125 FXUS65 KTFX 251439 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 839 AM MDT Sun Jul 25 2021 .UPDATE... Skies are clear this morning under widespread smoke and haze. Surface observations indicate thermal belts over mountain areas where mid- and upper-level temperatures were warmer than lower elevations, and poor overnight recovery of relative humidity. Forecast remains on track for a warm and dry day with elevated fire weather conditions. && .SYNOPSIS... A strengthening high pressure ridge will warm temperatures from 5 to 10 degrees above normal today, to between 10 and 15 degrees above normal by Tuesday, under mostly clear but hazy skies. There will also be periods of gusty west to northwest winds, mainly during the afternoon and evening hours. The weather pattern will then shift to a less hot one Wednesday through the weekend, but there will be a chance for thunderstorms most of these days. && .AVIATION... 500 AM MDT Sun Jul 25 2021 (25/12Z TAF period) VFR conditions will mostly persist across north central and southwest Montana through at least the next 24 hours. A westerly flow aloft will keep skies mostly cloud-free, but it will move wildfire smoke over the area, mostly causing hazy skies, but intermittent MVFR visibility is possible more dense smoke plumes. Gusty west to northwest winds will mix down to the surface at times between 17Z and 03Z. -Coulston Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 500 AM MDT Sun Jul 25 2021/ Today through Tuesday...A flat high pressure ridge over the Pacific Northwest and through Montana will keep temperatures 5 to 10 degrees above normal today with continued clear but smokey and hazy skies. Breezy westerly winds aloft will also mix down to the surface by this afternoon, but the strongest winds should remain in the 10 to 20 mph range with occasional gusts to 30 mph. Although afternoon humidity will fall well below 20 percent again today, confidence is low that winds will be strong enough for a long enough period of time to cause significant additional fire spread, so the Fire Weather Watch for Fire Weather Zones 117 and 118 has been cancelled. (For more details, please see the FIRE WEATHER section of the discussion.) The high pressure ridge will then strengthen and build north into Montana Monday into Tuesday, which will continue the very dry conditions with even warmer temperatures. Much of the area will warm to between 10 and 15 degrees above normal, with a few places approaching or going just over 100 degrees F. Regarding the Excessive Heat Watch for Fergus County, will keep it in effect as is for now for Monday through Tuesday, but there is less certainty that criteria may be met on Monday than on Tuesday. Will let the next shift check the next forecast model run to see if this trend continues. The strengthening of the ridge should also help decrease winds aloft, which, in turn, should limit the gusty winds across the area. The ridge axis will shift more so into eastern Montana on Tuesday as a low pressure trough deepens off the Pacific coast, putting the area under more of an increasingly moist and unstable southwesterly flow aloft. A weak disturbance in this flow may cause a few thunderstorms to develop over the southwest Montana mountains. The lingering hot and dry air will likely cause most of the storms to be on the dry side, with erratic wind gusts being the main threat. Just how strong these storms could become is still uncertain at this time. Wednesday through next Sunday...The National Blend of Models (NBM) indicates that the low pressure trough off the Pacific coast will generally remain there through this period, while the high pressure ridge stays centered over Great Plains. This will continue the trend of an unstable southwest flow aloft over Montana tapping into Pacific and Monsoonal moisture, keeping a chance of mainly afternoon and evening thunderstorms over the area. The threat for dry thunderstorms with erratic wind gusts will persist into Wednesday, but the increasing moisture should help the storm produce more wet thunderstorms later in the week and through the weekend. This kind of weather pattern lends itself to the potential for some of the storms to become strong to severe with heavy rain, hail, and strong winds; however, there is significant uncertainty as to whether, where, or when such storms may occur. Temperatures will also be not quite as hot during this period, mostly staying near normal to around 5 degrees above normal. Another uncertainty in this forecast is that individual forecast models have differing positioning of large-scale features, which could cause either a drier/calmer or wetter/more-unsettled weather pattern, so make sure to keep an eye out for potential adjustments to the forecast. -Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 94 55 96 61 / 0 0 0 0 CTB 89 52 91 61 / 0 0 0 0 HLN 96 60 100 64 / 0 0 0 0 BZN 94 53 98 56 / 0 0 0 0 WYS 87 42 90 44 / 0 0 0 0 DLN 91 53 94 56 / 0 0 0 0 HVR 93 58 95 63 / 0 0 0 0 LWT 92 57 95 60 / 0 0 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... Excessive Heat Watch from Monday morning through Tuesday afternoon Fergus. && $$ http://www.weather.gov/greatfalls