-- Discussion containing changed information from previous version are highlighted. --
546
FXUS65 KCYS 232317
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
517 PM MDT Mon Sep 23 2024

.KEY MESSAGES...

- Above average temperatures and dry conditions expected
  Wednesday onwards.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 259 PM MDT Mon Sep 23 2024

After a chilly start to the day this morning in some areas, most
have warmed up quite rapidly this afternoon into the 70s to low 80s.
This is due to a very narrow ridge moving over the area, but this is
already beginning to move out and become replaced by the next
trough. A progressive shortwave passing just north of the area is
moving through on the leading edge of an impressive upper level high
over the Pacific Northwest. Mid to high level cloud cover is already
moving into our northern and western counties and will rapidly
increase over the rest of the area over the next several hours. A
surface cold front is also tagging along today, but this will be
fairly weak, just enhancing northerly flow for a few hours and
knocking down boundary layer temperatures slightly. Cloud cover
through the night should also keep temperatures warmer than last
night for most, despite the cold front. We will be hard pressed to
get any precipitation out of this system, with a few sprinkles over
the High Plains at best.

Tuesday looks like a pleasant early autumn day with near average
temperatures and a modest northerly breeze over the plains. Morning
cloud cover should clear through the afternoon. The anomalous ridge
currently positioned just off of the Oregon coastline will move
eastward Tuesday into Wednesday, setting up directly overhead by
Wednesday. As a result, expect a fairly significant warm-up back to
summer-like daytime temperatures beginning on Wednesday. While the
center of the anomalous warmth looks to be more over northeast
Wyoming, our area will still see some fairly impressive values for
this time of year. 700-mb temperatures in the +14 to +16C range by
Wednesday afternoon will exceed the 99th percentile of climatology
for the majority of the forecast area. While less relevant for
surface temperatures, 500-mb temperatures are forecast by the NAEFS
mean to exceed climatological maximums over most of Wyoming,
Nebraska, Montana, and into the Dakotas. Most of the area should
warm back into the 80s on Wednesday afternoon, about 10-15F above
average. The typical warm spot will have a chance to notch another
90F day for the season too. No record highs are currently forecast,
but values will be within a few degrees.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 259 PM MDT Mon Sep 23 2024

Few changes made to the long term as the end of the week and into
the weekend still looks like an extended period of warm and dry
conditions. An upper-level shortwave passing well to the north of
the CWA will lead to zonal flow across much of the area. Westerly
downsloping winds combined with 99th percentile 700 mb temperatures
will lead to quite a hot September day, especially for areas
east of the Laramie Range. Temperatures will be anywhere from 15
to 20 degrees above average with some locations approaching
record high temperatures! Expect temperatures in the mid 80s to
mid 90s east of range, and low 80s for areas to the west. Broad
ridging over most of the country Friday and Saturday will lead
to continued warmth, albeit not as hot as Thursday. During this
time, mostly sunny skies will dominate with basically no chance
of precipitation. Long range models deviate from each other
Sunday and Monday. The GFS sends a strong trough and cold front
into the CWA Sunday night, which will lead to much colder
temperatures and increased precipitation chances. The ECMWF, on
the other hand, keeps an upper-level ridge firmly locked over
western CONUS with no fall temperatures or precipitation in
sight.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
-- Changed Discussion --
Issued at 506 PM MDT Mon Sep 23 2024

A thick band of cirrus clouds will continue to drift south and
east over all terminals this evening. However, ceiling heights
will remain well above MVFR thresholds at all terminals. Expect
clearing skies overnight with afternoon winds dropping overnight
as well at all terminals. Clear skies and VFR at all terminals
on Tuesday with light northwest winds.
-- End Changed Discussion --

&&

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

&&

$$

SHORT TERM...MN
LONG TERM...SF
AVIATION...MAC