Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 211738 AAA

Area Forecast Discussion...UPDATED
National Weather Service Cheyenne WY
1138 AM MDT THU JUL 21 2016

Issued at 546 AM MDT Thu Jul 21 2016

We are sending out a quick update to let the Heat Advisory expire.


.SHORT TERM...(Today through Saturday)
Issued at 237 AM MDT Thu Jul 21 2016

The main concern with this forecast package is how hot
temperatures will be during the next couple of days.

Latest radar loop was showing a few showers in the northern
Nebraska panhandle in association with a weak surface trof. These
showers should mostly dissipate by sunrise as the surface trof
shifts east of the area. Meanwhile, we are already seeing the
weak surface high building south from northern Wyoming which
should allow for the surface flow to turn north across the entire
area by midday. This trof should act to suppress the convection
this afternoon, but we still cannot rule out a few showers and
isolated thunderstorms in the mountains this afternoon. Otherwise,
it will be a dry and hot day, especially in the panhandle.
Although, it will not be quite as hot as yesterday, but highs
will still be generally above the century mark in the panhandle.
We do plan on letting the heat advisory expire since it is not
expected to be quite as hot as yesterday.

The surface flow should begin to turn back to the east which will
allow for the low level moisture to advect into the panhandle.
Temperatures should be able to cool off fairly well due to better
radiational cooling affects.

Latest water vapor loop was showing several upper level potential
vorticity (pv) anomalies spinning across the Eastern Pacific. The
southern most pv anomaly appears to be finally shifting east in
response to the other anomalies shifting south. The models have
been struggling on the timing of this feature moving through the
northern Rockies. In fact, they are much slower with moving this
anomaly into the Northern Plains than a couple of days ago. With
this in mind, it should allow for a better fetch of moisture into
the southeast Wyoming and the Nebraska Panhandle on Friday. As a
result, we have bumped up precipitation chances during this
timeframe with even the potential for a few strong storms in the
panhandle. The storms should gradually dissipate through sunset.

The slower trend of this wave may affect Saturday as well. We are
still thinking that the weak frontal boundary should shift east of
the forecast area on Saturday morning and keep things dry. However,
if things slow down we may have to keep a chance of showers and
thunderstorms in the picture for the Nebraska panhandle.

.LONG TERM...(Saturday night through Wednesday)
Issued at 237 AM MDT Thu Jul 21 2016

Temps will be around 5 degrees cooler on Sunday behind the Saturday
fropa.  Isolated to scattered convection will be possible each aftn
from Sunday through Tuesday for areas to the east of the Laramie
Range.  At this time it is difficult to pinpoint the day that will
have the most widespread tstms.  Both the GFS and ECMWF indicate the
best instability on Monday, so could be some potential for strong to
isolated svr storms. The subtropical ridge builds westward over the
Great Basin by Tuesday into the middle of next week.  Some drying
could occur by Wednesday as heights aloft rise and drier westerly
flow moves into the region.  Although RH values will fall to around
15 percent for areas to the west of the Laramie Range each aftn,
winds should not be overly breezy, so no fire weather concerns are
anticipated at this time.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1129 AM MDT Thu Jul 21 2016

VFR. Scattered high-based cumulus becoming broken invof southeast
Wyoming mountains mid-late afternoon with isolated showers/weak
tstorms developing (VCSH Laramie and Cheyenne from 21Z-03Z).
Convection dissipates after 03Z with scattered to broken clouds
AOA 15000 ft AGL through the night. North to northeast winds will
be breezy at times, except locally gusty/erratic winds invof of
showers. Winds will become light and variable later this evening.


Issued at 237 AM MDT Thu Jul 21 2016

It will continue to be very dry and hot today, but wind speeds
should continue to be 10kts or less which will limit any fire
spread. Low level moisture will be on the increase on Friday along
with a chance of thunderstorms. However, critical fire conditions
are not anticipated. The only potential fire starts could be from
lightning from the thunderstorms. Saturday looks to be a bit more
breezy...but relative humidities may be rather marginal. We will
continue to monitor this timeframe for potential red flag


.CYS Watches/Warnings/Advisories...


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