108 FNUS28 KWNS 162151 FWDD38 Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0448 PM CDT Wed Jun 16 2021 Valid 181200Z - 241200Z Dry thunderstorms are forecast beneath the broad upper-level ridge on Friday and Saturday. This ridge will break down on Saturday as a mid-level trough develops over the center of the CONUS into early next week. As this trough develops, northwesterly flow is forecast to strengthen which may bring some fire weather concerns to portions of the northern Rockies. An upper-level trough will approach the West Coast toward the middle of the next week which could bring fire weather concerns with regards to thunderstorms across northern California and the Northwest and dry and windy conditions across portions of the Great Basin and Southwest. ...D3/4 - Fri/Sat - Dry Thunderstorms in portions of the Sierra, Great Basin, central Rockies, and Southwest.... A plume of mid-level moisture beneath the upper-level ridge will continue to provide ample instability for thunderstorm development each day. These thunderstorms will mostly be dry given the extreme dewpoint depressions (50 to 70F) and PWAT values around 0.5 inches. The greatest storm coverage is expected on Saturday as the upper ridge weakens and mid-level temperatures cool. Therefore, 40 percent dry thunderstorm probabilities have been introduced for Saturday. A scattered dry thunderstorm area may also need to be considered on Friday during the Day1 or Day 2 forecast, but there is not a strong enough signal for scattered storm coverage at this time. However, considering the very dry to near record dry fuels across the region and storms which will struggle to produce any wetting rain, even borderline scattered coverage may be sufficient to warrant a scattered dry thunderstorm delineation. ...D4/Sat - Snake River Plain and portions of eastern Montana/central Wyoming... As westerly flow strengthens across the northern Rockies on Saturday, surface winds are also expected to increase as a result of the deeply mixed airmass. Relative humidity is forecast to be 10 to 15 percent in the area with winds of 15 to 25 mph. In addition, a corridor of stronger winds may be possible in eastern Montana in the wake of a cold front as it moves south across the state. There may be a brief window in this region where critical conditions may occur before cooler air and higher relative humidity arrives. ...D5/Sun - Portions of the Great Basin and northern Arizona... On Sunday, mid-level flow westerly flow is expected to strengthen somewhat. In addition, lee cyclogenesis is forecast in the central Plains into West Texas which should act to tighten the surface pressure gradient. As a result, 15 to 25 mph winds are forecast across much of the Southwest. The most likely region for critical strength winds overlapping the dry surface conditions will be across portions of northern Arizona into eastern Utah where 40 percent probabilities have been added. ...D7/8 - Tue/Wed - Portions of the Great Basin and northern Arizona... An upper level trough is forecast to approach the California coast early next week. The exact timing and evolution of this trough still has considerable uncertainty, but the overall pattern has shown a trough approaching the region for several days. As a result, downslope flow and dry/windy conditions are possible ahead of this trough as it approaches the coast. The exact location of the strongest winds may change as the evolution of the trough becomes more clear, but there was enough confidence in the overall pattern to warrant 40 percent probabilities on D7 and D8. ..Bentley.. 06/16/2021 ...Please see www.spc.noaa.gov/fire for graphic product... $$
