414
FXUS65 KCYS 191107
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
507 AM MDT Thu Sep 19 2024

.KEY MESSAGES...

- Dry conditions continue through the remainder of the week
  before precipitation chances return over the weekend.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 245 AM MDT Thu Sep 19 2024

Rather quiet in the short term as the storm system, which
brought windy conditions to the region yesterday, slowly moves
northeast into Canada today. The next Pacific storm system,
which will likely impact the Front Range this weekend, will
still be drifting onshore across southern California through
this afternoon. In between these systems, models indicate a
shortwave ridge axis developing over southeast Wyoming and
western Nebraska today and remaining over the area into Friday.
Other than some fire weather concerns, minimal impacts are
expected through Friday night as 700mb temperatures climb
between 10c and 14c. Expect a slow warming trend today and
Friday with highs pushing back into the mid 70s to mid 80s for
southeast Wyoming by Friday afternoon, and mid 80s to low 90s
for western Nebraska. Probability of precip will be near zero,
and around 10 percent Friday night as the Pacific upper level
low begins to track towards the Colorado/Wyoming border.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 214 AM MDT Thu Sep 19 2024

Little changes for the forecast package during the medium range to
extended outlook. Model guidance depicts multiple impulses of cooler
Canadian air advecting toward our cwa from this weekend into early
next week before we gradually begin to see an improvement in daytime
highs. Deterministic model guidance remains for appreciable rainfall
on Saturday and Sunday for the I-80 corridor east of the Laramie
Range to help some areas with drought concerns.

It will feel like fall this weekend as deterministic and ensemble
model data remain in modest agreement for an impactful weather
system to arrive. Lee cyclogenesis is anticipated as a mid-latitude
cyclone/Colorado Low scenario evolves. A longwave trough is
anticipated to have a slower trajectory over the Intermountain West
into the High Plains, as a split-flow weather regime at H5 aloft
occurs. The first measurable snowfall of the season is still modeled
for elevations above 10,000 feet in the Snowy Range Mountains on
Sunday. Temperatures will be chilly, especially on the eastern
foothills and lower elevations of southeast WY. An upslope regime is
anticipated to set up, translating to daytime highs in the lower 50s
to low 60s from cloud cover and rain showers. Looked up the
climatology for the day of 22 September for Cheyenne, and the record
low-high maximum for that day is 40 degrees. It`s doubtful we will
stay that cool, but it will most certainly be a day to have an extra
layer on while outdoors. Depending on that surface low track,
several drought-stricken areas could see beneficial rainfall between
0.5 and 1.0+ inches. Highest confidence for rainfall to persist is
across the I-80 corridor east of the Laramie Range and east of the I-
25 corridor.

The high plains will continue to see below normal temperatures early
next week. The cut-off Upper level low (ULL) will slowly become
absorbed into the mean steering flow again by Monday, with another
weak cool front on its way towards our cwa. The cool air will spill
down the spine of the Colorado Rockies via northwest flow aloft by
Tuesday, keeping the region below normal for daytime highs. By the
middle of next week however, upper level ridging will begin to
amplify over the western CONUS. The upper level ridge will begin its
trek towards the High Plains, and bring another opportunity for
slightly warmer temperatures and dry conditions.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 451 AM MDT Thu Sep 19 2024

VFR is expected for all terminals through the forecast period.
Southerly to southwesterly winds will pick up by late this
morning. Most terminals will see wind gusts of 15-25 knots
through 0z this evening once the wind gusts pick up later this
morning. After 0z wind gusts should transition to less than 10
knots, with east to southeast winds favored for terminals east
of the Laramie Range. VRB winds between 6Z-12Z Friday are likely
for most terminals.

&&

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

&&

$$

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