120
FXUS65 KCYS 262105
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
305 PM MDT Sat Apr 26 2025

.KEY MESSAGES...

- Patchy fog, some dense, may develop in the north Platte Valley
  and I-80 corridor late tonight and early Sunday morning.

- Warmer temperatures can be expected again on Sunday with
  scattered to numerous afternoon and evening showers and
  thunderstorms east of I-25. Some of these storms may be
  severe.

- Low pressure early to middle of next week continues our rain
  chances, with high pressure then drying the region out to end
  the week and start the weekend.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 222 PM MDT Sat Apr 26 2025

Latest satellite loop was showing some low convergence along
the front range this afternoon with some cumulus developing in
an environment with still some decent CINH in place east of the
Laramie Range. However, there is minimal CINH south of the
border. Surface based CAPE values are ranging from 1000-1500
j/kg south of the border with even 40 to 45kts of effective
shear. Low and mid level lapse rates appear to be fairly steep
at this time, but not confident that any storm that does develop
south of the border will be able to achieve severe limits due
to limited CAPE to overcome the shear. The 18Z HRRR is trying to
pop up some showers, but it appears to be very shortlived.
Meanwhile, the 12Z FV3 is a little more ambitious in showing a
stronger thunderstorm, but it is rather shortlived as well.
Otherwise, things should remain fairly quiet this evening.

Latest observations were showing dewpoints staying in the 40s
this afternoon. This low level moisture does not appear to be
mixing out especially over areas east of the I-25 corridor where
most of the models are showing things drying out fairly quickly
this afternoon. The only model that seems to have the better
handle on the low level moisture right now is the NAMNest. As a
result, we are following closer to this solution tonight which
also brings the low clouds/fog back into the picture after
midnight. We did go ahead and mention some patchy fog again
along the Cheyenne Ridge and North Platte Valley.

Once again we followed the NAMNest solution with the low level
moisture on Sunday. The rest of the models are drying us out in
the afternoon which seems to be a little ambitious considering
we have stiff south-southeast flow through the day ahead of the
surface low. The main question will be whether or not we will
see a Chugwater cyclone develop tomorrow afternoon. If it does
develop during the late afternoon, we may see the potential for
a couple of supercells develop and possibly move into the
Nebraska panhandle. The right movers would tend to favor the
northern Panhandle vs. the southern Panhandle, but we will need
to keep an eye where this surface low may develop. See the
latest SPC outlook for further details. The models are in favor
of showing the cold front surging through the area on Sunday
night bringing more widespread showers and thunderstorms over
much of southeast Wyoming and Nebraska panhandle during the
evening. Once the thunderstorms pass, we will see partial
clearing, cooler and more breezy conditions.


&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 222 PM MDT Sat Apr 26 2025

Monday, another shortwave moves through the Intermountain West to
continue our precipitation chances in the afternoon. There is some
strong isentropic lift on the tail end of the trough of the system
that moved through Sunday. There looks to be some warm air advection
as well to provide some extra lift for some stratified rain. Most of
accumulations are in our northern counties with the 25th percentile
showing around 0.05 inches and the 75th percentile around 0.2
inches. This is mainly tied to the amount of moisture available to
lift as a secondary front created by the upper level trough pushes
through around midday. There could isolated higher amounts if storms
do develop in the afternoon but we are not expecting anything like
on Sunday as we are in a general thunder risk.

Tuesday through Thursday, Multiple shortwaves will pass through the
Intermountain West to give us daily afternoon shower potential these
three days. With the limited vorticity and lack of vort maxes, there
is no a whole lot of forcing to really develop strong storms. Any
showers that do develop will be diurnal in nature and produce light
rain accumulations.

Friday and the weekend, there is model consensus with upper level
ridging building over the Intermountain West to give us a brief
break in this rainy pattern. There is a little bit of disagreement
on how long this ridge will last ahead of another low pressure
system arriving to give us renewed precipitation chances.


&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1143 AM MDT Sat Apr 26 2025

Skies are slowly clearing from West to East. However,
KCDR/KAIA/KSNY may not clear to VFR conditions as a Denver
cyclone looks to keep cloudy conditions as a warm front keeps
the lower atmosphere saturated. There is another nocturnal
inversion expected tonight that will mainly only apply to the
Wyoming terminals where dense fog may develop. For our Nebraska
terminals there will be a low level jet forming tonight that
will keep winds gusty and present a low level wind shear concern
for tonight around 06z. I didnt put fog in the Nebraska TAFs as
the winds seemed a little strong for fog development with the
weak inversion but there`s still a chance for fog to develop.
Tomorrow afternoon there`s a chance for thunderstorms to develop
also mainly in the Nebraska Panhandle but KCYS also has a
chance just as a heads up for planning purposes. Timing is a
little spotty but anything after 20z may be fair game for
storms.

&&

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

&&

$$

SHORT TERM...REC
LONG TERM...MM
AVIATION...MM