ZCZC SPCFWDDY1 ALL
FNUS21 KWNS 271621
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1121 AM CDT Sun Sep 27 2020
Valid 271700Z - 281200Z
...CRITICAL FIRE WEATHER AREA FOR MUCH OF NORTHERN CALIFORNIA...
...CRITICAL FIRE WEATHER AREA FOR THE MOUNTAINS OF VENTURA...LOS
ANGELES...AND SAN BERNARDINO COUNTIES IN SOUTHERN CALIFORNIA...
Morning satellite and radar data shows greater than expected cloud
cover and shower activity over much of the elevated area. While
winds are strong in the cool and relatively dry post front airmass,
light overnight precipitation will limit overall confidence in the
potential for widespread elevated fire weather conditions. As a
result, the elevated area has been trimmed considerably to the areas
with the least observed precipitation. Several localized pockets of
elevated fire weather potential will remain possible this afternoon
where strong surface winds of 25-35 mph and 20-30% humidity can
develop over drier fuels.
Elsewhere the risk areas remain valid with only minor adjustments
from the latest forecast guidance. Please see the previous
discussion for more details.
.PREV DISCUSSION... /ISSUED 1240 AM CDT Sun Sep 27 2020/
A mid-level trough will amplify across the northern Rockies/northern
Plains through the day with a belt of moderate to strong mid-level
flow along the periphery of this trough. At the surface, strong high
pressure will build into the Northwest/northern Rockies with lee
troughing in the Plains.
Strong northwesterly flow is expected to develop from eastern
Montana into the Plains this afternoon due to a combination of deep
mixing and a strengthening pressure gradient between the lee trough
in the Plains and the strong high pressure in the northern Rockies.
Winds of 25 to 30 mph are expected. Relative humidity is not
expected to be overly dry (20 to 30 percent), but the strong winds
should more than compensate for marginally dry surface conditions
warranting an elevated delineation.
A lee cyclone is expected to develop and slide south in West Texas
this afternoon. The pressure gradient between this low pressure
center and high pressure in the northern Rockies will lead to gusty
winds of 15 to 25 mph and relative humidity of 15 to 22 percent.
Therefore, elevated to locally critical conditions are expected.
Early this morning, the gradient has started to strengthen in
northern California with a 9 mb pressure gradient between MHS and
RDD. This pressure gradient will continue to strengthen through the
day today as high pressure continues to strengthen in the Northwest
and northern Rockies. Therefore, gusty northerly winds are expected
in the northern Sacramento Valley. Critical conditions are expected,
especially on the western edge of the valley. Late tonight, critical
conditions are expected to spread westward across the coastal
Mountains as the pressure gradient becomes more offshore. Some
guidance suggests critical conditions may reach nearly to the coast,
and therefore, the critical delineation is now near the coast in
some locations. Some downslope flow will develop along the Sierra
foothills with some elevated to locally critical conditions
...Ventura, Los Angeles, and San Bernardino County Mountains in
A weak offshore gradient is expected to persist through much of the
day today with some elevated conditions expected. Critical
conditions are expected to begin late tonight as the LAX-DAG
gradient increases to 4-5 mb by 12Z Monday.