Alliance, Nebraska 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

728
FXUS65 KCYS 152325
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
525 PM MDT Fri May 15 2026

.KEY MESSAGES...

- Severe weather will be possible both Saturday and Sunday. SPC
  has issued a Slight Risk for the Southern Panhandle on
  Saturday with a marginal risk for Sunday.

- Another round of accumulating late season snow is
  increasingly likely on Monday, mainly above 5000 feet in
  elevation.

- Near record cold Monday and Monday night will lead to
  widespread freezing temperatures, which may damage sensitive
  vegetation and outdoor irrigation systems.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 315 PM MDT Fri May 15 2026

Active weather is progged to return for Saturday and Sunday as the
next upper-level system starts to push towards the Intermountain
West. Saturday afternoon and evening, much of the CWA will be placed
broadly within the right entrance region of the upper-level jet,
favoring continued synoptic ascent and favorable dynamics across the
region. Multiple lobes of 500/700mb vorticity will eject out ahead
of the incoming trough, further aiding in the overall synoptic
ascent expected. Further down at 700mb, the associated low will
slowly wrap up throughout the afternoon and evening hours, leading
to stout, southerly to southwesterly flow for most locations east of
the Laramie Range. Warm air advection increases after 12pm (noon,
allowing for additional upward lift as the system pushes through.
The surface low begins to develop Saturday afternoon over northeast
Wyoming, inducing moist, southeasterly flow at the surface,
especially across western Nebraska. A modest warm front will move
northward, keeping the strong southeasterly funneling into the
surface low. With the warm front ample surface forcing is expected,
especially with the broader lift typically found within the warm
sector of a mid-latitude cyclone. With strong southeasterly flow,
dewpoints will surge into the mid-40s to low-50s across western
Nebraska, with far southeastern Wyoming increasing into the mid-40s.
Ample clearing is expected out ahead of the slowly advancing warm
front, leading to a prolonged period of destabilization after
sunrise Saturday morning. Hi-Res model guidance suggests around 1000
J/kg of MLCAPE with sufficient effective bulk shear, low-level
turning, and minimal capping after about 20Z. However, the lower-
levels look to remain fairly dry, increasing concerns for downburst
potential. DCAPE values are around 1200 J/kg across western
Nebraska, further increasing concern for a damaging wind potential
on Saturday afternoon. Isolated supercell thunderstorms look
possible on Saturday, but may grow upwards into a line fairly
quickly due to nearly parallel bulk shear vectors to the expected
warm front. Based on this information, discrete supercells could
develop Saturday afternoon, but will likely grow upscale into a line
a few hours after development. Forecast soundings suggest a
potential for large hail, damaging wind gusts, and an isolated brief
landspout cannot be ruled out due to low-level turning in the
atmosphere. The Storm Prediction Center has highlighted much of the
area in a Marginal Risk (Level 1 of 5), with portions of western
Nebraska under a Slight Risk (Level 2 of 5) for severe weather
Saturday afternoon. The main limiting factor for Saturday`s severe
threat will be the overall weaker forcing associated with a warm
sector and the potential for strong capping until after 18Z or so.
For Sunday, models show an upper level low over the Montana, Idaho,
and northern Utah area. If the upper level low digs further south
and is less progressive as it pushes into the Intermountain West,
then southeast Wyoming may see a late season snow storm. If the
upper level low is more progressive and moves further north, then
less precipitation is expected, and in the form of mostly rain. For
the 12Z, the deterministic models show the less progressive/further
south solution of the southern low as it digs south near the four
corners region late Sunday. The first of a series of cold fronts
will push across Wyoming and eventually the high plains midday
Sunday. At this time, it looks like the front will move through the
area quickly, however some models do slow the front down and produce
stronger convection from it. Low clouds and a strong capping
inversion looks to be likely on the soundings east of Interstate 25
for most of the day. Therefore, pretty low confidence in this event
so far. Severe thunderstorm wording was kept for mainly just the
southern Nebraska panhandle again.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 315 PM MDT Fri May 15 2026

Confidence is increasing in yet another significant, late season
snow event impacting portions of the area Sunday night through
Monday night. The overall synoptic setup will feature a double
barrel upper level low diving in across the western CONUS this
weekend. The main trough axis will be fairly slow moving, but a
strong, secondary vort-max will swing across the base of the trough
Sunday night into Monday, enhancing local forcing for ascent.
Showery type precipitation Sunday afternoon will transition to a
more stratiform precipitation by Monday morning. A reinforcing cold
front is also expected to move southward into the area Sunday
evening, leading to a surge in the northerly surface winds and
steadily dropping temperatures. The mid-level cyclone will dive down
into the interior Rockies during this period, which will close off
between about 700 and 500-mb. This will allow moisture and wind to
wrap in over the northeast side of the low, in a pseudo-TROWAL like
setup, just on the wrong side of the system. Models are rather
aggressive on strong isentropic lift and positive theta-e advection
over much of the area Sunday evening and continuing through at least
midday Monday. In addition, ensembles are in fairly good agreement
showing strong frontogenesis setting up along the I-80 corridor west
of Laramie. All together, we have numerous lifting mechanisms and
ample moisture with nearly saturated vertical profiles.

