312
FXUS65 KCYS 112026
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
226 PM MDT Thu Jul 11 2024

.KEY MESSAGES...

- Very hot temperatures are likely across all of southeast
  Wyoming and the western Nebraska Panhandle this weekend
  through early next week. A Heat Advisory has been issued for
  portions of southeast Wyoming Friday afternoon.

- Cooling trend expected next week with increased precipitation
  chances. Another warm up looks possible for the weekend.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 220 PM MDT Thu Jul 11 2024

Already have some radar echoes showing up in southeast Wyoming.
Expect this to expand a bit further eastward throughout the
afternoon with the slight chance of showers and storms expected
east of Interstate 25. As the upper-level high spins around the
Great Basin, a weak upper-level disturbance moving over the CWA
could spark some scattered convection later this afternoon. Not
expecting much in the way of impacts with these storms, but
severe gusts of 60 MPH cannot be ruled out with profound
inverted-v soundings from the dry low-level. DCAPEs are
presumably quite high, up to 1700 J/kg in some locations based
on the GFS! Despite the dryness, the panhandle will be able to
hold on to some modestly high dewpoints this afternoon, so some
rain and perhaps small hail could also be possible in storms.
Storm threat could continue into the overnight hours per Hi-Res
guidance.

Models continue to remain in excellent agreement regarding the
upcoming heatwave expected to impact much of the region. The next
three days will be some of the hottest of the season thus far, with
many locations in the running to break a few records. Over the next
several days, the upper-level high over the Great Basin will
gradually shift eastward, settling over Colorado by Sunday. This
strong 500 mb 598 decameter high will likely lead the hottest
temperatures on Sunday, with a gradual roasty warm up until
then. 700 mb temperatures will range from +18C to +22C over the
next few days, leading to highs ranging from the 90s to areas
west of the Laramie Range to potentially exceeding 105 degrees
in the Nebraska panhandle. Expect the first widespread 100
degree tomorrow. With forecast record highs for parts of Wyoming
Friday afternoon, went ahead and issued a Heat Advisory for
Laramie, Goshen, and Platte Counties. Hottest temperatures are
expected to be within the North Platte River Valley, where highs
could reach 103 degrees. Lower elevations surrounding the North
Platte River Valley will likely also see temperatures in excess
of 100 degrees, hence the need for a Heat Advisory. Expect
slightly cooler temperatures for Laramie County, with highs in
excess of 95 degrees, however, the current forecast high for
Cheyenne ties the current high temperature record for July 12,
hence the need for a Heat Advisory. Expect a likely eastward
progression of Heat Advisories into the Nebraska panhandle on
Saturday, where temperatures could potentially reach 105
degrees.

Aside from the heat, there are daily chances for afternoon storms as
upper-level disturbances move through the ridge. Likely not looking
at anything severe, but with the dry low-levels and strong inverted-
v soundings, cannot rule out a few rouge gusts to 60 MPH.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
Issued at 220 PM MDT Thu Jul 11 2024

The upper-level ridge that has kept the region hot and dry will
slowly begin to breakdown Monday, with zonal flow returning for
Tuesday. Several vorticity maxima will traverse through the
weakening ridge, leading to enhanced upward motion across the
region. Surface and 700mb winds turns southeasterly and bring in
additional moisture from the Gulf of Mexico. A trailing cold front
associated with a low off to the northeast is progged to push across
the region Monday, colliding with the moist, southeasterly flow.
With additional rising motion from the vorticity maxima, showers and
thunderstorms are favored along this frontal boundary. With
precipitable water values well above 1 inch in the Panhandle, any
showers and storms that do develop will likely have significant
precipitation with them. This could be the first wetting rainfall
for much of the region in. Temperatures will still be warm prior to
the cold frontal passage, with highs in the upper-80s to upper-90s
everywhere, but additional cloud cover from increased moisture may
help it feel slightly cooler on Monday.

The passing cold front Monday will drop temperatures into the low-
80s to low-90s across the region on Tuesday. With more zonal flow
developing for Tuesday, a 700mb shortwave trough will traverse
through the flow just to the southeast of the CWA. With
counterclockwise flow, additional moisture from the Gulf of Mexico
will be advecting into the region Tuesday. A strong vorticity maxima
aloft along with a weak cold front will push across the area,
leading to increased rising motion once more. With the additional
moisture from the developing surface low associated with the 700mb
shortwave trough and southeast flow colliding with the weak cold
front, showers and thunderstorms will be favored once again.
Increased moisture into the region will saturate the column and
precipitable water values increase towards the 1.5 inch mark across
the Panhandle. With these high PW values, any showers and
thunderstorms that develop will have significant rainfall with them,
leading to a second day of wetting rainfall across the region.
Additional cloud cover will help keep it cooler throughout the day.

Temperatures on Wednesday will be cooler than previous days behind
the second cold frontal passage and rainfall across the region on
Tuesday. Highs will be in the low- to mid-80s area wide.
Northwesterly flow aloft develops across the region as an upper-
level ridge tries to build across the Desert Southwest. With
northwesterly flow, temperatures will remain cooler with increased
chances for precipitation across the region. With this cooler, drier
flow than previously seen, PW values will decrease across the
Panhandle so any showers and thunderstorms should have less
precipitation with them. A similar story is expected on Friday as
northerly flow develops aloft with a large ridge building across the
western CONUS once more. Temperatures on Friday will be similar to
Thursday, but looks like the weekend may be another warm one across
southeast Wyoming and western Nebraska.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1109 AM MDT Thu Jul 11 2024

VFR conditions expected at all terminals this afternoon and
evening. Primary aviation concern will be gusty showers and
thunderstorms across the region. Showers or storms that develop
may produce 50kt winds or greater as they collapse. Included
VCTS/VCSH for all TAF sites. Gusty winds will return in the
next few hours, with several locations gusting to around 20kts.
Mostly clear to partly cloudy skies expected through the
afternoon and evening.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Heat Advisory from noon to 7 PM MDT Friday for WYZ107-108-118-
     119.
NE...None.

&&

$$

SHORT TERM...SF
LONG TERM...AM
AVIATION...AM