864
FXUS65 KCYS 131728
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1128 AM MDT Tue Aug 13 2024

.KEY MESSAGES...

- Scattered to numerous afternoon/evening showers and
  thunderstorms are expected the next few days. Storms will
  have the potential to produce torrential rainfall, gusty
  winds, and isolated large hail.

- An active pattern continues through the week ahead with near
  normal temperatures and daily chances for afternoon and
  evening showers and thunderstorms.

- Seasonable temperatures will continue through the period. Showers
  and thunderstorms will be most likely on Friday, Sunday and
  Monday, with drier conditions for Saturday.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 221 AM MDT Tue Aug 13 2024

Upper shortwave moving through the area this morning aiding in
the development of showers and storms. Seeing rain from Sidney
to Cheyenne early this morning. Another area associated with the
upper shortwave moving through Carbon County currently. These
showers/storms are efficient rain producers as the Cheyenne ASOS
has reported over an inch of rain the past 6-7 hours. Confirmed
with our local measurements...we are averaging about .3 to .4
inches of rain per hour. Area of rain expected to move off to
the east through 12Z.

Secondary shortwave approaches the CWA this afternoon and will
aid in shower/storm development.  HRRR/RAP simulated radar
shows showers and storms redeveloping this afternoon after 20Z
or so. NAM MUCAPE up near 2100 J/KG in the panhandle this
afternoon. Lapse rates and 0-6km shear on the other hand are not
that impressive...so confidence in severe storms is not that
high. PWATS are quite impressive however with the Panhandle up
near 1.5 inches and 1.1 inches east of the Laramie Range. Long
skinny CAPE values off the GFS suggest heavy rainfall as well.
Day shift will have to watch for training storms...especially
down along the I-80 corridor where abundant rainfall is
currently occurring. Look for showers and storms to continue in
the overnight period as the shortwave trough moves through the
area.

Looks like a repeat for Wednesday as a trough remains over the
CWA and we get pockets of energy moving through the trough. The
trough finally moves east into Nebraska Wednesday afternoon with
upper level ridging returning from the west. PWATS decreasing
through the day Wednesday under an inch in the Panhandle. Heavy
rainfall potential looks to decrease significantly over today.
Showers and storms continue Thursday as we stay in low level
easterly flow and upper level shortwaves move through the ridge.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Issued at 221 AM MDT Tue Aug 13 2024

Thursday night/Friday...Some leftover scattered showers and
thunderstorms will occur Thursday evening mainly west of a Douglas
to Sidney line, with widely scattered showers continuing after
midnight across the forecast area. Ridging aloft and drying west
winds in the mid levels of the atmosphere will help dry out the
airmass somewhat as precipitable water values decrease to 0.4 to 1
inch. Still though, with a surface trough in place near the Wyoming
and Nebraska state line, we expect isolated to widely scattered late
day showers and thunderstorms most numerous east of I-25. Warmer
temperatures anticipated with less cloud cover and with 700 mb
temperatures near 18 Celsius, maximum temperatures will be in the
80s.

Saturday...West flow aloft will continue to dry out the airmass and
thus we will see correspondingly warmer temperatures from the mid
80s to mid 90s. With precipitable water values lowering to 0.3 to
0.7 inches and warm temperatures aloft increasing the convective
inhibition. it looks dry.

Sunday...Despite ridging aloft developing, we will see an increase
in atmospheric moisture content with precipitable water values
increasing to 0.8 to 1.2 inches. Thus, we expect an increase in
widely scattered to scattered late day showers and thunderstorms,
most numerous from the Snowy Range to far southeast Wyoming.

Monday...Atmospheric moisture content remains about the same as on
Sunday, and thus we expect another round of scattered late day
showers and thunderstorms, most numerous near the Colorado state
line from the Snowy Range to far southeast Wyoming. With similar 700
mb temperatures, maximum temperatures should be about the same as
those from Sunday.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1118 AM MDT Tue Aug 13 2024

Changes to the 18z Aviation Forecast, with some details becoming
a bit more clear. Another active day expected today, with an
shortwave expected to push across the zone. Decent lift
associated with the shortwave and combined with the instability
areas east of I-25, thunderstorms are expected across the CWA
beginning in the early afternoon and lasting through the
overnight hours. Main threats include strong/erratic winds, 1
inch hail, and heavy downpours associated with stronger storms.
Past few days have seen fog and low CIGs in the morning hours
that persist through the late morning. At this time left all
mentions of fog and low CIGs out of the terminal forecasts, with
wind direction and speed being less favorable for upslope flow.
However, with plenty of moisture at the surface from the past
few days, could see the terminals visibility and ceilings drop
into IFR in the morning hours tomorrow. Will reevaluate in later
TAF issuances.

&&

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

&&

$$

SHORT TERM...GCC
LONG TERM...RUBIN/AM
AVIATION...MRD