Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 190858

Area Forecast Discussion
National Weather Service Cheyenne WY
258 AM MDT Wed Jul 19 2017

.SHORT TERM...(Today through Thursday night)
Issued at 258 AM MDT Wed Jul 19 2017

A hot day is expected for much of southeast WY, and the western NE
Panhandle today. Upper-level ridging will strengthen w/ the models
showing rising heights and H7 temperatures around +16 to +19 deg C
at 21z. High pressure centered over Kansas/Oklahoma does not quite
move as far east today as earlier thought, so guidance has started
to force the main push of monsoonal moisture to the north and west
this afternoon. It may be tough to get much E of the Laramie Range
today with warm air aloft and limited moisture, but if so we would
expect most activity to occur after 21z. H7-H3 RH does not seem to
increase much in the models until 00z, and recent runs of the HRRR
have suggested things to be fairly quiet until later. Main changes
were to lower overall PoPs, especially this afternoon. We did keep
mention of isolated/scattered convection after 0z w/ higher PoPs W
of the Laramie Range.

The aforementioned high should move east for Thursday, allowing a
better push of mid/high level moisture across the CWA along with
stronger disturbances lifting northeast along the edge of the
ridge. PWATs still fairly high (1-1.5 inches along and east of the
Laramie Range, and around 0.75 to 1.0 inches for areas to the
west), but overall dynamic support is lacking. A few storms may
contain heavy rain with a localized flash flood threat, but it
appears most of the convection may occur where PW values are lower
for the most part. Temperatures on Thursday should be a bit
cooler with the increase in cloud cover.

.LONG TERM...(Friday through Tuesday)
Issued at 258 AM MDT Wed Jul 19 2017

Model consensus has backed off a bit on coverages of showers and
thunderstorms for the weekend as the main piece of shortwave
energy tracks off to the east and the deepest moisture stays to
our south into southern Utah and western Colorado. We do see a
trend in bringing the deep moisture axis northeast into eastern
Wyoming and western Nebraska by Monday, with a diffluent upper
flow setting up over the area. This would be a pattern that we
would look for to indicate the potential for backbuilding storms
and heavier rainmakers for early next week. Being we in the 5-7
day range at this time, best to stay closer to the ensembles for
now but should this trend continue, we would need to bring
thunderstorm chances up in the Monday to Tuesday timeframe as well
as consider potential impacts from heavy rain.


.AVIATION...(For the 12Z TAFS through 12Z Thursday)
Issued at 258 AM MDT Wed Jul 19 2017

VFR expected to prevail for the southeast Wyoming and the western
Nebraska Panhandle airports through tonight. With warmer
temperatures aloft today, we don`t expect much in the way of
coverage for thunderstorms in the mid to late afternoon hours,
with most of any buildups potetially setting up around Rawlins
this afternoon, but not all of the higher resolution models
indicate much over there, so with diminished confidence on having
coverages high enough to impact airports over the western parts of
our area will leave mention out for now in the forecast. As for
low clouds out east around Sidney and Alliance, we are not seeing
the stratus setting up in the moist upslope flow as we did
yesterday morning but would not be surprised to see a few low
clouds and light fog around Sidney at daybreak should the east to
southeasterly low level winds pick up.


Issued at 258 AM MDT Wed Jul 19 2017

Daily chances for showers/thunderstorms will persist over the next
few days, mainly over the higher elevations of southeast Wyo. Main
concerns with this activity will be lightning as well as gusty and
erratic outflow winds. Otherwise, warm/dry conditions prevail with
afternoon RH values in the 15-20 percent range. However, winds are
expected to be light which will mitigate fire weather concerns.




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