564 FXUS65 KTFX 172004 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 204 PM MDT Sat Jul 17 2021 .SYNOPSIS... Temperatures will continue to increase this weekend as upper level high pressure builds into the area. Moisture will gradually work its way into the area early next week, which will lead to a few thunderstorms, some dry and gusty, to start the week. && .DISCUSSION... Upper level ridging continues to build into the area this weekend, which will cause us to continue get increasingly warm through Monday. Highs today should reach the 90s for most of the area, with some upper 90s in the northeastern part of our CWA, where the Excessive Heat Warning has gone into effect. Temperatures will warm further tomorrow, with most of the area reaching the upper 90s to low 100s. Aside from the heat over the next few days, we will also begin to bring some mid level monsoonal moisture into the area as it pivots around the ridge from the southwestern US. This will manifest in a few isolated showers and thunderstorms tomorrow, with some of those being on the dry side since moisture will mostly be in the mid levels. Additional moisture will arrive on Monday, resulting in more widespread shower and thunderstorm activity. These too will likely err on the drier side, with convective condensation levels (CCLs, or where air rising due to surface heating begins to form clouds) still remaining quite high around the 550 mb level (about 10,000 feet above the surface here in Montana). This will give any rain plenty of time to evaporate, and in addition to causing dry thunderstorms, may also produce some gusty outflow winds. This will be of concern for fire weather, as outlined in the Fire Weather Discussion below. Moisture will linger on Tuesday, but the low levels may moisten enough to allow some of this rain to reach the surface, but dry thunderstorms will still be a concern. As we head towards mid to late next week, an upper level trough will try to dig into the Pacific Northwest. While this should allow temperatures to moderate, it may also bring increased wind speeds, but details on that are still a bit uncertain. Ludwig && .AVIATION... 1215 PM MDT Sat Jul 17 2021 (17/18Z TAF period) Overall, VFR conditions are forecast to prevail through the period, though there may be temporary MVFR conditions due to smoke. Otherwise, the main concern over the next few days, and especially Sunday into Monday, will be density altitude issues due to the increasingly hot conditions. -Kredensor Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .FIRE WEATHER... Increasingly hot weather is expected this weekend, with little chances for wetting rainfall expected. A few isolated dry thunderstorms may be possible tomorrow, but the better chances for showers and thunderstorms (some dry and gusty) will continue to be Monday and Tuesday as monsoonal moisture begins to work into the area. Coverage of dry thunderstorms will likely be highest on Monday, and a Fire Weather Watch or Red Flag Warning may be needed in future updates, particularly for Fire Weather zones 116, 117, and 118. Ludwig && .PRELIMINARY POINT TEMPS/POPS... GTF 96 57 98 60 / 0 0 0 0 CTB 91 54 94 57 / 0 0 0 0 HLN 97 62 101 65 / 0 0 0 0 BZN 95 55 99 58 / 0 0 0 0 WYS 85 42 88 45 / 0 0 0 0 DLN 91 54 95 57 / 0 10 0 0 HVR 96 62 101 64 / 10 0 0 10 LWT 93 60 98 63 / 10 0 10 0 && .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 until 9 PM MDT Tuesday Blaine... Chouteau...Fergus...Hill. && $$ http://www.weather.gov/greatfalls