FNUS21 KWNS 191648

Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1048 AM CST Tue Jan 19 2021

Valid 191700Z - 201200Z


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/

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...