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238
FXUS65 KCYS 260951
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
351 AM MDT Sat May 26 2018

.SHORT TERM...(Today - Sunday Night)
Issued at 349 AM MDT Sat May 26 2018

A pretty warm day expected across the CWA today as a 7H thermal
ridge shifts east over the high plains along with the upper ridge
axis. Max temps in the 80s over the plains with 90s below about
5000 feet. Mainly dry today as the upper flow becomes southerly
ahead of an upper low that will edge into the desert southwest. A
weak impulse will lift north ahead of the upper low tonight and
should set off some showers and maybe a few storms initially
around the mtns, then over east-central areas tonight. Sunday
looks to be more active as the upper low drifts into Utah while a
cool front settles south over the high plains. With pretty decent
CAPE progged over the plains Sunday afternoon /over 2000J/kg/ and
decent shear should see a few strong to severe storms during the
afternoon with large hail the main threat. Convection will
progress across the Panhandle Sunday evening with lighter activity
persisting across se Wy Sunday night as the upper low moves
little.

.LONG TERM...(Monday - Friday)
Issued at 349 AM MDT Sat May 26 2018

An active start to the extended forecast period appears likely, as
medium range models continue to suggest the potential for a severe
weather episode across the CWA on Memorial Day. The GFS/ECM are in
excellent agreement with a large closed 500 hpa low over the Great
Basin at 12z Monday. Surface cyclogenesis should take place across
eastern Colorado during the morning/early afternoon hours, with an
inverted trough extending N across the high plains of southeast WY
and the western NE Panhandle. Dynamic forcing should be sufficient
for scattered to numerous afternoon/evening thunderstorms. The big
question right now is the location/progression of the inverted sfc
trough. Nonetheless, the air mass along & east of this feature may
be quite favorable for vigorous convection with strong heating and
near 60 dew points contributing to well over 2000 J/kg CAPEs. Deep
layer shear vectors of 40-50 knots per the GFS would be supportive
of supercells, but w/the orientation being parallel to the surface
boundary we could see fairly rapid upscale growth. Hail/wind would
be the primary hazards, although a tornado threat may evolve where
low level shear becomes maximized near the triple point during the
late afternoon/early evening. This appears more likely to be south
and east of our area, but we could still see a westward shift over
the next day or two. The latest SPC Day 3 Slight Risk does a great
job highlighting this threat.

A warm & fairly unsettled pattern is likely to persist through the
majority of the week. Daily chances for convection are expected to
linger through at least mid-week w/ multiple disturbances embedded
within southwest flow aloft. In general, limited moisture and weak
dynamics should keep any activity fairly isolated after Mon. A bit
cooler on Tue/Wed with the mid-level cold core, but still at least
in the 70s for highs. Widespread 80s will likely return by Thu and
Fri.

&&

.AVIATION...(For 00Z TAFS through 00Z Saturday afternoon)
Issued at 505 PM MDT Fri May 25 2018

VFR. Scattered cumulus clouds early this evening will give way to
mostly clear skies tonight. Winds will be light and variable.


&&

.FIRE WEATHER...
Issued at 349 AM MDT Sat May 26 2018

Overall concerns will be on the low side into early next week. It
will be quite warm today with some gusty winds and low humidities
over western districts this afternoon but fuels non-critical. An
approaching low pressure area will bring increasing chances for
showers and thunderstorms to the area especially Sunday and
Monday, along with a cooling trend.

&&

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

$$

SHORT TERM...RE
LONG TERM...CLH
AVIATION...MAJ
FIRE WEATHER...RE