621
FXUS65 KCYS 311130
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
530 AM MDT Mon Mar 31 2025

.KEY MESSAGES...

- Snow and rain showers expected during the day Monday. More
  stratiform precipitation is expected Monday night into Tuesday
  morning with accumulating snow expected for the mountains and
  areas west of the Laramie Range.

- Winter Weather Advisory in effect for the Snowy and Sierra
  Madre Ranges for snow accumulations between 5 and 10 inches.

- Active pattern this week bringing near daily chances for precipitation.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 446 AM MDT Mon Mar 31 2025

Current radar returns from across the area show light precipitation
across the Interstate 80 corridor. ASOS stations and webcams along
Interstate 80 corroborate this with observations of falling snow and
rain. Some webcams even show patchy fog in areas with weak upslope
flow. Shower activity and fog will diminish this morning, with only
a brief break from precipitation expected. An upper-level shortwave
will begin to push into Wyoming today, increasing mid-level moisture
and lift across the region. Along with increasing surface
instability and low-level frontogenesis, scattered showers will be
able to develop as early as mid-morning across western portions of
the CWA. As the shortwave pushes further east throughout the day,
showers will also spread eastward and increase in coverage. By this
afternoon, showers will be along the Interstate 25 corridor and into
the Nebraska panhandle. Given that daytime highs will be in the 50s
today, precipitation will most likely be rain with rumbles of
thunder possible as SBCAPE values exceed 400 J/kg.

Later tonight, the shortwave axis will swing into the CWA, bringing
a heavier bought of more stratiform-like precipitation to the
western half of the CWA and northern Wyoming zones. Strong southwest
flow aloft will fuel prolific orographic snow in the Sierra Madre
Range before shifting more northwesterly by Tuesday morning,
favoring orographics in the Snowy Range. Because of this, moderate
to heavy snow can be expected in both the Sierra Madre and Snowy
Ranges late tonight into Tuesday morning. Winter Weather Advisories
have been issued during this time for both of the Ranges as snow
accumulations of 5 to 10 inches can be expected. Outside of the
mountains, a few other locations will need to be monitored to see if
Winter Weather Advisories are needed. Rawlins, Arlington, and the
Saratoga Valley will have the potential to see 2+ inches of snow
which could cause slick conditions. Per Hi-Res guidance, snow and
precipitation should taper off across the CWA throughout the day
Tuesday. Advisories for the mountains come down Tuesday evening,
with a few lingering snow showers expected Tuesday night.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 446 AM MDT Mon Mar 31 2025

An active wet pattern continues through the long
term forecast. Over the course of the day Wednesday, the Low
pressure system will slowly meander into the central and Northern
plains as that amplified ridge slowly moves east. By the late
evening Wednesday there will be a brief break in precipitation as a
weak transient ridge moves overhead. This break doesn`t last long as
another wave impacts the Rocky mountains to rejuvenate our
precipitation chances for the region Thursday afternoon. A deep mid
level trough develops as a low pressure system dives down the
California coastline and into the southwestern portion of the United
states. Following this low pressure system a positive tilted ridge
moves into the Pacific Northwest. This sends a shortwave through the
Rocky mountain for some snow or rain/snow mix (Nebraska Panhandle)
Thursday afternoon and evening. A small area of low pressure forms
in Northeastern Colorado to provide enough synoptic lift over our
region to continue our precipitation chances into Friday afternoon.
By Friday evening the mid-level ridge axis is settled over the
Washington and Oregon. At the same time the ridge over the Atlantic
coastline continues to build to quasi cut off the low. Yesterday the
global models where in disagreement on where this system will stall
for Friday into Saturday. Today the global models have trended
farther south to where the GFS was yesterday however, GFS continues
to trend southward as well. This southern track pushed the band of
heavier snow to southeast Colorado and reduced our Snow total
percentiles 0 to 4 inches for the 25th/75th percentile. Whereas
yesterday, A more northern track was favored and we were sitting
between 4 and 12 inches for the 25th/75th. The timing of the ridge
moving into the Rocky Mountains looks to be the determining factor
in relation to how much precipitation Southeast Wyoming and the
Panhandle will receive. This system will continued to be monitored
as some ensemble members still have a northern track that could give
us a couple inches of snow. But if the southern trends continue we
could also remain dry for this weekend with an area of high pressure
over us.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 530 AM MDT Mon Mar 31 2025

IMC conditions look to prevail this morning and eventually
turning into VMC this afternoon. Some fog has developed in some
locations dropping visibility to below 3sm at times. Another
round of showers look to start around 16z for KRWL and possibly
KLAR. These showers look to miss KCYS and KSNY but hit the
remaining terminals east of I-25. There is some CAPE this
afternoon so thundersnow may occur but other ceilings should
gradually lift from MVFR to VFR later on tonight.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory from 9 PM this evening to 6 PM MDT
     Tuesday for WYZ112-114.
NE...None.

&&

$$

SHORT TERM...SF
LONG TERM...MM
AVIATION...MM