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241
FXUS65 KCYS 272143
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
343 PM MDT Thu Jun 27 2024

.KEY MESSAGES...

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- Scattered showers and thunderstorms are expected across much
  of southeast Wyoming and western Nebraska this afternoon and
  evening. A conditional threat for severe thunderstorms will
  exist across extreme southeast Wyoming and western Nebraska,
  with large hail and damaging winds the primary hazards along
  with the potential for an isolated tornado.

- Another round of strong to severe thunderstorms is expected
  Friday as a cold front sweeps across the CWA. At this time,
  the best chance for convection appears to be in the southern
  Nebraska panhandle.
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&&

.MESOSCALE...
Issued at 144 PM MDT Thu Jun 27 2024

Latest GOES WV imagery shows an upper level shortwave moving into
central WY with the latest RAP analysis showing the lee trough
shifting eastwards towards the WY/NE border. Despite morning dew
points east of the I-25 corridor in the upper 50s and low 60s,
daytime mixing and westerly winds off the Laramie Range continue to
push upper 50 dew points farther east in the NE panhandle near the
CWA border with LBF. The placement of this low-level moisture
through this afternoon will be important to watch as the atmosphere
continues to destabilize as it will have significant impacts on the
instability profiles as up to 2000 J/kg of CAPE could be available,
but it appears more likely that storms will only be able to tap into
~500 J/kg across the NE panhandle.

Latest GOES Daytime Microphysics RGB has shown late morning clearing
across the southern NE panhandle and northeast CO with stable low-
level billow clouds across much of Platte/Goshen Co where upper
level clouds have limited daytime heating. Cu fields have begun
developing over the last 30-45 minutes across these areas of
clearing which may be an area of concern for stronger storms to
develop early this afternoon before the more favorable low-level
moisture mixes east. These storms could could produce large hail and
strong winds this afternoon before quickly moving east of the CWA
into central NE. Will need to continue to monitor for additional Cu
development farther north near the Pine Ridge as CAMs have been
initiating storms across a localized moisture pool before quickly
moving east as well. There is a short window for severe
thunderstorms today, potentially ending by 5 PM MDT, with lingering
showers and storms through the evening.

Looking farther west, much of south-central WY has begun to
destabilize as indicated with latest satellite imagery.
However, forecast soundings continue to suggest mid-level
capping could inhibit deeper convection before better lift
arrives from the west. Recent WOFS runs continues to show higher
probabilities (40-60%) of strong winds (gusts >58 mph) entering
southwest Carbon Co by mid-afternoon with the ongoing
convection in the Uintas as it travels east and eventually
increasing in coverage through the early evening near the Sierra
Madre and Snowy Ranges.

&&

.SHORT TERM /THROUGH FRIDAY/...
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Issued at 335 PM MDT Thu Jun 27 2024

Another round of potentially severe storms will be possible Friday
afternoon. A progressive trough will swing down into Montana and
North Dakota on Friday, pushing a cold front down into the CWA.
Frontal passage appears to be later in the afternoon, but before
that, the incoming front will spark scattered convection. As the
front dives south, the CWA will be in the right entrance region of a
250 mb jet streak. This will put the CWA in a favorable location for
severe weather with ample lift. The environment will also be
favorable for severe weather, especially south of the North Platte
River Valley. Here, RAP soundings show the capping inversion eroding
by early afternoon and convection initiating shortly after. The
surface will be modestly moist as brief southerly flow into the
panhandle ahead of the front raises dewpoints into the low 50s.
MUCAPE values max out around 2000 J/kg by mid-afternoon. This
will lead to primarily a large hail threat as Hi-Res guidance
initially shows discrete cells. Effective shear values will also
be around 45 kts which could support more organized convection.
Strong winds are also possible as storms begin to cluster later
in the afternoon with DCAPE values around 1000 J/kg. It is
worth mentioning the PWs will also be around an inch in the
southern panhandle, leading to heavy rain. Luckily, storms will
be quick moving, reducing the flash flooding risk. Hi-Res shows
storms wrapping up by about 7 PM.

Aside form severe storms, the incoming cold front will lead to a
blustery day across southeast Wyoming. The GFS shows strong westerly
700 mb winds ahead of the front, maxing out around 50 kts over
the North Laramie Range. MSLP gradients aren`t too impressive as
a surface ridge sits over much of the CWA. Even downward omegas
are a bit lack-luster, but 700 mb CAG-CPR height gradients are
elevated mid-day Friday. Even in-house high wind guidance is
picking up on elevated winds across the wind prones and much of
the Interstate 25 corridor. Could see gusts of 40 to 50 MPH in
these areas. Behind the front, winds will turn more northwesterly
and begin to ease late in the afternoon.
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&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
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Issued at 215 AM MDT Thu Jun 27 2024

Daily afternoon shower and thunderstorm chances continue through the
long term forecast period. Upper-level troughing will slowly
move out of the area Friday night into early Saturday morning as
an upper- level ridge builds over the Intermountain West. With
the cold front moving across the region Friday, Saturday will be
much cooler as 700mb temperatures drop into the 6-8C range east
of the Laramie Range, but west of the Laramie Range looks to be
warmer as the upper- level ridge slowly moves closer to the
region. Highs on Saturday will be in the mid-70s to low-80s east
of the Laramie Range and mid- 70s to mid-80s west of the
Laramie Range. Despite the strengthening ridge overhead, some
500mb vorticity maxima will traverse underneath, resulting in
precipitation chances Saturday and most days throughout the long
term forecast.

The upper-level ridge will be at its maximum strength overhead on
Sunday, leading to rapidly warming 700mb temperatures into the 15-
17C range. Surface temperatures will increase into the upper-80s to
mid-90s east of the Laramie Range and upper-80s west, leading to a
very warm end to the weekend. A slightly cooler and more active
pattern returns for the work week as the upper-level ridge moves off
to the east and troughing pushes in. Disagreement begins to appear
in the long range models at this time. The GFS suggests zonal flow
moving in after the trough pushes through, while the ECMWF keeps
troughing overhead for Monday and Tuesday, with zonal flow arriving
Wednesday. Disagreement continues throughout the remaining long
term, but temperatures are likely to remain in the 80s and 90s, with
warmer temperatures arrive for the 4th of July.
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&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1123 AM MDT Thu Jun 27 2024

Scattered showers and thunderstorms are expected this afternoon and
into the evening. Severe thunderstorms are possible east of the
Laramie Range, mainly between 20Z and 01Z. Storms in these areas
could contain strong winds with gusts over 60 MPH and large hail.
The severe threat and storms in general will taper off in the
Nebraska panhandle this evening. Rain showers, with the potential
for heavy rain, will continue around southeast Wyoming terminals
through roughly 06Z tonight. Any storm passing over a terminal in
these areas will have the potential to reduce visibility.

&&

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

&&

$$

MESOSCALE...MB
SHORT TERM...SF
LONG TERM...AM
AVIATION...SF