Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 202017

Area Forecast Discussion
National Weather Service Cheyenne WY
217 PM MDT Tue Mar 20 2018

.SHORT TERM...(This evening through Wednesday)
Issued at 217 PM MDT Tue Mar 20 2018

Weak instability within northwest flow have sparked a few
shallow-topped snow showers across portions of the region. Latest
returns from KCYS 88D shows these popcorn showers across much of
the area. Area webcams confirm these snow showers reaching the
ground, if only for a brief time and w/o any impact. Progd
soundings suggest that this activity will continue until late
afternoon, before instability wanes and showers dissipate.
Northwest flow continues into Wednesday, but deepening upstream
system moving onto the Pacific Coast will result in amplification
of downstream ridge across the intermountain west. As a result,
don`t anticipate any afternoon shower activity Wednesday, with
low-level warm-air advection boosting high temps close to 50 west
and well into the 50s/low 60s across the eastern plains. Winds
will be breezy along and west of the Laramie Range with gusts of
30-40 mph expected.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 217 PM MDT Tue Mar 20 2018

Upper ridge axis continues amplifying along the Front Range
Thursday. Warm-air advection continues, with afternoon highs
warming well into the 50s west and into the 60s/low 70s across the
eastern plains. Mountain shower chances return Thursday afternoon
as instability creeps back into the region. Flow backs to
southwesterly Friday opening the gate for embedded shortwave
energy to move overhead. Above normal temps again on Friday will
yield weak afternoon instability (SBCAPES of 100-300 j/kg).
Isolated afternoon showers will be a good bet, with embedded
thunder likely west of the Laramie Range. Shortwave kicks into the
plains quickly, leaving conditions mostly dry and slightly cooler
compared to Friday.

Medium range guidance continues to point to a late weekend/early
next week storm system rolling thru the region. The system will be
in the process of splitting as it pushes into the rockies, which
always makes timing of impacts tricky. Nonetheless, both the
ECMWF/GFS begin to bring precip into the region Sunday
afternoon, with the bulk of if falling Sunday night and early
Monday. Temps will definitely be cold enough for snow, especially
with onset occurring at night. The ECMWF is slowest and farthest
west in splitting the energy off, which may result in snow
lingering into the day on Monday as well. Lots of details still to
be ironed out as it pertains to this system, but will likely see a
return to much cooler conditions along with some accumulating snow
Sunday night & Monday.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1134 AM MDT Tue Mar 20 2018

Breezy northwest winds at 15 to 25kts will continue to dominate
the area this afternoon. In addition, we will see more snow
showers, due to decent instability in place. However, these snow
showers will not be as widespread as yesterday, due to less
boundary layer moisture and more subsidence building from the
upper level ridge. Wind speeds are expected to be lighter
tomorrow, but it will still be breezy in KRWL.


Issued at 217 PM MDT Tue Mar 20 2018

Dry conditions with much above average temperatures setting up for
Wed-Fri. High temps will warm into the 50s/60s on Wednesday and
60s/70s for Thursday and Friday. Even so, minimum relative
humidities will generally fall into the 20-30 percent range.
Friday/Saturday look like the driest days with some afternoon
humidity values falling into the upper teens in the FWZ 310. Wind
gusts of 25-35 mph can be expected each afternoon in areas along
and west of the Interstate 25. The next shot of organized
precipitation returns for late in the weekend and into early next





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