Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 240540

Area Forecast Discussion
National Weather Service Pueblo CO
1140 PM MDT Sat Sep 23 2017

Issued at 848 PM MDT Sat Sep 23 2017

Updated to adjust precipitation chances across the region through
tonight. Out east, radar indicates the heaviest activity has moved
east into western Kansas, with just light activity for the next
several hours. Satellite imagery shows enhancements in cloud tops
over the Eastern Mountains, into the I-25 corridor. Expect this
activity to continue spreading northeastward ahead of the main
upper system ahead of the dry air wrapping up north for Sunday.


.SHORT TERM...(This evening through Sunday)
Issued at 256 PM MDT Sat Sep 23 2017

...Early Fall Storm System to Impact Much of the Area Next 24

An early fall storm system is spinning over southern Nevada and
southern Utah this afternoon. The center of the low is forecast to
pivot into northeast Utah by morning and then southwest Wyoming by
evening.  This track will allow for precipitation to continue for a
while this evening, with less activity over the area on Sunday as a
drier southwest flow spreads across.  An area to watch this evening
is the far southeast plains.  Limited severe potential, yes, but
also local flash flood potential.  Old runs held a long period of
training storm cells right along the Kansas border through the
night.  However, the 18z NAM has backed off on this a bit, moving
the area of training cells eastward more quickly and pushing them
farther east into Kansas.  So, not concerned enough to issue a Flash
Flood Watch for an area that has been very dry for the past several
weeks.  Regardless, there is still opportunity for local flash
flooding in a few areas, pending where the storms train and how
quickly they move east.  Additionally, a couple of storms could end
up going severe with primary concerns of 60 mph winds and quarter
hail.  The Storm Prediction Center has this area under a marginal
risk and this looks fine.

Another concern is the burn scars.  Some high res models bring
scattered showers and storms across the Hayden and Junkins this
evening.  The burn scars will need to be monitored for this

Yet another concern this evening is snow in the mountains.  Web cams
around the area so far today have shown some snow on the peaks up
above about 11,500 feet.  Fremont Pass is currently seeing some wet
snow, with some accumulations under an inch on grassy areas and even
some slush on the highway. The snow level will likely lower
overnight to as low as 10,000 feet or maybe even a little lower by
morning. Leadville could see some wet snow overnight, particularly
toward morning, with some light accumulations possible.  Forecast
has generally 1-4 inches in the higher elevations (above 10,000
feet) overnight, with even some locally higher amounts possible
above 12,000 feet.

Tomorrow, as the upper low pivots into southwest Wyoming, looks like
drier air will spread in across the region from the southwest.  This
should bring a big drop in the shower activity over most of the
area.  There will still be showers around but much more isolated
than today.  Possibility of some stronger storms gearing up later in
the day across the far southeast Colorado plains.  Temperatures will
remain cool. Fall in the Rockies has indeed arrived.

.LONG TERM...(Sunday night through Saturday)
Issued at 256 PM MDT Sat Sep 23 2017

Models in much better agreement and ensemble spreads are much less
than previous forecast cycles. This has lead to higher forecast
confidence that active, cool weather will prevail through the
extended period.

Sunday upper level disturbance over northwest Colorado
will continue to lift northeast into the Northern Plains
overnight. Models continue to southern Colorado under the dry
slot, with most activity remaining over the mountains, and across
the Palmer Divide, before lifting off to the northeast through the
late night hours. Meanwhile, a cold front is forecast to drop
south across the Plains through Monday morning.

Monday through Tuesday...the upper system is forecast to split,
with energy across the Northern Plains, while an area of low
pressure develops over Arizona. Expect northerly winds Monday
morning, to shift southeasterly through Tuesday. This will provide
low level upslope flow across the Plains and provide the focus for
shower and thunderstorm development along the Eastern Mountains,
into the I-25 corridor through Tuesday. Snow levels over the
mountains will also lower to around 9000 feet where an inch or two
of accumulation may be possible. Lower level temperatures will be
cool with 60s for highs. Overnight lows over the San Luis Valley
will fall into the lower to mid 30s.

Wednesday through Saturday...models in much better agreement with
an upper level low pressure center developing over Arizona, under
an upper ridge over the Northern Rockies. Models keep southerly
flow out of the Desert Southwest pumping moisture and energy
northward into Colorado through the end of the week. There could
be periods of heavy rainfall, especially Thursday, when models
lift the strongest energy north into the area. This will also
allow for cooler temperatures to remain across the region, with
60s to lower 70s for highs across the Plains, and snow levels over
the mountains around 9 to 10 kft.  Mozley


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1133 PM MDT Sat Sep 23 2017

Showers and isolated embedded thunderstorms will continue across
the southeast plains overnight...mainly to the east of KCOS and
KPUB. CIGS will remain predominantly MVFR for these
terminals...though could drop to near the top end of IFR category
at KCOS as winds lighten and shift to the southeast Sunday
morning. MVFR cigs should linger into the afternoon for both
KCOS and KPUB before rising back into VFR category by afternoon.
KALS will likely stay VFR though there could be a very low end
chance for some patchy ground fog to develop early Sunday morning.
Probability looks too low at this point to warrant mention in TAF
but will bear close watching. Otherwise...southwest winds will
with gusts to around 25 kts will spread in by afternoon.  -KT




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