914
FXUS65 KCYS 012353
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
553 PM MDT Wed May 1 2024

.KEY MESSAGES...

- Isolated thunderstorms will affect the Nebraska Panhandle this
  afternoon with a briefly gusty wind threat toward Sidney and
  Alliance.

- A cold front will move through the region on Friday with
  another round of mountain snow and shower activity possible
  over the region.

- Drier and warmer conditions will move in for the weekend.
  Gusty winds will move in by Sunday afternoon.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 113 PM MDT Wed May 1 2024

Afternoon satellite imagery and surface obs reveal a stream of
upslope flow over the Nebraska panhandle and far southeast
Wyoming with surface dewpoints generally in the mid to upper
30s. Aloft, southwesterly flow carrying a band of moisture
oriented southwest to northeast continues to drift east across
southeast Wyoming. Mesoanalysis reveals very low-end instability
on the order of 500J/kg of less has formed east of this feature
with a convective nature to some of the cloud cover east of
Cheyenne. CAM guidance supports the development of a few showers
and thunderstorms along the advancing surface convergence
boundary over the next few hours as it makes its way through
southwest Nebraska. Gusty outflow winds on the order of 30-40
knots and some small hail of pea size or less will be the
primary concern if any convection can become established.
Farther west, expect clearing skies through the afternoon and
evening as dry air moves in on westerly flow. Overnight
temperatures will run around 5 to 10 degrees below average in
the wake of today`s cold front.

Thursday will be a transition day between two shortwave troughs
as the region remains under the influence of broad longwave
troughing over the western half of the CONUS. Expect a mainly
dry day with mostly cloudy skies in place and temperatures
continuing to run around 5-10 degrees below average. As we move
into Thursday night, the vort max associated with the next
storm system will dive through the northern Rockies. Support for
lift will move in later on Thursday night with some mountain
snow breaking out in the higher elevations of the Snowy and
Sierra Madre ranges. Isolated showers are possible as well
across lower elevations of Carbon, Albany, Converse and
Niobrara counties as a cold front works southward.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 113 PM MDT Wed May 1 2024

The long term remains active, albeit with a brief quiet period over
the weekend before things ramp up again.

Friday, a shortwave will drop down from the Pacific Northwest,
keeping our temperatures on the cool side while bringing another
round of precipitation to the area. This system is progressive, so
it will only be a quick shot of moisture during the day Friday,
before it moves off into central Nebraska. 700 mb temperatures will
be below freezing, which will lead to below average temperatures.
Mountain snow is expected, but some flakes could mix in with rain
for areas west of the Laramie Range. East of the Laramie Range, rain
is expected. A few rumbles of thunder or a brief thunderstorm is
possible as non-zero CAPE values exist across the eastern plains.

By Saturday, upper-level ridging will move into the Rockies, leading
to drier and warmer conditions. 700 mb temperatures will be back
above freezing with sunny skies, so afternoon highs will be able to
climb back to around average for early May. An even warm day is
expected Sunday as the CWA sits in a region of warm air advection
ahead of the next system. Sunday will likely be the warmest day in
the foreseeable future with highs above average.

Headed into next work week, the forecast gets messy, both literally
and figuratively. There is a a good deal of discrepancy between
models regarding precipitation. The deterministic GFS shows a
progressive wave passing across the CWA, followed by yet another
trough that stalls out over the northern plains. The ECMWF has
a closed low pass over the CWA that then stall over the northern
plains. Both solutions give precipitation to the CWA but in
different areas. As a result of the uncertainty, went with NBM
for PoPs and QPF. There is more certainty that this system will
bring cooler temperatures and much windier conditions. First,
out ahead of the system, strong southerly winds will be possible
as MSLP gradients across the eastern half of the CWA become
tightly packed. Once FROPA occurs, expect very strong westerlies
behind it. Although this system is still quite a ways out, the
GFS has consistently been showing these strong winds from run to
run. A prolonged period of high winds with both the southerly
and westerly winds cannot be ruled out. In fact, in-house
guidance is already pinging high probabilities for high wind in
the usual wind prone spots, and even areas outside of it! Both
the strong winds and cooler temperatures look likely at least
through mid next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 541 PM MDT Wed May 1 2024

The main concern with this TAF issuance is the timing of when
the clouds will clear out this evening and how strong wind
speeds are expected tomorrow.

Latest IR/water vapor loop was showing the dry slot moving
through southwest Wyoming with quite a bit of wave clouds
stretching from areas west of Rawlins to Casper. That area is
expected to push east towards KRWL during the next couple of
hours, the I-25 corridor towards midnight and the rest of the
Nebraska panhandle afterwards. This area of subsidence may also
cause wind speeds to increase later this evening as it
approaches the Wyoming TAF sites. We had considered on bumping
up wind speeds when that area of subsidence moves in, but not
confident since we may also see more radiational cooling with
the limited cloud cover.

Thursday will most likely be another breezy day for most of the
TAF sites with plenty of sunshine and good mixing. However, some
mid level clouds may prevent deep mixing. At this point, we are
looking at gust speeds ranging from 25 to 35kts across the
majority of the TAF sites.

&&

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

&&

$$

SHORT TERM...MAC
LONG TERM...SF
AVIATION...REC