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229
FXUS65 KCYS 212030
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
230 PM MDT Fri Jun 21 2024

.KEY MESSAGES...

- Widespread showers and thunderstorms expected once again this
  afternoon into the early evening with a few severe
  thunderstorms capable of producing large hail and strong
  winds. Localized flooding is also possible with heavy
  rainfall.

- Warmer and drier trend starting on Saturday, but cannot rule
  out gusty winds with high-based storms in the afternoon near
  the CO/WY border.

- Hot temperatures in the upper 80s to 90s are expected for
  Sunday through much of next week. Elevations below 4500 feet
  will have approximately a 30 to 60% chance of exceeding 100F
  on Monday.

&&

.SHORT TERM /THROUGH SUNDAY/...
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Issued at 230 PM MDT Fri Jun 21 2024

Surface low analyzed over northern Albany County this afternoon
with a warm front extending south to just east of
Laramie...then continuing south into north central Colorado.
Storms are forming along this front so far with an easterly
movement of 25 to 30 mph. Storms right now are in surface based
CAPE around 1000-1500 J/KG...but are heading into higher CAPE of
2000 to 2500 J/KG across Platte and Goshen Counties. Upper
shortwave currently across central Wyoming this afternoon that
we believe will bring a second round of showers and storms mid
to late evening as it moves through the area.

For this afternoon...looking like we will see a few severe
thunderstorms as our current storms move into higher
instability. HRRR/RAP simulated radar shows a line of storms
over the next hour across Platte County moving east into
southern Niobrara/Goshen/northern Laramie Counties by 22Z and
eventually into far western counties of the Panhandle around
23Z/00Z. Would expect strong downburst winds with this line as
it moves east along with marginally severe hail and heavy rain.
Line really weakens as it moves into our extreme eastern row of
Nebraska Panhandle counties by 01Z/02Z.

Upper shortwave begins to move in from the west after 01Z this
evening with another round of storms developing from
Casper...south to Saratoga. This line moves east through the
evening hours...clearing the Panhandle by 06Z. Shortwave drives
the front east into central Nebraska...with west to northwest
winds returning.

Much warmer and drier Saturday with 700mb temperatures climbing
back to +12 to +14C Saturday afternoon. Looking at increasing
700mb temperatures for Sunday with temperatures climbing to +17
to +19C. Highs Saturday in the upper 80s to low 90s and near 90
to 100 Sunday.
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&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 345 AM MDT Fri Jun 21 2024

A potent ridge will build in over the Four Corners states this
weekend and usher in a much warmer and drier weather pattern that
will carry through a good portion of next week. Ensemble median 700-
mb temperatures climb to about +16 to +18C by Sunday and hold there
through Monday. This will support high temperatures reaching the
upper 80s to 90s for the majority of the lower elevations both days.
Monday still has a decent chance (30 to 60%) for 100F or higher
temperatures in certain hotter locations. The highest probabilities
are in the Scottsbluff area, but probabilities of 30 to 40% exist
for the rest of the North Platte River valley and the Chadron area.
With the dryline pushed to the eastern border of the forecast area,
precipitation opportunities will be limited Sunday and Monday.
However, precipitable water values remain at least near average for
this time of year due to decent mid/upper level moisture. Therefore,
expect to see a few radar echoes showing up each day, but
precipitation reaching the ground will be difficult. Of course, we
may need to watch for dry microbursts with this weather pattern.

A shortwave will push over the top of the ridge late Monday into
early Tuesday, compressing the ridge slightly. A weak cold front may
come along with this shortwave. Impacts will be confined to areas
east of the Laramie range, and mainly along and north of the North
Platte River valley. The US-20 corridor could be as much as 10F
cooler on Tuesday compared to Monday, but elsewhere the difference
will be more subtle. Despite the frontal forcing, precipitation
chances will remain limited with a similar story expected to Sunday
and Monday. The ridge re-consolidates over the west by Wednesday
allowing temperatures to warm once again. But, most ensemble members
allow the dryline to slide back westward on Wednesday which will
boost low-level moisture, and possibly allow for slightly higher
thunderstorm chances for Wednesday and Thursday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1154 AM MDT Fri Jun 21 2024

Active weather expected across the area this afternoon and into the
overnight hours. First, low stratus continues across much of the
Nebraska panhandle early this afternoon. Gradual clearing of the low
stratus will likely take place over the next few hours. Storms will
begin to develop this afternoon across southeast Wyoming and
eventually push eastward into Nebraska late this afternoon and
evening. This first round of storms could contain large hail,
damaging wind and heavy rain which could reduce visibility. Another
round of storms is expected later tonight, with lower probabilities
for severe weather, especially across southeast Wyoming terminals.
Low stratus may return to the Nebraska panhandle again overnight.

&&

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

&&

$$

SHORT TERM...GCC
LONG TERM...MN
AVIATION...SF