Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 231614

Area Forecast Discussion
National Weather Service Cheyenne WY
1014 AM MDT Mon Apr 23 2018

.SHORT TERM...(Today through Wednesday)
Issued at 300 AM MDT Mon Apr 23 2018

Main focus in the short term will be on the upper trough that is
currently over the nwrn CONUS. Satellite showing decent pcpn ahead
of it over eastern Idaho into Montana. This pcpn will spread east
across much of WY during the day today as the upper trough moves
slowly eastward. At the same time a cold front will move across WY
today, entering northwest parts of the CWA by noontime and
progressing across the rest of the CWA by early this evening.
Scattered showers should move across much of the CWA by late this
afternoon, with a few tstms possible as well given some weak
instability. Colder air filtering across the CWA through this
evening should change the rain over to snow. The bulk of the pcpn
will precede the colder air, so snowfall tonight should be light,
with a few inches or so possible over the higher mtn peaks.

Much colder across the CWA Tuesday with some gusty winds over the
plains as a surface high settles down the high plains. Widely sctd
snow showers will taper off during the day as the upper system
moves over Nebraska with clearing conditions from west to east
through the evening. Chilly temperatures Tuesday night with mins
in the teens and 20s. Return flow on the back side of the surface
high and upper ridging will allow temps to bounce back Weds with
maxs in the 60s over most areas outside of the mtns.

.LONG TERM...(Wednesday night through Sunday)
Issued at 300 AM MDT Mon Apr 23 2018

The mid-week through weekend forecast period is shaping up to be
somewhat active with a couple of shortwave upper troughs and
frontal passages. Wednesday will be milder with breezy westerly
winds developing west of the Laramie Range in the afternoon ahead
of the first wave and front. The front sweeps southeast across
the CWA late Wednesday night, with isolated post-frontal showers
west of I-25 lingering into Thursday morning. High temperatures
Thursday will be 5 to 10 degrees cooler, with gusty northerly
winds along and east of the Laramie Range. Ridging surface and
aloft will promote warmer and dry weather Friday, along with light
winds. Eastern Pacific upper low/trough approach the West Coast
late Friday, which is when the models diverge in their solutions
going into the weekend. The ECMWF/Canadian models take the low
pressure system into CA/NV, whereas the GFS` track is northeast
across OR/ID, becoming an open wave into western MT late Saturday.
Siding with the GFS would drag a weak upper level disturbance
through the CWA Saturday afternoon/evening, accompanied by widely
scattered showers/tstms across portions of southeast WY and
northwest NE. Saturday will be the warmest day of the long term
with highs in the 60s and lower 70s lower elevations. Sunday will
be a few degrees cooler, but dry. Southwest winds will be breezy
west of a Douglas-Laramie line Sunday afternoon with developing
surface trough over the far eastern WY plains.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1012 AM MDT Mon Apr 23 2018

Introduced thunderstorms into the 18Z TAFs this afternoon. Latest
HRRR guidance showing earlier than expected development this
afternoon, so moved up timing as well. Possibility of seeing KCYS
going IFR as winds turn northeasterly shortly after 00Z. WIll
continue to monitor unfolding events.

Issued at 300 AM MDT Mon Apr 23 2018

Concerns fairly low this week with weather conditions generally
non-critical. Min RHs fall to about 15-20 percent across lower
elevations of sern WY Weds and Friday, but winds are expected to
be below critical speeds. Cold front will pass across the districts
late this afternoon into this evening, with rain and snow over much
of the area, especially tonight into Tuesday morning.




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