Fire Weather Outlook Discussion
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FNUS28 KWNS 232159

Day 3-8 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0458 PM CDT Fri Oct 23 2020

Valid 251200Z - 311200Z

A potent mid-level trough will traverse the West Coast through the
Days 3-5/Sunday-Tuesday period before ejecting into the Plains Day
6/Wednesday, with upper ridging setting in across the West Coast
Days 6-7/Wednesday-Thursday. Medium range models differ late Days
7-8/Thursday-Friday regarding the upper level pattern, with some
guidance maintaining a ridge aloft across the west, with other
members depicting a progressive trough. Nonetheless, favorable fire
weather conditions are expected to accompany the passage of the
first trough in the Days 3-5 time frame, mainly across California
and parts of the southwest CONUS. Thereafter, dry conditions, but
calmer winds, will support relatively more quiescent fire weather
conditions across the West Coast and Inter-mountain west.

...Days 3-5/Sunday-Tuesday...
As the aforementioned trough approaches from the Pacific Northwest
Day 3/Sunday, strong mid-level flow and associated upper support
will overspread California, where a surface pressure gradient will
tighten, and very strong/dry surface offshore flow will occur. Winds
will likely be strongest across portions of the Sacramento Valley,
addressed by 70% critical probabilities. Given the presence of
critically dry fuels, robust wildfire-spread potential is expected,
especially Sunday afternoon. However, dry and breezy conditions
supporting wildfire growth may persist into the afternoon Day
4/Monday as the upper trough axis progresses southward, with
portions of north/central California remaining under high (70%)
critical probabilities.

Stronger flow aloft is also expected to overspread portions of the
southwest CONUS into the southern High Plains Day 3/Sunday,
promoting modestly dry/breezy westerly flow ahead of a southward
surging cold front. Given the lack of recent rainfall, 40% critical
probabilities were introduced to account for some wildfire-spread

The southern progression of the upper trough will then encourage
very dry/windy offshore surface flow across the southern Transverse
Ranges in southern California and western parts of the lower
Colorado River Basin Day 4/Monday. Moist low-level conditions and
light rainfall accumulations may precede the offshore flow on Day
3/Sunday in California. However, very dry fuels in place, along with
the very strong wind speeds/low RH expected to accompany the
offshore flow, are expected to support wildfire-spread potential,
necessitating the maintenance of 70% critical probabilities. As the
trough aloft begins to progress eastward on Day 5/Tuesday, offshore
flow will gradually subside. 40% critical probabilities have been
maintained for Day 5/Tuesday across southern California for
lingering dry and breezy conditions.

..Squitieri.. 10/23/2020

...Please see for graphic product...

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