Alliance, Nebraska 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

269
FXUS65 KCYS 302042
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
242 PM MDT Sun Mar 30 2025

.KEY MESSAGES...

- Snow and rain showers continue into the day Sunday with
  additional snowfall accumulations generally under an inch.

- Active pattern this week bringing more chances for wind and
  precipitation.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 133 PM MDT Sun Mar 30 2025

Afternoon visible satellite imagery and surface observations
reveal a widespread stable stratocumulus cloud deck covering
much of the high plains of southeast Wyoming east of the Laramie
range, as well as throughout the Nebraska panhandle. Easterly
upslope flow continues to transport a deep and moist boundary
layer westward toward the mountains. Farther west, drier west-
southwesterly flow over the higher terrain of southeast Wyoming
and the higher elevation basins continues with some breaks
evident in cloud cover. Short-term high-res forecast soundings
as well as SPC mesoanalysis support around 100-400 J/kg of
MUCAPE developing in this southwest flow regime over the next
few hours during peak heating. A few isolated weak
thundershowers and convective updrafts can be expected,
moving eastward over portions of Albany, Platte, Goshen and
Laramie counties. Outside of this region, the deep stable
boundary layer will likely negate any convective shower activity
east of the Laramie range through the remainder of the day.

An unsettled, zonal flow regime will remain in place overnight
tonight and through Monday and Monday night. After a cloudy but
relatively precipitation-free period on Sunday night through
Monday morning, weak convection is likely once again on Monday
afternoon. We will again see relatively drier southwesterly flow
over the Wyoming high country, interacting with a moist boundary
layer with stable upslope flow along and east of the Laramie
Range. Some of this moisture may spill over into the basins of
northern Carbon and Albany county as well on Sunday afternoon,
supporting surface-based instability values on the order of
200-500 J/kg aided by surface heating in the afternoon hours. A
weak impulse of energy, evident in 500mb vorticity fields, will
traverse across the Great Divide Basin of south- central
Wyoming by the 18-21z timeframe. All of these factors combined
will result in several weak showers and thunderstorms
developing by 19z and tracking eastward throughout the
afternoon. Isolated instances of pea-sized hail and bursts of
graupel are possible in these storms, along with westerly wind
gusts of around 30-40 mph. Some forecast guidance, particularly
the NAM Nest which is on the higher end of the range of HREF
members in terms of instability, support a few of these
thunderstorms making it as far east as the Nebraska Panhandle
extending the marginal hail and wind threat until around 0z in
these locations. Any convection will quickly wane with the loss
of daytime heating.

Behind this system, a broad stream of Pacific moisture will
arrive in southern Wyoming by nightfall. While any convective
snowfall during the day in the mountains will not add up to
much, this deeper Pacific stream of moisture will likely bring a
more steady round of accumulating snow to the Sierra Madre and
Snowy ranges by Monday night/Tuesday morning. Consideration was
given to a Winter Weather Advisory for these locations in this
forecast package, but will opt to wait a bit for more model
consistency in total QPF values. Overall forecast confidence is
high throughout the short-term in terms of cool and moist
weather. Specific precipitation totals will vary quite a bit
based on any convective cells that can form.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 133 PM MDT Sun Mar 30 2025

An active and messy pattern is expected this week into next weekend
as multiple disturbances push through the region. Tuesday will kick
off with a broad upper-level trough slowly moving southeasterly from
the Pacific Northwest into the Intermountain West. As the trough
slowly migrates southeasterly, a messy 500mb vorticity advection
pattern will act to slowly start cutting off the base of the trough,
forming an upper-level cutoff low by early Wednesday morning. The
messy upper-level pattern continues as the now cutoff low spins and
meanders around the Intermountain West, attempting to get caught
back up in the upper-level flow. This remains the case until Friday
morning, when long range models currently suggest that a deeper
upper-level trough will develop and absorb the cutoff low into the
upper-level flow once more. Once this occurs, the upper-level trough
will very slowly move easterly, keeping the Intermountain West under
the influence of upper-level troughing through most of the week.
Long range model guidance for the upper-level continues to show
significant differences, with the GFS cutting off the low once again
by Saturday morning and the ECMWF keeping the trough intact until
Saturday afternoon/evening, when the base of the trough attempt to
be cutoff once more. Long range models slowly kick the cutoff low
eastward and absorb it into the upper-level flow by Monday as an
upper-level ridge slowly builds over the western CONUS and northerly
flow develops aloft. Overall, a consistent trough pattern like this
will lead to mostly cloudy skies this week with on and off chances
for precipitation. Additionally, cooler temperatures are expected
throughout the week due to this messy, troughing pattern.

The overall pattern at 700mb remains equally messy as the upper-
level pattern with ongoing troughing and embedded disturbances. On
Tuesday a generally troughing pattern is expected at 700mb as a 700mb
low slowly develops over Montana and moves southeasterly into
western South Dakota and central Nebraska. As this low intensifies,
a 40 to 45kt jet develops on the southwestern side of the low with
an additional jet developing on the southeasterly side with a
strengthening 700mb jet across Missouri and eastern Kansas. Surface
cyclogenesis in the lee of the Rockies in eastern Colorado will
start early Tuesday morning. The surface low will slowly advect
north-northeast throughout the late morning and early afternoon
hours Tuesday. As a result, widespread precipitation is expected
with this system, as the surface cyclone is in a favorable location
for precipitation across the CWA. If this surface low develops
further south, less precipitation will be expected in southeast
Wyoming and western Nebraska. Tuesday evening into the early morning
hours Wednesday, the surface low is progged to take a sharp turn to
the northeast and speed up as it propagates across the Great Plains.
As a result, most of the region, especially the northern zones, will
see wrap-around moisture from this system, leading to continued
precipitation chances Wednesday. Strong winds will slowly come to an
end Wednesday afternoon, as the 700mb low continues it northeasterly
track and the strongest 700mb winds move away from the region.
Strong winds are most likely across southeast Wyoming and western
Nebraska will primarily see rising motion Tuesday through late
Tuesday night, which is not favorable for strong winds at the
surface.

Thursday onwards the 700mb pattern becomes dominated by a developing
low across far southern California and Arizona. This leads to a
fairly calm pattern at Thursday with light and variable winds. As a
result, Thursday will be the driest day of the week with only slight
chance to chance (15 to 25%) PoPs across the CWA. A lobe of 500mb
vorticity may lead to a brief period with higher chances of
precipitation before returning into the slight chance to chance
range. On Friday, 700mb flow slowly turns easterly throughout the
day into early Saturday morning with surface winds slowly turning
easterly throughout the day, leading to upslope flow across
southeast Wyoming. Precipitation chances increase once more as the
moist, upslope flow develops across the region. The bulk of the
precipitation is progged to remain south of the CWA at this time,
but a slightly northerly movement would result in significantly more
precipitation for the region. This will continue to be monitored
over the next couple of days.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1142 AM MDT Sun Mar 30 2025

MVFR to IFR ceilings will affect terminals east of the Laramie
Range today. Additional showers and possibly a rumble of thunder
will affect CYS and SNY, with brief VIS lowerings in the
heaviest precipitation. General light snow or a rain snow mix is
possible at LAR and RWL for a few hours later this afternoon
with some very light precip at BFF CDR and AIA as well. Expect
improving conditions late overnight and through the morning on
Monday.

&&

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

&&

$$

SHORT TERM...MAC
LONG TERM...AM
AVIATION...MAC