626
FXUS65 KCYS 290819
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
219 AM MDT Sat Jun 29 2024

.KEY MESSAGES...

- Possible severe thunderstorms Sunday afternoon and evening.

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

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 220 AM MDT Sat Jun 29 2024

Surface cold front currently lays across northern Colorado this
morning. A 1029mb surface high located over central Montana
behind this front. Radar echo free and satellite showing mostly
clear skies over the CWA.

A pretty nice day expected across southeast Wyoming and Nebraska
Panhandle today. Single digit 700mb temperatures across the
Panhandle to +16C over Carbon County to the west. Afternoon
temperatures in the upper 70s to near 80 for our eastern
forecast zones...while Carbon County will be the warm spot with
mid 80s expected. May see a few showers/storms over our western
mountains this afternoon as advertised in HRRR/RAP simulated
radar.  Most other locations expected to be dry.

Begin to see southeasterly winds returning to the Panhandle
this afternoon with increasing low level moisture late tonight
into Sunday morning. GFS advertising 850mb humidity near 90
percent in the Panhandle by 12Z Sunday. May be dealing with low
clouds Sunday persisting across the Panhandle. Looking at mid
50s to near 60 dewpoints by Sunday afternoon. Upper levels
showing a shortwave moving through overhead Sunday afternoon.
This will be our next best chance for thunderstorms...depending
on low cloud dissipation. SPC has a Marginal Risk area
identified for the Panhandle and southeast Wyoming east of the
Laramie Range.

Low level moisture stays in the area east of the Laramie Range
Sunday night into Monday. So another night of low clouds and fog
is possible. Upper shortwave moves through Monday morning that
looks to force the low level moisture east into central Nebraska
through the late morning hours.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Issued at 220 AM MDT Sat Jun 29 2024

Long range models remain in good agreement on the overall weather
pattern expected this coming week, with better agreement seen for
later in the work week. Upper-level troughing is expected to
dominate the region Tuesday and Wednesday as two troughs pass
overhead bringing northwest flow to the region. Northwest flow is a
favorable regime for southeast Wyoming and western Nebraska in July,
so attention turns to the potential severe threat posed by this flow
pattern. Moisture looks to be the main limiting factor for Tuesday,
as surface dewpoints struggle to increase with limited southerly
flow Tuesday and dry, westerly flow Wednesday. Forecast soundings
are not overly impressive with average PW values, very dry
atmospheric moisture profiles, and weak CAPE for Tuesday. Wednesday
looks to be much better, with MLCAPE values above 1500 J/kg in the
Panhandle, PW values approaching 1 inch, and decent shear across the
region. While this is still several days out, Wednesday will be a
day to watch for the potential of severe weather with northwesterly
flow aloft.

Cool, northwesterly flow will continue for Independence Day, with
seasonable temperatures expected across the region. Friday looks to
be the transition day as the upper-level trough continues its
eastward progression and an strong, upper-level ridge builds over
the western CONUS. This ridge will mostly end the best chances for
precipitation as strong subsidence moves over head. 700mb
temperatures will increase into the 15-17C range, per the GFS. The
ECMWF is a little slower with ejecting out the upper-level trough,
leading to the warmest 700mb temperatures lagging behind the GFS by
a day or so. Both models suggest a strong ridge remaining overhead
for most the weekend into the following week at this time. Expecting
temperatures to return to the roasty level by the weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 220 AM MDT Sat Jun 29 2024

VFR conditions for all southeast Wyoming and Nebraska Panhandle
airports today. Expect a few thunderstorms today mainly over
the mountains. Two main airports impacted by these
showers/storms will be KCYS and KLAR. Southeast winds return to
the Panhandle and southeast Wyoming plains late tonight which
could also increase chances for low level moisture. For now...it
looks like low clouds do not develop in the Panhandle until
after 12Z Sunday.

&&

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

&&

$$

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