####018002294#### FNUS21 KWNS 200657 FWDDY1 Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0156 AM CDT Wed Aug 20 2025 Valid 201200Z - 211200Z ...Synopsis... A strong ridge of high pressure building over the central US is forecast to gradually move west while a weak trough on the western edge, suppresses the northern extent. The increasingly strong height gradient along the western periphery of the ridge will bolster mid-level winds aloft over the Northwest and northern Great Basin. At the surface, a cold front will move into the western Great Basin before stalling this afternoon. The front, and increased flow aloft will support gusty surface winds and isolated storms, increasing fire danger today and tonight. ...Great Basin... Several hours of dry/breezy conditions are expected this afternoon with the breakdown of the upper-level ridge. Very warm temperatures are expected, supporting deep vertical mixing and low boundary-layer RH. West/southwesterly winds of 15-20 mph with gusts of 20-30 mph near the front, and RH below 15% on a widespread basis will support elevated to locally critical fire-weather conditions from southern ID into the Great Basin. Increased southwesterly flow aloft on the western edge of the ridge will help monsoon moisture (PWATs 0.6-0.8 inches) advect northward over NV and western UT. The surface cold front associated with the upper trough will stall over the western Great Basin, serving as a focus for isolated thunderstorm development through the afternoon. Uncertainty remains high regarding coverage of thunderstorms, especially with southern extent. While moisture and instability will be more limited, enough instability and forcing are expected to produce isolated high-based showers and thunderstorms capable of dry lightning. Should these storms develop they may track eastward, persisting overnight into eastern ID and western MT with a continued threat for dry strikes. Additionally, any active large wildfires may have increased chances of deep pyroconvection/localized extreme fire behavior given the steep lapse rates and unstable troposphere. ..Lyons.. 08/20/2025 ...Please see www.spc.noaa.gov/fire for graphic product... $$ ####018001496#### FNUS22 KWNS 200657 FWDDY2 Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0157 AM CDT Wed Aug 20 2025 Valid 211200Z - 221200Z ...Synopsis... The strong ridge over the western US is expected to continue to break down under the shortwave trough passing through the northern Rockies. This will support continued advection of monsoon moisture northward into the Great Basin and parts of southern California. By Thursday afternoon, PWAT values are likely to be between 0.5-0.8" with a dry sub-cloud layer and steep low-level lapse rates. Despite slower storm motions and isolated coverage over Utah and parts of Nevada, little wetting rainfall is expected. This should support isolated dry thunderstorm potential the under the upper high and into portions of eastern Idaho and western Wyoming. With dry fuels in place, some lightning ignitions are possible. In addition to the potential for thunderstorms, very warm and unstable conditions are expected on the periphery of the deeper monsoon moisture surge over parts of the southern Great Basin and southern California. Steep mid-level lapse rates and marginal buoyancy will support unstable conditions over much of the Southwest. This could support plume dominated fire growth and pyroconvection near large active fires, with localized extreme fire behavior possible. ..Lyons.. 08/20/2025 ...Please see www.spc.noaa.gov/fire for graphic product... $$