Fire Weather Outlook Discussion
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000
FNUS22 KWNS 240457
FWDDY2

Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1157 PM CDT Mon Oct 23 2017

Valid 251200Z - 261200Z

...CRITICAL FIRE WEATHER AREA FOR COASTAL RANGES OF SOUTHERN
CALIFORNIA...
...CRITICAL FIRE WEATHER AREA FOR MUCH OF CENTRAL AND EASTERN
MONTANA...
...CRITICAL FIRE WEATHER AREA FOR SOUTHEASTERN WYOMING AND FAR
WESTERN NEBRASKA...

...Synopsis...
The stout anticyclone initially centered over the Great Basin will
weaken throughout the day as a surface low and trough rapidly deepen
across the Canadian Prairies southward into the central Great
Plains.  Meanwhile, a trough will remain situated along the
California coast.  Fire weather concerns will remain high in coastal
ranges of southern California, while rapidly increasing D2/Wednesday
afternoon in the lee of the northern and central Rockies in response
to the aforementioned deepening low/trough.

...Coastal Ranges of Southern California...
With weakening high pressure across the Great Basin, the overall
pressure gradient in the region will weaken substantially throughout
the day.  However, enough of a gradient will remain through midday
in many areas for continued gusty northeasterly surface flow
(gusting to 40+ mph in terrain favored areas) along with areas of
very poor recovery and near-critical RH values persisting through
the morning.  A critical area has been introduced where winds will
be strongest during the morning hours amidst this dry airmass,
although winds should lessen progressively throughout the day.

...Portions of the northern Plains and adjacent Rockies from
Southeast Wyoming northward through much of Montana...
A dangerous fire weather scenario appears to be taking shape
especially across Montana D2/Wednesday afternoon.  The deepening
surface low/trough across the Dakotas and adjacent Canadian Prairies
will tighten the surface pressure gradient substantially throughout
the day, with surface flow also being strengthened by vertical
mixing of very strong flow aloft (60-70 kts at 500 mb).  20-30 mph
westerly flow will become common, with some areas gusting above 50
mph during peak heating hours.  Mid to upper 70s F surface
temperatures, 10-20% RH values (highest from central into
southeastern Montana), and dry fuels (evidenced by at least one
ongoing large fire) suggest the presence of a critical burn
environment with rapidly spreading fires becoming likely.

Surface flow will become progressively weaker farther south of
Montana D2/Wednesday afternoon, although a fairly localized area of
20+ mph surface flow will develop for several hours near the Laramie
Range of Wyoming and adjacent areas of western Nebraska.  Here,
guidance suggest that RH values will fall just below 15% for a few
hours during the evening, and with dry fuels across the region,
critical fire weather conditions are expected.  Farther west and
north (from central into northeastern Wyoming), latest guidance
suggest that strongest surface flow will not coincide with
sufficiently low RH for a critical delineation, although this
scenario will continue to be monitored.

..Cook.. 10/24/2017

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

$$


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