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Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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315 FXUS65 KTFX 130257 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 857 PM MDT Mon Aug 12 2024 .SYNOPSIS... Showers and thunderstorms will occur through at least Friday across at least some portion of North-central, Central, and Southwestern Montana. The showers and thunderstorms will be the most widespread on Tuesday. Isolated thunderstorms Tuesday afternoon and evening could produce severe wind gusts, large hail, and heavy rainfall. A cold front moves through on Tuesday which cools down temperatures on Wednesday. && .UPDATE... Main update to the overnight forecast period was to keep mention of scattered showers and weak thunderstorms through around midnight across much of North Central and Southwest Montana to better reflect current activity. SPC analysis still shows moderate instability over the area. However, the threat for additional strong to severe thunderstorms with strong wind gusts and large hail has decreased significantly. Another adjustment was to increase mention of fog in areas that received significant precipitation with this afternoon`s thunderstorms, which mainly includes areas of North Central Montana along and just south of US Highway 2. -Coulston && .AVIATION... 13/00Z TAF Period Showers and thunderstorms tracking ENE across the region downstream of an upper level trough situated west of the area will be the main concern this evening and again Tuesday afternoon/evening. KHVR and KLWT are likely to see thunderstorm impacts through 02z as stronger storms in the area track near these terminals. More isolated convection currently developing upstream over western MT and ID will maintain a slight chance (20-30%) for additional showers and thunderstorms across portions of central/north-central MT through around 08z tonight. Gusty and erratic winds and brief local terrain obstruction are the main concern near any showers and thunderstorms through this evening with VFR conditions prevailing otherwise. Hoenisch Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 613PM MDT Mon Aug 12 2024/ This afternoon through Tuesday... This afternoon an upper-level ridge remains over North-central, Central, and Southwestern Montana. This afternoon through this evening an upper-level level shortwave moves through the upper-level flow. This will cause there to be showers and thunderstorms in the Golden Triangle region (the region from Cut Bank to Havre to Great Falls) and Southwestern Montana through this evening. This afternoon the Storm Prediction Center (SPC) has issued a Marginal Risk for severe weather (5% chance for severe wind gusts within 25 miles of point) for the Golden Triangle region, Madison and Gallatin Counties, and eastern Beaverhead County. Isolated thunderstorms will produce severe wind gusts (wind gusts greater than 58 mph). The upper-level ridge remains over North-central, Central, and Southwestern Montana through Tuesday morning before an upper-level trough begins moving over the area Tuesday afternoon. A cold front associated with the upper-level trough will move through North-central, Central, and Southwestern Montana Tuesday afternoon through early evening. On Tuesday the SPC has issued a Marginal Risk for severe weather (5% chance for severe wind gusts and a 5% chance for golf ball-sized hail withing 25 miles of point) for eastern Beaverhead, southeastern Madison, and Gallatin Counties and Eastern Fergus and Blaine Counties. Isolated thunderstorms will produce severe wind gusts (wind gusts greater than 58 mph) and hail the size of golf balls (primarily in eastern Beaverhead, southeastern Madison, and Gallatin Counties). Some thunderstorms will produce heavy rainfall. On Tuesday locations across Southwestern Montana have a 20 - 50% chance for receiving a quarter inch of rain or greater. On Tuesday locations in Central Montana have a 30 - 60% chance for receiving a tenth of an inch of rain or greater. Wednesday through Friday... On Wednesday the upper-level trough remains over North-central, Central, and Southwestern Montana. This will allow for showers and thunderstorms in the afternoon and evening across the area. Due to the cold front that moves through on Tuesday temperatures will be 5 to 10 degrees below seasonal averages across the lower-elevation`s of North-central, Central, and Southwestern Montana on Wednesday. On Wednesday locations across Southwestern Montana have a 40 - 60% chance for receiving a tenth of an inch of rain or greater. 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 all lower-elevations of North-central, Central, and Southwestern Montana have a 20 - 40% chance for a tenth of an inch of rain or greater. 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. Saturday through next Monday... On Saturday clusters show an upper- level ridge over North-central and Central Montana with an upper- level trough beginning to move over the area. This will keep similar weather on Saturday to Friday. On Sunday and Monday deterministic models and clusters begin to diverge. This will continue to be monitored for details. -IG && .PRELIMINARY POINT TEMPS/POPS... GTF 55 83 56 79 / 10 40 50 20 CTB 52 82 54 79 / 30 20 20 20 HLN 56 83 55 79 / 20 60 50 40 BZN 50 80 49 78 / 30 60 60 50 WYS 42 70 39 69 / 10 80 60 80 DLN 49 76 46 73 / 10 70 50 50 HVR 56 89 59 85 / 30 20 40 20 LWT 52 83 52 76 / 20 30 60 40 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls