492
FXUS65 KCYS 300859
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
259 AM MDT Sun Jun 30 2024

.KEY MESSAGES...

- A few strong to severe thunderstorms this afternoon and
  evening. Maybe better chances for severe thunderstorms Monday
  afternoon and evening.

- Cooler week ahead before strong ridge and toasty temperatures
  return for the weekend.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 300 AM MDT Sun Jun 30 2024

Frontal boundary lays along a line from northeast New
Mexico...north along the front range to Laramie and eventually
north central Wyoming this morning. Southeasterly low level
winds have raised dewpoints this morning east of this front.
Seeing mid 50 dewpoints in the Panhandle so far this morning
with low 50s here at Cheyenne. West of the front...dewpoints in
the 40s being reported across Carbon County.

Dilemma of the day will be whether severe storms are going to
form or not. Looks like the Panhandle stays pretty capped
through 00Z today. Towards 00Z...low level capping inversion
finally break...with GFS MUCAPE increasing to around 1500 J/KG
over Sidney. NAM MUCAPE more unstable with a narrow band of 2000
J/KG developing near the Wyoming/Nebraska state line. HRRR/RAP
simulated radar showing storms developing over the Laramie Range
around the 19Z to 20Z timeframe...drifting eastward. Certainly
possible for some of these storms to become supercells. Not the
greatest environment...but can`t rule out a few severe storms.
Large hail and strong downburst winds will be the primary
hazards with these storms.

Better day Monday for storms as upper shortwave tracks across
the CWA and front gets forced east. Northern Panhandle seeing
much better instability with MUCAPE near 2500 J/KG Monday
afternoon. Much drier Tuesday as westerly winds return to the
area.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Issued at 111 AM MDT Sun Jun 30 2024

A cooler, active week is in store for southeast Wyoming and western
Nebraska. Upper-level troughing turns upper-level winds
northwesterly for Wednesday. Northwesterly flow will usher in cooler
air in the region, but not without the threat for strong to severe
thunderstorms. Southerly surface flow develops Wednesday, advecting
in additional moisture from the Gulf of Mexico ahead of an incoming
cold front. The GFS and ECMWF are both on board with a strong
dryline developing off the Laramie Range Wednesday afternoon, but
the exact position of this boundary is uncertain. Right now, it
looks to set up along the Wyoming/Nebraska border, bringing the best
storm chances to the Panhandle, with southeast Wyoming missing out
once more. However, a slight westerly shift of this dryline will
drastically change the output, with much of southeast Wyoming
experiencing an increased chance for showers and thunderstorms. At
this time, kept PoPs confined mostly to the Panhandle with low end
values, around 25-40%. This setup will continue to be monitored as
northwest flow tends to produce ample convection to the CWA.

Westerly, upper-level flow returns to the region for Thursday
through the end of the work week. Relatively benign weather is
expected for the latter half of the week, with only slight chances
for precipitation in portions of the Panhandle. The cold front that
passes through Wednesday will drop temperatures back into the 70s
and 80s for Thursday and Friday. Model disagreement returns for the
weekend, with the previously advertised ridge now stuck over the
Pacific Ocean just off the coast of California for the weekend.
Despite this, 700mb temperatures will increase back into the 10-15C
range and surface temperatures return to the 80s and 90s once more.
Little to no precipitation chances exist at this time for Friday and
Saturday, with significant model disagreement in play for Sunday.
Kept temperatures for Sunday near the NBM, as the GFS suggests
700mb temperatures in the single digits, whereas the ECMWF keeps
700mb temperatures around 15-16C.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1101 PM MDT Sat Jun 29 2024

VFR conditions currently across area terminals with a few
lingering showers late this evening. Expecting the southerly LLJ
to increase across the NE panhandle over the next few hours
with winds gusting 30-40 kt. This southerly flow will begin to
increase moisture advection across the area, potentially leading
to low cloud development along the I-80 corridor from KCYS to
KSNY. However, HREF probability of MVFR ceilings is only around
20% at this time starting around 12z Sunday morning.
Thunderstorms are expected Sunday afternoon that could lead to
strong winds and reductions to visibility with heavy rainfall.
Will leave any mention of potential TSRA and timing until the
next TAF issuance.

&&

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

&&

$$

SHORT TERM...GCC
LONG TERM...AM
AVIATION...MB