156
FXUS65 KCYS 130959
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
359 AM MDT Thu Jun 13 2024

.KEY MESSAGES...

- Seasonable warmth persists today. Scattered to numerous
  showers and thunderstorms are expected this afternoon into the
  early evening hours, especially south. While the overall
  severe threat appears low, a couple of stronger storms cannot
  be ruled out.

- Strong to severe thunderstorms are possible across the high
  plains of southeast Wyoming and the western Nebraska Panhandle
  on Friday. Torrential rainfall and the potential for flash
  flooding will be the primary concern. However, large hail and
  damaging winds will be possible early in the afternoon prior
  to storm mergers.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 303 AM MDT Thu Jun 13 2024

It will be quite warm across much of the area again today w/ not
much of a change in the overall synoptic pattern. However, would
expect daytime highs to be a few degrees cooler given the 700-mb
temperatures falling to +10 to +15 deg C across southeast WY and
the western NE Panhandle. Shower and thunderstorm chances should
increase by early-to-mid afternoon along a weak frontal boundary
draped from from NW-SE across the CWA. There is still a good bit
of uncertainty with regard to storm intensity today. Despite the
decent shear profiles courtesy of pronounced veering and 500-hpa
flow over 40 knots, thermal profiles seem modest at best w/ only
around 500-750 J/kg CAPEs expected. The overall severe threat is
expected to be fairly low as a result, but still expect to see a
few SPS products and/or a marginal warning or two.

Friday still appears to have more potential for organized severe
storms as the sharp mid-level short wave ejects to the north and
east from the Four Corners into the central High Plains. Surface
cyclogenesis over eastern Colorado will support a continuous low
level moisture fetch with dew points climbing into the upper 50s
and lower 60s, which combined with steep low and mid-level lapse
rates may support CAPEs in excess of 2000 J/kg. However, one big
limitation for our CWA could be the robust WAA at 700 millibars,
which could lead to substantial capping and weaker updrafts. The
potential for torrential rainfall (and localized flash flooding)
will exist regardless with widespread PWATs over one inch. Seems
the overall better environment for hail and/or strong winds will
be focused over northeast Colorado, but we will see how the next
few high-res model cycles trend.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 303 AM MDT Thu Jun 13 2024

The long term forecast will start off with relatively tranquil
weather through the weekend with increasing chances of showers and
thunderstorms early next week. Throughout the period, general
southwesterly flow will be in place aloft, with stronger flow to the
north and much weaker flow to the south. The outcome of
Friday/Friday night`s convection will likely have a large impact on
the forecast for Saturday, as a larger, more robust MCS/thunderstorm
complex will likely clear a large majority of the surface moisture
in place well to the east of southeast Wyoming/NE Panhandle. Global
models likely do not yet have a handle on these impacts, however
generally speaking surface moisture is currently progged to be much
lower on Saturday afternoon. Still, with a bit of faster southwest
flow aloft impinging on the CWA from the north, a few isolated high-
based showers will be possible in the Laramie Range and through east-
central Wyoming. A surface frontal boundary evident in both the GFS
and ECMWF will dive southward on Sunday morning, squeezing surface
moisture into a narrow band somewhere over the Nebraska Panhandle
and perhaps as far west as southeast Wyoming. Typically, these post-
frontal moisture-squeeze setups can produce severe weather in the
high plains. However, we will once again be struggling to find much
in the way of favorable wind shear as the bulk of faster flow aloft
will remain to the north and west. Isolated multicell and outflow-
dominant clusters will likely be the favored storm mode wherever the
moisture corridor sets up given strong surface heating, inverted V
soundings, and warm air in the mid-layers of soundings.

By Monday and Tuesday, precipitation and thunderstorm chances look a
bit more interesting across the CWA as a more robust trough attempts
to swing through the northern Rockies embedded in the broad
southwesterly flow regime. This system has seen quite a bit of
spatiotemporal variability in the past few days of guidance cycles.
As of early this morning, the main trough axis appears to be just a
bit too far west to result in a more widespread thunderstorm threat
on Monday afternoon. Still, moisture return in south southeasterly
flow across the high plains is noted. Additionally on Monday
afternoon into Tuesday, southwest surface flow west of the Laramie
Range will also increase dramatically. Will have to watch the Monday
evening and especially Tuesday timeframe for possible high winds
over south-central Wyoming as this system approaches. As far as the
thunderstorm threat goes, Tuesday looks a bit more favorable given
the closer proximity of faster flow aloft associated with this
trough. However, model guidance has shifted northward with the
position of the center of the low, keeping cooler temperatures aloft
and better wind shear/thermodynamic profiles farther north into
northeast Wyoming and the northern Plains states. Again, with a
plentiful reserve of surface moisture just off to the east and a
potent trough in the vicinity, we will have to keep a close eye on
this system over the next few days. Any shift farther south with the
main low pressure system would certainly result in a more
significant severe weather threat for eastern Wyoming and western
Nebraska. Overall, temperatures will run above normal this weekend,
and gradually cool off early next week. Forecast confidence is high
in the temperature forecast, but only moderate with the
precipitation forecast given the variable nature of model guidance
from Monday onward.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 303 AM MDT Thu Jun 13 2024

VFR conditions will dominate at all terminals today. Expect light
east-northeasterly flow east of I-25 today with light westerly flow
at RWL and LAR. A few isolated showers may affect CYS and BFF after
5pm ending before 8pm. Low-level upslope flow develops on Thursday
night into Friday morning which may result in lowered CIGs at SNY,
AIA, and possibly BFF.

&&

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

&&

$$

SHORT TERM...CLH
LONG TERM...MAC
AVIATION...MAC