372
FXUS65 KCYS 292105
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
305 PM MDT Sat Jun 29 2024

.KEY MESSAGES...

- A few strong to severe thunderstorms Sunday afternoon and
  evening.

- Cooler week ahead before strong ridge and toasty temperatures
  return for the weekend.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 305 PM MDT Sat Jun 29 2024

Current observations across the region show pleasant weather
with temperatures generally in the 70s to low 80s and light
winds. A few showers have developed in the mountains, but have
generally weakened as they pushed east into the I-25 corridor.
Can`t rule out a few thunderstorms this afternoon and this
evening as WAA and the low level jet strengthen. However,
moisture will be limited, so expect coverage to remain isolated
or widely scattered through tonight across southeast Wyoming and
mainly the southern Nebraska Panhandle. Otherwise, expect south
to southeast winds to increase overnight with gusts up to 40 MPH
possible. Not seeing a clear signal for any fog tonight, so will
keep out of the forecast for now.

A more active day on Sunday expected as gulf moisture advects
into the region with upslope south to southeast winds. A quick
look at NAEFS shows PWATs in the 90th to 98th percentile across
most of the area, including Carbon and Albany counties.
Thermodynamic profiles look good with 0-6km shear of 40 to 50
knots and 1000 to 2000 j/kg of CAPE. The only limiting factor is
the lack of any forcing with an upper level ridge axis pushing
over the area and increasing 500mb to 700mb
temperatures...indicating upper level subsidence. There is some
weak jet energy aloft, but forcing appears pretty limited at the
jet stream level. Kept POP between 20 to 35 percent for this
reason, even though a few strong to severe thunderstorms are
possible across eastern Wyoming and western Nebraska. Agree with
SPC`s marginal risk along and east of I-25, so will not word the
forecast too aggressively quite yet.

For early next week, all models are in agreement and show
another Pacific cold front and associated broad upper level
trough digging southeast and then progressing eastward across
the northern Front Range Monday and Monday night. Most of Monday
should be a nice day with highs in the 80s...to around 90 for
areas below 5000 feet. It should start out pretty warm in the
morning due to persistent cloud cover and low temperatures
likely in the mid 50s to mid 60s...possibly as high as 70
degrees across the northern Nebraska Panhandle due to the
persistent low level jet. Winds are forecast to shift into the
west and increasing through the afternoon with gusts as high as
50 MPH possible. Would like to note that a few of our previous
wind events have overperformed lately, so may need a last minute
High Wind Warning for a few locations along and west of the
I-25 corridor. As of right now, in-house wind models have
trended lower on probabilities of wind gusts higher than 55 MPH.
These winds will also bring in some much drier air with a
dryline-like feature develop just east of the Laramie Range and
progressing rapidly eastward into western Nebraska through early
to mid afternoon. This should greatly limit convection across
the area, even with better forcing compared to Sunday. Kept POP
mainly between 20 to 30 percent, with higher probs in the
mountains. The most favorable area to see some strong to severe
thunderstorms (likely outflow winds) will be the southern and
central Nebraska panhandle.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 205 PM MDT Sat Jun 29 2024

We`ll be heading into a fairly messy weather pattern for summer next
week. The overall synoptic weather pattern for much of the week will
be characterized by a very strong ridge located roughly near the
west coast, leaving northwest-ish flow over our area. Frequent
shortwave intrusions are expected over the course of the week that
should help moderate the heat somewhat, at least through the end of
the operational forecast period. There is reasonably good agreement
amongst models that the first in this shortwave series will push
through around Tuesday, but with westerlies pushing the dryline
towards the eastern boundary of the forecast area. With reduced
moisture, we probably won`t be looking at a lot of precipitation
with this aside from the ever present high-based showers and
thunderstorms. The influence of the shortwave will also lead to a
cooler day with highs potentially a few degrees below average for
the time of year. Look for a brief rebound in temperatures on
Wednesday between shortwaves with a period of southwest flow aloft
and warm air advection before the next wave arrives. Models are also
in good agreement on a very sharp dryline developing somewhere
across the area. Most have this fairly close to the WY/NE border.
The dryline combined with a strong surface cold front may lead to
stronger convective forcing Wednesday. Right now this looks like the
day to watch for the week, but this setup will be sensitive to
subtle changes in dryline position, frontal timing, etc., so this
isn`t a sure bet yet. If we have strong thunderstorms develop, the
best area looks to be in the Nebraska panhandle.

After this, there is good confidence in a northwest flow pattern
developing for the Independence day holiday, but ensembles are split
on how strong this trough will be. Both major deterministic models
have a strong trough coming through for Thursday and Friday, leading
to well below normal temperatures, but there is quite a bit of
spread. The 25th to 75th percentile of 700-mb temperatures at 00z
Saturday ranges from 7C to 14C at KCYS. Due to this uncertainty,
decided not to deviate much from the NBM forecast. Temperatures
should return back to normal around Saturday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1140 AM MDT Sat Jun 29 2024

Fairly quiet weather expected today with a modest southerly
breeze at KLAR and KCYS, and a few showers or very weak
thunderstorms developing near Wyoming terminals. Can`t rule out
brief light to moderate rain and some gusty winds, but this
activity will be pretty isolated. A strong low-level jet will
develop tonight, with gusts of 30 to 40 knots possible at most
terminals between this evening and Sunday morning. There is a
slight chance for some low clouds Sunday morning, mainly near
KCYS, KSNY, and KAIA, but the probability is too low to add to
the TAF at this time.

&&

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

&&

$$

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