398
FXUS65 KCYS 090001
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
601 PM MDT Sat Jun 8 2024

.KEY MESSAGES...

- Scattered to numerous showers and thunderstorms are expected
  over the next 24 to 36 hours.

- Monday and Tuesday will see the greatest coverage of late day
  showers and thunderstorms, while Wednesday and Thursday will
  be warmer with a general decrease in shower and thunderstorm
  coverage. Showers and thunderstorms look to return again for
  Friday.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 340 PM MDT Sat Jun 8 2024

Will keep short term discussion brief due to ongoing severe
weather threat this afternoon.

High resolution models performed pretty well today with severe
weather reported in Laramie County, with even some flooding
reported east of Cheyenne along with 2 inch diameter hail
earlier this afternoon. Current KCYS radar loop shows most of
this activity is further south into Colorado with another area
of weaker thunderstorms around the southern Nebraska Panhandle.
Another line of thunderstorms has developed across northern
Carbon County and is currently moving southeast across region
slowly. We`re not totally confident that the severe weather is
over, so will keep the Severe Thunderstorm Watch going for
Laramie, Kimball, and Cheyenne counties for now. However,
believe the most organized convection is coming to a close over
the next hour or two as these lines of storms move into less
favorable thermodynamic environments. As we head into tonight,
expect these thunderstorms to slowly become more isolated...but
activity could linger through midnight along and east of
Interstate 25 due to moist upslope flow and some elevated CAPE
still present in the upper part of the boundary layer.
Otherwise, expect showers and thunderstorms to come to an end
tonight with low stratus and some patchy fog becoming the main
concern overnight towards early Sunday morning. Added fog to the
forecast for portions of far eastern Wyoming and western
Nebraska.

Considerable uncertainty exists for the thunderstorm forecast
for Sunday as shortwave upper level ridge axis develops and
translates eastward over the region by Sunday afternoon. High
resolution guidance and the NAM showing hardly any thunderstorm
activity for most of southeast Wyoming and western Nebraska.
Believe this is partly due to lingering low clouds across the
eastern plains and enhanced subsidence aloft associated with the
ridge axis...even though CAPE values will likely range from 800
to 1500 j/kg. Synoptic models are a little more bullish with
thunderstorm activity compared to high res modeling. Lowered POP
a bit, but kept them between 20 to 40 percent for now. If
current model trends continue, may need to lower POP/prob of
thunder even more for Sunday. High temperatures today were a few
degrees higher compared to previous forecasts, so increase high
temperatures a few degrees on Sunday with a little more sunshine
expected. Overnight lows should be near average for this time of
the year and generally in the upper 40s to upper 50s.
Thunderstorm forecast looks a little more promising on Monday as
another weak upper level disturbance moves east across the area.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 356 PM MDT Sat Jun 8 2024

The unsettled weather pattern will come to an end on Tuesday as the
ridge re-strengthens across the southwest CONUS. Drier air and
modest subsidence will also work its way into the area as another
warming trend begins. For Tuesday, look for temperatures just about
5F warmer than average with more sunshine than the preceding days.
The ridge strengthens further on Wednesday, drawing 700-mb
temperatures up to around +17C on the ensemble median over KCYS.
Wednesday`s highs look to be about 10+F warmer than Tuesday`s,
climbing into the upper 80s to 90s for much of the area along and
east of I-25. Records don`t look very likely, but several locations
will be within 5 degrees or so of daily record highs. Significantly
drier air in the mid-levels will lead to limited convective chances,
mainly to isolated showers/storms focused on the higher terrain.

There is a little more uncertainty on Thursday. A weak shortwave
riding over the top of the ridge may be able to get a cold front
into our High Plains counties and knock down temperatures a touch.
Other ensemble members keep this further north, which would result
in a continuation or possible intensification of the hot
temperatures. If the front manages to get further south, this would
also allow for a little bit more afternoon convection with an
increase in low-level moisture. The ridge axis shifts just east of
our area by Friday. However, guidance is in pretty good agreement on
the closed low that will be stuck off of the California coast all
week finally getting picked up by the flow aloft. A fairly vigorous
closed low will then move across the Four Corners states and into
our area on Friday into Saturday. This will result in increased
chances for precipitation and slightly cooler temperatures by Friday
and Saturday. Details on rainfall and severe weather potential, if
any, remain uncertain.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 542 PM MDT Sat Jun 8 2024

The main concern with this TAF issuance is the thunderstorm
potential this evening followed by the dense fog potential
overnight especially in KCYS and perhaps Sidney.

Latest radar loop was showing scattered showers and
thunderstorms continuing to develop west of the I-25 corridor.
This cluster of showers and thunderstorms may impact KLAR and
KCYS during the next couple of hours. For now, we have kept VCTS
in both TAF sites and monitor before amending these TAF sites.
The next concern is the low ceiling/fog potential later tonight.
Rich dewpoints (50s) have stayed in place through much of the
afternoon across KCYS, KBFF, KAIA and KSNY this afternoon. This
combined with moist advection of south-southeast flow this
evening and overnight will aid in low IFR/MVFR ceiling
development tonight across many of these TAF sites. The best fog
potential appears to be near KCYS where upslope flow will be in
place late tonight. The HREF even keeps these low ceiling over
the Cheyenne ridge most of the day tomorrow. The remainder of
the TAF sites should see clearing skies by midday.



&&

.HYDROLOGY...
Issued at 254 PM MDT Sat Jun 7 2024

Above normal temperatures have resulted in accelerated mountain
snowmelt across the Rocky Mountains. Temperatures in the Snowy
and Sierra Madre Ranges are expected to remain elevated this
weekend. Flood warnings for snowmelt continue for the Little
Laramie River west of Laramie, and the Encampment River south of
Saratoga, mainly due to minor flooding concerns. Emergency
Managers have reported some flooding in these areas over the
last 48 hours. Flood Watches continue for the upper North
Platte River valley and Medicine Bow River near Elk Mountain for
potential impacts this weekend. Current forecasts suggests
river levels will peak later this weekend and remain elevated
into early next wee. Will continue to monitor the potential for
locally heavy rainfall due to thunderstorms in and around the
mountains this weekend. However, the last round of thunderstorms
generally produced less than a quarter inch of rain Saturday
afternoon.

&&

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

&&

$$

SHORT TERM...TJT
LONG TERM...RUBIN
AVIATION...REC
HYDROLOGY...WFOCYS