Area Forecast Discussion
Issued by NWS Cheyenne, WY

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292
FXUS65 KCYS 150351
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
951 PM MDT Mon Aug 14 2017

.UPDATE...
Issued at 943 PM MDT Mon Aug 14 2017

Evening water vapor loop/00Z upper air analyses showed a mid/upper
level trough axis over the Intermountain West. Ample moisture and
shortwave energy in the southwest flow aloft contributed to several
convective clusters from mid-afternoon through early evening. The
main threats from the stronger convection was 50-60 mph winds,
intense lightning and locally heavy rain. Most of the heavier
convection has exited to the east of the CWA, with scattered
showers and isolated thunderstorms spreading northeast across
central and southern Wyoming ahead of a slow moving cold front.
Updated the PoP and weather grids to account for these trends.

&&

.SHORT TERM...(This Evening through Wednesday)
Issued at 300 PM MDT Mon Aug 14 2017

Scattered showers and thunderstorms have developed in the past few
hours across southeast WY. Current thinking is the main threat
from these storms will be gusty downdrafts with deep boundary
layers and large DCAPE values in place. Also cannot rule out small
hail as the SPC mesoanalysis shows SBCAPE of 500-750 J/kg and
decent bulk shear of 30-40 kts across northern zones. Chance of
showers and isolated thunder will continue into the early night.
Shortwave trough currently across the Great Basin will move
eastward into central WY by Tuesday. Temps will be around 5-10
degrees cooler for tomorrow behind a weak fropa overnight. Expect
another round of aftn/evening storms to develop, with the coverage
highest for areas to the east of the Laramie Range. There will be
a better chance of strong storms mainly over the Nebraska
Panhandle during the aftn with CAPE of 1000-1250 J/kg and good
deep layer shear. Shortwave trough axis will move into northeast
Colorado by late Tuesday night into Wednesday morning. Wednesday
will be coolest day with a more stable airmass in place and only
isolated storms possible along the Laramie Range.

.LONG TERM...(Wednesday night through Monday)
Issued at 300 PM MDT Mon Aug 14 2017

Somewhat active northwest flow on Thursday will gradually become
westerly by week`s end and southwesterly for the weekend and into
early next week. The latest GFS and to a lesser extent the ECMWF
show shortwave energy diving southeast towards the Dakotas on
Thursday. The associated sfc frontal boundary to be the focus for
at least weak afternoon/evening convection. Progd SBCAPE`s are at
most 500 j/kg across our eastern portion of the Panhandle, so
would not expect much organization to the convection. Dry, stable
air mass will yield a dry day on Friday. Flow turns more southwest
as the weekend wears on, which should advect moisture back northeast
into the CWA. Have added afternoon precip chances to the Snowy/Sierra
Madres on Saturday/Sunday as a result. This pattern would be
conducive to afternoon/evening shower/thunderstorm chances lingering
on Monday afternoon as well. For now, have confined these to areas
in east-central Wyoming after 18z.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 519 PM MDT Mon Aug 14 2017

Area of showers and embedded thunderstorms moving eastward across
the plains currently. These showers and storms will affect the
Nebraska terminals through 04Z with occasional MVFR vis and gusty
winds to 30kt. Elsewhere generally VFR through the night with
scattered showers through 03Z. Active day tomorrow with a strong
disturbance pushing across the area from west to east. Expect
scattered to numerous thunderstorms to develop by mid/late
afternoon east of the Laramie Range. A few of these storms may be
strong/severe with hail and gusty downdrafts being the main
threat.

&&

.FIRE WEATHER...
Issued at 200 PM MDT Mon Aug 14 2017

Minimal fire weather concerns through midweek. We expect good chances
for showers and thunderstorms this afternoon through Tuesday. Some
of the storms will produce wetting rains. Afternoon humidities
could drop down to 15-20 percent across portions of southeast
Wyoming by this weekend.

&&

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

$$

UPDATE...MAJ
SHORT TERM...ZF
LONG TERM...CAH
AVIATION...DEL
FIRE WEATHER...ZF



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