Fire Weather Outlook Day 1

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FNUS21 KWNS 201517

Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1017 AM CDT Thu Sep 20 2018

Valid 201700Z - 211200Z


Overall the ongoing forecast is on track. The only change was to
join the two elevated areas across the Great Basin as breezy and dry
conditions are expected across much of southeast ID into northeast
UT. For more details, see discussion below.

..Leitman.. 09/20/2018

.PREV DISCUSSION... /ISSUED 0119 AM CDT Thu Sep 20 2018/

An upper-level trough will pass over the northern/central Rockies
today. A well-timed mid-level jet will overspread southern Wyoming
and adjacent areas during peak afternoon heating. At the surface, a
deepening cyclone in the Central Plains will progress to the
northeast with its attendant cold front pushing through the northern
Great Basin into the central Rockies. Farther west, high pressure
off the northern California coast, in conjunction with surface
troughing within the Sacramento Valley, will lead to strong
northerly flow through the Valley and adjacent terrain-favored

...Sacramento Valley...
Strong northerly flow will reach 15-20+ mph, particularly in areas
where flow is channeled by the terrain. The strongest surface winds
will occur earlier in the day with the pressure gradient diminishing
by late afternoon. Though RH recovery overnight will likely abate
fire weather concerns early on, high resolution guidance is in
agreement that RH values will fall to 5-15% for long enough duration
to warrant a critical designation. Just outside the terrain-favored
regions, at least elevated fire weather conditions can be expected.

...Southern Wyoming and vicinity...
While temperatures behind the cold front will be cooler, the dry,
continental air mass behind it will still foster critical fire
weather conditions during the afternoon. The strong, post-frontal
pressure gradient with the deepening cyclone to the east will be
supplemented by modest mixing of the mid-level jet to the surface
and lead to 20-25 mph surface winds. Elsewhere, surrounding the
critical region, elevated conditions can be expected with similarly
low afternoon RH and lighter surface winds of 15-20 mph.

...Portions of eastern Utah...
An elevated fire weather area has been introduced into parts of
eastern Utah where latest guidance shows a strong surface pressure
gradient causing surface winds behind the cold front to increase to
15-20 mph. Afternoon RH values are expected to fall to 5-20%.
Locally critical conditions may also develop within favored terrain
areas where flow will be channeled and enhanced.

...Snake River Valley...
Strong surface pressure gradient behind the cold front will drive
15-20 mph winds through the Valley. Afternoon RH values falling to
5-20% will lead to elevated fire weather conditions.

...Please see for graphic product...


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