ZCZC SPCFWDDY1 ALL
FNUS21 KWNS 181541
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1041 AM CDT Fri Aug 18 2017
Valid 181700Z - 191200Z
...NO CRITICAL AREAS...
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/
...Synopsis...
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
regions.
...Portions of the Pacific Northwest into the Northern Rockies/High
Plains...
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 www.spc.noaa.gov/fire for graphic product...
ZCZC SPCFWDDY2 ALL
FNUS22 KWNS 181940
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0240 PM CDT Fri Aug 18 2017
Valid 191200Z - 201200Z
...NO CRITICAL AREAS...
No changes needed to Day 2/Saturday forecast, with elevated fire
weather conditions developing over portions of the northern Great
Basin/Rockies into the northern Plains owing to the combination of
sustained surface winds of 15-20 mph, RH values of 15-20%, and very
dry fuels. While critical conditions may briefly develop across the
northern Great Basin -- particularly where terrain-induced
channeling is enhanced through the Snake River Valley --
probabilities of sustained surface wind speeds exceeding 20 mph over
a sufficiently large area remain too low to delineate a critical
area at this time. If future trends in model guidance suggest an
increase in wind speeds, then a critical area may be needed in
future outlooks.
Elsewhere, diurnally-driven thunderstorm activity is forecast to
develop during the afternoon across much of central NV. While fuels
are somewhat receptive across this area, recent bouts of at least
some wetting rainfall combined with weak steering flow is expected
to keep probabilities of dry thunderstorms below 10%.
..Elliott/Picca.. 08/18/2017
.PREV DISCUSSION... /ISSUED 0150 AM CDT Fri Aug 18 2017/
...Synopsis...
An upper trough over AB/SK will progress eastward towards MB on Day
2/Saturday. 30-40 kt of mid-level westerly winds attendant to this
upper trough will overspread eastern MT into ND by Saturday
afternoon. At the surface, a low over southern SK will also develop
eastward into MB by Saturday evening, with a trailing cold front
advancing southeastward across the northern Plains.
...Portions of the Northern Great Basin/Rockies into the Northern
Plains...
Strong/gusty low-level winds should develop both along and ahead of
the surface cold front Saturday afternoon across eastern MT into
western ND and northwestern SD. Consensus of short-term guidance
suggests sustained west-northwesterly winds of 15-20 mph will likely
occur in conjunction with RH values lowering into the 15-25% range
with diurnal heating of a relatively dry boundary layer, supporting
an elevated fire weather threat. RH values are forecast to increase
behind the front, although strong surface winds approaching 20 mph
and veering to northwesterly may allow for continued elevated fire
weather concerns into the evening hours. Locally critical conditions
may be realized briefly across a small part of the elevated
delineation, but confidence in widespread winds in excess of 20 mph
remains too low to include a critical area at this time.
Elevated fire weather conditions should also develop across part of
the northern Great Basin into a small part of the northern Rockies,
as the southern fringe of enhanced mid-level westerlies overlies
this region Saturday afternoon. Favored channeling and localized
enhancement to the low-level winds appears likely across part of the
Snake River Valley and vicinity, with sustained west-southwesterly
winds of 15-20 mph combining with RH values of 10-15% and dry fuels
to support an elevated fire weather threat. The lack of even
stronger forecast low-level flow precludes critical designation
across this region.
...Please see www.spc.noaa.gov/fire for graphic product...
