Fire Weather Outlook Discussion
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FNUS21 KWNS 181542

Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1041 AM CDT Fri Aug 18 2017

Valid 181700Z - 191200Z


No changes are needed to Day 1/Friday forecast.

Morning water vapor imagery and objective analysis depicts
mid/upper-level ridging quickly translating eastward across MT as a
upper-level trough continues to progress eastward across far
northern BC/AB.

While the strongest flow is forecast to generally remain north of
the Canadian border, belt of 15-20 mph sustained surface winds is
expected to sag across portions of the Pacific Northwest into the
northern Rockies this afternoon along base of the aforementioned
trough. Gusty afternoon winds coupled with low afternoon RH values
and relative dry fuels across this region support continuation of
the elevated fire risk. Some locally-critical fire weather
conditions may briefly develop in the lee of the Cascades this
afternoon where terrain induced channeling enhances low-level flow.
Locally-critical conditions may also develop closer to the stronger
mid-level flow across far northern MT.

Please see previous forecast below for more detailed evolution of
the fire weather threats.

..Elliott/Picca.. 08/18/2017

.PREV DISCUSSION... /ISSUED 0150 AM CDT Fri Aug 18 2017/

An upper trough will move eastward from BC to AB/SK today, while a
related weak surface low likewise develops eastward across southern
AB/SK through this evening. A surface trough will extend southward
from this low across parts of the northern Rockies/High Plains.
Enhanced mid-level westerly winds associated with the upper trough
will overspread parts of the Pacific Northwest and northern
Rockies/High Plains, elevating fire weather concerns across these

...Portions of the Pacific Northwest into the Northern Rockies/High
Low-level winds will strengthen to the lee of the Cascades and
northern Rockies this afternoon as the enhanced mid-level westerly
winds mentioned previously become diurnally mixed to the surface.
Sustained west-southwesterly surface winds around 15-20 mph appear
likely across parts of the interior Pacific Northwest into the
northern Rockies/High Plains. Diurnal heating of a dry airmass and
downslope warming/drying will act to lower RH values generally into
the 15-25% range across these regions this afternoon and early
evening. This combination of strong/gusty winds, lowered RH values,
and dry to very dry fuels supports the continuation of an elevated
delineation. Locally critical conditions may be realized across
parts of eastern WA into north-central OR (within the Columbia River
Gorge) where winds may exceed 20 mph on a brief/spotty basis.
However, confidence in sustained winds in excess of 20 mph for
multiple hours this afternoon is too low to include a critical area.

...Please see for graphic product...

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