Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 211734

Area Forecast Discussion
National Weather Service Pueblo CO
1134 AM MDT Thu Sep 21 2017

.SHORT TERM...(Today and tonight)
Issued at 412 AM MDT Thu Sep 21 2017

The main concern for today will be the expected critical fire
weather conditions.

An upper level trof will be over the western U.S. today and
tonight, with moderate southwest flow aloft over southeast and south
central CO.  It will remain dry thru the day and temps will be about
10-15 degrees warmer than yesterday acrs the southeast plain, with
temps in the high valleys being similar to yesterday.

The high elevations will continue to see strong winds today and
tonight, while at the lower elevations, southwest winds will pick up
later this morning and in the afternoon. It is assumed that the
fuels are dry acrs southern CO.  RH values acrs the southeast plains
are expected to reach minimum values of about 10-15 percent this
afternoon.  RH values in the San Luis Valley are forecast to be
around 15 percent and in the Upper Arkansas River Valley should be
just under 15 percent.  These high valleys will have conditions that
are marginally critical but not widespread enough for long enough to
warrant a warning. Widespread critical fire weather conditions are
expected over the I-25 corridor and southeast plains this afternoon
and will leave the Red Flag Warning as is. The only are that may end
up with just marginal conditions is Baca county, where dew points
may remain high enough that RH values may stay a little above 15

Tonight the winds at the lower elevations will generally decrease,
but will still be somewhat breezy acrs portions of the southeast
plains and in some areas of the San Luis Valley.  Tonight, an
increase in moisture over western CO is expected to result in some
pcpn developing over the southwest mtns, and maybe portions of the
central CO mtns.  The rest of the area will remain dry. Overnight
low temps will mostly be above average.

.LONG TERM...(Friday through Wednesday)
Issued at 412 AM MDT Thu Sep 21 2017

Friday-Friday night...Models remain in agreement with moderate to
strong south to southwest flow aloft across the area as an upper
disturbance rotates around the main system digging across the Great
Basin. Latest models differ, though, with the latest GFS a tad
further east and north with the main system, where as the EC and GFS
ensemble mean dig the system into southern Nevada by early Saturday
morning. At any rate, this will set the stage for near critical fire
weather conditions across the lower eastern slopes and I-25 corridor
and the potential for severe storms across the far southeastern
plains, with the downslope flow helping to develop lee troughing
with low level moisture pooling along and east of the dryline as it
lifts out near the western Kansas border through the day. Have not
issued a Fire Weather Watch at this time with latest models keeping
min RHs across the I-25 corridor in the 15-20 percent range.
However, with gusty southerly winds of 20 to 35 mph expected Friday
afternoon and lack of substantial moisture recently, care should be
taken to prevent any fire starts across the area. Isolated to
scattered showers and thunderstorms are expected over the higher
terrain, with best coverage expected across the southwest mountains.

Further east across the Plains, models have been consistent in
developing a dryline, generally east of Haswell to Kim line, with
thunderstorms developing by mid to late afternoon along and east of
this line. Modest CAPE and ample unidirectional shear should allow
for at least a few severe thunderstorms with gusty winds in excess
of 60 mph and large hail up to around one inch in diameter the main
severe threats. This activity should spread east into Kansas during
the evening hours. Expect more scattered showers, and possibly an
isolated thunderstorm across the region Friday night. Temperatures
on Friday will remain warm with highs in 80s to lower 90s across the
lower elevations and mainly in the 50s and 60s across the higher

Saturday-Sunday...Model differences become more pronounced, with the
latest EC further south and slower with the main upper low than the
GFS, which is faster and further north with the ejecting the system
through the day Sunday. With that said, have followed a blended
model pops, keeping the best chances of showers and storms across
the higher terrain and far eastern plains on Saturday, with frontal
boundary sliding south across the eastern plains Saturday night,
owning to cooler temperatures and better chances of showers across
the area Sunday and Sunday night with upslope flow in place and
increased uvv with upper low lifting out into the northern Rockies.
Could again see strong to marginally severe storms across the far
southeast plains on Saturday, with cool air associated with the
upper low allowing for a few inches of snow across the higher
mountain peaks, though could see snow levels down to around 9000
feet with some of the stronger storms. Could also see overnight
lows at or below the freezing mark across the high mountains

Monday-Wednesday...Main upper low continues to lift north and east
across the northern Rockies on Monday, with models indicating
secondary energy digging down the backside of the system into the
Great Basin through the day Monday. This will keep cool and
unsettled weather across the area, with isolated to scattered
showers expected, especially over and near the higher terrain.
Models continue to differ on strength and location of this secondary
energy, with the latest EC the strongest, developing another closed
low across the 4 corners region on Wednesday. At any rate, forecast
will keep cool and unsettled weather in the picture, especially
over and near the higher terrain, into the middle of next week.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1129 AM MDT Thu Sep 21 2017

VFR conditions are anticipated during the next 24 hours at all 3
taf sites; KPUB, KALS and KCOS.

Gusty southwest winds will occur at all 3 taf sites this afternoon
and early evening. Winds will decrease later this evening but will
pick up from the south-southwest again tomorrow afternoon.


Red Flag Warning until 7 PM MDT this evening for COZ226>237.



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