285
FXUS65 KCYS 270901
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
301 AM MDT Mon May 27 2024

.KEY MESSAGES...

- A much warmer, milder week ahead expected as an upper-level
  ridge overtakes the region.

- Chances for an active weather patter with organized strong to
  potentially severe afternoon thunderstorms may be possible
  from Wednesday through this weekend.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 300 AM MDT Mon May 27 2024

Light rain showers are quickly moving to the east across the NE
Panhandle during the early morning hours. Northwest flow aloft
from a departing shortwave should quickly assist with the rain
showers pushing east by daybreak. A few sprinkles across the
central and southern tier of western Nebraska are anticipated at
best, with a non-severe threat to any vertically developed
cumulus clouds the remainder of the night hours. A semi-
stationary surface cold front is draped along the Laramie Range
and Front Range of Colorado as of 8Z this morning as well. This
surface cold front is anticipated to remain close to Cheyenne,
with it retrograding to the east through the remainder of
today. As we continue to see this frontal boundary remain semi-
stationary, it will have some weak forcing and modest
atmospheric lapse rates by this afternoon. We can expect mostly
sunny conditions across most of the cwa, but a few cumulus
clouds could bring light sprinkles or a quick shower along and
east of the Laramie Range. It will be another pleasant day, with
mostly sunny conditions helping temperatures rise to near-
seasonal levels: Highs in the upper 60s to middle 70s for the
lower elevations and high plains of western Nebraska.

Tuesday will bring slightly warmer temperatures, and another
round of mostly sunny conditions for a majority of the cwa.
Highs in the 70s to lower 80s are expected for the lower
terrain. While we will be under the influence of an amplifying
upper level ridge, there will be weak ripples of shortwave
energy at the H5 level on Tuesday afternoon. Model guidance is
trending with the majority of any organized rain showers and
thunderstorms to remain south of our cwa for the most part.
However, surface CAPE is modeled to creep upwards towards 500
J/kg for the I-80 corridor. Have bumped up PoPs slightly for
the higher terrain of the Snowy/Sierra Madre Mountains, and the
I-80 Summit. Model soundings are showing an inverted-V
signature, with calculated DCAPE readings approaching 750-1000
J/kg by 0Z Wednesday. The main impacts that could result are
elevated virga rain showers, that could create some gusty
microburst winds over a small area, potentially up to severe
thresholds. Have not bumped up the wind forecast for Tuesday
just yet, but if we see this signal on model guidance continue,
there may be a need to bump up the wind forecast for Tuesday
afternoon along and near the I-80 corridor of southeast WY.

Wednesday will bring warm temperatures to the region, as we
begin to feel the effects of an upper level ridge axis. WAA will
be present, and there will be widespread middle 70s to middle
80s for daytime highs in the lower terrain. There will be an
approaching longwave trough by Wednesday afternoon from the
Pacific Northwest, digging southward toward the Four Corners by
0Z Thursday. It is modeled for diffluent flow to set up across
the Central Rockies, as the Polar Jet stream and Subtropical jet
stream phase partially. Additional weather metrics to consider
will be moisture advection from the Gulf of Mexico, steep
atmospheric instability/lapse rates, effective bulk wind shear,
and the potential for rotating, isolated severe thunderstorms.
The overnight Day 3 Storm Prediction Center severe thunderstorm
outlook does indeed have portions of our cwa from the I-25
corridor toward the Nebraska Panhandle in a Marginal Risk
(Category 1 out of 5). We will continue to monitor trends in the
coming days as warmer weather and the potential for organized
thunderstorms exists for the some areas. Until then, enjoy the
pleasant holiday forecast for today.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Issued at 300 AM MDT Mon May 27 2024

Generally, an active pattern looks to persist through the long-term
period with daily chances for showers and thunderstorms as multiple
shortwaves pass in the flow through the weekend. Best chances for
precipitation CWA-wide will be on Wednesday and Friday evenings (30-
40%). Latest Euro keeps a lower amplitude shortwave trough farther
north on Friday with minimal precipitation across the area, however
~40% of EC members depict a sharper trough with better southerly
moisture return and instability (MLCAPE ~800-1200 J/kg) into areas
along and east of I-25 and the NE panhandle. Enhanced flow aloft
with the approaching upper level trough would support strong enough
shear profiles (30-35 kt) for a few severe storms to develop, so
will need to continue to monitor potential severe weather
ingredients over the coming days.

While 500mb height rises appear likely early next week, an active
pattern may persist with multiple weak shortwaves passing overtop of
the ridge along with an upper level low undercutting to the
southwest. This will also support above average temperatures for the
first week of June, potentially leading to the first 90F degree day
over portions of the NE Panhandle ~15% chance per latest NBM
guidance.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 935 PM MDT Sun May 26 2024

Northwest flow aloft will continue.

Wyoming TAFS...Mostly clear skies will prevail. Winds will gust
to 22 knots from 15Z to 00Z.

Nebraska TAFS...Ceilings near 8000 feet will prevail until mid
morning Monday, then skies will become mostly clear. Showers
will be in the vicinity of Chadron and Alliance until 15Z.
Winds will gust to 25 knots at all terminals from 15Z to 00Z.

&&

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

&&

$$

SHORT TERM...BW
LONG TERM...MB
AVIATION...RUBIN