289
FXUS65 KCYS 092333
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
533 PM MDT Sun Jun 9 2024

.KEY MESSAGES...

- There is a risk for a couple of strong thunderstorms in the
  vicinity of the Laramie Range this afternoon and evening.

- A more widespread threat for showers and thunderstorms will
  occur with a cold frontal passage on Monday afternoon and
  evening. A few storms may be severe.

- Mainly dry and rather warm conditions will prevail for Tuesday
  through Thursday, with increasing chances for showers and
  thunderstorms for Friday and Saturday, along with slightly
  cooler temperatures.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 400 PM MDT Sun Jun 9 2024

It`s a much quieter afternoon than yesterday, but not quite a blue
sky day. Moist southeasterly flow over the High Plains was able to
maintain a stratus deck into the early afternoon hours, which is
finally almost fully broken up at this time. Even though sunshine is
breaking through now, much of the areas east of I-25 is pretty
strongly capped. This is leading to lower overall storm coverage
compared to yesterday. However, an axis of uncapped and fairly
potent instability is still present along the Laramie range,
primarily in Albany and Converse counties. Low level southeast winds
have been able to pull deeper moisture up into the Laramie Valley,
holding the dryline in the western part of Albany county. This is
the primary zone of concern for strong thunderstorms today, and we
are indeed already seeing the best updrafts here. Storm motion
vectors are expected to be pretty slow, so some locally heavy
rainfall will be possible through the afternoon and early evening
hours today. Storms could also briefly produce large hail and/or
gusty winds. Any storms will probably struggle once they get east of
the Laramie range/I-25 as they run into the more capped environment.
A few additional showers and storms will remain possible through the
night, mainly north of US20. Continued moist southerly flow will
lead to some areas of patchy fog once again, but this time more
limited to the I-80 summit and I-80 corridor across Laramie county.

A more active weather day is expected for Monday as an upper level
shortwave approaches from the west. A rapid but brief period of warm
air advection will occur across the area tonight into Monday morning
ahead of this wave. Expect highs warmer than today especially east
of the Laramie range with a decent chance at 90F between Wheatland
and Scottsbluff. Expect storms to initially fire off the dryline in
Laramie/Goshen/Platte counties, but then get carried eastward more
rapidly once a potent surface cold front arrives later in the
afternoon. Forecast soundings show steeper lapse rates possibly
exceeding 8C/km and CAPE in the 1000-2000 J/kg range. The flow aloft
doesn`t look overly strong, but veering profiles atop southerly
surface flow will provide sufficient shear to get a few strong to
severe storms. HiRes models show fairly rapid upscale growth into a
more linear system by the time the convection reaches the eastern
side of the forecast area. Storms will be more progressive, but will
still include locally heavy rainfall. While the main line of storms
is expected to reach the eastern edge of the area around 5-7PM, we
will need to watch for some post-frontal convection developing later
in the evening hours as the front will actually increase low-level
moisture. Lastly, a trailing vort-max may keep the chance for
thunderstorms around through the night in zones north of roughly
US20.

Drier air works into the middle atmosphere on Tuesday, leading to
reduced precipitation chances. Storms should be confined to the
higher terrain and adjacent areas, and will be much more isolated
than preceding days. Expect temperatures some 5-10F above normal as
the ridge re-strengthens over the southwest CONUS. &&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Issued at 400 PM MDT Sun Jun 9 2024

Models in reasonable late this week and into next weekend. Hot
temperatures expected on Wednesday with all models showing a
flat upper level ridge over the Front Range and 700mb temperatures
of 15c to 18c across southeast Wyoming and western Nebraska
under westerly flow. With mostly sunny/partly cloudy skies,
expect high temperatures to peak in the mid 80s west of I-25,
and range from 90 to 95 degrees along and east of I-25 including
the western Nebraska Panhandle. May see a few late afternoon
showers or thunderstorms, but hardly any of this rain is
forecast to reach the ground, so kept POP below 15 percent for
most areas.

For later in the week, models show a backdoor shallow cool front
moving into the high plains for Thursday as the upper level
ridge axis amplifies northward west of the continental divide.
Not as warm on Thursday, but highs in the 80s to low 90s are
still expected. Very little moisture to work with on Thursday,
even as the shallow cool front moves south across the area, so
kept POP between 10 to 15 percent with a slight chance of
showers and thunderstorms in and near the mountains. Our next
forecast concern will be Friday and Friday night as models are
in good agreement on the movement and placement of a central
Pacific upper level low tracking northeast across southern
California and into Arizona and Utah. Will have to watch this
system since NAEFS is already showing 90th to 95th percentile
precipitable water values and low level east to southeast winds.
Deterministic models and ensembles showing a good chance for
some widspread moderate to heavy rainfall due to scattered to
numerous thunderstorms, mainly east of the Laramie Range. It`s
unclear what the severe potential is 6 days from now, but the
overall pattern is favorable for strong to severe thunderstorms.
Temperatures will trend cooler as we head into Friday and
Saturday, but still remain near seasonal averages.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 529 PM MDT Sun Jun 9 2024

Occasional fluctuations to MVFR/low-end VFR is expected for
KCYS this evening as southerly flow brings additional moisture
to the region. KCYS will trend towards IFR/LIFR between 9Z to
13Z Monday morning. After that, expect VFR until we see an
increase in VCSH and VCTS during the Monday afternoon timeframe.
All other terminals are anticipated to remain at VFR through
the forecast period. Wind gusts on Monday will ramp up 20-35
knots at times. Please see individual TAFs for further
information.

&&

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

&&

$$

SHORT TERM...MN
LONG TERM...TJT
AVIATION...BW