Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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961 FXUS65 KTFX 132100 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 300 PM MDT Sat Jul 13 2024 .SYNOPSIS... Critical fire weather conditions across much of southwestern and central Montana will continue through the rest of the afternoon and early evening. Further north, the threat of severe weather will continue through the evening hours before tapering off. Winds and storms will decrease overnight, but another hot and dry day is forecasted on Sunday. && .DISCUSSION... Today and Tonight... Thunderstorms are already underway along Hill and Blaine counties. The severe weather threat for these two counties is higher with up to 2 inch hail and over 60 mph gusts possible. These storms will continue to push east with more storms coming down from Canada over the next few hours. The thunderstorm threat is expected to diminish after 7 PM. The other main threat for this afternoon will be critical fire weather conditions in southwestern Montana with gusty winds and low relative humidity that will make fires hard to contain. The winds will start to taper off after sunset but poor recovery overnight will lead to near-critical fire weather conditions tomorrow afternoon. Despite the near-critical environment, the duration of the highest winds is quite narrow and winds are generally expected to be lighter Sunday than today. However, it will be something to watch in case conditions deteriorated further. -thor Sunday through Monday... A high pressure ridge is forecast to build back into the forecast area on Sunday, maintaining the hot and dry conditions. However, it will also help decrease winds aloft, which will in turn keep winds from becoming quite as strong as those today. Weak energy in the resulting flow aloft may bring a few weak thunderstorms to the Hi-Line and to the Southwest Montana mountains once again during the afternoon. A shortwave trough is then forecast to move southeast on the leading edge of the ridge across southern Saskatchewan Sunday night through Monday, which will swing a Canadian cold front south over at least the plains of Montana. An overall lack of moisture will limit the possibility of thunderstorm activity, but a few storms cannot be ruled out. The main impact of this frontal passage will be to cool temperatures back closer to seasonal averages with a shift to more northerly winds, at least over the plains. Tuesday through next Saturday... The ridge is forecast to remain unusually strong over the Western United States through this period, as indicated by good agreement among model ensemble clusters. This will likely result in a return to widespread much above normal temperatures through this period, with most lower elevations continuing to have high temperatures in the 90s and possibly over 100 degrees. The chance for afternoon and evening thunderstorms will mainly be focused over the mountainous area of Southwest Montana. However, the heat will likely be the greater threat, so prepare for it now if you need to. -Coulston && .AVIATION... 13/18Z TAF Period VFR conditions will prevail throughout the 1318/1418 TAF period; however, monsoonal moisture lifting northeast from the Great Basin and towards the Northern Rockies this evening will overspread Southwest Montana by Sunday morning and bring increasing mid- to upper level cloudiness to the KWYS, KEKS, and KBZN terminals. Smoke from wildfires burning across the Western US will also lead to hazy skies across much of Southwest Montana (i.e. KWYS, KEKS, and KBZN terminals) through the early evening hours tonight, mainly reducing slantwise visibility on approach. At the KHLN terminal, west to northwest winds will keep most of the smoke and haze from the Horse Gulch fire west of the terminal through this evening, but decreasing winds overnight may allow for reductions in slantwise visibility through the morning hours on Sunday at the terminal. Finally, temperatures in excess of 90 degrees across all terminals this afternoon will lead to density altitude concerns. A weak disturbance moving over Southeast Alberta/Southwest Saskatchewan this afternoon and through the early evening hours will help to initiate isolated to scattered thunderstorms near and east of the KHVR terminal in North Central Montana. The best chance, approximately 30-40%, for any thunderstorms impacting the KHVR here appears to be between 19-23z this afternoon; but may linger as late as 04z this evening. Main threat from any thunderstorm, especially east of the KHVR terminal over Blaine County, would be a period of heavy rain, hail, and strong outflow winds. An isolated thunderstorm or two can`t be ruled out across Southwest Montana near the KEKS and KWYS terminals this afternoon and evening, mainly between 18z and 00z, but the probability for said activity is less than a 20% chance. Should any storm develop the main threat to terminal operations would be gusty and erratic outflow winds. - Moldan/Coulston Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .FIRE WEATHER... The Red Flag Warning remains in effect from 2 pm today through midnight tonight for Fire Weather Zones 117 and 118 due to hot temperatures, low humidity, and gusty winds. The forecast remains on track with keeping the main focus for critical fire weather conditions today over portions of Southwest and Central Montana (including Fire Weather Zones 117 and 118). Significantly dry fuels will combine with increasing westerly winds (gusting mostly to 35 mph at times) and continued low afternoon humidity (as low as 10 percent). The area of most concern in Zone 117 is Meagher County, as fuels in areas farther north in the Zone (including Cascade and Judith Basin Counties) have not dried out as much. Similarly hot and dry conditions are forecast for Sunday, but winds are not forecast to be quite as strong. After a brief and minor cooldown on Monday, hot and dry conditions are forecast to return for at least the next week after that. -Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 58 95 57 89 / 0 0 0 0 CTB 55 90 52 87 / 0 0 0 0 HLN 62 98 60 95 / 0 0 0 0 BZN 57 96 56 91 / 10 10 10 10 WYS 47 83 46 82 / 10 10 20 30 DLN 56 92 55 88 / 10 10 0 10 HVR 58 93 56 86 / 10 0 10 0 LWT 57 89 54 84 / 10 0 0 10 && .TFX WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until midnight MDT tonight for Central and Eastern Lewis and Clark National Forest Areas. Red Flag Warning until midnight MDT tonight for Helena and Townsend Ranger Districts of the Helena National Forest. && $$ http://www.weather.gov/greatfalls