Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 231136
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
536 AM MDT Wed Aug 23 2017

.SHORT TERM...(Today through Thursday tonight)
Issued at 219 AM MDT Wed Aug 23 2017

The upper level ridge will move over the forecast area today while
a subtropical jet advects up from the southwest. Midlevel energy
and moisture will ride up on the nose of the jet within the
ridge, so expect to see chances for showers and storms increase
through the afternoon/evening from southwest to northeast. Not
anticipating particularly vigorous convection due to effects of
ridging aloft and the fact that the stronger jet winds will remain
to our south. However, gusty downdraft winds are possible as
forecast soundings still indicate low level inverted-V profiles
for this afternoon. Moderate rainfall is possible as well with
roughly a 200mb deep moist layer in the midlevels, but the higher
rain rates may only occur if the low levels can moisten
sufficiently. Models do paint a couple tenths of QPF over the
mountains, which seems very reasonable as the higher peaks will
not be subjected to as dry of a boundary layer. Shortwave energy
is expected to take it`s time traversing the forecast area
tonight, so we may see a few showers/storms persist overnight.

A second midlevel impulse is expected to cross over Wyoming on
Thursday with stronger southeasterly sfc flow across the plains
as the leeside pressure trough deepens. H7 temps look to be a few
degrees cooler than Wednesday which should yield steeper low-mid
level lapse rates within the moist midlevels. That will allow CAPE
values to rise between 1000-2000 J/kg over the plains for
THursday afternoon. Deep layer shear looks to max out in the 25-30
kt range which isn`t conducive to severe, but certainly could see
some weakly sheared storms produce small hail and gusty winds
within the moderately unstable environment. The midlevel wave
will shift to the east Thursday evening with convection coming to
an end by midnight.

.LONG TERM...(Friday through Tuesday)
Issued at 219 AM MDT Wed Aug 23 2017

After a wet start to the month, it is looking more and more like
August will end dry.  Chances for storms will be low on Friday with
west to northwest boundary layer flow and PW values falling to 0.5-
0.75 inches.  The Euro has sfc winds becoming easterly on Saturday
with some moisture advection and better instability right along the
Colorado Border. Could see an isolated storm in areas near I-80. A
strong upper ridge develops over the Great Basin by Sunday into
early next week, keeping the CWA in dry north to northwesterly flow
aloft.  Highs through early next week will be around normal for late
August.  Although min RH values will fall to 15-20 percent most
aftns over lower elevations of Carbon county, no fire weather
concerns are anticipated with rather weak gradients and sfc winds.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 534 AM MDT Wed Aug 23 2017

Vfr conditions through the taf period.  Isolated to scattered
showers/thunderstorms will develop across areas near I-80 from mid
afternoon through the early evening. The main threat from these
storms will be gusty and erratic outflow winds.

&&

.FIRE WEATHER...
Issued at 219 AM MDT Wed Aug 23 2017

Increasing monsoonal moisture expected today and Thursday will
bring a better chance for showers and thunderstorms to the
district through this time. Wetting rains are a good possibility
especially over the high country, and gusty winds are likely with
thunderstorms. Humidities overall should remain around 20 percent
or higher both days, although western portions of Converse County
could drop as low at 15% today. Winds here should remain light
though. As a result, fire weather concerns will remain minimal.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

SHORT TERM...RJM
LONG TERM...ZF
AVIATION...ZF
FIRE WEATHER...RJM



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