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453
FXUS65 KCYS 260332
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
932 PM MDT Tue Jun 25 2024

.KEY MESSAGES...

- Critical fire weather conditions continue this afternoon over
  the High Plains, generally south of the North Platte River.

- Moisture will return to the High Plains on Wednesday and
  Thursday, leading to the potential for some strong
  thunderstorms and heavy rainfall in the afternoon and
  evening.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 300 PM MDT Tue Jun 25 2024

Hot, dry, and breezy afternoon across southeast WY and western
NE with GOES WV imagery continuing to show a dry airmass
moving overtop of the southwest CONUS ridge. Much of the I-80
corridor has reached Red Flag criteria with gusty northwest
winds around 25-35 mph. A frontal boundary positioned north of
the North Platte River valley has held on to higher dew points
across the northern NE panhandle, limiting fire weather
potential despite hot temperatures in the upper 90s. At this
hour, Scottsbluff has reached 100F degrees which will likely be
the warm spot for the day.

Isolated high-based showers and thunderstorms have been moving
across the CO/WY border this afternoon and will continue to do
so into early this evening with weak shortwave energy passing
overtop of the ridge. Currently there are a few storms south of
the border near Red Feather Lakes with additional storms
developing out of the Uintas that will need to be monitored
along the CWA border for gusty outflow winds. Headed into
tonight, the frontal boundary will begin to slide south turning
winds more easterly with the return of low-level moisture up
against the Laramie Range.

Turning ahead to Wednesday, expect the return for showers and
thunderstorms across southeast WY and western NE with a
shortwave passing over the ridge centered over the southern
Rockies ahead of an upper level trough approaching the PacNW.
CAMs suggest CI by the early afternoon over the higher terrain,
increasing in coverage through the afternoon with better lift
associated with the shortwave a DPVA approaching from the west.
Additionally, storms will intensify upon crossing the moisture
boundary where 1000-1400 J/kg of MLCAPE sits across
Platte/Goshen Co. Upper level flow will be better across east-
central WY with speed shear, but regardless 0-6 km shear values
will be 45-50 kt leading to strong to severe thunderstorms with
hail and strong winds late in the afternoon into early
Wednesday evening. Favorable lift will likely lead to cold pool
organization and upscale growth as storms move across the NE
panhandle. PW values are also forecast to reach 1.25" leading
to efficient rain producing storms and the potential for
localized flooding. The limiting factor there will be the quick
progression of the eventual system as the shortwave passes
through.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 300 PM MDT Tue Jun 25 2024

The medium range to extended forecast includes near to above
average temperatures and an active weather pattern. Thursday
will be the most active for the medium range portion of the
forecast, with daily chances for afternoon thunderstorms for
parts of our cwa as we look to the end of June and the first
part of July. A weak cool front will pass through the area
Thursday before we gradually begin to warm up through the
weekend.

Thursday will be another hot day as we are under the influence of a
decaying upper level ridge. During peak diurnal heating, we will see
the atmosphere become unstable. PWATs will surge as the GoM moisture
advects northward by late Thursday. Lapse rates will be sufficient
for thunderstorm initiation. Effective bulk wind shear will not
arrive until closer to Thursday evening, however. At this time of
inspection, would expect convection to develop thanks in part of the
elevated mixed layer becoming involved with the higher terrain
across southeast WY. Thunderstorms will potentially cause heavy
downpours for areas that see a strong thunderstorm or two. Highest
confidence for this to occur would be across southeast WY before any
type of discrete thunderstorm begins to become more of a line
segment in the NE Panhandle where the best moisture, lapse rates,
instability and  forcing from the weak cold front is realized most.
Daytime highs in the 80s and 90s are anticipated for locations east
of the Laramie Range, and 70s for regions west of the Laramie Range.

Friday will have cooler temperatures as we are on the periphery of a
passing shortwave disturbance to our north. Daytime highs will be
approximately 5-10 degrees cooler for Friday compared to Thursday.
The decaying upper level ridge across the Central Rockies will allow
for weak instability to become present by Friday evening. A few
showers and isolated rumbles of thunder along the I-80 corridor look
to be favored for Friday evening before dusk. Monsoon moisture off
the Mexican plateau will advect north on Saturday as a broad,
surface high over the southeast U.S. brings additional impulses of
moisture to our area. Thunderstorms will be possible for portions of
our cwa, but coverage will be limited. Daytime highs will be similar
to that of Friday on Saturday.

Sunday will be the next best opportunity for a couple of strong
thunderstorms. Lee side troughing east of the Rockies will combine
with moisture and daytime heating for thunderstorm activity to
increase in coverage by the afternoon. Coverage appears to be larger
for CO, but wouldn`t be surprised for that convection to slowly
propagate north into portions of our cwa. Warmer temperatures make a
return as well by early next week. Daytime highs in the 80s and 90s
east of the Laramie Range will become prevalent. Our forecast area
will become wedged between broad troughing to our north, and the
weak upper level ridging to our south. This quasi-zonal flow aloft
will likely help instigate another round of thunderstorms by early
next week. Stay tuned for further updates on the extended forecast
as we may have the potential for isolated severe weather once
again.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
-- Changed Discussion --
Issued at 927 PM MDT Tue Jun 25 2024

West northwest flow aloft will continue, with increasing low and
mid level moisture and a weather disturbance helping to increase
cloud cover and the coverage of showers and thunderstorms
Wednesday afternoon and evening.

Clear skies will prevail until 15Z, except for occasional fog
reducing visibilities to 4 miles and ceilings to 1500 feet from
09Z to 13Z at Chadron, Alliance and Scottsbluff. After 15Z,
scattered to broken clouds from 5000 to 10000 feet will occur,
with thunderstorms in the vicinity at all terminals except
Rawlins after 00Z. Winds will gust to 25 knots at the Wyoming
terminals after 15Z Wednesday, and to 30 knots at the Nebraska
terminals after 15Z to 21Z Wednesday.
-- End Changed Discussion --

&&

.FIRE WEATHER...
Issued at 300 PM MDT Tue Jun 25 2024

Elevated to critical fire weather conditions continue this afternoon
along and south of the North Platte River valley with gusty west to
northwest winds colocated with RHs in the low teens. Fuels are
currently listed as non-critical west of the Laramie Range, but
have recently switched over farther east and extending into the
southern Nebraska panhandle. Expecting good recoveries east of
the Laramie Range as overnight easterlies behind the frontal
passage will bring back low-level moisture. Temperatures will be
cooler, but still above average for the remainder of the week
into this weekend decreasing fire weather concerns. Afternoon
showers and thunderstorms likely Wednesday and Thursday
afternoon with the chance for wetting rainfall, especially
across the Nebraska panhandle.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
WY...None.
NE...None.
-- End Changed Discussion --

&&

$$

SHORT TERM...MB
LONG TERM...BW
AVIATION...RUBIN
FIRE WEATHER...MB