017
FXUS65 KCYS 221001
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
401 AM MDT Sat Jun 22 2024

.KEY MESSAGES...

- Warmer and drier trend starting today, but cannot rule out
  gusty winds with high-based storms in the afternoon near the
  CO/WY border.

- Hot temperatures in the upper 80s to 90s are expected for
  Sunday through much of next week. Elevations below about 4500
  feet may exceed 100F.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 400 AM MDT Sat Jun 22 2024

After an active few days of thunderstorms, the area will be entering
a much quieter summer weather pattern for the next several days.
Current satellite imagery in the water vapor channel shows much
drier air working in pretty much to the eastern edge of the forecast
area at this hour. This dry air is positioned right behind the axis
of the upper level shortwave which is now skirting off to the east.
Behind this, mostly clear skies are pushing across the entire
region, aside from some lingering low clouds which are lingering
east of the dryline from roughly Chadron to Sidney. West of there,
surface winds have turned to light westerlies, ushering a gradual
low-level drying trend on top of the rapid drying aloft. As we head
into the day today, the synoptic flow will transition from the
current regime of largely zonal flow to a growing ridge over the
Four Corners states. While very dry air is moving overhead now, this
won`t last long with mid to upper level moisture expected to begin
to recover this afternoon. A more moist region of air is in fact
visible on satellite in western Wyoming, and this will head our way
today. Precipitable water values will end up near to slightly above
climatology this afternoon despite fairly dry low levels a deep
boundary layer mixes out. With some decent moisture remaining aloft,
expect isolated radar echoes to develop in the early afternoon
today. Storm character will be dramatically different from the last
few days though. Precipitation will struggle to reach the ground
because of the deep inverted-v soundings expected to reach nearly
500-mb today, but these showers/storms may produce gusty winds in
excess of 40 to 50 MPH. This activity is expected to go up over the
higher terrain, and probably not make it very far east, but the main
focus of any activity today will be along the WY/CO border. We`ll
also begin a warming trend today as 700-mb temperatures climb to
around +13 to +15C. Expect highs about 5F above average for this
time of year.

The ridge will strengthen further over the southwest and southern
Plains on Sunday, marking the beginning of a fairly prolonged heat
wave across the area. 700-mb temperatures climb to +16 to +18C
across the area with abundant morning sunshine and modest westerly
winds. Expect a rapid warm up peaking at some pretty hot
temperatures in the afternoon and early evening hours. All valleys
will hit at least the upper 80s, but 90s for most, and the
Torrington to Scottsbluff area will have about a 30% chance at
breaking 100F. A few afternoon and evening showers/storms will try
to develop over the higher terrain once again on Sunday, but it
looks similar to Saturday, with precipitation struggling to reach
the ground and instead producing localized gusty winds.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 400 AM MDT Sat Jun 22 2024

Monday will probably be the hottest day of this stretch as the
potent ridge axis shifts directly overhead. Highs a few degrees
higher than Sunday will boost probabilities of 100+F temperatures to
around 80% in Scottsbluff, 60% in Chadron, Torrington, and
Bridgeport, and 40% in Wheatland, Alliance, and Sidney. A weak
shortwave trough will slip over the top of the ridge on Tuesday,
which may bring a surface front far enough south to knock a few
degrees off of Tuesday`s highs. This is most likely north of the
North Platte River Valley. Ensemble median 700-mb temperatures over
KCDR drop to around +12C by 12z Wednesday before rebounding to +16C
by 00z Friday as the ridge rebounds over the Four Corners states. It
will still be hot Tuesday but perhaps 5-10F cooler than Monday in
the US-20 corridor. This front will have fairly little impact on
areas further south and west. Both Monday and Tuesday will carry on
the theme of Saturday and Sunday, e.g. a few isolated showers/storms
with gusty dry microburst winds as the only impact.

The ridge will re-strengthen Wednesday and Thursday over the
southwest CONUS, leading to a second peak in the heat most likely on
Thursday across the area. However, ensemble members are in fairly
good agreement showing low-level moisture recovery east of the
Laramie range for Wednesday and Thursday. As a result, expect a
little bit greater shower and storm coverage these afternoons, and a
better chance for rainfall to actually reach the ground. Forecast
confidence breaks down somewhat for Friday, as models are split on
the potential arrival of a more potent shortwave trough, which could
have the potential to break the streak of hot weather.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 942 PM MDT Fri Jun 21 2024

A weather disturbance will move across the region this evening
producing widely scattered showers and thunderstorms, then drier
air will move in on northwest flow aloft later tonight and
Saturday.

Wyoming TAFS...Scattered clouds from 8000 to 15000 feet will
prevail, with occasional 3 miles in fog and ceilings near
1500 feet at Cheyenne until 10Z, and 2 miles in fog with
ceilings near 1500 feet at Rawlins from 09Z to 15Z. Winds will
gust to 25 knots at all terminals from 15Z to 00Z.

Nebraska TAFS...For Chadron and Alliance, ceilings will be near
3500 feet until 08Z with thunderstorms in the vicinity, then
areas of fog with visibilities near 4 miles and ceilings near
1500 feet will occur from 08Z to 15Z, then skies will be clear.

For Scottsbluff and Sidney, ceilings will be near 3500 feet
until 08Z, with occasional fog and 4 mile visibility at Sidney,
and occasional thunderstorms at Scottsbluff with wind gusts to
35 knots, visibility to 4 miles and ceilings near 2500 feet.
Ceilings will be near 1500 feet with visibilities in fog near
3 miles until 15Z, then skies will be clear.

&&

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

&&

$$

SHORT TERM...MN
LONG TERM...MN
AVIATION...RUBIN