Area Forecast Discussion
Issued by NWS Cheyenne, WY

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218
FXUS65 KCYS 130820
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
220 AM MDT Sun Aug 13 2017

.SHORT TERM...(Today through Monday Night)
Issued at 1213 AM MDT Sun Aug 13 2017

Upper trough over the Dakotas early this morning will shift slowly
eastward this afternoon. A couple of weak mid level disturbances
will affect the CWA today. One of these will move from eastern ID
across western and northern WY will a second will track into
northern CO from UT this afternoon. At the surface, the stronger
southerly return flow that we saw yesterday will shift east of our
area leaving the plains with a bit weaker and more nebulous
surface forcing. It does appear that by mid to late afternoon, the
low level flow will turn more easterly especially over southern
parts of SE WY and this combined with the weak mid level impulse
nearby will likely set off scattered thunderstorms once again.
With the weaker low level winds, shear will not be as strong this
afternoon as yesterday. Steep mid level lapse rates will still
contribute to MLCAPE values around 1000 to 1500 J/Kg especially
over the southeast part of the panhandle near Sydney. Model
soundings show CAPE profiles that are a bit narrower than
yesterday so while large hail is a possibility with the stronger
storms over the Panhandle, hail size will likely be smaller than
Saturday.

Upper flow will turn more westerly and southwesterly on Monday as
a rather robust shortwave emanating out of the deep trough moving
into western Canada will track over northern Wyoming. Large scale
forcing will increase ahead of this feature and shower and
thunderstorm activity is a good bet especially over Converse and
Niobrara counties during the afternoon. Could see a few strong to
severe storms Monday as well over our northern counties with deep
layer shear around 35kt above a deeply mixed boundary layer.
Strong winds will likely be the main threat with these high based
storms. Farther south, more isolated activity will form over the
higher terrain of SE WY by late afternoon with some gusty winds
possible in more pulse type storms with deep inverted v profiles
in the boundary layer.

.LONG TERM...(Tuesday through Saturday)
Issued at 1213 AM MDT Sun Aug 13 2017

A rather broad trough will take over the western Conus from Tuesday
through Thursday with a trend toward weak ridging for the week`s
end. Temperatures are looking to hover just below normal for this
time of year in the mid 70s to mid 80s with perhaps some breezy
westerly winds west of the Laramie Range each afternoon. We should
see vigorous midlevel disturbances moving overhead especially on
Tuesday and Thursday bringing continued chances for showers and
storms through this time. As the trough shifts east and the ridge
builds in from the west on Fri- Sat, conditions should warm a bit
and dry out. Cannot completely rule out some convection each
afternoon as models are showing some weak midlevel disturbances
moving atop the ridge, but models are not very consistent with the
details so will keep PoPs low for this timeframe.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1148 PM MDT Sat Aug 12 2017

Radar has cleared of precip echoes this evening with satellite
imagery showing mostly mid and high clouds passing overhead. There
does appear to be some very localized fog/stratus over the
Panhandle, so will not completely rule out the redevelopment of
shallow fog/stratus at KAIA, KBFF, and KSNY between 08-15Z this
morning. Elsewhere, expect light winds and mid/high clouds until
later this afternoon when another round of scattered showers and
thunderstorms will spread west to east across the forecast area.
KCDR may be the one site that remains clear of convection.


&&

.FIRE WEATHER...
Issued at 1213 AM MDT Sun Aug 13 2017

Minimal fire weather concerns are expected through mid week with
seasonable temperatures and chances for afternoon showers and
thunderstorms. Temperatures begin to warm by late week and drier
conditions will return to the region.

&&

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

$$

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



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