Area Forecast Discussion
Issued by NWS Cheyenne, WY
FXUS65 KCYS 271129
Area Forecast Discussion
National Weather Service Cheyenne WY
529 AM MDT WED JUL 27 2016
.SHORT TERM...(Today through Thursday night)
Issued at 315 AM MDT Wed Jul 27 2016
Current KCYS radar loop early this morning shows scattered
thunderstorms from north of Douglas...extending eastward into the
northern Nebraska panhandle between Harrison and Chadron. This
activity is mainly due to a combination of a 65 knot jet max
pushing into eastern Wyoming along with the release of potential
instability above 800MB in the residual boundary layer. A few of
these thunderstorms have been pretty strong thus far with one of
them west of Chadron near severe thresholds. Increased POP along
and north of the Platte River valley between 25 to 35 percent for
scattered thunderstorms early this morning and gradually lowered
them after sunrise.
Forecast for today will be tricky as the cold front has settled
along the Laramie Range and Cheyenne Ridge. Stratus and fog has
not yet developed early this morning...and unless thunderstorms
dissipate and temperatures drop quick...do not expect stratus to
develop any time soon. Winds at Cheyenne and Pine Bluffs are
currently out of the west northwest...so it appears that the cold
front got hung up around the Cheyenne Ridge which may play a role
in convection initiation later today. Do not expect thunderstorms
further north to play much of a role in thunderstorm coverage this
afternoon due to available dynamics and moisture...but most of the
activity may be pushed back into the evening hours. There is a
marginal risk of severe thunderstorms east of a line from Casper
to Laramie today with 1000 to 1500 J/KG of CAPE and bulk shear
between 35 to 45 KTS. Today looks similar to yesterday with just
deeper moisture and greater amounts of moisture further to the west.
Believe most of the thunderstorms will be over SE Wyoming through
late this afternoon...and then shift east into western Nebraska.
Once again...models are hinting towards another round of nocturnal
convection tonight in the same areas as early this morning...but
maybe located a bit further south this time around.
Thursday looks on track as a possible high impact day for strong
to severe thunderstorms...mainly across the high plains of SE
Wyoming and central and southern Nebraska panhandle. Models have
consistently shown 2000 to 2500 J/KG of CAPE in these areas along
with 0-6km shear around 50 knots in addition to a stalled
frontal boundary along the Laramie Range. Added severe wording to
the forecast mainly along and east of the Laramie Range with
strong winds...large hail...and even a few tornadoes possible.
Large hail over 2 inches in diameter is also a concern with model
soundings showing high lapse rates between 600mb to 400mb...which
coincides with the critical 0C to -20C layer. However...timing is
still uncertain due to the constant fluctuating position of the
frontal boundary. Kept POP between 30 to 60 percent Thursday
afternoon through late in the evening. Patchy fog and low stratus
is also a concern after midnight. High temperatures will be
noticeable cooler Thursday afternoon...although there is
considerable amount of variability in model consensus and
ensemble members. Kept highs near or slightly below average for
now across the eastern plains...although would not be surprised
to see some locations struggle to reach the mid to upper 70`s due
to cloud cover and persistent upslope flow.
.LONG TERM...(Friday through Tuesday)
Issued at 255 AM MDT Wed Jul 27 2016
Friday...Flow aloft remains northwest. With less low and mid level
moisture available...believe mainly isolated thunderstorms will
occur in the afternoon and evening.
Saturday...With the ridge aloft moving overhead, thunderstorm chances
will decrease, thus have painted only isolated late day
Sunday...Ridge axis moves to our east. With warm temperatures aloft
again progged, thunderstorm coverage only isolated at best.
Monday...Flow aloft becomes southwesterly with the models hinting
at a return of isolated thunderstorms in the afternoon on the
leading edge of monsoonal moisture
Tuesday...Southwest flow aloft will aid in the infiltration of
increased low and mid level moisture and an increased chance of
thunderstorms along and west of I-25...where a low level
convergence boundary will set up in the afternoon.
.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 525 AM MDT Wed Jul 27 2016
Wyoming TAFS...VFR prevails. Isolated thunderstorms this
afternoon and early evening producing wind gusts to 35 knots.
Localized IFR at Cheyenne after 09Z Thursday morning.
Nebraska TAFS...VFR prevails. Isolated to scattered thunderstorms
this afternoon and evening producing localized MVFR and wind
gusts to 35 knots. Localized IFR at Scottsbluff after 09Z
Issued at 207 AM MDT Wed Jul 27 2016
Minimal Fire Weather concerns through the remainder of this week.
Showers and thunderstorms will increase in coverage over the High
Plains as moist upslope flow will become more dominant through
Thursday. There is a good chance of wetting rains east of the
Laramie Range into Friday along with daytime relative humidities
between 35 to 50 percent. It will be drier west of the Laramie
Range...but winds will be variable and relatively light.