National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS65 KCYS 281726
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1126 AM MDT Fri Jul 28 2017

.SHORT TERM...(Today through Saturday)
Issued at 416 AM MDT Fri Jul 28 2017

The focus for thunderstorms this upcoming aftn will shift eastward
into the western Nebraska Panhandle as drier air works into much of
southeast WY.  The models show a sfc trough along the WY-NE border
from 18-21Z with very high dewpoints (55-65F) to the east across the
Panhandle.  The NAM has CAPE values increasing to around 2000 J/kg
by early aftn.  Instability is actually a bit higher today compared
to yesterday with slightly warmer temps.  Decent northwesterly flow
will produce bulk shear values of 40-45 kts.  Thus, with an
environment very similar to yesterday that produced large hail and
damaging winds, supercells will once again be possible over our far
eastern zones.  PW values are much lower over areas to the west of
the Laramie Range (0.5-0.75 inches) so the storm threat will be the
lowest we have seen in the last couple of days.

Sfc winds by Saturday morning will become easterly across the plains
with higher dewpoints pushing westward to along the Laramie Range.
All models indicate better convective chances over southeast WY by
Saturday aftn as plentiful moisture (PW values rise to 1-1.2 inches)
returns to the area after a one day hiatus.  Also starting to get a
bit more concerned about heavy rain potential along and just east of
the Laramie Range due to a number of factors.  A weak shortwave will
move into northern Colorado with improving large scale ascent.  In
addition, steering flow is rather weak at around 10 kts along the
Colorado Border.  Went ahead and added heavy rain in areas near the
Colorado Border and this is something we will definitely have to
monitor with future model runs.

.LONG TERM...(Saturday night through Thursday)
Issued at 416 AM MDT Fri Jul 28 2017

A few storms look to continue on Saturday evening and overnight
east of the Laramie Range as a shortwave trough moves overhead.
PW`s around 1.25" will support heavy rain, so kept this mentioned
in the forecast through the evening. A broad area of high pressure
will then set up over the western Conus through the remainder of
the weekend and will persist through much of next week. Energetic
WNW flow will reside at the jet level initially, becoming more NW
on Wednesday. Persistent llvl upslope flow in this pattern will
maintain chances for showers and t-storms each day especially
along the Laramie Range and nearby locations so maintained at
least . slight chance pops each day. However, PW`s will dry out
some within NW flow, thus threat for heavy rain will diminish.
Temperatures through the period will not stray far from the 70s
and 80s so should be a rather pleasant start to August.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday morning)
Issued at 1126 AM MDT Fri Jul 28 2017

Expect low stratus/MVFR cigs over parts of the Panhandle to break up
early this afternoon leaving VFR areawide.  Isolated showers and
tstms again late this afternoon and evening mainly over the panhandle
with brief pd of MVFR cig/vsby around them.  Some low stratus may
develop again later tonight east of the mtns.

&&

.FIRE WEATHER...
Issued at 416 AM MDT Fri Jul 28 2017

No fire weather concerns through early next week.  A drier airmass
will exist today across areas to the west of the Laramie Range.
Minimum humidity values will drop to around 20 percent across lower
elevations of Carbon county this afternoon.  However, winds will be
relatively light.  Good monsoonal moisture will produce a chance of
thunderstorms through early next week.  Some of the storms will
produce heavy wetting rains, especially over the weekend.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

SHORT TERM...ZF
LONG TERM...RJM
AVIATION...RE
FIRE WEATHER...ZF