Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 181729

Area Forecast Discussion
National Weather Service Pueblo CO
1029 AM MST Mon Dec 18 2017

.SHORT TERM...(Today and tonight)
Issued at 409 AM MST Mon Dec 18 2017

Today and tonight...The upper low is forecast to remain well south
of Colorado through tonight, so light westerly flow aloft will
remain across the region. This will produce dry and gradually
warming conditions for the forecast area through the short term.
Look for max temps in the 40s to around 50F for the high valleys
today, and 50s for the e plains. Overnight lows will cool into the
20s, while dipping into the 5 to 15 degree range for the San Luis
Valley. Moore

.LONG TERM...(Tuesday through Sunday)
Issued at 409 AM MST Mon Dec 18 2017

...More active pattern with a couple of rounds of snow possible and
much colder temperatures for next weekend...

Dry weather with moderating temperatures can be expected for Tuesday
and Wednesday as a shortwave ridge shifts over the area...then
flattens out as the upper flow increases from the southwest ahead
of the next upper trof digging towards the Great Basin. Overall
winds should remain fairly light on Tuesday...but will increase
across the mountains and adjacent I-25 corridor on Wednesday as
southwesterly downslope winds spread in ahead of the system. This
could mean some near critical fire weather conditions in the
afternoon on Wednesday as RHs will be down around 15 percent or
less. For now...area with the greatest risk will be southern I-25
corridor and perhaps far southeast plains on the east side of the
deepening lee trof...but RHs may end up more marginal out that

Bigger changes arrive Wednesday night and Thursday as the upper
low closes off across UT then weakens as it moves across CO/nrn NM
Thursday night as an elongated upper trof axis. Snow and wind
will spread into the Continental Divide region in earnest
Wednesday night with southwest flow briefly favoring the eastern
San Juan mountains. A cold front drives southward through the
plains on Thursday...with GFS the quickest of the models (vs the
slower NAM and EC). NAM, EC and the Canadian all keep the closed
low farther west Thursday morning which could bode for a slower
front timing. For now didn`t stray too far from blended model
output which leans a little warmer than guidance as temperatures
could warm quickly Thursday morning across the plains. However,
did drop temperatures during the afternoon as gradient looks
pretty tight once the front does come through during the day.
Expect there will be a quick change over to snow across the I-25
corridor and southeast plains Thursday afternoon and
evening...though amounts look light for now. Suspect that central
mountains will fair the best as flow aloft shifts to a more
favorable northwesterly component to enhance orographic snow
through the tail end of the event...but for now am only seeing
advisory criteria at best. The I-25 corridor over the Palmer
Divide and Raton Ridge could see impacts to travel given the
potential for a rapid drop in temperatures and slick roads...but
so far snow amounts look light. Too soon to pin down many of these
details as timing and evolution of the storm is bound to change
over the next several stay tuned.

Friday will be a brief reprieve, though temperatures will stay below
normal.  Then an upper jet dives out of Canada carving out another
trough across the NW U.S. which drops southward into CO Friday
night and Saturday. With upper jet dynamics over the area, off
and on light snow will be possible through the weekend, though for
now accumulations look light with low liquid to snow ratios.
If EC is correct, temperatures may only top out in the teens for
Sunday and Monday as H7 temperatures remain around -20C or colder.
This will be our first taste of winter in a while. -KT


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1027 AM MST Mon Dec 18 2017

VFR at all taf sites the next 24 hrs, with weak diurnal wind cycle




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