962
FXUS65 KCYS 150435
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
Issued by National Weather Service Riverton WY
1035 PM MDT Wed May 14 2025

.KEY MESSAGES...

- Very windy conditions expected for most of southeast Wyoming
  and portions of western Nebraska on Thursday. Gusts over 50
  mph possible.

- Active weather pattern creates daily precipitation chances in
  the afternoon and evening into the beginning of next week.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 113 PM MDT Wed May 14 2025

An upper level trough will be passing through the Intermountain
West today to give us some chances for some widespread showers
and chances for scattered thunderstorms in the afternoon. Hi-Res
guidance shows showers in the late morning to the early
afternoon for our mountainous regions west of I-25. Later in the
afternoon for areas east of I-25, thunderstorms look to develop
around 2pm and push eastward into the late evening.
Temperatures have cooled down compared to yesterday allowing for
the lower levels to saturate easier which any precipitation
will be able to hit the ground. However, this morning and
current satellite shows low level clouds dissipating over the
Nebraska Panhandle. These clouds may inhibit some of the severe
potential despite SPC placing a marginal risk (level 1 out of 5)
risk for severe t-storms with hail and winds as the main
threats. The 12Z model guidance places MUCAPE between 400 to
600 joules across the eastern portion of the Nebraska Panhandle
with a bulk shear between 35 to 45kts of shear. This is a
sufficient amount of CAPE and shear to sustain thunderstorms and
possibly produce severe thunderstorms. The most favorable area
for any severe storms to develop is the eastern portion of the
Panhandle due to the increased moisture, temperature, and higher
CAPE values with favorable shear. If severe thunderstorms do
develop, then hail sized up to quarters and winds greater than
60 mph can be expected underneath or near these storms. On a
synoptic scale, the surface low looks to pass through the
Intermountain West as well as jetstreak divergence aiding in
the lift generation needed to make the environment favorable for
storm development. However, some of the Hi-Res guidance shows a
mix of cluster and QLCS storm modes depending on which model is
viewed. This disagreement in storm modes could signal some
messy development to which the severe thunderstorms may conflict
with each other and end up hindering each storms potential and
we end up with some strong showers and small hail. Given its
planting season, the latter scenario of heavy rain and small
hail will be more beneficial to the Nebraska farmers. There is
also pretty good agreement between models with timing being
around 20Z-21Z for initiation east of I-25 and storms being
finished or moved out of the area by 23Z. As this trough pushes
into the Central/Northern Plains, there is some chances for
isolated to scattered showers on Thursday. Most of the better
forcing and dynamics will be further east on the front side of
this low however some synoptic support is still there with weak
divergence aloft. So any severe potential is not expected and
the SPC day 2 outlook shows us in the general thunder category
which meets our expectations for any storms that do develop for
tomorrow.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Issued at 113 PM MDT Wed May 14 2025

Friday...West-northwest flow aloft develops and with 700 mb
temperatures near 5 Celsius, maximum temperatures will be in the
60s. A bit less available moisture, so areal coverage of
showers and thunderstorms will be reduced.

Saturday...The flow aloft turns west-southwest, and with a
slight increase in mid level temperatures, high temperatures
will show a warming trend. Still enough low and mid level
moisture for scattered afternoon and evening showers and
thunderstorms.

Sunday...Southwest flow aloft develops in advance of the
approaching shortwave trough. With increasing low and mid level
moisture, and lift generated by a passing shortwave trough
aloft, scattered to numerous showers and scattered thunderstorms
will develop, focused along a low level convergence axis and
surface trough along the Wyoming-Nebraska state line.

Monday...The trough aloft moves into Wyoming. Decent low level
upslope and a moist airmass will lead to scattered to numerous
showers and thunderstorms. Cooler temperatures due to increased
cloud cover and precipitation coverage.

Tuesday...As the trough aloft moves into the Northern Plains
states, northwest flow aloft will develop over our forecast
area, helping to decrease precipitation chances. Warmer
temperatures also expected with a rise in 700 mb temperatures.

Wednesday...Similar conditions to Tuesday with brisk northwest
flow aloft. It looks breezy to windy based on low and mid level
gradients. Temperatures should be a bit warmer than Tuesday
based on 700 mb temperature trends.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1023 PM MDT Wed May 14 2025

Light rain lingers over portions of the Nebraska Panhandle into the
early Thursday morning hours. Conditions at all terminals will be
VFR after 09Z/Thursday as a mid-level low drifts to the northeast
into South Dakota Thursday morning. A broad trough and thermal
trough remain across the region Thursday. A tight pressure gradient
associated with the South Dakota low leads to gusty west to
northwest wind 20-35kts from 15Z/Thursday until 02Z/Friday. Mid-
level cloud decks will be plentiful Thursday afternoon in this flow
regime. Instability will be minimal, but the presence of the colder
air aloft leads to sporadic, light showers. In general, terminals
remain dry through the forecast period. Surface west-northwest wind
diminishes after 02Z/Friday, but 12-22kts speeds should linger
east of the Laramie Range.

&&

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

&&

$$

SHORT TERM...MM
LONG TERM...RUBIN
AVIATION...WFO-RIW