344
FXUS65 KCYS 122344
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
544 PM MDT Fri Jul 12 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, and for all
  areas east of the Laramie Range for this weekend.

- Widespread precipitation possible Monday and Tuesday with a
  brief cooldown Monday through Wednesday. Warmer, drier
  conditions return Thursday onward.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 216 PM MDT Fri Jul 12 2024

Most likely looking at a quiet, but hot afternoon and evening across
the CWA. Hi-Res guidance has trended precipitation chances down from
earlier runs. Lack of any real cumulus field across the plains and
high terrain is also indicative of decreased precipitation chances.
There is a bit of a cumulus field over and south of the Black Hills,
which could lead to a Dawes County clipper later this afternoon and
again later tonight per the HRRR. As usual with such hot and dry
conditions, the main concern with any storms will be strong gusty
winds. Cannot rule out wind gusts over 60 MPH with storms.

Models continue to remain in excellent agreement regarding hot
temperatures over the weekend. The next few 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 day or so, the upper-level
high over the Great Basin will gradually shift eastward, settling
over Colorado by Sunday. Compared to previous runs, both the GFS and
ECMWF have trended 700 mb temperatures down slightly. Ranging from
roughly +16C to +20C, temperatures will of course still be very hot,
with afternoon highs in the 90s to low 100s. Saturday potentially
could be the hottest day of the weekend, as models show the
warmest 700 mb air in place during this time. Less afternoon
cloud cover will also likely lead to warmer temperatures
Saturday afternoon. Heat Advisories remain in place for much of
southeast Wyoming and the Nebraska panhandle through the
weekend.

Aside from the heat, precipitation chances could be possible
Saturday and Sunday. Decreased PoPs Saturday afternoon as the
HRRR was not showing much in the way of convection across the
CWA. Model soundings from the GFS also paint a very dry picture
during the day Saturday. Very profound inverted-v profiles and
lack of any decent mid-level moisture could lead to the
development of high based clouds, but not much else.
Precipitation chances look a bit better later Sunday afternoon.
Increased mid-level moisture will lead to more cloud cover on
Sunday, with models showing increased chances for scattered
convection.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 216 PM MDT Fri Jul 12 2024

The upper-level ridge that has been impacting the region and
bringing in near-record high temperatures will begin to breakdown
starting Monday. An upper-level trough is progged to propagate
eastward along the United States/Canada border, forcing the ridge to
weaken an be pushed back to the west throughout the day. A 594dam
high will remain centered across the Four Corners region, ushering
in Monsoonal moisture around the high and into southeast Wyoming and
western Nebraska. As the ridge weakens and the high is pushed over
the Four Corners region, zonal flow will develop overhead with a
500mb shortwave pushing through. Atmospheric moisture will increase
significantly as upper-level southwesterlies and surface
southeasterlies bring in Monsoonal and Gulf moisture. PW values will
surge to over an inch for western Nebraska and most of southeast
Wyoming. A weak cold front associated with the upper-level trough
will slide across the region and interact with well above average PW
values and southeasterly flow, leading to the development of showers
and thunderstorms. With PW values well over an inch and weak
steering flow, heavy rainfall is possible on Monday with the passage
of the cold front. Some strong storms may be possible as modest
instability will exist across the region. This setup will need to
continued to monitored to assess the threat of severe weather for
Monday. Increased cloud cover is expected as well due to the
additional moisture across the region. High temperatures will be in
the mid-80s to mid-90s area wide.

Slightly cooler temperatures are forecast for Tuesday behind the
passing cold front on Monday. Highs are progged to be in the low-80s
to low-90s area wide. The upper-level ridge will attempt to
redevelop and restrengthen west of the CWA, but the 500mb high
remains in place across the Four Corners region and slightly wobbles
back to the west. The continued presence of the high over this
region will favor Monsoonal moisture being advected into the region
for another day. Similar to Monday, surface southeasterlies will
advect in additional Gulf moisture leading the PW values once again
above an inch for the Nebraska Panhandle and far southeast Wyoming.
A 700mb trough off to the northeast will lead to northwesterly flow
at this level and slightly cooler temperatures as cooler air moves
into the region. With a few passing 500mb vorticity maxima, showers
and thunderstorms are favored for Tuesday once again. Steering flow
will be weak again, leading to the potential for heavy rainfall
across the region for Tuesday. Severe weather may be more favored
for Tuesday as more MLCAPE will be available across the Nebraska
Panhandle. However, forcing across the region will be slightly
weaker as a very week cool front pushes through.

For the remaining long term forecast, the upper-level ridge will
continue to try to build across the western CONUS with primarily
northwesterly flow over the region Wednesday through the weekend.
The ridge is progged to strengthen and move easterly throughout the
latter half of the week. Therefore, a warm up is expected beginning
Thursday and continuing through the weekend. Next weekend does not
look as hot as what is currently ongoing across southeast Wyoming
and western Nebraska, but temperatures will be back into the 80s and
90s everywhere. With the ridge moving back overhead, precipitation
chances will begin to decrease for the latter half of the week. Some
daily chances for a shower or thunderstorm off the higher terrain
exist, but coverage will be much less than what is expected Monday
and Tuesday. Wednesday will be the coolest day of the week with
highs in the upper-70s to mid-80s area wide.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 540 PM MDT Fri Jul 12 2024

West northwest flow aloft will continue. Mostly clear skies will
prevail, with occasional periods of scattered clouds near
10000 feet. Thunderstorms may be in the vicinity of Chadron and
Alliance from 02Z to 06Z. Winds will gust to 25 knots at all
terminals except Scottsbluff until 03Z, and to 23 knots at the
Wyoming terminals after 15Z Saturday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Heat Advisory from 10 AM Saturday to 8 AM MDT Monday for
     WYZ101-102-107-108-118-119.
     Heat Advisory until 7 PM MDT this evening for WYZ107-108-118-
     119.
     Red Flag Warning until 8 PM MDT this evening for WYZ425-
     428>430.
NE...Heat Advisory from 8 AM Saturday to 8 PM MDT Monday for NEZ002-
     003-019>021-054-055-095-096.

&&

$$

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