Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 252104

Area Forecast Discussion
National Weather Service Cheyenne WY
304 PM MDT THU AUG 25 2016

.SHORT TERM...(This evening through Saturday)
Issued at 242 PM MDT Thu Aug 25 2016

An unsettled weather pattern remains in place this afternoon as mid-
level troughing dominates the flow aloft, along with several smaller
scale waves rounding the base of the trough. At the surface, a near-
stationary frontal boundary was draped from west-east along the I-80
corridor over southern Wyoming. Persistent low stratus has and still
is limiting instability across the area today, but forecast sounding
information shows a very moist boundary layer which is allowing some
weak convection to develop over Albany/Laramie counties. Showers and
thunderstorms should increase in coverage this evening as a 100 knot
H25 jet translates across east central WY into western SD. HRRR runs
have been consistent with this idea as well, so maintained scattered
to numerous coverage of precip through tonight with thunder dropping
off after 06z based on CAPE progs from the NAM. There is also modest
chance for patchy fog development late tonight. We opted to leave it
out of the forecast for now as pressure gradients would support wind
staying high enough to keep the boundary layer mixed, and pcpn could
play a role in this as well. Little change in the synoptic/mesoscale
pattern through Friday, so expect more of the same tomorrow. Trended
a couple of degrees below consensus guidance for highs given how the
stratus today impacted things.

On Saturday, GFS/NAM/ECM all show broad upper-level ridging along w/
considerable drying in the H7-H3 layer. Temperatures will be quite a
bit warmer with H7 temperatures around +10 deg C. Even though we are
not expecting Saturday to be a Red Flag Day, this will likely be the
start of a much warmer/drier pattern heading into the extended.

.LONG TERM...(Saturday night through Thursday)
Issued at 242 PM MDT Thu Aug 25 2016

We really start to dry things out by Sunday as the Pacific tap
turns off and the main upper jetstream slips north towards the
Canadian border. Initially there may be enough residual moisture
in the mountains for isolated showers/thunderstorms Saturday
evening. We then see a prolonged dry period through much of next
week as most of any upper level systems pass well to our north
and we remain in a fairly subsident and dry airmass.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 110 PM MDT Thu Aug 25 2016

Active period for scattered showers and isolated thunderstorms
through the overnight period expected. HRRR, GFS and NAM develop
buildups and showers with isolated thunderstorms over the southern
Wyoming mountains this afternoon and move that activity east
northeast across the region through early Friday morning. Expect
scattered coverage overnight. Brought in some lower MVFR ceilings
and visibilities at Laramie and Cheyenne toward morning due to
upslope moist boundary layer flow.


Issued at 242 PM MDT Thu Aug 25 2016

Minimal fire weather concerns in the near term with good chances for
wetting rains and a generally cool/moist air mass in place. Expect a
trend toward much warmer and drier conditions after Saturday, w/ RHs
frequently in the teens through much of next week. Gusty winds could
occur each afternoon, especially west of the Laramie Range. As such,
periods of critical fire weather conditions will be possible through
the week.


.CYS Watches/Warnings/Advisories...


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