Area Forecast Discussion
Issued by NWS Cheyenne, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

FXUS65 KCYS 291751

Area Forecast Discussion
National Weather Service Cheyenne WY
1151 AM MDT Mon May 29 2023

.SHORT TERM...(Today through Wednesday night)
Issued at 250 AM MDT Mon May 29 2023

Main forecast concerns deal with severe thunderstorms the next few

Currently...Surface analysis shows a cold front extending from a
surface low over northwestern South Dakota...south to
Alliance...then southwest to Denver this morning. Dewpoints in the
40s west of the front this morning...with mid 50s to low 60s east
across central Nebraska and northeast Colorado.

Westerly winds continue today. GFS PWATs fall through the
day...down to .4 inch across Carbon County to .6 inch in the
Panhandle. Today we would expect convection to be much less than
previous days. HRRR and RAP simulated radar only showing widely
scattered to low end chance PoPs across the CWA...mainly east of
the Laramie Range overall. Best location for showers and storms
appears to be Cheyenne east to Sidney along Interstate 80. This is
where we focused the highest PoPs for today.

Best instability will be along that front today with NAM MUCAPE
around 1400 J/KG here at Cheyenne to 1700-1800 J/KG near Sidney if
there are going to be any severe storms today...this is where we
would expect them to occur.

Begin to see a change for Tuesday afternoon as low level southeast
winds return to the Panhandle. PWATs begin to increase once again
with .8 inch returning to the I-25 corridor and over an inch in
the panhandle Tuesday afternoon. Upper low that was in southern
California is forecast to be near the 4 Corners area Wednesday
afternoon. Energy from the low forecast to move northeast into our
western CWA Wednesday afternoon. Best chances for severe storm
appears to be Wednesday afternoon across the Panhandle as GFS
MUCAPE up near 2000J/KG over Sidney.

.LONG TERM...(Thursday through Monday)
Issued at 250 AM MDT Mon May 29 2023

The extended forecast continues to include near-normal, to slightly
above average daytime highs, and an active weather pattern. Upper
level troughs will become stagnant across the western CONUS, with
multiple shortwaves embedded within the H5/H2 upper level flow. At
first glance, it appears that there will be pronounced ridging
aloft, but multiple cut-off upper level lows (ULL) will reside
within the ridge pattern. We will have daily chances of showers and
thunderstorms for portions of our cwa due to continued moisture
advection toward our cwa from the southern Rolling Plains/Gulf of
Mexico. The abundant moisture will provide ample opportunities  for
some heavy downpours from some of the thunderstorms that develop.

Thunderstorms are expected during the afternoon and evening hours
from Thursday to Monday. Moisture advection from the Gulf of Mexico
(GoM)will be transported northward to the central plains each day
courtesy of a weak LLJ. Steering flow aloft will not transport
thunderstorms that develop quickly, allowing for potential heavy
downpours. This pattern could assist with improving drought
conditions across the cwa, which would be welcomed. Steep lapse
rates, daytime instability, and weak steering flow will combine for
a renewed chance of diurnal convection. Multiple lobes of vorticity
maximums will likely propagate across the cwa from southwest to
northeast as the shortwaves propagate downstream. The potential for
strong thunderstorms is possible daily due to model soundings
showing appreciable MUCAPE numbers daily. Shear is not all that
impressive, but enough atmospheric dynamics would be sufficient to
bring the QPF from rainfall to much appreciated values. GFS and the
EC have a deterministic output of between 0.5 to 2+ inches of QPF
locally from early Thursday through the beginning of next Monday
morning, especially east of I-25.

The favorable trend for multiple chances of diurnal and evening
convection may make the public weary, but it will certainly help
with the late spring green up. Per inspection of climate data, it
will be the entirety of May without a hard freeze, and that has
happened only a handful of times for some of our locations across
the cwa over the course of several decades. We will continue to
monitor the trends to keep everyone updated regarding the daily
chances of thunderstorms through the extended forecast period. One
highlight to keep in mind is that temperatures should be mild for
the extended forecast, so that is a plus despite the active weather
pattern remaining across the region.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1142 AM MDT Mon May 29 2023

VFR conditions currently across area terminals with Cu beginning
to develop per latest GOES imagery. Main aviation hazard this
afternoon and early evening will be scattered thunderstorms,
especially around KLAR, KCYS, KSNY, and KBFF. MVFR conditions
could be possible with any storms moving directly over terminal
sites, but mostly left VCTS in the TAFs at this issuance. KLAR and
KCYS should see VCTS developing in the next hour or two. Hi-res
guidance shows the greatest coverage along the I-80 corridor in
the NE Panhandle after 21z. Can`t rule out a brief period of IFR
conditions for KSNY with visibility reductions in heavy rainfall
similar to yesterday afternoon`s thunderstorms. Thunderstorms
should mostly clear out of the area by 02z with a few lingering
showers through 04z.


Issued at 250 AM MDT Mon May 29 2023

Cold front lays across the Nebraska Panhandle...with a high
pressure center over southwest Carbon County. Fire weather
concerns low this week as we stay in a wet pattern. There may be
some low humidity out around Carbon County Tuesday and
Wednesday...but winds are forecast to be light. Wetter pattern
returns Wednesday as a low pressure system moves into the area
from the southwest. Good chances for wetting rains across the
entire forecast area...keeping fire weather conditions in check.




FIRE WEATHER...GCC is the U.S. government's official web portal to all federal, state and local government web resources and services.