Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 252128

Area Forecast Discussion
National Weather Service Cheyenne WY
328 PM MDT MON JUL 25 2016

.SHORT TERM...(This evening through Wednesday Night)
Issued at 328 PM MDT Mon Jul 25 2016

The surface trough is lined up just to the lee of the Laramie
Range this afternoon with east-southeast upslope flow in place
across the plains and westerly winds over the high country. Both
radar and vis satellite imagery show some activity along the
convergence zone, however nothing has really sustained until the
past few scans. GFS/NAM continue to show dry conditions today
while the RAP/HRRR/ECMWF develop activity for late this afternoon
along and east of this boundary. Believe more of the latter
solutions based on mesoanalysis showing CAPE of 500-1500 J/kg
analyzed across over the plains with a steadily weakening the cap.
So maintained chances for isolated storms this afternoon and
evening across the east with perhaps a vigorous storm or two
producing small hail and gusty winds.

Active west-northwest flow will remain overhead for Tuesday with
more moisture expected to be available for afternoon showers and
thunderstorms. The sfc trough/dryline will shift east toward the
WY/NE border during the late morning so the main focus for
development will be along this convergence boundary in the
afternoon. Do think more activity will occur over the mountains as
well with higher overall moisture in place. Once again, could see
a couple strong storms in the pool of higher instability over
the Nebraska counties.

Flow aloft will veer to the northwest on Wednesday while a weak
cold front drops south across the area early in the morning
hours. Increasing sfc dew points behind the front will increase
overall deep layer moisture while northeast sfc flow increases
deep layer shear. So still thinking the risk for better coverage
of strong/severe storms could be higher.

.LONG TERM...(Thursday through Monday)
Issued at 328 PM MDT Mon Jul 25 2016

Ridge of high pressure centered over the Great Basin will yield
relatively active northwest flow across the nrn Rockies at least
through Friday. Meanwhile at the surface, a quasi-stationary
frontal boundary across the eastern plains will the focal point
for afternoon and evening convection. Convective coverage and
organization look to be the best on Thursday with instability and
shear progs suggesting a few potentially strong to severe
thunderstorms (especially over the western Nebraska Panhandle).
Ridge axis passes overhead late Friday and Saturday, bringing in
dry conditions at least for Saturday and potentially into Sunday.
Model differences arise for early next week as the GFS wants to
strengthen the central CONUS ridge, which would back the flow to
the southwest across the Intermountain west (more active).
Comparatively, the ECMWF depicts a less active zonal flow.
Temperatures will be fairly cool Thursday and Friday, with some
warming by early next week.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1213 PM MDT Mon Jul 25 2016

Main concern to aviation ops will be the timing and coverage of
thunderstorm activity later this afternoon and into early this
evening. Latest forecast information suggests KCYS...KAIA and KCDR
will be best positioned to see thunderstorm activity 21-04z.
Coverage appears to be less compared to yesterday. Thunderstorms
will dissipate by late evening...with another round anticipated
Tuesday afternoon.


Issued at 328 PM MDT Mon Jul 25 2016

Marginal critical conditions are occurring this afternoon across
FWZ 306 and 309. Northwest wind speeds have been quite variable
gusting 15-25 mph...briefly to 30 mph at times...with humidities
in the low teens. Increasing cloud cover over these areas should
maintain lower wind speeds through the rest of the
afternoon...with gusts looking to hover around 20 mph through the
early evening. Tuesday looks to be another mostly dry day with
northwest wind gusts along and west of the Laramie Range around 20
mph once again. Coverage of showers and thunderstorms will remain
very isolated across the plains today, with increasing chances
across the district for Tuesday and Wednesday.


.CYS Watches/Warnings/Advisories...


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