Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 242334

Area Forecast Discussion
National Weather Service Cheyenne WY
534 PM MDT Wed May 24 2017

.SHORT TERM...(This evening through Thursday)
Issued at 256 PM MDT Wed May 24 2017

Vigorous shortwave trough over central MT trailing from an upper
low over Alberta will continue to track SE`ward and drive a weak
cold front through SE WY and W NE Thursday. Models are showing
weak instability developing mainly over southern sections of the
area on Thursday afternoon along this front. The combination of
this instability and lift from the weakening shortwave/front will
allow scattered coverage of showers and thunderstorms tomorrow
afternoon. Relatively fast flow aloft will provide around 25 to 35
kt of effective bulk shear so could see a couple of strong storms
with small hail given freezing levels around 6200 ft.

On Friday, a second shortwave trough will rotate S`ward into western
part of the state.  SE`ly return flow will set up east of the
Laramie Range with sfc dewpoints rising into the mid 40s.  Steep mid
level lapse rates of 7.5 to 8 C/km will contribute to weak
instability once again.  Effective bulk shear will be stronger with
values of 40-50 kt Friday afternoon. This may be enough for a few
severe storms especially along and east of the Laramie range and
along the Cheyenne Ridge. Some question as to how far north the best
severe threat will be as the 12z NAM was indicating most of the
activity remaining south of the WY/CO border with the GFS being more
aggressive with the coverage of convection over SE WY and western

Any remaining convective activity should push south and east on
Friday night as a reinforcing shot of cooler air pushes in from the

.LONG TERM...(Thursday night through Wednesday)
Issued at 256 PM MDT Wed May 24 2017

Shortwave trough axis will move overhead on Friday night, with a
fropa occurring on Saturday morning.  Showers and isolated tstms
will be possible through Saturday aftn, especially across the
southern half of the CWA.  Temps will be around 10-15 degrees below
average on Saturday.  Northwesterly flow aloft will dominate the
pattern Sunday into early next week.  Things will dry out some, with
isolated to scattered storms mostly confined to the higher terrain
along and west of the Laramie Range where the best instability is
forecasted.  While highs will moderate back toward seasonal levels,
no big warmup is seen through the middle of next week.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 531 PM MDT Wed May 24 2017

Wyoming TAFS...VFR. Wind gusts 30 to 42 knots through 02Z, then
wind gusts 25 to 30 knots after 15Z Thursday. Isolated showers
after 16Z Thursday.

Nebraska TAFS...VFR. Wind gusts 25 to 30 knots through 08Z at
Chadron and Alliance, with wind gusts to 23 knots through 04Z at
Sidney. Wind gusts to 22 knots after 16Z Thursday. Isolated
showers at Sidney after 20Z Thursday.


Issued at 256 PM MDT Wed May 24 2017

Fuels are in greenup and with the recent heavier precipitation
and the expected continued chances of showers over the next few
days, fire weather concerns will be minimal.




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