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000
FXUS65 KCYS 060841
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
241 AM MDT Thu May 6 2021

.SHORT TERM...(Today through Saturday)
Issued at 238 AM MDT Thu May 6 2021

Today...Quite a pleasant warming trend on tap as a ridge aloft moves
over western Wyoming with dry northwest flow aloft over our
counties. With 700 mb temperatures near 5 Celsius, expect maximum
temperatures from the mid 60s to near 70 degrees.

Tonight...Mostly clear and not as cool with the ridge axis
aloft moving over Wyoming.

Friday...The warming trend continues as the ridge axis aloft moves
over the Wyoming and Nebraska state line. Maximum temperatures in
the mid 70s to lower 80s with 700 mb temperatures near 10 Celsius.
With adequate low and mid level moisture, along with low level
southeast winds converging across the Laramie Range, we may see
isolated afternoon showers and thunderstorms between Laramie and
Cheyenne.

Friday night...Low level convergence may spark isolated evening
showers and thunderstorms north of a Douglas to Scottsbluff line.
Minimum temperatures not as cool as the previous night as the
atmosphere moderates.

Saturday...Significantly cooler in the wake of passing cold front
and cooling north winds. With daytime heating, cool temperatures
aloft and adequate low and mid level moisture, will see isolated to
scattered afternoon showers and some thunderstorms.

.LONG TERM...(Saturday night through Wednesday)
Issued at 238 AM MDT Thu May 6 2021

Overall, a low confidence forecast for late this weekend and into
early next week as a slow moving Pacific system stalls across the
northern Rocky Mountain region by Monday. The lower confidence
mainly relates to the precipitation type and how cold
temperatures may be Sunday through Tuesday. There is moderate
confidence that a decent amount of precipitation will fall across
southeast Wyoming and western Nebraska between Sunday night and
Tuesday, with snowlevels lowering below 8000 feet.

All models show the initial cold front and surge of cooler air
entering the Front Range late Saturday into Saturday night with
shower activity and some thunderstorms expected. All models also
show the Rex Block developing Sunday across the Great Plains and
into Canada. This will easily slow down this initial Pacific
system as it eventually retrogrades westward on Monday. Once the
system retrogrades into the Great Basin region, Pacific jet energy
will increase across the central Rocky Mountains along with WAA
aloft, with easterly upslope flow near the surface. Depending on
the position of the storm system, this is classic moderate to
heavy precipitation producer in the spring months as the slow
moving upper level trough/low takes it time to drift east across
the region with ample dynamic forcing in place along the Front
Range. Kept POP above 60 percent for the bulk of the forecast
area. Did not go quite as high as model consensus suggests, mainly
due to minor timing differences in the ensembles/ensemble plumes.

Temperatures are expected to be much below seasonal averages
between Sunday and Tuesday as the Pacific system takes its time
drifting southeast, and then eventually east, across the area.
Highs may struggle to reach the mid to upper 30s across the area,
especially on Monday. Did not go quite that cold with the official
forecast, but we`re not far away from those numbers either.
Models are also trending colder compared to 48 hours ago, with
precipitation type becoming more of a concern. GFS model soundings
show temperatures below freezing across most of southeast Wyoming,
with temperatures near freezing even across most of western
Nebraska late Sunday night through Monday night. WAA
aloft/overrunning can be clearly seen at the 700mb to 600mb layer
several times during the event and is within the lower range of
the suitable dendritic growth zone around -12c to -8c. For now,
this system bares watching with a good chance at heavy snow above
7000 feet. Towns and locations between 5000 to 7000 feet in
elevation also need to watch this system closely. For now, kept
mainly snow above 6500 feet and rain/snow mix down to 5000 feet.

Models in agreement for Wednesday showing the system slowly moving
east of the forecast area. Expect warmer temperatures and
decreasing cloudiness through Thursday of next week.

&&

.AVIATION...(For the 06Z TAFS through late Thursday evening)
Issued at 1135 PM MDT Wed May 5 2021

An upper level ridge axis will begin pushing into southeast Wyoming
and western Nebraska tonight and Thursday. Dry and quiet weather is
expected for Aviation over the next 24 hours.

HAZARDS/WEATHER TRENDS: VFR conditions will continue through 18z
Thursday. West winds may gust around 20 knots after 18z.

&&

.FIRE WEATHER...
Issued at 238 AM MDT Thu May 6 2021

Afternoon humidities will be low today and Friday
west of Interstate 25, with gusty winds developing, especially on
Friday. However, the green-up will limit concerns. Cooler
temperatures and increasing chances for precipitation will limit
concerns for the weekend and early next week.

&&

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

$$

SHORT TERM...RUBIN
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...RUBIN