640
FXUS65 KCYS 032158
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
358 PM MDT Mon Jun 3 2024

.KEY MESSAGES...

- Scattered to numerous high-based showers and a few
  thunderstorms may produce gusty winds near 50 MPH through
  sunset this evening. A few showers will likely linger into the
  night.

- A widespread, prolonged episode of strong winds with gusts up
  to 65 MPH is expected from this evening through Wednesday
  afternoon. High Wind Watches and Warnings have been issued.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 314 PM MDT Mon Jun 3 2024

Scattered to numerous high-based rain showers & perhaps a couple
of thunderstorms are expected across southeast Wyo & the western
Neb Panhandle through the evening and overnight as a strong mid/
upper-level short wave traverses the flow. Severe weather is not
expected given very limited instability. However, large inverted
V profiles w/ LCLs above the freezing level suggest a risk for a
few stronger downdrafts capable of gusty winds w/ any convective
activity through sunset as suggested by an experimental research
sounding from CSU/Fort Collins earlier this afternoon.

Non-convective high winds will be the primary concern during the
next 24 to 48 hours, in response to rapidly increasing low-level
height gradients associated w/ intense pressure falls downstream
of the aforementioned trough across the western Dakotas, as well
as the RFQ of a 120+ knot H25 jet supporting strong subsidence &
potential downward momentum transfer. Confidence remains low for
the overall intensity of the supporting flow aloft, with the GFS
showing considerably stronger 700-800 hpa winds than the NAM/ECM
although the GFS usually reflects a more realistic response with
low-level flow in these synoptic regimes. As such, expect to see
a broad swath of 50-60+ knot H7 to H8 flow spreading across much
of southeast Wyoming in two distinct waves from late tonight and
early Tuesday, then again from late Tue night through Wed. 700 &
850 CAG-CPR gradients are progged to climb to 65-75 meters which
should be very favorable for Arlington/Elk Mountain, starting as
early as this evening and persisting through Wednesday. In-house
Random Forest model guidance suggests 60+% probabilities of high
wind exceedance at ARL for much of this period, and suggests the
potential for high winds spreading outside of the wind corridors
as well at various intervals through Wednesday. Given the robust
subsidence and very steep lapse rates noted on forecast sounding
data, as well as MAV/MET guidance for CYS/LAR/RWL all showing 28
to 32 knot sustained winds, confidence was sufficiently high for
High Wind Warning issuance for several zones. Most zones will be
valid until 00z Thursday, except for eastern Platte county which
will expire at 18z Tuesday as the initial cold fropa should help
shut winds down for that area by Tuesday afternoon after a brief
threat for mountain waves overnight into early Tuesday. Did also
add a High Wind Watch for Cheyenne as GFS and NAM soundings both
show a significant mountain top inversion favorable for mountain
wave development during the early morning hours on Tues/Wed with
deep mixing each afternoon.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 314 PM MDT Mon Jun 3 2024

The medium range to extended forecast includes much above average
temperatures, making it officially feel like summer for this first
week of June. The medium range will remain dry as an upper level
ridge amplifies through the end of the week. While we will be under
the effects of this pronounced upper level ridge, there will be
shortwave disturbances embedded within the flow to give the region
an opportunity for rain showers and thunderstorms during the
afternoons of Friday through Monday.

Thursday and Friday will be the warmest days of the extended
forecast, with afternoon high temperatures being in the 80s and 90s
for the lower terrain and high plains. The mountain elevations will
remain pleasant as daytime highs in the 60s are expected. Northwest
flow will dominate the region due to the upper level ridge axis
being firmly entrenched across the Great Basin area. Diurnal
thunderstorms are expected to pop up by Friday afternoon, with some
of them being potentially on the stronger side.

The weekend into early next week will see a weak cold front pass
through the area, but daytime highs are still expected to remain
near average to slightly above average. Afternoon highs in the 70s
and 80s for the lower terrain are favored. SLightly cooler
temperatures for the mountain zones. Model guidance has the upper
level ridge become flattened temporarily, resulting in quasi-zonal
flow aloft becoming realized due to a shortwave trough further
upstream of our cwa. Strong to potentially even severe thunderstorms
may be favored on Sunday and Monday afternoon and evening of next
week if model guidance remains consistent in the coming days.
Overall, expect a dry and warm weather pattern to start off the
extended forecast transitioning to a more active weather pattern by
the weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1125 AM MDT Mon Jun 3 2024

VFR for all terminals expected in the forecast period. A weak
weather disturbance will move across the area later this
afternoon, bringing a chance of VCSH and VCTS to the area for a
couple of terminals. The main concern will be gusty winds this
afternoon and overnight. Wind gusts of 20-35 knots can be
expected this afternoon and evening for most terminals. KRWL
will see isolated gusts approaching 40 knots at times this
afternoon. Tuesday morning will bring another round of gusty
winds near 40 knots to most terminals through 18Z Tuesday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from midnight tonight to 6 PM MDT Wednesday
     for WYZ106-116-117.
     High Wind Warning from midnight tonight to noon MDT Tuesday
     for WYZ107.
     High Wind Warning from 6 AM Tuesday to 6 PM MDT Wednesday for
     WYZ109-115.
     High Wind Warning until 6 PM MDT Wednesday for WYZ110.
     High Wind Watch from Tuesday morning through Wednesday
     afternoon for WYZ118.
NE...None.

&&

$$

SHORT TERM...CLH
LONG TERM...BW
AVIATION...BW