Storm Prediction Center Day 1 Fire Weather Outlook
Created: Mon Dec 4 15:31:02 UTC 2017 ( | )
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ZCZC SPCFWDDY1 ALL FNUS21 KWNS 041530 Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0930 AM CST Mon Dec 04 2017 Valid 041700Z - 051200Z ...EXTREMELY CRITICAL FIRE WEATHER AREA FOR PARTS OF VENTURA AND LOS ANGELES COUNTIES IN SOUTHERN CALIFORNIA... ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN CALIFORNIA... ...Portions of Southern CA... Ongoing forecast is on track, no changes needed. Wind speeds were already gusting to 40-50 mph in some locations with lighter winds in lower elevations. Expect wind speeds to increase later today into tonight with critical to extremely critical conditions developing by this evening. See previous discussion below for further details. ...Portions of the Central/Southern Plains... No changes needed, see previous discussion for details. ..Leitman.. 12/04/2017 .PREV DISCUSSION... /ISSUED 0150 AM CST Mon Dec 04 2017/ ...Synopsis... The primary upper trough over the northern Rockies/High Plains early this morning will move east-northeastward across the northern Plains into the Upper Midwest/Great Lakes region today. A positively tilted trailing portion of this upper trough will remain over portions of the Great Basin and Southwest through the period. At the surface, a cold front will sweep southeastward across much of the central/southern Plains as a low develops northeastward across the Upper Midwest. Large-scale subsidence in the wake of the upper trough will support a broad and strong surface high across the northern Rockies and Great Basin. The surface pressure gradient across southern CA will strengthen this evening into early Tuesday morning, and high-end critical to extremely critical fire weather conditions are expected across parts of this region. ...Portions of Southern CA... Extremely critical area: A very strong surface pressure gradient (evidenced by a LAX-DAG difference of -8 to -10 mb and LAX-TPH difference of -15 to -20 mb) coupled with strong low-level northeasterly flow will easily support sustained offshore winds of 30-40 mph across parts of Ventura into Los Angeles counties beginning later this evening and continuing through early Tuesday morning. Wind gusts of 60-80 mph will be possible across the mountains/foothills of these counties where channeling and terrain effects can locally enhance the already strong flow, with gusts of 45-60 mph likely at lower elevations. RH values will quickly plummet below 10% later today, and will likely remain below 10% through the end of the period owing to no overnight RH recovery given the strength of the winds. Coupled with very dry and receptive fuels, these expected meteorological conditions support the continuation and eastward expansion of the extremely critical fire weather delineation. Critical area: Surrounding the extremely critical area, critical fire weather conditions will occur across a broader part of coastal southern CA today into tonight. RH values will rapidly fall to 5-15% later this morning as diurnal heating and downslope warming/drying act on an already dry airmass. Sustained winds of 20-30 mph will be common across the critical delineation, with higher gusts of 40-60 mph likely, especially in higher terrain. Similar to the extremely critical area, the pressure gradient across this region will be strongest from late this evening through the end of the Day 1/Monday period, and overnight RH recovery will be very poor. Elevated area: Lower confidence in sustained winds in excess of 20 mph and/or sub-15% RH values exist across the elevated delineation surrounding the critical area. However, winds will rapidly strengthen across the mountains/foothills of southern CA, resulting in a relatively tight gradient between elevated and critical fire weather conditions. ...Portions of the Central/Southern Plains... In the wake of the cold front mentioned above, strong/gusty northwesterly winds of 20-30 mph will occur across much of KS into OK, the TX/OK Panhandles, and eastern NM this afternoon and early evening. Higher gusts up to 40 mph will be possible given the strength of the mid-level flow that will likely be diurnally mixed to the surface. With a dry airmass already in place across the central/southern High Plains, RH values will likely become lowered into the 15-25% range for at least a few hours behind the cold front passage. Some locally critical conditions may briefly occur across portions of southern/central KS into western OK and the TX/OK Panhandles immediately behind the front, where RH values may become critically reduced. Still, latest guidance continues to suggest that these conditions should occur for just an hour or two. Have therefore not included a critical area at this time. Regardless, widespread elevated conditions are anticipated across parts of the central/southern Plains where generally dry/dormant fuels should support large fire spread given the expected meteorological conditions. ...Please see www.spc.noaa.gov/fire for graphic product...
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