Fire Weather Outlook Discussion
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FNUS28 KWNS 222141
FWDD38

Day 3-8 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0340 PM CST Wed Nov 22 2017

Valid 241200Z - 301200Z

Mid-level ridging over the southwestern United States will become
suppressed farther southward into northern Mexico Day 4/Friday, as a
shortwave trough shifts eastward over the northern Plains, upper
Midwest, and upper Great Lakes. At the surface, a cold front is
forecast to shift southward across the Northern/Central Plains and
become quasi-stationary over portions of the Southern Plains.
Re-amplification of the West Coast ridge is then expected Day
4/Saturday into Day 5/Sunday, as a large-scale mid/upper-level
trough over the eastern Pacific gradually approaches the coast.
Long-range guidance is in good agreement regarding the evolution of
the trough, shifting it (and an associated cold front) across the
western United States early next week. An expansive area of surface
high pressure is then forecast to settle into the Great Basin in the
wake of the front on Day 7/Tuesday.

...Day 3/Friday: Portions of eastern New Mexico, the southern Texas
Panhandle, and far southwest Oklahoma...
Breezy pre-frontal westerly/southwesterly low-level flow is expected
by afternoon, as the nose of the stronger mid-level flow (associated
with aforementioned shortwave trough) impinges on the area.
Meanwhile, downslope compressional warming of a dry low-level air
mass will allow afternoon minimum RH values to approach critical
values. The ongoing 40% area was maintained with some expansion
eastward into southwest Oklahoma. While it currently appears the
greatest likelihood for Critical fire weather conditions is across
eastern New Mexico, uncertainty regarding the degree of the
low-level drying/warming precludes higher probabilities at this
time.

...Day 6-7/Monday-Tuesday: Portions of northeastern New Mexico,
southeastern Colorado, and the Oklahoma/Texas Panhandle...
Breezy pre-frontal westerly/southwesterly winds are forecast to
strengthen Day 6/Monday, as lee troughing over the Rockies becomes
established and stronger mid-level flow near the base of the
aforementioned trough approaches the area. Meanwhile, downslope
warming of a dry low-level air mass will allow RH values to approach
critical values. While there is still some uncertainty regarding the
areal extent of the threat, enough confidence exists to introduce
40% probabilities for Day 6/Monday across portions of the area. The
fire weather threat could extend into Day 7/Tuesday, however,
uncertainty regarding the evolution of the cold front and its
associated impact on wind/RH is too large to introduce Critical
probabilities at this time.

...Day 6-8/Monday-Wednesday: Portions of southern California...
A strong Santa Ana wind event is possible beginning late Day
6/Monday and perhaps lasting into Day 8/Wednesday, as offshore flow
develops/strengthens with the aforementioned surface high building
over the Great Basin. Furthermore, positioning of the
mid/upper-level trough nearby will increase upper-level support,
thereby enhancing the low-level flow. While near-critical conditions
may arise beginning late Day 6/Monday, timing uncertainties
currently precludes introduction of probabilities for that period.
The best overlap of favorable fire weather ingredients (i.e., strong
winds and reduced RH values) is currently expected on Day 7/Tuesday.
Confidence is now great enough to introduce 40% Critical
probabilities for Day 7/Tuesday. If guidance continues to suggest a
strong Santa Ana event, then Critical fire weather probabilities
would need to be increased in future updates. While fire weather
conditions may linger into Day 8/Wednesday, uncertainty regarding
wind/RH profiles is too large to introduce probabilities at this
time.

..Elliott.. 11/22/2017

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

$$



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