FNUS73 KLSX 200913 FWSLSX Spot Forecast for McDonnell unit...St. Louis County Parks Forestry National Weather Service Saint Louis MO 413 AM CDT Fri Mar 20 2026 Forecast is based on ignition time of 1100 CDT on March 20. If conditions become unrepresentative, contact the National Weather Service. .DISCUSSION... Well-above average temperatures will continue today along with seasonably low RH and no precipitation. An inversion will break around 11 am with RH quickly falling below 40 percent and mixing heights rising above 1000 ft AGL. Conditions will improve through early afternoon with 8 to 12 mph westerly winds and minimum RH as low as 25 to 30 percent along with mixing heights of 4500 to 5000 ft AGL, favoring excellent smoke dispersion. A weak, dry cold front will arrive this evening, veering winds to northerly. As temperatures cool through sunset, RH will rise again this evening along with mixing heights collapsing with the development of another inversion. .REST OF TODAY... Sky/weather.........Mostly sunny (25-35 percent). Temperature.........73 at ignition...Max 85. RH..................43 percent at ignition...Min 27 percent. Eye level winds.....West winds 3 to 4 mph with gusts up to 8 mph in the afternoon. An adjustment factor of 0.4 used. Wind (20 ft)........West winds 8 to 10 mph with gusts up to 20 mph in the afternoon. Mixing height.......1200 ft AGL at ignition...otherwise max 4900 ft AGL. Transport winds.....West 17 to 23 mph. Smoke dispersal.....Poor /2910 m/s-m/ at ignition. Max...excellent /15510 m/s-m/. TIME (CDT) 11 AM 1 PM 3 PM 5 PM 7 PM 9 PM Sky (%).........21 26 34 32 40 43 Weather cov..... Weather type....NONE NONE NONE NONE NONE NONE Tstm cov........ Temp............73 81 84 84 78 71 RH..............43 32 28 27 35 46 20 ft wind......W 8 W 9 W 9 W 8 NW 5 N 4 20 ft wind gust.15 17 17 14 11 9 Eye level wind..W 4 W 4 W 4 W 4 NW 2 N 2 Eye lvl wnd gst.7 8 8 6 5 4 Mix hgt (kft)...1.2 3.0 4.7 4.2 0.4 0.3 Transport wind..W 17 W 20 W 22 W 21 NW 12 N 9 Vrate kt-ft/1K..19 50 89 76 5 3 Ventrate Cat....POOR FAIR GOOD GOOD POOR POOR $$ Forecaster...Pfahler Requested by...Jason Pratte Type of request...PRESCRIBED .TAG 2606580.0/LSX .DELDT 03/20/26 .FormatterVersion 2.0.0