Area Forecast Discussion
Issued by NWS Great Falls, MT

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566 FXUS65 KTFX 211000 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 400 AM MDT Fri Jun 21 2024 .SYNOPSIS...
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Thunderstorms develop and move through the area, today. Some thunderstorms are forecast to become severe, producing gusty and erratic strong winds, large hail, frequent lightning and periods of heavy rain. A warming trend is forecast for the next few days. By Sunday, low elevation highs range in the 90s.
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&& .DISCUSSION...
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Note: The forecast area for the National Weather Service Great Falls Weather Forecast Office includes north central, central and southwest Montana. Today...A low amplitude upper level trof enters our region, today. An unstable atmosphere with deep layer 35KT to 40KT wind shear favorable for the development of severe thunderstorms is forecast. There is high confidence that some of these thunderstorms will become severe, producing gusty and erratic high winds, large hail, frequent lightning and periods of heavy rain. Although it looks like these storms will move through the area at a decent pace, some localized flash flooding is possible. Saturday through Sunday...A weak upper level ridge builds into the area, favoring warming and drying. By Sunday, low elevation high temperatures push into the 90s, with minimum Relative Humidity values falling into the teens. Sunday, the next upper level trof approaches from the west; however, a building bubble of high pressure over Arizona/New Mexico, adds mass to the trof, allowing most of it`s energy to be directed northward into Canada. A few thunderstorms and rain showers develop on Sunday. Monday through Wednesday...In response to the building upper level closed area of higher heights over Arizona/New Mexico, an upper level trof dominates The Treasure State. Low elevation high temperatures continue in the 80s and 90s, through mid-week, while conditions remain dry for our region. Thursday and Friday...As the end of the week approaches, the next upper level trof enters the region, temperatures cool a bit, and widespread rainfall is forecast. - Fogleman
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&& .AVIATION... 21/06Z TAF Period VFR conditions are mostly expected through at least 22/06Z across North Central (KCTB, KHVR), Central (KLWT, KGTF, KHLN), and Southwest (KBZN, KEKS, KWYS) Montana, unless otherwise mentioned. A weakly unstable southwesterly flow aloft will mainly move mid- and high-level cloudiness over the area through at least 15Z; a few light showers or weak thunderstorms are also possible, but confidence that any will directly impact terminals is low, so have not mentioned them in the TAFs. However, the airmass will become increasingly moist and unstable after 15Z as a shortwave low pressure trough approaches from the west. This will bring at least scattered showers and thunderstorms to the area along and east of a line from the Continental Divide southeast through the KHLN and KBZN terminal areas. Some storms may become strong to possibly severe at times over the plains between 18Z and 02Z, mainly east of a KCTB to KGTF line, where heavy rain and lower ceilings could cause periods of MVFR conditions. These stronger storms could also bring hail and strong erratic wind gusts. Showers and storms will start to decrease from the west after 00Z as the shortwave moves through the area, which will also bring some mountain wave turbulence as the westerly flow aloft increases. -Coulston Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS...
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GTF 76 50 82 55 / 60 20 0 0 CTB 72 44 81 51 / 70 30 0 0 HLN 83 53 88 58 / 30 10 0 0 BZN 81 48 85 52 / 20 10 0 0 WYS 76 41 79 45 / 10 10 0 0 DLN 80 47 85 51 / 0 0 0 0 HVR 76 49 82 56 / 60 60 10 0 LWT 72 47 77 54 / 70 50 10 0
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&& .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls