-- Discussion containing changed information from previous version are highlighted. --
254
FXUS65 KCYS 172325
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
525 PM MDT Mon Jun 17 2024

.KEY MESSAGES...

- A strong capping inversion in place throughout the day will
  lead to fairly benign weather. However, if the cap breaks
  later this evening, severe thunderstorms with large hail and
  gusty winds could be possible.

- Strong winds are still expected late tonight and early
  Tuesday. Wind gusts in excess of 50-55mph are favored in the
  wind prone corridors of southeast Wyoming. Please see the
  latest High Wind Watches/warnings for further details.

- A cold front will bring cooler temperatures for Tuesday and
  Wednesday. A warming trend will develop for Thursday through
  Sunday, along with daily chances for afternoon and evening
  showers and thunderstorms.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 247 PM MDT Mon Jun 17 2024

A stationary front remains entrenched to the west of the Laramie
Range early this afternoon, with gusty winds and very dry conditions
present as well. Surface temperatures have quickly increased for
areas along and west of the Laramie Range, and humidity readings
have bottomed out in the 10-15 percent threshold. Further to the
east, pesky cloud cover has been hard to erode in the northern tier
of the NE Panhandle. Thus, temperatures from west to east go
from warm to mild. As of 20Z, temperatures have struggled to get
out of the middle 60s for the northern Panhandle. Satellite
imagery shows the low clouds eroding however, so would expect
the entire NE Panhandle to clear out in the next hour or two.
All this being said, once we have enough clearing occur, the
atmospheric lid, or cap, will erode after 0Z. A similar timeline
of convective initiation is anticipated after 0Z, with the
southern NE Panhandle likely to see the first onset of towering
Cumulus, before propagating to the northeast quickly. SPC Day 1
Outlook has a Marginal/Slight Risk for severe weather mainly
east of I-25. Would expect a discrete strong thunderstorm or two
to occur this evening between 1Z-5Z before propagating
northeast into SD/central NE.

Overnight, wind gusts will ramp up quickly due to an exceptionally
strong surface pressure gradient between 700-800mb. Upgraded the
High Wind Watch to a Warning headline for most of the forecast zones
that were under a Watch due to increased confidence of wind gusts
overcoming the nocturnal inversion along and just east of the
Laramie Range. Omega fields depicts strong subsidence in these areas,
with a weaker signal for the Arlington/ELk Mountain area overnight.
Have left that as a Watch for now, and will see if it needs another
look by the overnight shift with hi-res data.

A cold front will sweep through the area by Tuesday morning, and
cause well below normal temperatures to extend across the cwa.
Morning lows on the order of 5-15 degrees below normal are
anticipated on Tuesday morning. The cool temperatures will continue
through the remainder of the day under partly to mostly cloudy
conditions. Daytime highs will struggle to eclipse the 70 degree
mark for most locations, as 50s and 60s will be present for most of
southeast WY. Surface high pressure will slide over the region
Tuesday night, bringing the opportunity for chilly surface
temperatures to parts of the forecast area. Cloud cover will be slow
to move out of the area however, so temperatures should remain near
or above 40 degrees for most of the lower terrain through early
Wednesday morning. Breezy conditions will be present for most of the
cwa Tuesday, and subside slowly overnight as well.

Cold air advection will be present on Wednesday as the departing
shortwave and cloud cover slowly propagates eastward. Started the
trend of bringing temperatures down a couple degrees east of the
Laramie Range. Model guidance keeps it downright chilly in the
southern NE Panhandle, with daytime highs potentially sticking
around the middle to upper 50s range. Have gone with the lower 60s
for now, and middle 60s to low 70s for areas further to the north
where more clearing for the day will allow for warmer afternoon
highs. A few showers may creep north from the Central Rockies on
Wednesday afternoon, so have included the mention of sprinkles and
slight chance for rain showers and Thunder into the forecast for
parts of the I-80 corridor. Wednesday will be the coolest day of the
week before we start a gradual warmup trend in the medium range to
extended forecast period.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 247 PM MDT Mon Jun 17 2024

An active pattern is expected to prevail through the remainder
of the week into the weekend. Thursday and Friday still looks to
be the most active timeframe with a couple of shortwaves
rotating through the upper level trof in the western U.S.

At this point, we are looking at Thursday being one of our best
chances of seeing strong to severe storms. The models have been
fairly consistent showing the lee side trof over northern
Colorado causing the low level flow to back more towards the
southeast which will help enhance the shear potential in the
Panhandle and parts of the I-25 corridor. The main question will
be how soon the low clouds will clear out due to the low level
moisture advection and capping between (750-650mb). If we do see
clouds clear out by mid afternoon across the panhandle we could
see the potential for some discrete supercells. These will also
be fairly rapid movers (40-50kts). Friday will most likely be
dependent on how much moisture we can scour out from Thursday`s
convection but the main thing Friday will be lacking is the
shear potential.

The upper level pattern is still progged by the Ensembles/WPC
clusters to become more quasi-linear on Saturday. This regime
will continue to keep the low level moisture in place this
weekend which will tend to keep the chance of afternoon showers
and thunderstorms in the picture. The models/ensembles are
still showing the upper level ridge trying to build over the
area on Sunday, but confidence is still limited based on our
trends over the past couple weeks where these upper level ridges
end up becoming more dampened by the waves moving across the
Canadian Providences.

Overall, temperatures will be on warm side the remainder of the
week with temperatures pushing into the 90s on Sunday.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
-- Changed Discussion --
Issued at 521 PM MDT Mon Jun 17 2024

A strong cold front will move across the terminals tonight,
producing windy conditions along with cooler temperatures.

Wyoming TAFS...Scattered to broken clouds from 7000 to
15000 feet will occur. Winds will gust to 45 knots.

Nebraska TAFS...Scattered to broken clouds from 6000 to
15000 feet will occur, with broken ceilings near 2300 feet
until 01Z at Chadron. Thunderstorms will be in the vicinity at
Chadron and Alliance from 01Z to 05Z. Winds will gust to
35 knots at the terminals.
-- End Changed Discussion --

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from midnight tonight to 9 AM MDT Tuesday
     for WYZ106-116-117.
     High Wind Watch from midnight MDT tonight through Tuesday
     morning for WYZ110.
NE...None.

&&

$$

SHORT TERM...BW
LONG TERM...TJT/REC
AVIATION...RUBIN