Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 241034

Area Forecast Discussion
National Weather Service Cheyenne WY
434 AM MDT Sat Mar 24 2018

.SHORT TERM...(Today through Sunday night)
Issued at 400 AM MDT Sat Mar 24 2018

Current observations across the area show some low clouds and
patchy fog across east central Wyoming from Casper to Douglas, and
also across the northern Nebraska panhandle this morning. Kept
some patchy fog in the forecast through sunrise, but then expect
it to lift rapidly. Should be a nice day today with windy
conditions west of Interstate 25, and perhaps a little breezy
further east. Highs in the upper 50`s to mid 60`s are expected,
slightly cooler across the ridges of western Nebraska due to south
to southeast winds at the surface. With a weak llvl convergence
boundary near or just east of the Laramie Range, some showers
might try to develop in the afternoon, but not expecting much
other than sprinkles into this evening with marginal instability
and relatively dry conditions. A 100 kt jet will move into central
Wyoming late this evening, possibly resulting in scattered rain
showers with any remnant daytime instability from Carbon county
northeast into Converse and Niobrara counties tonight.

For Sunday and Sunday night, models are in good agreement showing
a weak upper level trough moving eastward across the Great Basin
region with some jet dynamics aloft across southeast Wyoming and
western Nebraska through late Sunday evening. A cold front is
expected to slowly push south through the day with limited
available colder air to work with. With colder air aloft moving
into the area, should be a good chance of thunderstorms across the
eastern plains later in the day. Better dynamic forcing in the
evening hours as a surface low forms across northeast Colorado,
so added thunderstorms to the forecast with some heavy rainfall
possible. Cold air will be limited behind the cold front with
models showing the system splitting as it moves into Wyoming. The
best chance for some appears to be across Carbon county and
further north near Douglas, Lusk, and possibly Chadron. Increased
POP between 50 to 70 percent across the eastern plains Sunday
evening, with maybe up to one inch of snow north of I-80.

.LONG TERM...(Monday through Friday)
Issued at 323 AM MDT Sat Mar 24 2018

The primary forecast concern/challenge in the extended period will
continue to be the evolution of an upper-level trough encompassing
much of the western CONUS on Monday and Tuesday. Overall, guidance
has trended considerably less aggressive with both the GFS and ECM
now keeping more of an open wave versus the significant closed low
we have been saying over the last few days. This results in a more
progressive pattern. In addition, the pattern is still expected to
split over the CWA by mid-day Monday with the bulk of the dynamics
shunted to the north and south. This would suggest more in the way
of shower activity instead of a widespread snow event. Also, still
some questions with precipitation type as even though 700 mb temps
should be plenty cold enough (-5C or lower), low-lvl winds are not
supportive of notable cold advection at the surface until later in
the day when the energy begins to split. The most likely areas for
any snowfall accumulations will be over our northwestern zones Mon
morning. this area will be in the deeper cold air, and might stand
a better chance of precipitation banding early with decent fronto-
genesis before dynamic support dwindles. Otherwise, this continues
to look like a fairly low impact event overall.

The pattern remains somewhat unsettled through the week, w/ active
northwesterly flow aloft and numerous disturbances embedded within
the flow. The GFS/ECM are in agreement w/one of the stronger waves
affecting the area Wed night and Thu, likely resulting in at least
isolated to widely scattered showers.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 323 AM MDT Sat Mar 24 2018

Some patchy fog has developed across the area, with MVFR
conditions to near IFR VIS expected near KCDR early this morning.
Fog is also possible around KAIA and KCYS this morning, but
confidence is pretty low at this time, so will exclude from TAF
for now. Gusty southwest winds will develop by late this morning
with gusts between 30 to 40 knots expected, mainly near KRWL and
KLAR through this afternoon.


Issued at 323 AM MDT Sat Mar 24 2018

Minimal Fire Weather concerns this weekend and early next week.
Relative humidities will lower between 20 to 30 percent today
ahead of the next cold front with southwest winds gusting up to 40
mph at times, mainly west of Interstate 25. Otherwise, an
unsettled weather pattern is expected through the middle of next
week with some snow and rain, colder temperatures, and higher





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