Area Forecast Discussion
Issued by NWS Cheyenne, WY

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075
FXUS65 KCYS 301716
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1116 AM MDT SAT JUL 30 2016

.UPDATE...
Issued at 1020 AM MDT Sat Jul 30 2016

A tricky forecast for this afternoon. It still appears the overall
best chance for severe thunderstorms will be over east central Wyo
and the northern Neb Panhandle from the late afternoon through the
evening hours, closer to the upper jet. However, low clouds appear
to have completely eroded per visible satellite imagery. Much like
yesterday, widespread surface dew points in the 55-65 degree range
should support a very unstable environment. The only difference is
capping/subsidence in the wake of morning convection, so there are
still questions whether anything will develop at all today. Latest
HRRR runs show absolutely nothing, while other high-res model data
at least shows convection over the northern Panhandle. Best course
of action is to leave isolated/widely scattered PoPs as-is, mainly
along and east of the Laramie Range. Convection is possible toward
KCYS with good low-level convergence still in place.

&&

.SHORT TERM...(Today through Monday)
Issued at 315 AM MDT Sat Jul 30 2016

Today...May see some patchy fog across western Nebraska and far
southeast Wyoming through the early morning hours based on the
current temperature and dewpoint spreads.

Warming temperatures aloft as seen on thicknesses and 700 mb
temperatures expected to limit areal thunderstorm coverage this
afternoon. Still though, with a well pronounced low and mid level
theta-e ridge axis over our eastern counties and decent low level
convergence along a pseudo dryline, still expect widely scattered
afternoon thunderstorms to erupt along and east of Interstate 25.

Agree with the Storm Prediction Center outlook with marginal risk
east of a Douglas to Cheyenne line and slight risk over our northern
Nebraska panhandle where CAPES of 2000 to 3000 J/kg and shear of near
50 knots is progged. Warmer temperatures today and have gone close
with the agreeing NAM and GFS mos maximums.

Tonight...NAM indicating some type of convective cluster developing
this evening near our northeast counties, which seems reasonable
based on convective parameters and the mesoscale scenario, thus
will paint 20 to 30 percent evening pops north of a Lusk to
Bridgeport line with a few severe storms possible. Dry elsewhere.
Boundary layer progs suggest patchy fog again possible late night
over much of western Nebraska.

Sunday...Flow aloft becomes more zonal. With additional mid level
moisture and cooler mid level temperatures, along with a decent low
level convergence boundary across our counties, expect isolated to
scattered thunderstorms again in the afternoon and evening, most
numerous near the Colorado state line where the moisture will be
deepest. Compromised between the NAM and GFS MOS maximums for
highs.

Sunday night...Isolated to widely scattered evening thunderstorms
will end by midnight with loss of daytime heating, then clearing skies.

Monday...Zonal flow aloft prevails. Warm temperatures aloft with 700
mb temperatures near 16 Celsius will limit areal thunderstorm coverage
significantly, though agree with the NAM which depicts isolated
thunderstorms erupting in the afternoon along the Colorado state
line from Laramie to Cheyenne near the low and mid level theta-e
ridge axis. NAM and GFS MOS high temperatures look good and have
been accepted.

.LONG TERM...(Monday night through Friday)
Issued at 345 AM MDT Sat Jul 30 2016

The latest medium range model guidance remains consistent with the
eastward translation of the upper high center from the Four Corners
to the south central Great Plains by midweek. Meanwhile, a Pacific
upper low/trough will track east along the U.S./Canadian border
Wednesday through Thursday. The flow aloft will be west to southwest
through much of the week, with little in the way of synoptic scale
lift. Most of the subtropical/monsoon moisture will remain over
Colorado and the Southwest. Afternoon convection will mainly be
confined to the mountains due to upslope, with some activity
spreading east onto the southeast Wyoming plains and southern
Nebraska panhandle through the evening both Wednesday and Thursday.
Above average warmth is forecast Tuesday with highs in the 80s to
mid 90s. A cool front will pass through the CWA Wednesday, with
temperatures moderating back to seasonal normals for Thursday and
Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1114 AM MDT Sat Jul 30 2016

Convection mainly out over the Nebraska Panhandle this afternoon
and evening. Confidence low for KCYS experiencing a repeat of
yesterday...but the threat is there. So did continue VCTS wording
in the KCYS TAF for this afternoon and early evening.

&&

.FIRE WEATHER...
Issued at 315 AM MDT Sat Jul 30 2016

Humidities will be relatively low along and west of Interstate 25
through Monday, with winds and wind gusts gradually increasing each
day. Thunderstorm coverage wil be less today compared to Friday,
then an increase in coverage will occur on Sunday before mostly
dry conditions prevail for much of next week.

&&

.CYS Watches/Warnings/Advisories...
WY...None.
NE...None.
&&

$$

UPDATE...CLH
SHORT TERM...RUBIN
LONG TERM...MAJ
AVIATION...GCC
FIRE WEATHER...RUBIN



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