526 FNUS28 KWNS 222052 FWDD38 Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0350 PM CDT Thu Oct 22 2020 Valid 241200Z - 301200Z A strong western upper-level trough and surface high pressure in the northern Rockies/Great Basin will be the primary features of interest during the extended period. Downslope and offshore flow in California will be the primary concern from this weekend into early next week. Fire weather concerns near and east of the Divide will likely be low on account of cool/cold temperatures and precipitation. ...Northern California... After a brief respite from northerly/northeasterly flow, an inside slider trough is expected to impact portions of the West Coast beginning late D3/Saturday into D5/Monday. Model agreement in the placement of the upper-level trough has improved significantly. Strong mid-level winds will be well-aligned with the Sacramento Valley. A strong surface high from the northern Rockies into the Pacific Northwest will promote strong northerly to northeasterly surface winds. The most significant fire weather conditions are expected to begin during Sunday evening and persist into Monday morning and perhaps early afternoon. As the mid-level jet progresses south, the expectation is for dry, downslope flow push southward and eventually impact the Bay Area. The favorable combination of the surface gradient and mid-level winds should allow winds to reach 30 mph in some locations with higher gusts. Strong subsidence on the back side of the trough will help to dry out the airmass where very low RH can be expected. Given the ongoing drought and near-record to record dry fuels, rapid spread of fires is probable. Conditions should finally improve by sometime Monday afternoon as the mid-level winds decrease from west to east and the surface gradient diminishes. ...Southern California... As the upper-level trough shifts to the southeast, surface high pressure will continue southward into the Great Basin. This pattern will favor offshore flow across parts of southern California. Unlike earlier offshore wind events, mid-level flow will be stronger. The main caveats for this event are the chance for light precipitation to impact fuels prior to the offshore flow as well as somewhat cooler temperatures than previous events. Even so, fuels within the higher terrain remain quite dry with similarly record dry fuels in some locations. Precipitation is not likely to impact the heavier fuels enough to eliminate fire weather concerns. With the mid-level wind support and strength of the surface gradient in model guidance, confidence has increased in critical fire weather for D5/Monday with lingering potential into D6/Tuesday. ...Lower Colorado River Valley... High pressure in the Great Basin with drive potentially strong northerly winds into the lower Colorado River Valley. This flow may also be augmented by the mid-level jet, though the position of this feature is somewhat uncertain. Given the low RH and winds that may exceed 20-25 mph, highlights have been added for D5/Monday. ...Southern High Plains... Westerly flow will increase across the Divide as the strong western trough evolves and digs southeastward on D3/Saturday. This will help to deepen another southeastern Colorado surface low during the afternoon. With mid-level flow increasing during the day, strong downslope flow is likely in the lee of the Sangre de Cristo Mountains. With a cold front having just moved into the region on Thursday, enough airmass modification to support high enough temperatures (and low enough RH) away from the lee of the terrain is not probable. ..Wendt.. 10/22/2020 ...Please see www.spc.noaa.gov/fire for graphic product... $$
