Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 240324
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
924 PM MDT SAT JUL 23 2016

.UPDATE...
Issued at 911 PM MDT Sat Jul 23 2016

We continue to monitor a few weak showers and thunderstorms across
far southern WY and the southern NE Panhandle this evening, mainly
along a frontal boundary draped from west-east across the area. We
have seen a few strong wind gusts around 40-50 MPH due to the high
based nature of this convection; however, believe that threat will
diminish after sunset with higher T/Td spreads.

One major change to the inherited forecast for the rest of tonight
with respect to PoPs. The GFS/NAM both suggest very good low-level
warm air advection over the Plains after 06z, likely associated w/
the next shortwave currently upstream over northwest CO. Models do
show upwards of 1000-1500 J/kg of elevated CAPE overnight, and all
available guidance shows at least light QPF. The HRRR continues to
show robust convection well after midnight, which definitely makes
sense with an H25 speed max over our northern zones, and resulting
divergence aloft. Added mention of scattered showers/thunderstorms
through the night. Organized severe weather is unlikely with shear
being quite weak, but a few stronger storms are possible.

UPDATE Issued at 550 PM MDT Sat Jul 23 2016

Numerous showers and thunderstorms are occurring along I80 between
Pine Bluffs and Sidney late this afternoon. Based on recent trends
in radar/satellite imagery and HRRR guidance, added likely PoPs in
these areas through 03z this evening. Updates have been sent.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 310 PM MDT Sat Jul 23 2016

Afternoon water vapor loop showed the CWA between a upper trough
moving across the northern Rockies and another lifting northeast
across the northern Great Plains/Upper Midwest. Mesoanalysis/radar
analysis placed a weak front just east of I-25 with north-northeast
winds across the Nebraska Panhandle and far eastern Wyoming plains.
As predicted by the short-range models, isolated convection formed
along and just north of the Colorado border. Much of this activity
is high-based with inverted-v soundings indicating potential for
gusty outflow winds to 50 mph along with occasional lightning.
The convection should remain confined to far southeast Wyoming,
but a few could sneak into far southwest corner of Nebraska late
this afternoon. Convection should dissipate later this evening.

The short term model consensus shows the west-southwest flow aloft
veering to west-northwest and amplifying somewhat Sunday through
Monday as the southern CONUS upper high retrogrades westward across
the Four Corners region. Diurnal convection under this flow regime
will be limited to the higher terrain and nearby plains of southeast
Wyoming. Models prog a upper level disturbance to move southeast
across the Dakotas late Monday which may trigger isolated thunderstorms
over northwest Nebraska. Sunday will be about 10 degrees cooler than
today across the plains with highs in the 80s. Temperatures warm
into the upper 80s-mid 90s Monday with the amplifying ridge.

.LONG TERM...(Sunday night through Saturday)
Issued at 310 PM MDT Sat Jul 23 2016

West-northwest flow will be overhead at the start of the long
term period, veering more northwest by Friday as the upper high
retrogrades westward. A fairly steady stream of Pacific moisture
with embedded shortwave disturbances will remain overhead through
midweek, meaning there will be chances for showers and
thunderstorms each day across the region. Still looks like
Wednesday and Thursday could be the best chance for strong/severe
storms with increased llvl moisture, shear, and upslope flow
behind a cold front dropping south across the region late
Tuesday/early Wednesday. Temperatures will trend cooler, back to
more seasonable readings for this time of year. A reinforcing
front on Friday will maintain chances for t-storms over the
forecast area.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 530 PM MDT Sat Jul 23 2016

Showers/TStms to continue this afternoon along the I-80 Corridor
from KSNY to KCYS. Downburst winds of 30-35kts along with brief
heavy rain main hazards along with cloud to ground lightning. This
should continue through the 02Z-03Z timeframe before convection
eases. VFR and no hazards elsewhere for southeast Wyoming and
points north in the Panhandle.


&&

.FIRE WEATHER...
Issued at 310 PM MDT Sat Jul 23 2016

Warm, breezy and dry conditions will continue for much of east
and south central wyoming through monday with a ridge of high
pressure along the continental divide. Fire weather danger will
remain high in these areas. Across portions of southeast wyoming
and western Nebraska, there wil be slight chances for afternoon
and evening showers and thunderstorms. As the ridge shifts further
west next week, a northwest flow aloft and a couple of upper level
disturbances will increase chances for late day showers and
thunderstorms east of the Laramie Range.

&&

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

$$

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


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