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Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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580 FXUS65 KTFX 131711 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1111 AM MDT Tue Aug 13 2024 ...Updated Aviation Section... .SYNOPSIS... Daily chances for showers and thunderstorms through the forecast period. On Tuesday afternoon, some storms can become strong to severe and can produce strong winds, hail, frequent lightning, and localized areas of heavy downpours. Temperatures cool by a few degrees after today, and stay consistent through the week && .UPDATE... Main changes made this morning were to increase POPs a bit, especially across the plains of North Central Montana, and to add gusty wind wording to thunderstorms this afternoon. Ludwig && .AVIATION... 13/18Z TAF Period VFR conditions will prevail during this TAF period for all terminals except during any thunderstorms that go over and/or near a terminal. There is a 20 - 40% chance for thunderstorms at the KCTB and KHVR terminals this afternoon and evening. There is a 60% chance for showers and thunderstorms at the KHLN, KGTF, KBZN, and KLWT terminals this afternoon and evening. There will be showers and thunderstorms at the KEKS and KWYS terminals this afternoon and evening. The main threats from thunderstorms today will be brief heavy downpours that will reduce visibility to MVFR levels, strong to severe wind gusts (at all terminals excluding KCTB), frequent lightning, and small hail (primarily in Southwestern Montana). During showers and thunderstorms there will be brief periods of mountain obscuration. There is a 40% chance for showers and thunderstorms at all terminals excluding the KCTB and KHVR terminals Wednesday morning through the end of the TAF period. -IG Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 540 AM MDT Tue Aug 13 2024/ Isolated showers linger across the Northern Rocky Mountain Front and Hi-Line region this morning. An upper level shortwave moving through starting in the late morning and a cold front passage will develop scattered to widespread showers with embedded thunderstorms. There will be enough shear, CAPE, and moisture to produce some strong to severe storms with strong wind gusts, hail, frequent lightning, and brief heavy downpours possible. The Storm Prediction Center has put most areas (besides the northern Rocky Mountain Front) in a Marginal Risk for severe weather. There`s a 5% for those locations to have storms produce 58mph gusts or greater, and a 5% for Southwest Montana storms to produce 1" hail or greater. PWATs up to 1"-1.25" suggests that localized heavy downpours are possible with the strongest storms. There`s a 40-70% of locations across the CWA of receiving 0.25" or greater of rainfall. This is also reflected in the Weather Prediction Center`s excessive rainfall outlook, with a 5% for areas west of a line from Gallatin County to Teton County for excessive rain. This can also raise some concern for rapid runoff or debris flow over burn scars/burned over fire areas, especially the Horse Gulch burn scar(see Hydrology section). Storm coverage decreases after sunrise, but there is a slight chance for showers to linger mainly across North Central Montana overnight into Wednesday morning. Model guidance suggests that the weather pattern for daily precipitation and near normal temperatures stays through the forecast period. PWATs generally stay around up to an inch daily, so a few stronger showers and storms can bring heavier rainfall, and gusty winds. Heading into the weekend, chances of precipitation decreases slightly as the upper level ridging in place will help limit storm coverage. However, ensemble models are still a little uncertain of how long this area of upper level troughing stays next week, and therefore there`s uncertainty for when we have a break in the rain chances. -Wilson && .PRELIMINARY POINT TEMPS/POPS... GTF 85 56 80 54 / 60 40 30 10 CTB 83 54 79 53 / 20 20 20 10 HLN 83 55 80 54 / 70 50 30 10 BZN 81 49 77 48 / 70 60 50 10 WYS 69 39 67 36 / 80 70 70 20 DLN 73 46 73 45 / 80 50 50 10 HVR 90 59 85 58 / 20 40 20 20 LWT 85 52 76 51 / 40 70 40 20 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls