ZCZC SPCFWDDY1 ALL
FNUS21 KWNS 261640
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1140 AM CDT Mon Oct 26 2020
Valid 261700Z - 271200Z
...EXTREMELY CRITICAL FIRE WEATHER AREA FOR PORTIONS OF THE SOUTHERN
TRANSVERSE RANGES IN SOUTHERN CALIFORNIA...
...CRITICAL FIRE WEATHER AREA FOR PARTS OF SOUTHERN CALIFORNIA...
...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF NORTHERN AND CENTRAL
...CRITICAL FIRE WEATHER AREA FOR PARTS OF SOUTHERN NEVADA INTO THE
COLORADO RIVER BASIN...
Current visible satellite depicts clear skies across California and
the Great Basin, allowing for ample boundary-layer heating and
continued mixing. As such, near-critical to critically low RH is
expected to persist across much of California into the southern
Great Basin through the day. Current METAR observations depict 20-30
mph sustained winds, with higher gusts from the Sacramento Valley in
northern California, down to the southern Transverse Ranges in
southern California and eastward into the Colorado River Basin. In
addition, 60-80 kt mid-level flow continues to overspread California
into Nevada. Upper support, downslope flow, and downward momentum
transport of the stronger mid-level flow will continue to foster
strong northerly/offshore flow across portions of the Sacramento/San
Joaquin Valleys and the southern Transverse Ranges in California
through the day, as also suggested by the latest model guidance
consensus. Critical/Extremely Critical Highlights have been
maintained across California, although widespread Extremely Critical
conditions in the southern Transverse ranges may gradually subside
by late afternoon. Critical conditions however, are still expected
to persist across southern California into tomorrow morning.
At the moment, temperatures are rather cool across parts of southern
Nevada, with temperatures in the upper 30s to mid 40s. However,
temperatures are expected to warm into the 50s by afternoon peak
heating, that combined with continued 25-40 mph sustained northerly
flow and 10-25% RH, will foster Critical wildfire-spread conditions
through the afternoon.
.PREV DISCUSSION... /ISSUED 0152 AM CDT Mon Oct 26 2020/
A very steep pressure gradient will persist across dry areas of the
West and Southwest today in response to 1) very strong high pressure
over the western Great Basin and 2) surface troughing from the
California coastline southeastward through Arizona and western New
Mexico. Additionally, very strong flow aloft will persist across
these areas in response to a vigorous mid-level wave expected to be
centered over Utah at 12Z and Arizona in the evening. Continued dry
fuels and areas of drought will continue to support higher-end
fire-weather conditions particularly in portions of California.
Models/high resolution guidance continue to indicate very strong
flow across typical, terrain-favored areas of the southern
Transverse Ranges throughout the forecast period. Northeasterly
surface flow will range from 25-35 mph, with gusts perhaps as high
as 70 mph in spots. Meanwhile, very low RH will continue given the
dry airmass in place, with 5-15% values becoming common during the
day as surface heating commences. Fuels remain dry and favorable
for fire spread given continued dry conditions over the past several
months. Guidance suggests that these conditions will continue even
into the evening hours, owing to poor overnight recoveries and the
continued offshore gradient.
...Northern California and the Bay Area...
Elevated to critical fire-weather conditions will likely be ongoing
at the start of the period as current (05Z-06Z) observations
indicate areas of 25-35 mph northerly low-level flow and 7-15% RH
values, indicating very poor recovery. The strong surface pressure
gradient and favorable upper support suggest that these conditions
will continue throughout the day, with RH values remaining low amid
surface warming. A few areas may experience gusts to 70 mph. Fuels
remain extremely dry/combustible, and a few areas will likely exceed
extremely critical thresholds at times - especially in areas between
Sacramento and San Francisco/Oakland and including the North Bay
Mountains and East Bay Hills.
...Southern Nevada through the Lower Colorado River Valley...
Recent high-resolution guidance indicates that enough surface
warming will occur for temperatures to reach the 60s F during peak
heating hours despite northerly surface flow and modest cold
advection. The residing airmass across the region is quite dry, and
as temperatures increase, surface RH values will fall into the 5-15%
range during the afternoon. Additionally, surface winds will
increase into the 25-35 mph range given the surface pressure
gradient across the region. Critical fire-weather delineations
exist where the aforementioned conditions are most likely to occur
amidst dry fuels/fuel beds.