Fire Weather Outlook Discussion
Issued by NWS
FNUS22 KWNS 271956
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0255 PM CDT Thu Apr 27 2017
Valid 281200Z - 291200Z
...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF THE LOWER CO RIVER
VALLEY INTO ARIZONA...
The ongoing critical area has been expanded eastward to include more
of central/southern AZ. A 80+ kt mid-level jet maximum will
overspread this region through Friday evening, and efficient
downward momentum transfer within a well-mixed boundary layer will
support sustained northwesterly surface winds of 20-30 mph, with
higher gusts to 45 mph possible. RH values will fall as low as
5-15%, which along with dry fuels supports the critical designation.
Strong northwesterly winds associated with a mid-level jet should
overspread portions of central/southern CA Friday afternoon. A
strengthening surface pressure gradient across the Great Basin and
CA should also lend support to strong/gusty offshore northerly to
northeasterly surface winds across portions of southern CA in the
vicinity of Los Angeles beginning Friday morning and continuing
though early Saturday morning (end of Day 2 period). RH values will
likely become lowered into the 8-15% range for a few hours Friday
afternoon across this region, although overall fuel receptiveness
remains questionable per latest guidance from the local Weather
Forecast Office in Oxnard CA. While an elevated to locally critical
meteorological fire weather threat will exist, have not included an
elevated area with this update due to most fuels remaining
unreceptive to large fire starts (exception being fine grasses and
associated small fire potential).
No changes have been made to the elevated area across the central FL
peninsula. For more information, see the previous discussion below.
.PREV DISCUSSION... /ISSUED 1259 AM CDT Thu Apr 27 2017/
An embedded shortwave trough in larger-scale cyclonic flow will lead
to stronger height falls over the southwestern deserts on Friday.
This will bring even stronger north/northwesterly flow to the region
as compared to the past few days. Further east, the mid/upper level
west/southwesterly jet streak will continue to spread across NM into
the southern Plains. At the surface, low pressure will extend from
the southwest deserts to the southern High Plains while higher
pressure begins to settle into the Pacific Northwest and northern
portions of the Great Basin. This will lead to a tightening pressure
gradient across much of the southwestern U.S, and widespread strong
winds are expected with fire weather concerns again impacting parts
of the southwestern states into TX.
Across FL, a tightening surface pressure gradient is forecast as
strong high pressure resides over the western Atlantic and the
deepening low pressure over the southern High Plains. Drying will
occur over portions of the central peninsula and fire weather
concerns are anticipated.
...Lower CO Valley into western AZ...
Intense north/northwest winds are expected to develop across the
region by midday as temperatures warm into the 80s and low 90s. As
this occurs, RH values will plummet from the single digits to low
teens. Sustained winds from 20-30 mph with higher gusts will be
common. Where fuels are available, critical fire weather conditions
...Portions of southern NM into west TX...
Wind speeds will not be as strong as on Thursday, but still
sufficient for fire weather concerns with sustained westerly winds
from 15-25 mph expected. RH values will be somewhat marginal from
12-18 percent. Some brief/locally critical conditions will be
possible, but these concerns are not expected to be as widespread as
...Portions of the central FL Peninsula...
Strong heating during the day will allow temperatures to climb into
the 90s and deep boundary-layer mixing will occur. This will allow
relative humidity values to fall into the 35-45 percent range. Due
to the modest surface pressure gradient increase across the region,
wind speeds will be somewhat stronger than on Thursday at 10-15 mph.
Some brief/spotty critical conditions can not be ruled out and an
upgrade to critical could be needed in subsequent outlooks should
wind speeds trend stronger and RH values lower.
...Southern CA coastal ranges and foothills...
Strong northerly winds are expected across the region on Friday,
along with warm temperatures and low RH values. While meteorological
conditions would support elevated to critical conditions, fuels
across the region are too moist and unreceptive to fire spread.
...Please see www.spc.noaa.gov/fire for graphic product...