-- Discussion containing changed information from previous version are highlighted. --
245
FXUS65 KCYS 091733
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1133 AM MDT Thu May 9 2024

.KEY MESSAGES...

- Winter Weather Advisory remains in effect for accumulating
  mountain snow, especially on northern slopes of the North
  Laramie Range.

- Scattered rain/snow showers expected to continue through
  Thursday afternoon and evening. Minimal snow accumulation
  expected, if any. Severe weather is not expected at this time.

- Warming trend likely headed into the weekend with the return
  of above normal temperatures for mid-May.

&&

.UPDATE...
Issued at 1047 AM MDT Thu May 9 2024

Based on current visible satellite imagery and model progs, have
lowered maximum temperatures slightly for this afternoon based
on recent temperature trends. Also adjusted other meteorological
variables based on recent model guidance.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 428 AM MDT Thu May 9 2024

The Winter Weather Advisory remains in place for the Northern
Laramie Range where an additional 6 to 8 inches of snow is possible
through Thursday morning. The generally northerly flow will continue
to favor the north facing aspects, especially the North Laramie
Range. As part of the low departs to the east and an additional part
retrogrades southwestward, rain showers will continues to move
across southeast Wyoming and western Nebraska. Precipitation will be
mainly snow or a rain/snow mix west of the Laramie Range and rain
east of the Laramie Range. HiRes guidance is showing the next wave
of precipitation moving in from South Dakota between now and early
this afternoon. This initial wave is followed by another this
afternoon into early evening which mainly stays along and north of
the North Platte River Valley. Along with these rain/snow showers we
may see a few rumbles of thunder. The HREF has 100-500 J/kg of CAPE
in east-central Wyoming and the Nebraska panhandle this afternoon
and early evening which is sufficient to kick off a weak
thunderstorm. Main shower and thunderstorm activity will be winding
down between 7 PM and 11 PM.

By Friday the low continues to circulate in central Nevada, blocking
the ridge from really getting into southeast Wyoming and western
Nebraska and being able to warm and dry out the air. That being
said, temperatures are still forecast to be a few degrees warmer,
but precipitation chances will stick around. The best chances for
showers and thunderstorms will be along and west of the Interstate-
25 corridor. The continued moisture and easterly flow at 700 mb, as
well as orographic enhancement from the Laramie Range will allow for
the potential for isolated to widely scattered showers and a rumble
of thunder Friday afternoon.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 428 AM MDT Thu May 9 2024

The long term forecast will begin to look more spring-like with
chances for isolated afternoon thunderstorms possible over the
weekend, with better chances for more scattered showers and
thunderstorms next week. Temperatures are also expected to increase
beginning this weekend into next week with temperatures likely to
remain in the upper 60s to low 70s throughout much of the long term
forecast period.

The weekend chances for showers and isolated thunderstorms will be
driven by a slow moving and large upper level low moving across the
Four Corners region Friday and into Saturday. Much of the dynamics
associated with the upper level low are confined along the southern
periphery as this upper level low taps into the subtropical jet.
Models are advertising a setup where this upper level low is south
of a ridge building across the northern Pacific northwest with
another upper level low sitting in near northern Michigan. This
overall setup of upper level low and high pressure systems looks
like a messy col setup across the Front Range states. The wind
fields show the col pattern better as light easterly winds in close
proximity of light westerly winds suggest that some type of
stationary or quasi-stationary front will be located across SE
Wyoming and the Nebraska Panhandle. This boundary will be the focal
point for potential convective initiation Friday and again on
Saturday. These storms that do develop will be in a weakly shear and
low CAPE/instability environment so not expecting much in the way of
deep convection, but towers that go up along the boundary or are
orographically supported could reach heights enough to foster the
development of some storms that could produce small hail.

This overall pattern remains in place well into Saturday evening
before the closed upper low across the Four Corners begins to weaken
and open into an open wave trough as it crossed through southern
Colorado. Remaining stationary boundary should still be draped
somewhere across the Front Range and we will also have lingering
outflow boundaries in play on Saturday IF we can get a few deeper
convective cores going on Friday. This system begins to speed up on
Sunday but the threat for some afternoon diurnal convection will
again be possible.

Monday may be quiet day across the region as a weak upper level
ridge axis moves but this too will quickly move east of the region
throughout the day on Monday. We will see the benefits of some
warmer 700mb temperatures which will allow for temperatures to jump
into the 70s across much of SE Wyoming and the Nebraska Panhandle.

Heading into Tuesday and beyond, we will have to start watching for
the potential for a chance for some lower bound severe weather
events. Our region gets locked into this northwest flow that will
have multiple shortwaves and vorticity lobes transversing through.
This type of setup usually suggests some severe weather is possible
as the cool NW flow aloft encounters somewhat warm surface
temperatures. The determining factor in these events is just how
much boundary layer moisture we can advect into the region.
Something to keep an eye on as we head into next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
-- Changed Discussion --
Issued at 1123 AM MDT Thu May 9 2024

An upper level trough and abundant low and mid level moisture,
along with northeast low level winds, will produce plenty of
cloud cover and scattered showers much of the day.

Wyoming TAFS...Ceilings will be near 4000 feet until 06Z, with
occasional rain showers limiting visibilities to 4 miles and
ceilings near 2500 feet until 21Z. From 06Z to 15Z, ceilings
will range from 800 to 1500 feet with fog reducing visibilities
to 1 to 2 miles, then ceilings will improve to 2500 to 3500 feet
after 15Z Friday. Winds will gust to 25 knots until 01Z.

Nebraska TAFS...Ceilings will range from 3500 to 5000 feet
until 01Z, with occasional showers lowering ceilings to
1500 feet and visibilities near 4 miles until 21Z. After 01Z,
ceilings will improve to 7000 feet.
-- End Changed Discussion --

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until noon MDT today for WYZ103.
NE...None.

&&

$$

UPDATE...RUBIN
SHORT TERM...LEG
LONG TERM...AW
AVIATION...RUBIN