Ensembles are pretty aggressive on liquid precipitation.
Fortunately, this system looks to deliver beneficial moisture to a
larger portion of the area, unlike the previous snow event this
month which was mainly confined to Laramie, Cheyenne, and areas in
between. The 25th percentile liquid precipitation exceeds 0.5" for
the entire area, suggesting a good chance for widespread moisture.
50th percentile amounts exceed 1.0" over much of southeast Wyoming
where the dynamics are a bit stronger and there will be more of a
boost from orographic lift. This would ordinarily be great news for
our drought stricken area, but unfortunately, this system will be
very cold for this time of year. LREF mean 700-mb temperatures drop
to around -4 to -7C over much of southeast Wyoming, and -2 to -5C
over western Nebraska. A shallow cold air layer is also expected to
undercut a deep warm nose aloft, but this warm nose is expected to
remain largely below freezing. These temperatures will support
accumulating snow down to about 5000 ft in elevation, and snowflakes
mixing in with the rain for the entire area, even in the lower
elevations of western Nebraska. Accumulations and impacts (due to
snow) are less likely below 5000 ft. Rain will transition over to
snow Sunday night in southeast Wyoming, so we may be able to get
some snow sticking to the ground before the sun comes up. With the
sun angle just a month away from the summer solstice, it will be
very difficult to accumulate snow during the day, but we still
should see some sticking to grassy/elevated surfaces. Most likely
snow amounts are currently sitting around 4-7" in Rawlins and
Arlington/Elk Mountain, 3-6" in Laramie, 2-4" in Cheyenne, Douglas,
Saratoga, and Lusk, and a trace to 2" elsewhere. The mountains,
particularly the Snowy Range, Laramie Range, and Muddy Gap area can
expect higher amounts in the 6 to 12" range. While these are the
most likely amounts, there is some concern for high end potential
with this event. The strong signal for frontogenesis in Carbon
county is particularly noteworthy. There is a plausible high end
scenario where 10 to 16 inches falls in Carbon county, and 5 to 10
inches falls in other populated areas of southeast Wyoming. The
current probability of this scenario is around 10 to 25%.

Deciduous trees are now fully leafed out across the area. With
heavy, wet snow expected, the primary impact of this event is
expected to be tree damage. Snow will have trouble sticking to the
roads, but the higher elevations of I-80 in Carbon and Albany county
may anticipate some road impacts. Unlike the previous snow event
this month, this one will unfortunately be accompanied by
significant surface winds. The high plains can expect a steady, cold
north wind gusting around 25 to 35 mph. The surface high pushing up
against the higher terrain and stalling will lead to an impressively
strong reverse pressure gradient, which is likely to lead to strong
winds in Carbon and Albany counties. There is high confidence gusts
of 35 to 45 mph in this area, with the possibility of gusts
approaching 55 mph. Blowing snow impacts will be reduced by the
expected wet consistency of the snow, but we will need to keep an
eye on this as well. There is some uncertainty concerning how these
winds will affect snow accumulations on leafed out trees. On one
hand, this could help knock snow off, but it also might increase the
strain on branches and lead to more downed limbs.

The last impact of this event will be the expected cold
temperatures. 700-mb temperatures are around the 2.5 percentile of
climatology. With plentiful cloud cover, forecast high temperatures
for Monday were nudged down towards the NBM 25th percentile, but
this may even be still too warm. Highs will struggle to get above
the mid 30s in southeast Wyoming where snow is falling, and even
western Nebraska will get stuck in the low 40s. Monday night will
bring the coldest temperatures of the event. Expect widespread
freezing temperatures, with essentially the entire area expected to
fall below freezing. Rawlins and Laramie are favored to drop below
25 degrees, with Cheyenne event maintaining a probability of around
40%. The main question will be cloud cover. If we can maintain some
low cloud cover through the night, we may be spared the worst of the
impacts of the freezing temperatures. However, early clearing will
likely lead to widespread 20s and even some pockets of teens showing
up. Record low maximum temperatures are likely during the day
Monday, and record low minimum temperatures are likely by Tuesday
morning. Those with sensitive vegetation or outdoor irrigation
systems should take steps this weekend to prepare for the upcoming
cold temperatures.

Behind this storm system, the warmup will be fairly slow as general
troughing is expected to remain over the area through the week
ahead. Expect temperatures to remain below seasonal averages through
at least Wednesday, and possibly Thursday. The storm track will
remain active as well with a continued stream of vort maxes moving
through the area, which will keep slim chances for showers and a few
thunderstorms going, but the potential for widespread rainfall will
be fairly low after the main event concludes Monday afternoon.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 525 PM MDT Fri May 15 2026

VFR conditions will prevail across all terminals for the remainder
of this afternoon through tonight with winds becoming 10 knots or
less. A system will push into the region from the southwest,
increasing the threat of thunderstorms. So, this activity will begin
around 18Z for KLAR and gradually later for the terminals to the
north and east. All sites, except KRWL, will have the possibility by
23Z Saturday. So, a PROB30 group was added to account for this. In
any thunderstorm, especially if one comes near or goes over a
terminal, expect gusty and erratic winds, lowering CIGs, and reduced
VIS.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...Red Flag Warning until 7 PM MDT this evening for NEZ434>437.

&&

$$

SHORT TERM...MM
LONG TERM...MN
AVIATION...RZ