Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 240359 AAA

Area Forecast Discussion...UPDATED
National Weather Service Cheyenne WY
959 PM MDT Sun Jul 23 2017

Issued at 953 PM MDT Sun Jul 23 2017

An evening zone forecast update to remove slight chance PoPs for
Converse and Niobrara counties. Recent HRRR radar reflectivity
trends keep showers and thunderstorms to the north of these
counties late this evening.


.SHORT TERM...(This evening through Tuesday)
Issued at 217 PM MDT Sun Jul 23 2017

Pretty quiet and hot weather pattern will be in place through Monday
with strong ridging aloft and limited monsoonal moisture. Visible
imagery shows scattered cumulus across southeast WY with the best
vertical develop along the southern Laramie Range near the Colorado
border. While much of the CWA will remain storm free through the
evening, the HRRR has been consistent at showing isolated convection
developing by late aftn over the Laramie Range, spreading eastward
into adjacent plains. Will maintain PoPs around 20 percent through
the early evening. With deep boundary layers and high T/Td spreads,
thinking that gusty outflow and downdrafts will be the main threat.

The pattern will be similar for Monday with ridging/subsidence aloft
keeping tstm chances rather limited. It will be the warmest day
in the short term with highs rising into the 90s to low 100s across
the plains. A sfc trough will stretch from around Laramie to Chadron
during the aftn. Not expecting much convective initiation along
the trough except in areas near the southern Laramie Range. The
models continue to show midlvl flow becoming more southwesterly by
Tuesday, which will transport subtropical moisture into the CWA,
especially across southeast WY. The GFS has PW values rising to
around 1 inch over areas to the west of the Laramie Range by Tuesday
aftn. With a weak shortwave trough moving into northwest Colorado,
there will be a much better chance of storms, particularly over
the western mtns (Sierra Madre/Snowy Range). Heavy rain will
definitely be a possibility with deep monsoonal moisture in place.
Went ahead and increased PoPs over areas to the west of the Laramie
Range by Tuesday aftn.

.LONG TERM...(Tuesday night through Saturday)
Issued at 217 PM MDT Sun Jul 23 2017

Energetic west-southwest flow aloft will keep an active pattern
in place Tuesday night through Thursday. Monsoonal moisture will
ride overhead within this flow pattern, so expect to see a good
chance for showers and thunderstorms through this time. A front
riding south across the forecast area Tuesday night will keep
showers/storms ongoing through the night, with upslope stratus a
good possibility in the post frontal environment Wednesday morning.
The best coverage for convection Wednesday afternoon will be along
and west of I-25. Return moisture in low level southeasterly
upslope flow looks to combine with moderate values of bulk shear
on Thursday to set the stage for a broader coverage of activity
across the area, with perhaps a stronger storm or two. A ridge
will build to our west on Friday, with a shortwave moving across
Wyoming in west-northwest flow. This wave will drag another front
south across the area with convection likely to be confined along
the front and within the higher terrain. Saturday will be drier
overall with warm temps and subsidence aloft.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 518 PM MDT Sun Jul 23 2017

VFR conditions are expected through the period. Light winds for the
most part into Monday morning then becoming a bit gusty by late
morning over parts of the Panhandle.


Issued at 217 PM MDT Sun Jul 23 2017

Minimal fire weather concerns through the middle of next week. With
a warm and dry airmass in place, minimum humidity values will drop
to 13-20 percent over portions of southeast Wyoming this afternoon
and Monday afternoon. We are not expecting any critical fire weather
conditions however, as winds will be relatively light. An increase
in monsoonal moisture on Tuesday and Wednesday will bring higher
relative humidity values and a better chance of wetting rains.




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