491 FNUS21 KWNS 191648 FWDDY1 Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1048 AM CST Tue Jan 19 2021 Valid 191700Z - 201200Z ...CRITICAL FIRE WEATHER AREA FOR THE LOWER COASTAL HILLS OF CENTRAL TO SOUTHERN CALIFORNIA... The Elevated and Critical areas have been adjusted to reflect current observations and the latest model guidance. Across central California, the Elevated area was expanded towards the western slopes of the Sierra, as the latest METARs depict 15-25 mph sustained downslope flow and RH dropping below 20% in spots. Here, fuels are at least marginally receptive to fire spread. Farther west towards the Bay Area, widespread 20-30 mph north-northeasterly winds are in place, with RH dropping below 30%. Visible satellite imagery shows clear skies across central California, with diurnal mixing expected to contribute to further lowering RH and resultant widespread Elevated/Critical conditions. The marginal receptiveness of fuels continues to be the primary factor in a Critical upgrade. Farther south across the southern Foothills of southern California, Critical highlights have been maintained. The current LAX-DAG pressure gradient is near -7 mb, and the latest guidance consensus suggests the gradient should maintain this intensity to the end of the period. While visible satellite imagery shows widespread clouds across all of southern California, widespread 20-40 mph offshore winds are being observed at several METAR sites, with a couple instances of 60+ mph gusts noted. The prolonged exposure of very dry fuels to these very strong winds will continue to foster Critical wildfire-spread potential despite the cool, cloudy, and relatively moist conditions, characterized by surface RH up to 25-35% in spots. Elsewhere across the CONUS, 25-35% surface RH is expected across much of eastern Alabama into Georgia, southern South Carolina, and northern Florida by afternoon peak heating. 10-hr fuels remain below 10%, with ERC-G seasonal percentiles exceeding 90% in spots across the Southeast. Nonetheless, model guidance consensus continues to show weak winds, suggesting that wildfire-spread concerns should remain relatively localized, precluding any fire weather highlights. ..Squitieri.. 01/19/2021 .PREV DISCUSSION... /ISSUED 1235 AM CST Tue Jan 19 2021/ ...Synopsis... Recent water vapor imagery reveals a leading upper-level shortwave trough off the southern California/Baja California coast. This feature is preceding a more potent upstream low associated with a meridional jet streak over the Pacific Northwest. This stronger low will deepen further over the next 24 hours as it stalls off the southern CA coast. As this occurs, surface pressure falls offshore juxtaposed with a building surface high to the north will induce strong pressure-gradient winds over much of the southern two-thirds of CA. These winds, coupled with dry fuels, will support a fire weather concern today through early Wednesday. Elsewhere across the CONUS, cool temperatures and/or weak winds will limit most fire weather concerns. ...Coastal Southern California... Surface observations from Santa Barbara, Ventura, and Los Angeles counties show winds gradually beginning to increase with wind gusts into the 25-35 mph range. Surface pressure analyses reveal low pressure developing along the CA coast ahead of the approaching upper-level low to the north. While the proximity to the surface trough is maintaining somewhat reasonable winds early this morning, winds will begin to increase through the day as the surface low deepens and moves offshore. Peak winds are expected by early to mid afternoon, and sustained winds near 30-50 mph and potentially damaging wind gusts up to 60-80 mph remain likely (especially for portions of Ventura and Los Angeles counties). As winds become more east/northeasterly through the day, downslope effects will be maximized for the coastal hills and lower mountains, allowing humidity reductions to 15-20%. While RH values may not consistently meet critical thresholds throughout the day, the strong winds and unseasonably dry fuels should compensate and support a fire weather threat. The offshore pressure gradient is forecast to remain in place into the overnight hours, and may support at least elevated fire weather conditions well into Wednesday morning (depending on overnight RH recoveries in the coastal areas). ...Sacramento Valley region... Wind gusts into the 45-60 mph range and humidity values as low as the mid teens have been noted in recent observations from the greater San Francisco Bay area and southwestern Sacramento Valley. While early morning RH recoveries are expected for this region, winds will likely maintain intensity through the late afternoon hours. Recent guidance has come into somewhat better agreement in the potential for RH values to fall back into the low 20s and teens during the afternoon. Fuels across this region have only recently begun to dry out after a few dry/windy days. However, recent fuel moisture analyses suggest fine fuel moisture has fallen into the single digits and may support fire spread. This factor, combined with the strong winds and borderline humidity, warrants the northward expansion of the elevated risk area. ...Please see www.spc.noaa.gov/fire for graphic product... $$
