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000
FXUS65 KCYS 211813
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1213 PM MDT Wed Jun 21 2017

.UPDATE...
Issued at 1201 PM MDT Wed Jun 21 2017

Latest satellite loop was showing some decent convection starting
to develop across western Carbon and southern Natrona counties.
Latest look at the LAPS data was showing some decent instability
(800-1000j/kg) developing across northern Wyoming with decent
shear. This may be enough to produce some strong and perhaps a severe
storm or two near Converse, Niobrara and the northern Nebraska
panhandle later this afternoon. If any storms do manage to move
through these areas they may have the potential to be left movers
due to fairly linear hodographs or they become oriented in a
cluster. This is something we need to keep an eye on this
afternoon, especially if some of the storms become left movers and
produce large hail.




UPDATE Issued at 1048 AM MDT Wed Jun 21 2017

We are sending out a quick update to raise temperatures a couple
of degrees based on the latest trends and good downslope flow in
place. Still looks like the potential for a few scattered showers
and thunderstorms again late this afternoon. Otherwise, a hot and
breezy day is expected.

&&

.SHORT TERM...(Today through Friday)
Issued at 300 AM MDT Wed Jun 21 2017

Another very warm day today with highs similar to yesterday, in the
mid 80s to mid 90s over lower elevations. The surface trough will
shift eastward into central Nebraska by this morning, with
northwesterly winds across the plains. By the late aftn and early
evening, a lee trough will be located just east of the Laramie
Range, with winds weakening and gaining more of an easterly
component to the east of this trough. Convective activity should
be very similar to this past aftn, with isolated to widely
scattered tstms developing over southeast WY after 21-22Z.
Overall, only weak CAPE is shown due to the warm temps aloft,
however the GFS and NCAR ensembles do indicate some better llvl
moisture and instability (CAPE of 750 J/kg) in the convergence
along the surface trough by 00Z. While gusty outflow/downdraft
winds will again be the main threat, cannot rule out a stronger
storm producing small hail.

The cold front for Thursday morning is now coming in stronger than
previous model runs. High temps will be around 10 degrees cooler,
mainly across the plains. Along with the stronger northerly winds
through the morning, the GFS/NAM now push the best llvl moisture
into northeast Colorado with very limited instability and capping
across Laramie county eastward into the southern Panhandle. SPC
still has areas along Interstate 80 in a marginal/slight risk,
however current thinking is the best threat will be southward into
Colorado. Will have to watch model trends over the next day to
see if higher dew points can work northward. A cool, stable, and
mostly storm free day is depicted on Friday in the post frontal
air mass. This is the beginning of a cool stretch that will persist
into the weekend.

.LONG TERM...(Friday night through Tuesday)
Issued at 300 AM MDT Wed Jun 21 2017

00Z medium range models and their ensembles are in good agreement
with an active northwest flow aloft between a long wave trough
over the central/eastern CONUS and ridge over the western CONUS.
A couple of shortwave troughs will bring unsettled weather and
unseasonably cool temperatures this weekend. A reinforcing shot
of cool Canadian air will spread south and west across the CWA
Saturday. NAEFS ensembles continue to depict mean sea Level
pressure standard deviations of 2 to 3 mb higher than normal for
late June. Models, especially the ECMWF, have maintained the
cooler then normal trend for the past several days. Temperatures
Saturday will average 15-20 degrees below normal with highs in
the 60s lower elevations, with 40s and 50s for the high country.
Lows Saturday night will be chilly with 30s and 40s. Shower
coverage will be isolated to widely scattered, mainly along and
east of the Laramie Range. Snow levels will fall to 8500 feet
Saturday night, so there could be a few snow showers. QPF are
forecast to be light, though. Temperatures warm to near seasonal
normals early next week as the western CONUS ridge shifts east
across the Rockies and high plains.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1148 AM MDT Wed Jun 21 2017

Wyoming TAFS...VFR. Isolated thunderstorms from 22Z to 02Z. Wind
gusts to 35 knots through 02Z, then gusts up to 25 knots after 15Z
Thursday.

Nebraska TAFS...VFR. Isolated thunderstorms near Scottsbluff from
00Z to 03Z. Wind gusts to 30 knots through 00Z, then wind gusts
again to 30 knots after 15Z Thursday.


&&

.FIRE WEATHER...
Issued at 300 AM MDT Wed Jun 21 2017

Very warm temperatures will occur once again today, which will cause
minimum humidity values to drop to 12-20 percent across lower
elevations of southeast WY.  West to northwest winds will also gust
to 20-25 mph from late morning through the afternoon.  However,
fuels are still green and thus fire weather concerns are limited.
Isolated thunderstorms will be possible late this afternoon through
the evening with gusty outflow winds.

&&

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

$$

UPDATE...REC
SHORT TERM...ZF
LONG TERM...MAJ
AVIATION...RUBIN
FIRE WEATHER...ZF