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Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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666 FXUS65 KTFX 150159 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 759 PM MDT Wed Aug 14 2024 .SYNOPSIS... Showers and thunderstorms will continue across North-central, Central, and Southwestern Montana through Friday with the greatest coverage and precipitation amounts on Friday. Thursday morning the West Yellowstone area will see patchy fog. Sunday through the middle of next week it will be about seasonal averages for high temperatures with isolated showers and thunderstorms Monday through Wednesday. && .UPDATE... Showers and thunderstorms are slowly waning across the region with loss of daytime heating. Radar imagery shows a few outflow boundaries across North-central Montana, which will maintain chances for showers and thunderstorms over the next few hours across portions of the plains. Otherwise, activity across much of Central and Southwest Montana has either fully dissipated or is weakening significantly. Looking toward the rest of the night, a brief, weak period of upper level ridging will build in. This will promote mostly, if not entirely clear skies across most areas tonight. Given a few areas saw heavy rain today, the clearing skies will raise concerns for fog, especially in elevated valleys such as the West Yellowstone area. Minor tweaks were made to the forecast to account for latest trends, otherwise no significant update was needed this evening. -AM && .AVIATION... 15/00Z TAF Period The initial concern this TAF period will be for lingering showers and thunderstorms, primarily in and near terrain through sunset. Clearing skies will lend to opportunities for fog overnight where precipitation fell today, most notably at KWYS. Given heavy rain has fallen here, clear skies forecast tonight, and the tendency for KWYS to fog up the morning after rain, I went ahead and prevailed 1/4SM late tonight through mid-morning tomorrow. Otherwise the next concerns will be for additional afternoon and evening showers and thunderstorms tomorrow afternoon, along with a bit of wildfire smoke near the Canadian border (KCTB and KHVR). Mention of both of these was largely omitted at this time due to lack of confidence in impacts directly at terminals. -AM Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 529 PM MDT Wed Aug 14 2024/ This afternoon through Thursday... This afternoon an upper-level trough is over North-central, Central, and Southwestern Montana. This will allow for isolated showers and thunderstorms in the afternoon and evening across the area. Due to the cold front that moved through yesterday temperatures will be 5 to 10 degrees below seasonal averages across the lower-elevation`s of North-central, Central, and Southwestern Montana this afternoon. This afternoon locations across southern Beaverhead, Madison, and Gallatin Counties have a 40 - 70% chance for receiving a tenth of an inch of rain or greater. North-central and Central Montana have 15 - 40% chance for a tenth of an inch of rain. This afternoon and evening isolated thunderstorms in the West Yellowstone area will produce strong to severe wind gusts. Due to the rain this afternoon and evening and clearing skies tonight, Thursday morning patchy fog is likely (60% chance) in the West Yellowstone area. On Thursday an upper- level ridge moves back over North-central, Central, and Southwestern Montana. However, an upper-level shortwave moves through the upper-level flow and will bring showers and thunderstorms to the area. On Thursday Southwestern Montana has a 30 - 60% chance for a tenth of an inch of rain or greater. Thursday along the Rocky Mountain Front and adjacent plains there is 20 - 50% chance for a tenth of an inch of rain or greater. Friday through Sunday... On Friday the upper-level ridge remains over North-central, Central, and Southwestern Montana. However, an upper-level shortwave moves through the upper-level flow and will bring showers and thunderstorms to the area. On Friday there is a 25 - 40% chance for a quarter inch of rain or greater. On Friday along the Rocky Mountain Front and adjacent plains there is a 50 - 75% chance for a quarter inch of rain or greater. On Saturday the upper-level ridge remains over North-central, Central, and Southwestern Montana. However, an upper-level shortwave moves through the upper-level flow and will bring very isolated showers and thunderstorms to the area. On Sunday the upper-level ridge remains over North-central, Central, and Southwestern Montana. However, an upper-level shortwave moves through the upper-level flow and will bring very isolated showers and thunderstorms to the area. On Saturday and Sunday it will warm back up to about seasonal averages. Monday through Next Wednesday... On Monday and Tuesday clusters show that an upper-level ridge remains over North-central, Central, and Southwestern Montana. This will keep warm and mostly dry conditions across the area on Monday and Tuesday (isolated showers and thunderstorms will occur). On Wednesday two of the clusters (67% of ensemble members) keep the upper-level ridge over North-central, Central, and Southwestern Montana. On Wednesday one cluster (29% of ensemble members) has a trough moving over the area. On Wednesday the other cluster (4% of ensemble members) has a strong ridge beginning to move over North-central, Central, and Southwestern Montana with northwest flow aloft. This indicates that isolated showers and thunderstorms are likely to continue across the area on Wednesday. -IG && .PRELIMINARY POINT TEMPS/POPS... GTF 54 85 57 81 / 0 10 50 60 CTB 52 83 54 75 / 20 20 60 80 HLN 54 87 56 83 / 20 20 60 50 BZN 48 86 49 83 / 20 20 50 30 WYS 36 76 38 73 / 30 20 60 20 DLN 46 80 46 79 / 20 40 50 20 HVR 58 89 60 85 / 0 10 20 60 LWT 51 82 55 80 / 20 10 30 70 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls