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977
FXUS65 KCYS 121045
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
445 AM MDT Wed Jun 12 2024

.KEY MESSAGES...

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- Hot today. Scattered to numerous high-based showers and a few
  rumbles of thunder in the afternoon and evening, possibly
  associated with 45+ MPH wind gusts.

- Widespread showers and thunderstorms are expected across the
  high plains on Friday. Some storms may be severe, with all
  hazard types possible.
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&&

.SHORT TERM /THROUGH FRIDAY/...
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Issued at 402 AM MDT Wed Jun 12 2024

A very hot day for much of the area w/ 700-mb temperatures of 16
to 18 deg C beneath quasi-zonal flow aloft. Members of both HREF
and NBM spectrums suggest 20+ percent probabilities of exceeding
90 deg F for most areas along and east of I-25, with the highest
probs along the Platte River Valley from Wheatland to Torrington
to Scottsbluff and Bridgeport. A fair amount of mid & high level
moisture will overspread the region today as numerous weak short
waves traverse the flow regime, supporting potential for several
high-based showers and storms through the afternoon/evening. The
main concern w/ this activity should be strong wind gusts, given
the very dry sub-cloud layer w/ LCLs above the 0 C level. Expect
the increase in cloud cover & convective outflow to impact highs
to some degree, but 85-95 deg F should still be easily achieved.

The seasonable warmth persists on Thursday w/ potential for more
robust convective activity focused along a frontal zone which is
progged to be draped from northwest to southeast from central WY
into the southern NE Panhandle. Low-level moisture pooling along
this boundary with dew points near 50 deg F may support a narrow
ribbon of up to 1000 J/kg CAPE immediately along the boundary w/
45+ knots of effective bulk shear parallel the frontal zone from
mid afternoon through early evening. This should support a mixed
storm mode with multicell and embedded supercell structures with
potential for marginally severe hail and wind. Any upward trends
in the instability profiles would significantly increase concern
for organized severe storms.

Friday will be the more likely day for organized severe thunder-
storms as a sharp, negatively tilted short wave lifts rapidly NE
from the 4 Corners into the central Rockies. Significant surface
cyclogenesis over eastern Colorado will give way to robust moist
southeasterly flow supporting 50s to perhaps low to mid 60s dew-
points in far southeast Wyoming, and especially the southern Neb
Panhandle. This coupled w/ steepening mid-level lapse rates will
support strong instability with 2000+ J/kg MLCAPEs. Veering wind
profiles and persistent 35+ knot 500-mb flow will support strong
deep layer shear favorable for supercell storm structures w/ all
hazards possible, including potential for significant hail & the
risk for a few tornadoes.
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&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
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Issued at 402 AM MDT Wed Jun 12 2024

Headed into the weekend, the weather will quiet down as the
shortwave responsible for Friday`s storms pushes eastward into the
Central Plains. Weak ridging behind the shortwave on Saturday will
advect +16C 700 mb temperatures into the CWA, leading to a toasty
afternoon across the area with highs in the mid 80s to low 90s.
Winds will turn more zonal late Saturday afternoon, leading to a
windy afternoon and evening for areas west of the Laramie Range.
Temperatures on Sunday will cool off a few degrees as a broad trough
over the Pacific northwest begins to dive southeast. This will push
slightly cooler 700 mb temperatures into CWA. Overall, conditions
over the weekend look to remain dry.

Could potentially see better precipitation chances for the start of
the work week. Both the GFS and ECMWF have the trough moving across
northern Wyoming Monday night into Tuesday. However, they both have
the better moisture north of the CWA. Could possibly see some light
precipitation develop across the area, but the low and mid-levels
remain fairly dry. There is higher confidence in temperatures
becoming colder as the trough drags a strong cold front along with
it. Frontal passage Monday night could lead to high temperatures in
the 70s on Tuesday.
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&&

.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...CLH
LONG TERM...SF
AVIATION...SF
HYDROLOGY...MB