FNUS28 KWNS 162151

Day 3-8 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0448 PM CDT Wed Jun 16 2021

Valid 181200Z - 241200Z

Dry thunderstorms are forecast beneath the broad upper-level ridge
on Friday and Saturday. This ridge will break down on Saturday as a
mid-level trough develops over the center of the CONUS into early
next week. As this trough develops, northwesterly flow is forecast
to strengthen which may bring some fire weather concerns to portions
of the northern Rockies. An upper-level trough will approach the
West Coast toward the middle of the next week which could bring fire
weather concerns with regards to thunderstorms across northern
California and the Northwest and dry and windy conditions across
portions of the Great Basin and Southwest.

...D3/4 - Fri/Sat - Dry Thunderstorms in portions of the Sierra,
Great Basin, central Rockies, and Southwest....
A plume of mid-level moisture beneath the upper-level ridge will
continue to provide ample instability for thunderstorm development
each day. These thunderstorms will mostly be dry given the extreme
dewpoint depressions (50 to 70F) and PWAT values around 0.5 inches.
The greatest storm coverage is expected on Saturday as the upper
ridge weakens and mid-level temperatures cool. Therefore, 40 percent
dry thunderstorm probabilities have been introduced for Saturday. A
scattered dry thunderstorm area may also need to be considered on
Friday during the Day1 or Day 2 forecast, but there is not a strong
enough signal for scattered storm coverage at this time. However,
considering the very dry to near record dry fuels across the region
and storms which will struggle to produce any wetting rain, even
borderline scattered coverage may be sufficient to warrant a
scattered dry thunderstorm delineation.

...D4/Sat - Snake River Plain and portions of eastern
Montana/central Wyoming...
As westerly flow strengthens across the northern Rockies on
Saturday, surface winds are also expected to increase as a result of
the deeply mixed airmass. Relative humidity is forecast to be 10 to
15 percent in the area with winds of 15 to 25 mph. In addition, a
corridor of stronger winds may be possible in eastern Montana in the
wake of a cold front as it moves south across the state. There may
be a brief window in this region where critical conditions may occur
before cooler air and higher relative humidity arrives.

...D5/Sun - Portions of the Great Basin and northern Arizona...
On Sunday, mid-level flow westerly flow is expected to strengthen
somewhat. In addition, lee cyclogenesis is forecast in the central
Plains into West Texas which should act to tighten the surface
pressure gradient. As a result, 15 to 25 mph winds are forecast
across much of the Southwest. The most likely region for critical
strength winds overlapping the dry surface conditions will be across
portions of northern Arizona into eastern Utah where 40 percent
probabilities have been added.

...D7/8 - Tue/Wed - Portions of the Great Basin and northern
An upper level trough is forecast to approach the California coast
early next week. The exact timing and evolution of this trough still
has considerable uncertainty, but the overall pattern has shown a
trough approaching the region for several days. As a result,
downslope flow and dry/windy conditions are possible ahead of this
trough as it approaches the coast. The exact location of the
strongest winds may change as the evolution of the trough becomes
more clear, but there was enough confidence in the overall pattern
to warrant 40 percent probabilities on D7 and D8.

..Bentley.. 06/16/2021

...Please see www.spc.noaa.gov/fire for graphic product...