-- Discussion containing changed information from previous version are highlighted. --
739
FXUS65 KCYS 240338
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
938 PM MDT Sun Jun 23 2024

.KEY MESSAGES...

- Hot temperatures are expected today through the middle of next
  week. Highs exceeding 100F are possible for elevations
  generally below 4500 feet. Heat Advisories have been issued
  for the central Nebraska Panhandle and Goshen County for
  Monday afternoon.

- A few isolated showers/weak thunderstorms may bring gusty
  winds to parts of southeast Wyoming today. Monday looks
  similar, but with slightly greater storm coverage. COuld see
  fire starts from dry lightning on any storms across the CWA.

&&

.UPDATE...
Issued at 622 PM MDT Sun Jun 23 2024

No major updates to the short term forecast as the forecast
remains on track. Did increase hourly temperatures several
degrees as the late afternoon/evening cool off was not
progressing as quickly as forecast. Minimal changes made aside
from that. Looking to be very toasty tomorrow with highs in the
100s across Nebraska and 90s across southeast Wyoming.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 240 PM MDT Sun Jun 23 2024

A 1020mb surface high resides over western Colorado this
afternoon with surface ridging from this high into southeast
Wyoming. The surface trough that was giving us the showers and
thunderstorms now located across southwest South Dakota into
central Nebraska. Temperatures have climbed this afternoon into
the 90s across the CWA...Sidney currently reporting 100 degrees.
Radar showing isolated convection mainly west of the Laramie
Range this afternoon. Starting to see development near Laramie
as well. From the observed 2PM humidity...would think these are
very high based cells...not producing much in the way of rain at
the surface.

Based on latest HRRR/RAP simulated radar...these isolated storms
could continue past 00Z this afternoon. Did paint some isolated
to widely scattered storms from the Laramie Range west through
03Z before ending them for the evening.

Moving into Monday...Still seeing an increase in mid and high
level moisture across southeast Wyoming that would suggest an
increase in coverage of high based thunderstorms. Not a lot of
rainfall from these storms Monday afternoon...with all guidance
only showing a couple hundredths rainfall. Will need to be on
the lookout for fire starts with dry lightning Monday
afternoon/evening.

Going to be a hot day Monday as GFS 700mb temperatures remain
similar to today...around +17 to +19C. Temperature breaking the
century mark in the Panhandle with low to mid 90s in southeast
Wyoming. Getting to record highs in the Panhandle Monday
afternoon at Alliance and Scottsbluff. Decided to issue a Heat
Advisory for the Platte River Valley and adjacent counties for
Monday afternoon for these areas.

For Tuesday...GFS suggesting possibility of a backdoor boundary
moving in from the northeast. Afternoon humidity increasing
slightly north and east of this front as it moves in Tuesday
afternoon.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 240 PM MDT Sun Jun 23 2024

Few changes made to the long term forecast with warm temperatures
still expected throughout much of the week with near daily
precipitation chances. Cooler weather looks possible by the end of
the week.

Warm temperatures continue into mid-week as a ridge of high pressure
persists over the Desert Southwest. This will allow +14C to +18C 700
mb temperatures to hang over the CWA through Thursday. As a result,
temperatures across much of the area will be above average and
roasty. Wednesday and Thursday will see highs across much of the
area in the upper 80s to 90s. Although the region will be under the
influence of a ridge, it is a dirty ridge, with increasing
precipitation chances on Wednesday and Thursday. As the ridge axis
shifts further east, the CWA will be under southwest flow which will
allow the region to tap into a plume of monsoon moisture. GFS
soundings show above normal PWs for most of the CWA on both
Wednesday and Thursday, with WPC already issuing a Marginal Risk for
excessive rainfall for portions of the CWA on both of these days.
NAEFS backs this up by showing PWs in the 90th percentile and
higher. Luckily, model soundings indicate quick cloud layer winds,
so storms will be fast moving, but have the potential to drop
torrential rains with PWs over an inch. Newest GFS soundings do not
look as spicy for severe weather as previous runs, but will still
continue to monitor the threat for severe weather on both of these
days.

By Friday, a trough will dip into the northern Rockies, bringing a
cold front along with it. Temperatures on Friday and Saturday will
cool off to near to slightly below average for late June. Could
potential see some precipitation with the frontal passage, but
overall, looks like a pleasant end to the week.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
-- Changed Discussion --
Issued at 936 PM MDT Sun Jun 23 2024

Westerly flow aloft will continue. Scattered clouds around
10000 feet will prevail, otherwise skies will be clear. Winds
will gust to 25 knots at the Wyoming terminals from 15Z to 00Z.
-- End Changed Discussion --

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Heat Advisory from 1 PM to 6 PM MDT Monday for WYZ108.
NE...Heat Advisory from 1 PM to 6 PM MDT Monday for NEZ003-019>021-
     096.

&&

$$

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