 BZN 43 76 46 73 / 0 0 10 50 WYS 35 69 37 65 / 10 10 10 60 DLN 42 76 46 73 / 0 0 10 30 HVR 48 76 49 80 / 50 10 30 30 LWT 45 70 46 71 / 20 30 20 30 && .TFX WATCHES/WARNINGS/ADVISORIES... Flood Watch through Sunday morning for Bears Paw Mountains and Southern Blaine. Flood Watch through Monday morning for Cascade County below 5000ft-Fergus County below 4500ft-Judith Basin County and Judith Gap-Little Belt and Highwood Mountains-Meagher County Valleys- Snowy and Judith Mountains-Western and Central Chouteau County. && $$ http://www.weather.gov/greatfalls