913
FXUS65 KCYS 151104
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
504 AM MDT Wed May 15 2024

.KEY MESSAGES...

- Cooler today w/ scattered to numerous showers and a few
  thunderstorms. Severe weather is not expected.

- A warming trend will occur through the remainder of the week,
  with lower to middle 80s possible by Friday especially for
  areas along and east of I-25.

- Elevated wind gusts are expected in the southeast Wyoming wind
  corridors on Friday and Friday night.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 407 AM MDT Wed May 15 2024

Scattered to numerous showers & a few thunderstorms are expected
across a large portion of southeast Wyoming and western Nebraska
today. The greatest coverage of this activity is likely to occur
in the morning (12z-18z) given more favorable dynamic support w/
lingering mid-level vort energy associated with the strong short
wave responsible for the strong/severe storms on Tuesday. Should
see this support gradually wane during the afternoon and evening
as the bulk of the energy pinches off and drifts south/southwest
into the Four Corners region. As such, overall storm coverage is
likely to decrease with time. Despite this, the 700-500-hpa cold
pool associated w/ the mid upper-level low should promote decent
mid-level instability over much of the CWA and thus an increased
chance for scattered storms. Modest shear precludes any concerns
for organized clusters or stronger storms. Much cooler for today
with 700-mb temperatures close to 0C, likely restricting daytime
highs to the mid/upper 50s to near 60 deg F. Overall, conditions
should rapidly improve for Thursday & Friday, courtesy of rising
mid-level heights as the primary disturbances remain well to the
north and south of the CWA. A warming trend will commence w/ 700
mb temperatures climbing to +10 to +12 C across much of the area
by Friday, supporting the potential for widespread daytime highs
in the 80s especially along and east of I-25. An episode of high
winds will be possible across the southeast WY wind corridors on
Friday, given significantly increased low-level height gradients
as a sharp mid-level short wave tracks across the inter-mountain
west and northern high plains.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Issued at 407 AM MDT Wed May 15 2024

Models have continued to come into better agreement on the passage
of a cold front and upper-level trough Friday into Saturday. The
upper-level trough will slowly progress easterly Friday night into
Saturday with westerly winds developing at 700mb and the surface.
Some disagreement remains between the GFS and the ECMWF for how
strong the westerly 700mb winds will be, but the GFS suggests it
could be around 50kts, while the ECMWF keeps it much lower around
30kts. The GFS solution is significantly more favorable for a
potential short lived, high wind event for the wind prone regions of
southeast Wyoming. The ECMWF solution suggests the potential for
elevated winds Saturday, but likely not near the high wind criteria
line. Craig to Casper height gradients increase to around 50-55m,
which suggests the potential for some gusts near 50mph at the
Arlington wind prone. In house guidance is not overly onboard with
the potential high winds and only suggests a 30-40% chance for
elevated winds Saturday. This system will need to be monitored to
determine if ingredients come together for another strong wind event
across the region.

As the upper-level trough continues to move out of the region, a
split flow regime takes shape with a dominant subtropical jet and a
weaker polar jet across the western CONUS. This setup will turn
upper-level winds southwesterly, with 700mb and surface winds
following suit. Precipitation will be favored Sunday into Monday at
the region will be under two separate forcings for synoptic lift.
The right entrance region of the northern jet will be overhead and
supported by the left exit region of the southern jet. Therefore,
favorable conditions for widespread synoptic lift is favored.
However, the ECMWF keeps the northern jet more zonal and further
north, with significantly decreases the lift across the region and
makes PoPs continue to be a headache early into the week. Did
decrease PoPs for most days for the upcoming week, with 30-40% PoPs
in place across the region Monday into Tuesday. Decided to keep PoPs
relatively low due to the uncertainty in the upper-level evolution.
Additionally, the GFS suggests a secondary cold front moving through
the region Monday, while the ECMWF does not have this front. Decided
to decrease temperatures slightly for Monday and Tuesday, as
slightly cooler temperatures are favored, despite the poor model
agreement.

Further model disagreement persists into the mid-week timeframe. The
ECMWF and GFS both suggest and incoming upper-level trough by mid-
week, but the GFS is about a day behind the ECMWF with displacement
to the west, compared to the ECMWF. Decreased PoPs for Tuesday
onward to the 20-30% range, due to the uncertainty between the long
range models at this time. Despite model disagreement in
precipitation, warm temperatures are expected throughout the long
term, with highs consistently in the 60s, 70s, and 80s across the
region.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 501 AM MDT Wed May 15 2024

Rain showers will be the primary concern for the 12Z TAF
period. Isolated to scattered rain showers will drift across
southeast Wyoming and western Nebraska this morning through the
late afternoon hours. Every terminal has the potential to see a
rain shower overhead with conditions dropping to MVFR to near-
IFR as the rain showers move through. Best chances for
precipitation in the vicinity of the terminals will be 13-00Z
today. Winds will remain relatively calm throughout the day.

&&

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

&&

$$

SHORT TERM...CLH
LONG TERM...AM
AVIATION...AM