National Weather Service Raw Text Product

918 
FXUS65 KCYS 160537
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1137 PM MDT Sun Jun 15 2025

.KEY MESSAGES...

- Another round of scattered strong to severe thunderstorms is
  expected this afternoon and evening over the High Plains.

- Coverage of showers and thunderstorms will increase for Monday
  and Tuesday with continued potential for isolated to scattered 
  strong to severe thunderstorms and locally heavy rainfall. 

- Warm to hot temperatures are expected through Monday before a
  modest cool down on Tuesday. Well above average temperatures 
  are expected to return late in the week.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 145 PM MDT Sun Jun 15 2025

The stubborn stormy weather pattern continues today across the area. 
GOES water vapor imagery shows an area of increased midlevel 
moisture moving over Carbon and Albany counties this afternoon with 
mostly clear skies over the High Plains. This is kicking up ahead of 
a broad but subtle upper level shortwave moving across the Northern 
Rockies over the top of the strong upper level ridge today. 
Temperatures are surging to some of the hottest values of 2025 so 
far across the area under the axis of the ridge. A few locations are 
already pushing 90F and should crest in the lower 90s early this 
afternoon. The CIN that reduced our severe weather potential 
yesterday is still in place today, but it is noticeably weaker than 
it was 24 hours ago, particularly over the Nebraska panhandle. This 
is likely coming from an elevated dry mixed layer positioned on top 
of a slightly more moist near surface boundary layer. The warmer 
temperatures in the near surface layer combined with improved 
moisture flow with steady southerlies over the Nebraska panhandle 
are likely why the CIN is slightly weaker. Vertical wind shear has 
also come up slightly thanks to the approaching shortwave to our 
northwest. Overall, this points to another round of scattered strong 
to severe thunderstorms this afternoon and evening. Cumulus activity 
is already pushing up across southeast Wyoming, but probably will 
take another 1-2 hours to get going. The stronger CIN and weaker 
instability may cause storms to struggle initially until they 
encounter a more favorable environment over the Nebraska panhandle. 
While there is the potential for a low-end scenario similar to what 
we saw yesterday, the probability of this failure mode is lower than 
what it was yesterday. The main concerns are strong, gusty winds and 
isolated large hail once again, but there is sufficient low-level 
wind shear to get a quick tornado spin-up. 

Showers and storms should depart fairly quickly by around 9PM this 
evening and lead to partly cloudy skies overnight as a few mid-level 
clouds drift through the area. Monday will another round of severe 
storm potential across the area, but the setup looks different from 
what we saw the last several days. Today's shortwave ejecting east 
of the Rockies well to our north will push in a weak surface high 
from the northeast Monday morning, replenishing the low-level 
moisture up to the Laramie Range. Meanwhile, a stronger upper level 
shortwave trough will begin to suppress the ridge and deliver 
improved upper level moisture above 500-mb with a modest tap from 
the Pacific. As a result, expect stronger deep layer shear along 
with much higher precipitable water values climbing closer to the 
climatological 90th percentile. Southwest flow ahead of the trough 
will also produce modest overrunning lift across the area. A dry 
layer is still expected around 700-mb which will likely provide 
another modest cap through much of the daytime hours. There is then 
the same uncertainty in whether the cap will break and allow for 
strong to severe thunderstorms to develop, but the environment looks 
fairly potent for any storm that manages to break through. A second 
phase will continue late into Monday evening or even after midnight 
as isentropic lift continues and helps to moisten the elevated mixed 
layer. This will lead to an unusually potent severe weather 
environment well into the evening hours. Without the diurnal lift, 
coverage may be limited, but the environment could support isolated 
supercell thunderstorms. The stalled frontal boundary will surge 
westward late Monday night, bringing higher surface dewpoints into 
the valleys of Carbon and Albany county by Tuesday morning and 
possibly some fog along the Laramie range and/or the Cheyenne
ridge.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 145 PM MDT Sun Jun 15 2025

The trough passage on Monday sets us up for severe 
weather chances on Tuesday. Model guidance (3 globals) depict some 
cyclogenesis occurring Tuesday developing from this passage. If 
cyclogenesis occurs this will likely provide enough synoptic support 
to kick start some storm development in the afternoon. However, we 
will have a little bit less energy but a little more moisture to 
play with on Tuesday. MUCAPE is set at 2000 joules with 1800 of that 
being MLCAPE. Model soundings are showing a very pronounced inverted 
V sounding indicative of severe winds with 687 joules of DCAPE. Once 
again our effective shear is a little lower with a progged speed of 
26 knots. Again there are a couple progged lobes of vorticity 
allowing some enhancement of the storms as well. SPC has us in a 
marginal risk for severe weather on Tuesday. Wednesday, A broad 
ridge sets up over us and turns the heat back up into the 80's for 
Wednesday. The models have taken CAPE and vorticity lobes out of our 
area in today's model runs. Makes sense for the setup as the 
subsident flow under a ridge suppresses almost all convection. 
There is still a weak shortwave that passes through the 
intermountain west. However, given the westerly flow and 
increased subsidence we look to be getting a few more clouds to 
possibly develop and a maybe a slight breeze. This ridge is 
expected to last through at least Friday and possibly Saturday.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1137 PM MDT Sun Jun 15 2025

Storms have subsided for the night, leading to quiet conditions at 
all terminals. VFR conditions are expected for the remainder of the 
overnight and through Monday morning. Some upper-level clouds will 
be possible. Storms will begin to move into the are once again 
Monday afternoon.

&&

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

&&

$$

SHORT TERM...MN
LONG TERM...MM
AVIATION...SF