ZCZC SPCFWDDY1 ALL
FNUS21 KWNS 181615
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1115 AM CDT Sat Sep 18 2021
Valid 181700Z - 191200Z
...CRITICAL FIRE WEATHER AREA FOR THE GREAT BASIN AND NORTHERN
Today's fire weather forecast remains on track, with only minor
modifications needed based on the latest weather and fuel guidance.
The primary adjustment with this forecast update was to extend the
northern Rockies Elevated fire weather area farther east into
portions of west-central South Dakota, western Nebraska, and north
eastern Colorado, where minimum RH values less than 10% (near 5%
locally), sustained surface winds of 15-20 mph, and receptive fuels
are expected. While some of these areas may see a bit lighter wind
speeds (e.g., across portions of Northeast Colorado where sustained
winds of 10-15 mph are more likely) ERC values exceeding the 90th
percentile across the area coupled with the extremely low minimum RH
values should foster Elevated fire weather conditions this
Please see the previous discussion below for more information on
today's fire weather forecast.
.PREV DISCUSSION... /ISSUED 0107 AM CDT Sat Sep 18 2021/
Elevated to critical fire weather conditions remain likely today as
winds increase in response to an approaching upper-level trough in
the Pacific Northwest. Hot, dry, and windy conditions across much of
the West yesterday aided in curing fuels, which will help support
widespread fire weather concerns today. While this system will bring
beneficial rainfall to parts of the Pacific Northwest, thunderstorm
chances across Utah, western Colorado, and southwest Wyoming may
pose a low-end lightning-driven fire weather concern.
...Western Great Basin into Southwest Montana...
VWP observations over the past few hours from ID and MT show
strengthening mid-level flow as the upper-level wave continues to
move onshore across the Pacific Northwest. This trend is expected to
continue through the day as an axis of stronger flow becomes
established from northwest NV into ID and western MT ahead of a cold
front. Diurnal boundary-layer mixing and a nearly uni-directional
wind profile will allow for efficient downward transfer of stronger
winds aloft. Ensemble guidance continues to show high probabilities
for 20-25 mph winds through this corridor with gusts up to 30-40 mph
(and possibly up to 40-50 mph for wind-prone locations). Receptive
fuels are already in place for most locations and RH reductions into
the low teens are expected. Critical conditions remain most likely
through this northwestern NV-southwest MT corridor, but may extend
as far south as the lee of the central/southern Sierra. There is
some uncertainty regarding the westward extent of both critical and
elevated conditions due to cloud cover/rainfall associated with the
approaching cold front.
...Southern Montana to northeast Wyoming...
Southwesterly winds will likely increase to 15-25 mph this afternoon
as a surface low deepens over the Canadian Prairies. Downslope
affects will aid in RH reductions into the low teens to low 20s, and
boundary-layer mixing will support wind gusts upwards of 25-35 mph.
Critical conditions are expected across south-central MT into
northeast WY where downslope warming/drying will be strongest in the
lee of the terrain, but may occur as far north as northeast MT.
...Utah, Western Colorado, and southwest Wyoming...
Thunderstorms are likely today across much of UT and into adjacent
areas of western CO and southwest WY as a surge of monsoonal
moisture shifts northward in tandem with a weak upper-level impulse.
Recent fuel analyses indicate some locations have receptive fuels
with ERC values above the 75th percentile and fine fuel moisture
values below 5%. As such, lightning may pose a low-end fire weather
concern. However, no highlights will be introduced given the overall
modest fuel status of the region and high wetting rain potential.
U.S. Day 2 Fire Weather Outlook
ZCZC SPCFWDDY2 ALL
FNUS22 KWNS 180651
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0151 AM CDT Sat Sep 18 2021
Valid 191200Z - 201200Z
Fire weather concerns will become limited spatially Sunday as
showers and thunderstorms overspread the inter-mountain West behind
a cold front. A trailing surface trough along the High Plains will
induce downslope flow across eastern WY and CO, which may result in
elevated fire weather conditions. Likewise, increasing winds ahead
of a cold front may support areas of elevated conditions across
southeastern Nevada. Fire weather concerns may also evolve across
parts of the southern Sierra, but will likely remain too localized
...Eastern Wyoming and High Plains...
Downslope west to southwesterly winds will likely increase to 15-20
mph across eastern WY Sunday afternoon, and a few locations may see
sustained winds near 25 mph prior to a cold frontal passage late in
the afternoon. RH reductions into the teens are possible, but may be
hindered by increasing clouds through the day. Elevated conditions
appear most likely across east-central WY, but may evolve as far
south as eastern CO.
A cold front is forecast to gradually translate southeastward across
the Great Basin through the day Sunday. Ahead of this boundary, warm
temperatures and mostly clear skies will support deep boundary-layer
mixing that will likely result in RH reductions into the teens with
breezy 15-20 mph winds. Elevated conditions are possible, but the
spatial extent of the threat remains somewhat uncertain, especially
given the potential for wetting rainfall across far eastern NV and
western UT over the next 24 hours.
U.S. Day 3-8 Fire Weather Outlook
ZCZC SPCFWDD38 ALL
FNUS28 KWNS 172025
Day 3-8 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0325 PM CDT Fri Sep 17 2021
Valid 191200Z - 251200Z
The fire-weather pattern will start off relatively active as dry and
breezy conditions precede a cold front across the interior West,
overspread by strong winds aloft associated with a mid-level trough
Days 3-4/Sunday-Monday. Thereafter, an upper ridge will traverse the
West Days 5-6/Tuesday-Wednesday before the passage of a second
mid-level trough Day 7/Thursday. However, favorable wildfire-spread
conditions appear more localized after Day 4/Monday.
Gradient-induced flow ahead of the cold front, along with downward
momentum transport of the stronger flow aloft within a dry and
well-mixed boundary layer, will promote dry and windy conditions
across portions of the Great Basin into the central Rockies Day
3/Sunday, where 40% Critical probabilities have been maintained.
Portions of the central/southern High Plains have had 40% Critical
probabilities withheld this outlook for Day 3/Sunday. However,
Elevated highlights may be introduced in either the Days 1 or 2
Outlooks pending drier trends in future guidance. By Day 4/Monday,
the surface cold front and associated preceding dry/breezy
conditions (and 40% Critical highlights) will then move
southeastward, towards the Four Corners/southern High Plains. Areas
highlighted with 40% Critical probabilities Days 3-4 have the
greatest chance at experiencing 15-25 mph sustained winds
overlapping 15-20% RH for at least a few hours each day, and where
fuels are at least modestly receptive to wildfire spread.
As upper-support begins to wane across the interior West beyond Day
5, fire weather concerns are expected to become more localized
overall, constrained to terrain-favoring areas. It is possible that
regional areas of Elevated-equivalent conditions may develop, but
forecast uncertainty remains too low to address with any
probabilities at this time.