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FNUS21 KWNS 221650

Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1149 AM CDT Thu Jun 22 2017

Valid 221700Z - 231200Z


A Critical area has been added for portions of western CO,
eastern/southern UT, northern AZ, and northwestern NM. In these
areas, very deep mixing is expected, associated with hot afternoon
surface temperatures in the 90s to around 105F. This will manifest
enhanced midlevel flow, peripheral to an amplifying shortwave trough
over portions of the northern Rockies vicinity, at the surface. The
latest short-range model guidance and observational data suggest
that west-southwesterly to northwesterly surface winds of 20-25 mph
with higher gusts will combine with minimum RH of 4-10 percent amid
dry fuels across the Critical area.

No other changes have been made to the ongoing forecast.

..Cohen.. 06/22/2017

.PREV DISCUSSION... /ISSUED 0318 AM CDT Thu Jun 22 2017/

Zonally oriented flow across the northern tier of the Lower 48 will
break down some as a positive-tilt mid-level trough amplifies from
Montana into the Dakotas.  As this occurs, mid-level flow will
strengthen in portions of Wyoming, northern Utah, and Colorado
throughout the day.  A ridge centered over Arizona will further
weaken throughout the day, but remain nearly stationary.  At the
surface, a stout ridge will build into areas of the northern Rockies
and adjacent Plains, while a surface trough/heat low remains
stationary from the Lower Colorado River Valley into portions of
interior California.  Near-record heat and dry conditions will once
again occur in the West and Southwest today, with areas of low-level
flow and isolated thunderstorm development leading to elevated fire
weather conditions in several areas of the Great Basin, Rockies,
northern High Plains, and interior northern California.

...Southern Arizona/New Mexico northward to southern Wyoming...
Widespread elevated to locally critical fire weather conditions will
develop in the afternoon and early evening hours.  Broad areas of
15-25 mph westerly flow (with a few higher gusts) will develop this
afternoon amidst a very hot and dry airmass, with surface
temperatures exceeding 100F in many areas (especially lower
elevations) and RH values falling into the single digits.
Widespread areas of dry fuels also support this enhanced fire
weather threat.

The combination of weak instability developing atop deeply mixed
boundary layers will also lead to isolated to scattered
thunderstorms, especially in eastern Utah and western Colorado.
Increasing mid-level flow in this region and ascent associated with
the approaching mid-level trough from the north may locally increase
convective coverage in northwestern Colorado.  0.5-0.6 inch PW and
20-30 mph storm motions may aid in limiting precipitation in any
particular area.  Isolated dry lightning strikes are possible in
this region, and an attendant delineation has been made to address
this threat.

A secondary area of potentially dry lightning will develop in
southwestern New Mexico.  Storms should develop along higher
terrain/ridgetops and move very slowly during the afternoon in
response to very light steering flow aloft.  Wetting rains are
likely in localized areas, with isolated dry lightning strikes
possible on the outer peripheries of the wetting cores.

...Southern and southeastern Montana...
Northwesterly surface flow will increase throughout the day,
exceeding critical thresholds in the afternoon as a surface ridge
builds in behind a surface cold front southeast of the area.
Warming surface temperatures (reaching the lower to mid 70s F)
amidst a dry airmass (RH values falling to 20-25%) are all
characteristic of elevated fire weather conditions.  Finer fuels are
dry and will support some fire spread as well.  Similar conditions
will exist farther east into northern South Dakota, although areas
of antecedent rainfall will likely temper any large-scale fire
weather threat during the afternoon.

...Northern California...
Areas of northwesterly surface flow will develop in the region this
afternoon, with gusts approaching 25 mph.  This, in conjunction with
continued record-breaking heat, dry conditions during the afternoon
(RH values falling to 10-15%), and dry fuels, supports an elevated
fire weather delineation in the region this afternoon.

...Southern California...
Very dry conditions will exist in the inland coastal ranges of
southern California this afternoon.  Areas of gusty southwesterly
flow will approach 20 mph (with higher gusts in terrain-favored
areas) as temperatures rise into the 90s F.  Minimum RH values will
also fall into the single digits to around 10% during peak heating.
Given dry fuels in the region, an elevated fire weather delineation
has been included in this outlook.

...Please see for graphic product...

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