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000
FXUS65 KCYS 230952
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
352 AM MDT Tue Apr 23 2024

.KEY MESSAGES...

- Cooler temperatures will be present Tuesday, with a chance of
  isolated showers and thunderstorms west of the Laramie Range.

- Relatively mild temperatures are expected Wednesday & Thursday
  along with a chance of late day showers and thunderstorms.
  Strong to potentially isolated severe thunderstorms are
  possible east of the Laramie Range on Thursday.

- Cooler, wet and unsettled weather is likely for Friday and
  the weekend.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 330 AM MDT Tue Apr 23 2024

Seasonal overnight temperatures remain present across the area
early this morning, with tranquil weather conditions as well.
Temperatures are in the 40s for the the North Platte River
Valley, with most of the remaining portions of the cwa in the
30s. Lingering cloud cover from the jet stream aloft, and a
semi-stationary surface frontal boundary will assist with
keeping temperatures elevated the remaining hours of this
morning. Surface frontal analysis shows the weak cool front
draped across the northern Front Range of Colorado as of 9Z,
with the surface low also co-located in this vicinity.

As the day presses onward, this weak surface boundary is
anticipated to lift north slightly, and become draped along the
Laramie Range. A weak warm front will remain present west of
this boundary, thus daytime heating will allow for slightly
warmer temperatures to occur. East of the Laramie Range, a
departing shortwave disturbance across the northern Plains will
bring CAA southward into the high plains region. This CAA will
limit temperatures from reaching much higher than the middle to
upper 50s. 700mb temperatures are progged to remain between 0C
and -5C between 18z and 0z this afternoon east of the Laramie
Range. However, the North Platte River Valley will be able to
reach the lower 60s of the NE Panhandle. Warmest locations west
of the Laramie Range will be western Albany County and Carbon
County. Afternoon heating will help shift the lower atmosphere
lapse rates slightly, as 700-500mb lapse rates of 7 to 9
degrees C/km increase in coverage west of the Laramie Range.
MUCAPE values are progged to remain under 500 J/kg along and
south of the Interstate 80 corridor. Would not be surprised to
see a few isolated rumbles of thunder, but the most likely
outcome are light rain showers. This weak warm frontal boundary
will shift to the east by later this evening, so the potential
for a few rain showers may reach into the Interstate 80 corridor
east of the Laramie Range by sunset.

Wednesday will bring a shift to increased daytime highs. The
axis of an upper level ridge will amplify slightly as it
propagates from the Great Basin toward our cwa. Model guidance
does show a few weak shortwave disturbances embedded within the
H5 and H3 flow aloft. MUCAPE remains on the lower side,
approximately 500 J/kg along the Interstate 25 and 80 corridors
during peak heating if we take the HRRR into account. However,
the NamNest and NAM are more aggressive, with MUCAPE reaching
towards 1000-1500 J/kg across pockets of our cwa. Sufficient
lapse rates of 7-9 degrees C/km from 700-500mb and diffluent
flow aloft from an approaching longwave trough across the Four
Corners should provide enough of the necessary ingredients for
showers and isolated thunder. Day 2 of SPC`s outlook does have
Gen Thunder across our entire cwa. Not expecting anything severe
at this time of inspection, but afternoon high temperatures in
the 60s and 70s will make it feel like spring around the area.
Model guidance does show that the isolated rain showers and
thunder could persist into the overnight hours of Wednesday
night.

Thursday will bring our warmest day of the week into the fray as
an approaching cold front from the Pacific Northwest treks
toward our cwa by late Thursday afternoon. An attendant longwave
trough at H5 will become negatively tilted by midday Thursday
across the Intermountain West. Lee surface cyclogenesis east of
the Front Range in Colorado will rapidly occur from Thursday
morning into the afternoon hours. At this time of inspection, a
1005mb surface low at 12Z is progged to deepen rapidly to 987mb
by 0Z Friday. The GFS is the most aggressive with this solution.
Sufficient lapse rates, diffluent flow aloft, and rich moisture
advection northward from the GoM (Gulf of Mexico) is anticipated
to occur on Thursday, especially east of the Laramie Range into
the NE Panhandle. One caveat is that Bulk Shear from 0-6km isn`t
all that impressive, but it should be sufficient for convective
initiation when combined with MUCAPE of 500-1000 J/kg. SPC Day
3 has a Marginal Risk for Severe wx extending into portions of
our cwa from a line of Cheyenne to Torrington and to the east,
including the southern tier of the NE Panhandle. The main
hazards would be gusty winds and large hail. We will need to
monitor the trends as there also is the potential for strong
winds ahead of the surface cold FROPA across portions of Carbon
County on Thursday afternoon. Expect daytime highs to range from
the upper 60s to near 80 degrees for the lower elevations. The
potential for isolated strong to potentially severe
thunderstorms exists Thursday, before the cold front arrives
Thursday evening and brings cooler air to the region.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Issued at 311 AM MDT Tue Apr 23 2024

The GFS/ECMWF remain in excellent agreement w/ regard to general
upper-level troughing across the Rockies through the majority of
the extended forecast period. This should result in an unsettled
pattern w/ daily chances for numerous rain & high elevation snow
showers. Medium-range deterministic models suggest several mid &
upper level disturbances pivoting around the base of the larger-
scale troughing over the Four Corners, before ejecting north and
east across the southern & central High Plains. This will result
in several waves of lee cyclogenesis over eastern CO, first late
Thursday night into early Friday, then again from Saturday night
through Sunday. Slight model differences remain w/ regard to the
overall storm track, but the general signal strongly favors good
wrap-around moisture/deformation precipitation in the north-west
quadrant of both lows. A more northern track may be favored with
the first system, keeping the higher probabilities of widespread
stratiform precipitation just to the north & east of the CWA. It
appears a more southern trajectory of the jet energy should help
place the CWA in a more favorable location for widespread rain &
snow with the second system. At this time, it appears most lower
elevation areas should see minimal impacts with rain as the main
precipitation type. 700-hpa temperatures falling to -2 to -4 deg
C will support high-elevation snow w/ 6-12+ inches possible over
the Snowys and Sierra Madres over several days. Could also see a
risk for impactful snow accumulations over the Laramie Range and
the I-80 Summit with the second system. Temperatures will remain
on the cooler side of normal for the majority of the period with
the anticipation of widespread clouds and precipitation.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1059 PM MDT Mon Apr 22 2024

A cloud deck around 10kft will move over the Nebraska terminals
overnight. Light winds expected overnight. Wind gusts up to 20
knots at KLAR on Tuesday afternoon. VFR for all terminals.

&&

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

&&

$$

SHORT TERM...BW
LONG TERM...CLH
AVIATION...AM