794
FXUS65 KCYS 171100
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
500 AM MDT Fri May 17 2024

.KEY MESSAGES...

- Warm & dry conditions prevail through Saturday. Daytime highs
  today may reach the lower to middle 80s for areas along and
  east of I-25.

- Windy today as a strong disturbance tracks across the northern
  high plains. Wind gusts 45-55 MPH are expected for Arlington
  and Bordeaux. A couple brief gusts in excess of 60 MPH cannot
  be ruled out.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 438 AM MDT Fri May 17 2024

A very warm (and breezy) day ahead for much of southeast Wyoming
& the western Nebraska Panhandle as the thermal ridge axis moves
overhead in advance of a vigorous mid and upper-level short wave
tracking across the intermountain west & northern high plains in
the next 6-12 hours. 700-mb temperatures soaring to +10 to +12 C
along w/ a strong west-to-east oriented MSLP gradient supporting
strong westerly downslope flow along/E of the Laramie Range will
likely support highs in the 80s for many along/east of I-25 this
afternoon. H7/H85 CAG-CPR gradients of 40-50 meters will support
potential for occasional 55-58 MPH gusts across the southeast WY
wind corridors. A few rogue gusts to 60 MPH are possible, but do
not believe a warning is necessary at this time w/ in-house high
wind probabilities favoring sub-warning gusts. Moisture profiles
look to be quite modest today, but high-res guidance suggests we
may have enough to generate isolated high-based showers and weak
thunderstorms by mid/late afternoon. If they develop, a very dry
sub-cloud layer would certainly support convective wind gusts in
excess of 60 MPH. Finally, expect elevated to near-critical fire
weather conditions today with RHs falling into the lower teens &
widespread 30+ MPH wind gusts. Fuels only remain critical across
the western Nebraska Panhandle zones, where winds should be much
less than areas further west. Even so, we will need to watch the
area closely for possible fire weather headlines.

Warm & dry for Saturday before a deepening trough over the north
western US leads to increasing southwesterly flow aloft over the
central Rockies. As such, the general theme of unsettled weather
continues with increasing chances for showers & storms likely on
Sunday.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Issued at 438 AM MDT Fri May 17 2024

An active pattern expected for much of the long term forecast.
Several upper-level disturbances will pass overhead, leading to
afternoon shower chances nearly every day. Sunday night into Monday
a longwave, upper-level trough is progged to drag across much of the
western CONUS, with a tighter trough depicted in the GFS and a
broader trough in the ECMWF. As this upper-level trough pushes
towards the area, an attendant cold front will move across the
region. This cold front with concentrate the lift near the surface
on Monday and lead to decent precipitation chances area wide, around
40-60%. Winds are expected to increase behind the front.
Temperatures on Monday will be several degrees colder than Sunday,
with highs int he mid-50s to low-70s across the region.

On Tuesday, the upper-level trough will continue to swing through the
area, though the GFS is notably a few hours behind the ECMWF on the
propagation of the trough. Forcing will once again be present ahead
of the trough as reinforcing cool air remains overhead. Temperatures
are expected to be in the mid-50s to low-60s with the reinforcing
cold air aloft. Afternoon showers will be possible as the trough
slowly swings overhead and forcing out ahead of the trough favors
the development of showers. Zonal flow will move overhead once the
upper-level trough finally advects out of the reason by early
Wednesday. Riding at 700mb and 700mb temperatures increasing to 0-2C
will promote high temperatures on Wednesday in the low-60s to mid-
70s across the region. Minimal precipitation chances will exist
during the day Wednesday, but cannot rule out a few isolated showers
as weak forcing from cyclonic vorticity advection at 500mb favors
subtle lift across the region. Any showers that develop will likely
not be strong or long-lived.

For the remaining long term, a secondary upper-level is progged to
swing around the upper-level trough and impact the region Thursday
and Friday. There is significant disagreement between the GFS and
the ECMWF on the exact placement, speed, and timing of this
secondary low. The GFS places the low over northern Idaho Thursday
afternoon and over Montana and Wyoming by Friday morning. The ECMWF
on the other hand is about a day behind, with the upper-level low
still off the coast of the Pacific Northwest Friday morning and does
not approach the region until late in the weekend. Instead, the
ECMWF favors zonal flow across the region for Thursday and Friday.
Decided to drop temperatures just a little for Friday, as long range
model suggest 700mb temperatures just above 0C for Friday. Kept
precipitation chances low, around 20-30% for both days to account
for the uncertainty in the upper-level evolution.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1003 PM MDT Thu May 16 2024

Northwest flow aloft this evening will become west Friday, and
continue through the period. A cold front will enter southeast
Wyoming Friday evening. Scattered clouds around 15000 feet will
prevail. Winds will gust to 28 knots at Rawlins until 08Z, and
from 22 to 38 knots at all terminals from 14Z to 01Z.

&&

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

&&

$$

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