748
FXUS65 KCYS 120519
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1119 PM MDT Tue Jun 11 2024

.KEY MESSAGES...

- Hot weather expected Wednesday as daytime highs climb into
  the 85 to 95+ degree range across the entire area.

- Thunderstorm chances return to the region late this week,
  along with the risk for severe weather Thursday and Friday.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 342 PM MDT Tue Jun 11 2024

Latest GOES WV imagery shows primarily zonal flow aloft with an
upper level closed low off the southern CA coast while the
polar jet sits near the Canadian border with an upper level
trough moving into BC. Zooming into southeast WY, latest visible
imagery shows cumulus development over east-central WY as well
as eastern Laramie Co with an enhanced convergence zone based on
surface observations. Precipitation chances are low, but
nonzero through early this evening as an isolated storm could
still develop. Will continue to monitor latest satellite trends,
but any storms that develop will likely be short-lived with
little to no precipitation.

Zonal flow aloft will continue Wednesday with 700mb temps climbing
near 15C as an upper level ridge builds just to the south over the
central Rockies. This will lead to a warm day across much of the CWA
with much of the NE panhandle reaching the mid-90s. With 700mb temps
will climb near the climatological 90th percentile value, we are not
looking to break record highs, but still could see temperatures just
a few degrees below for select locations. Latest NBM probability of
exceeding 100F degrees Wednesday afternoon is highest in the North
Platte River valley, up to 25%. Farther west of the Laramie Range,
scattered showers will develop in the afternoon with a weak
shortwave passing in the flow. Forecast soundings show inverted-V
profiles with dry low-levels and LCLs climbing above the freezing
level. While minimal precipitation is likely from these storms,
strong outflow winds will be possible in the vicinity. Hi-res
guidance does continue showers east along the I-80 corridor towards
Kimball before dissipating early in the evening.

Better chances for showers and thunderstorms arrive later this week,
starting on Thursday. SPC Day 3 Outlook currently has a Marginal
Risk reaching up into Laramie Co. Post-frontal upslope flow with an
upper level system passing over the central CONUS will increase
moisture convergence across southeast WY and northeast CO. Despite
southeasterly low-level flow, wind profiles are fairly
unidirectional aloft supporting of straight hodographs and splitting
storms. MLCAPE climb near 1000 J/kg with 40+ kt shear that will
support strong to severe thunderstorms Thursday afternoon along the
South Laramie Range and adjacent plains to the east and south of the
North Platte River valley.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Issued at 342 PM MDT Tue Jun 11 2024

An active start to the long term forecast is expected across
southeast Wyoming and western Nebraska. On Friday, a potent,
upper- level shortwave trough is progged to dig northeasterly
from southern Nevada to western Colorado throughout the day. As
this upper-level shortwave pushes towards the region, ample
synoptic lift is expected to develop from a combination of jet
dynamics and cyclonic vorticity advection at 500mb. A subtle,
700mb jet maximum is progged to be just southeast of the CWA,
broadly placing western Nebraska within the left exit region of
this low-level jet and further favoring lift across the region.
Strong southeasterly flow at the surface will advect in
significant moisture with dewpoints increasing into potentially
into the 60s for portions of western Nebraska, with 50F dewpoint
expected across far southeast Wyoming. NAEFS mean precipitable
water for 00Z Saturday is currently progged to near the 99th-
percentile for this area at this time of year. Looking more in-
depth into some of the convective parameters, MUCAPE values are
progged to well over 2000 J/kg with MLCAPE values approaching
2000 J/kg as well. Forecast soundings from the GFS suggest good
directional shear in the lowest levels of the atmosphere, steep
low- level lapse rates, and DCAPE values near 1000 J/kg.
Forecast soundings across western Nebraska suggest bulk shear
values approaching 50kts, with precipitable water values
approaching 1.5 inches. These indicate a potentially significant
hail threat across far southeast Wyoming and western Nebraska.
However, hodographs are progged to be straight across this
region, leading to an additional concern of slow-moving storms.
Slow-moving storms accompanied by 95th-99th percentile
precipitable water leads to and increase concern of torrential
downpours with any storms that develop and the slow moving
nature could lead to a significant flooding threat. The Weather
Prediction Center has a small portion of the CWA under a
Marginal risk for excessive rainfall on Friday, but this could
move further west over the next few days. Overall, Friday looks
to be a favored day for severe weather across western Nebraska
and far southeast Wyoming. This setup will continue to be
monitored as it approaches and more consistency develops within
the models and hires models.

The remaining long term forecast will feature quasi-zonal flow aloft
across the region with 700mb temperatures increasing into the 10 to
20C range throughout the long term. Warm temperatures are expected
with highs in the 70s to near 90s across western Nebraska. Could see
some daily chances for isolated showers and maybe a thunderstorm or
two, but coverage will be very low. Additionally, zonal flow aloft
will lead to breezier conditions across the region, though winds
should remain well below high wind criteria.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1118 PM MDT Tue Jun 11 2024

Looking at a quiet overnight with mostly clear skies and VFR
conditions. VFR conditions will continue into the day on Wednesday,
but with gustier winds and increasing cloud cover during the
afternoon. A slight chance of showers will be possible.

&&

.HYDROLOGY...
Issued at 342 PM MDT Tue Jun 11 2024

Flows remain just below flood stage on the Medicine Bow River
near Elk Mountain with a slight trend downward the past few days
with early morning crests. However, with the warm weather
expected the next few days including overnight lows in the
mid-40s at higher elevations, decided to extend the Flood Watch
for snowmelt through Thursday morning.

&&

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

&&

$$

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