067
FXUS65 KCYS 141032
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
432 AM MDT Sun Jul 14 2024

.KEY MESSAGES...

- Red Flag Warning for the majority of southeast Wyoming and
  portions of the Nebraska Panhandle today. Dry thunderstorms
  will become scattered to numerous, and possible fire starts
  from lightning strikes may occur.

- Very hot temperatures will continue through Monday. Heat
  Advisories remain in effect for the High Plains along and east
  of I-25.

- Increased precipitation chances and cooler temperatures are
  expected late Monday through Wednesday.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 431 AM MDT Sun Jul 14 2024

The warm and very dry conditions persist across our cwa early
this morning. Relative humidity observations after 9Z show most
of the region in 20-40% range, which is very poor for overnight
humidity recovery. Surface observations also show temperatures
remaining elevated with 60s and 70s for most locations. The
only areas that are cooler remain above the nighttime inversion
in the highest elevations of the mountains. Evening showers and
thunderstorms have moved out of the area, but a few lightning
strikes did create a few grass fires in the late evening hours.

The hot and dry conditions will prevail for one more day across
most of the forecast region. The upper level ridge axis will be
centered over the Central Rockies today, resulting in the
warmest day of this prolonged heat event being today. The low
relative humidity and light winds will make it toasty outdoors,
so the heat advisory has been continued. With yesterday`s uptick
in dry thunderstorm activity, have included that in the forecast
for most of the cwa. We will have broad, clockwise flow bringing
a weak impulse of monsoon moisture by this afternoon. The
daytime thermals will help create high-based clouds. Expect the
trend of isolated rain showers and weak thunderstorms to
initially begin between 18Z-21Z, with a scattered to potentially
numerous amount of weak thunderstorms after that period. This
has prompted a Red Flag Warning for most of our fire weather
forecast zones that have flashy fuels listed as ready to burn if
ignition occurs from the dry thunderstorms.

The warm overnight temperatures will be present over the NE
Panhandle, so have continued the heat advisory for that region
through Monday evening. Warm temperatures will still be present
on Monday as our upper level ridge axis propagates to the east
slowly. Daytime highs in the 80s and 90s are forecast, but the
increasing cloud cover should limit the warmest of temperatures
from reaching the century mark. Afternoon showers and
thunderstorms are still anticipated to persist into the late
evening hours as the daily push of monsoon moisture occurs
again. Our first night in a prolonged period of time where
overnight lows remain in the 40s and 50s for most of the cwa
will be Monday night into Tuesday morning. The remainder of
Tuesday will remain warm, with temperatures being another 5-10
degrees cooler thanks to cloud cover and showers/thunderstorms.
This will be another opportunity for wetting rainfall where the
strongest of thunderstorms persist. Stay tuned as the first part
of the week remains active regarding the forecast.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Issued at 431 AM MDT Sun Jul 14 2024

For the extended period, weather across SE WY and E NE will be
dominated by a persistent ridge of high pressure over the western
half of the United States. A broad upper trough centered over
Ontario at the beginning of the period will shift east into Quebec
by Thursday, allowing the western ridge to expand north and east
causing height rises and weakening flow aloft through Saturday.
Abundant mid-upper level mositure will continue to round the ridge
over WY and W NE. At the surface, persistent southerly/southeasterly
flow will keep low-mid-50s dew points in W NE through the weekend.
Confidence in the large scale evolution through Saturday is high
given ensemble and deterministic model agreement. By Sunday, models
begin to diverge on the timing of a trough digging into the
northwest US, which may begin to break down the ridge for the end of
the weekend and start of next week.

For Wednesday, showers and thunderstorms look to be most abundant
for this day given the position of the ridge  allowing for better
flow aloft and embedded disturbances to force development. With PW
values ranging from 0.75" to over 1" over much of E WY and W NE,
above normal for this time of year, storms that develop could
produce heavy rainfall. Flash flooding potential will be enhanced by
relatively slow storm movement. Both Instability (adequate moisture
beneath steep ll and ml LRs) and borderline deep layer shear (still
decent flow aloft) should support a strong-severe storm, especially
further east into NE. Temperatures across the region will be the
coolest of the forecast, with highs ranging from the low to mid 80s
for most. Confidence in the general precip+temp forecast for Wed is
moderate-high, with details regarding exact location of storms and
severe potential low-moderate.

Thursday through Saturday, as the ridge expands and heights rise,
flow aloft will weaken, and temperatures will rebound. Although deep
layer shear and instability will be slightly weaker, abundant
moisture aloft and very deep inverted V profiles will support
showers and storms producing gusty winds, along with a dry lightning
potential, especially further into WY. The strongest thunderstorm
potential will be confined to W NE where ll mositure and shear will
be best. High temps each day are expected to rise into the upper 80s
to low 90s for the lower elevation areas. Confidence in the forecast
during this period is moderate, while that in thunderstorm intensity
is low given cross-model and run-run inconsistencies in the degree
of ll moisture return and extent during this period.

Sunday and beyond, the upper trough digging into the US should
dampen the ridge at some point impacting our sensible weather.
However, timing and impact differences yield low confidence in when
and what that impact will be.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 538 PM MDT Sat Jul 13 2024

A few isolated high-based showers are moving through the area
this evening, and may bring localized gusty winds to terminals
over the next 1-3 hours. Otherwise, good aviation conditions
through the night and Sunday morning, before another round of
showers and possibly a few thunderstorms develops early Sunday
afternoon. This activity may be a little more widespread than
the last few days.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning from 10 AM this morning to 10 PM MDT this
     evening for WYZ417-418-425-428>433.
     Heat Advisory until 10 PM MDT this evening for WYZ101-102-107-
     108-118-119.
NE...Heat Advisory until 8 PM MDT Monday for NEZ002-003-019>021-054-
     055-095-096.
     Red Flag Warning from 10 AM this morning to 10 PM MDT this
     evening for NEZ435>437.

&&

$$

SHORT TERM...BW
LONG TERM...BL
AVIATION...MN