619 FXUS65 KTFX 170549 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1145 PM MDT Fri Jul 16 2021 Updated Aviation Discussion .SYNOPSIS... A few showers and thunderstorms are expected again this afternoon and evening, especially over the higher terrain of Southwest and Central Montana. The warming trend will continue, with temperatures Sunday and Monday at lower elevations peaking between 95 and 105 degrees. && .UPDATE... Southwesterly flow aloft continues to advect smoke and haze from Western USA wildfires into Montana... and no letup is expected any time soon. Currently, scattered showers and a few thunderstorms are affecting portions of southwestern Montana with a few gusts of up to 50 mph having been reported earlier this evening. Have updated the forecast to fine tune PoPs and weather based upon current observations and early evening models updates. Have also expanded coverage for haze and smoke. Remainder of the forecast is on-track and no further updates are anticipated this evening. mpj && .AVIATION... 1145 PM MDT Fri Jul 16 2021 (17/00Z TAF period) A few showers lingering across central and SW MT will track NE while dissipating overnight with some brief gusty/shifting winds possible near this activity with mainly mid level cloud-cover and VFR conditions prevailing. Some isolated lightning cannot be ruled out from the KBZN to KLWT but should be rather limited. Areas of smoke/haze continue over the region with surface visibility generally greater than 6SM, but could be lower for a period Saturday morning again in areas directly downwind of wildfire activity. Hoenisch Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .FIRE WEATHER... Isolated to scattered thunderstorms, some of which may be dry, are expected again this afternoon and evening. Overlying layers of smoke appear to be suppressing temps and convective initiation somewhat so far this afternoon, but t-storm development is expected eventually, similar to yesterday. This weekend will feature increasingly hot conditions with little to no chance for rainfall. Chances for showers and thunderstorms increase again across the Northern Rockies on Monday, with the best chance and coverage of storms expected on Tuesday as monsoonal moisture lifts northeast from the Great Basin and Desert Southwest. Temperatures will remain hot and afternoon relative humidity low through the next seven days, with the hottest and driest days being on Sunday and Monday. -Kredensor/Moldan && .PREV DISCUSSION... /ISSUED 243 PM MDT Fri Jul 16 2021/ Today through Saturday... A few more showers and thunderstorms are expected across Southwest and portions of Central and North Central Montana through the evening hours tonight. Best chance for these showers and thunderstorms will be during and just after peak heating hours, with the best coverage of precipitation primarily residing over the higher terrain. With PWATs generally 0.75" or less and cloud bases likely to be on the order of 10,000ft, with well-mixed dry air below, at least isolated dry thunderstorms are possible. Given dry boundary and mid-level layers, denoted within soundings, concerns for gusty and erratic winds approaching 45-55 mph do exist. One potential limiting factor on temperatures and convection today may be the overlaying smoke and what appears to be some modest suppression of temps this afternoon. Temps may struggle to reach 90F in Great Falls and points southward. Saturday is expected to be dry day across the Northern Rockies as the upper level ridge amplifies across the western 2/3rds of the CONUS and into Canada, with high temps warming into the low 90s to low 100s. As a result, the Excessive Heat Watch was upgraded to a warning for the four zones, and it was moved up a day to start at noon on Saturday. While high temps on Friday may not quite reach warning criteria, they quickly will for Sun & Mon, so the decision was made to go with simplified headline of just a warning for those zones. -Kredensor Sunday through next Friday... The primary concern over the period will be the heat and increasing thunderstorm chances. Upper level ridge will continue to amplify through Monday, allowing heat to progressively build into early next week. Then the ridge gradually shifts eastward, allowing for subtle waves and increasing monsoonal moisture on SW'ly flow aloft to begin to lift into the area. Sunday and Monday are currently clearly expected to be the warmest of the forecast period, with widespread highs in the 95 to 105 degree range. The zones under an Excessive Heat Warning are currently in that warning through Tuesday. Highs on Tuesday would be marginal for a warning, but with forecast lows in the EHW area Tuesday morning expected to remain in the 70s, significant heat stress due to a lack of overnight cooling will remain a concern on Tuesday. Surrounding the Excessive Heat Warning, a Heat Advisory has been issued for much of the remainder of the forecast area, starting at Noon on Sunday. Some zones have the advisory end Monday evening, and others continue it through Tuesday evening, mainly based on the confidence level of maintaining Advisory worthy temperatures and heat stress concerns. The confidence in significant heat stress continuing for mid-week and beyond just is not there currently to justify extending the Warning or Advisories beyond Tuesday. That is certainly something that can be assessed in the coming days, and if needed, headlines can be extended deeper into next week as appropriate. Regardless of whether an area will be under a Warning, Advisory, or no highlight, it will remain hot across the entire area. Even after temps peak on Monday, widespread highs in the low to mid-90s are expected through at least Thursday. Overnight lows in the 60s to mid-70s will limit overnight cooling for homes with out air conditioning, which is an important factor in assessing heat stress and the potential for increased heat-related illnesses. Monsoonal moisture will begin to lift across the area on Monday, with isolated chances for showers and thunderstorms across southern portions of Southwest Montana. Shower and thunderstorm chances increase further in both potential and areal extent on Tuesday, with the potential for some storms to produce localized heavy rainfall given forecast PWATs approaching an inch. Daily chances for afternoon showers and storms linger across portions of Southwest through Central Montana from Wednesday through Friday as the upper level ridge slowly shifts east. -Kredensor && .PRELIMINARY POINT TEMPS/POPS... GTF 57 96 56 99 / 10 0 0 0 CTB 55 91 53 93 / 0 0 0 0 HLN 60 97 62 101 / 20 0 0 0 BZN 53 96 54 99 / 30 0 0 0 WYS 41 87 42 89 / 20 10 0 0 DLN 51 92 53 95 / 20 0 0 10 HVR 62 99 61 101 / 10 0 0 0 LWT 60 94 60 97 / 20 0 0 10 && .TFX WATCHES/WARNINGS/ADVISORIES... Heat Advisory from noon Sunday to 9 PM MDT Monday Eastern Pondera...Eastern Teton...Gallatin...Jefferson...Madison... Meagher. Heat Advisory from noon Sunday to 9 PM MDT Tuesday Broadwater... Cascade...Central and Southern Lewis and Clark...Judith Basin... Liberty...Toole. Excessive Heat Warning from noon Saturday to 9 PM MDT Tuesday Blaine...Chouteau...Fergus...Hill. && $$ http://www.weather.gov/greatfalls