Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 202156

Area Forecast Discussion
National Weather Service Cheyenne WY
356 PM MDT Tue Jun 20 2017

Issued at 354 PM MDT Tue Jun 20 2017

Quick update to add some isolated thunderstorms into western
Carbon County late this afternoon and early this evening based on
latest satellite and radar trends. Any storms should be high-based
and may not produce much in the way of precip but isolated
instances of gusty winds may occur with any of these showers or
storms due to the deep, dry sub-cloud layer.


.SHORT TERM...(This evening through Thursday)
Issued at 150 PM MDT Tue Jun 20 2017

Weak shortwave energy will
track to our north tonight.  The strong upper ridge currently in
place over the SW US will flatten somewhat on Thursday as a stronger
shortwave moves quickly eastward along the Canadian border.  At the
surface, a weak trough/front will be located over western NE on
Wednesday trailing southwestward into CO.  This trough will
weaken/wash out on Wednesday night as a second front drops south and
across the area early Thursday.

Wednesday will be another warm day and with the surface trough to
our east initially, westerly to northwesterly boundary layer winds
will limit moisture and thus chances for convection, especially with
the continued presence of warm and dry air aloft. Early on Wednesday
evening some isolated to widely scattered convection is possible
over the mountains and along/east of the Laramie Range as winds turn
more easterly and upslope.

Heights aloft fall slightly on Thursday as the above-mentioned
shortwave tracks to our north. In the post frontal environment on
Thursday afternoon, models show fairly rich boundary layer moisture
characterized by dewpoints in the upper 40s to low 50s returning
east of the Laramie Range in northeasterly to easterly upslope flow.
This moisture will be topped by steep lapse rates and moderately
fast westerly flow aloft providing favorable instability/shear
parameter space for the development of locally strong/severe
convection.  Best chances for this will be along the Cheyenne Ridge
east of the Laramie Range where upslope flow should be able to be
maximized and any cap overcome.  Large hail looks to be the primary
threat with this convection.

.LONG TERM...(Thursday night through Tuesday)
Issued at 150 PM MDT Tue Jun 20 2017

Thursday night:
A few strong to severe thunderstorms still looks like a good bet
mainly across the southern portions of Wyoming into the southern
Panhandle. The NAM/GFS still are showing some capping taking place
especially across the panhandle, but we are still concerned that
some storms may fire along the Laramie range and may be able to
push into the southern Panhandle Thursday evening despite the
capping potential.

Cooler and drier conditions are in store for the area on Friday
ahead of a much stronger cold front. This unseasonably strong
front is progged to push through the area Friday night. A strong
gradient is possible along this front, which may result in some
abrupt changes Friday night. Temperatures may tumble into the 40s
by midnight along with the potential for rain showers with even
some snow showers possible in elevations above 9000ft. On
Saturday,the ensembles are showing the surface high pressure
(1028mb) nosing its way south along the Laramie Range on Saturday.
In fact, the NAEFS ensembles are showing mean sea Level standard
deviations about 2 to 3mb higher than normal for this time of
year. This will most likely result in a very chilly morning on
Saturday with lows starting out in the upper 30s in the Laramie
Valley, and low to mid 40s east of the laramie Range. Meanwhile,
afternoon highs may struggle to reach the 60s depending on how
long the rain and cloud cover hangs on.

Temperatures should begin to moderate during this period as the
upper level ridge slows builds into the area. In addition, drier
conditions should be in store early next week.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1152 AM MDT Tue Jun 20 2017

Latest satellite loop was showing very limited cloud cover around
noon with light winds. A weak shortwave is progged to move
through the northern sections of the forecast area overnight which
may trigger a few showers around CDR and AIA. Otherwise, gusty
west-northwest winds are expected to develop behind the shortwave
Wednesday morning.


Issued at 150 PM MDT Tue Jun 20 2017

Warm and occasionally breezy conditions will occur
each afternoon through Thursday to the west of the Laramie Range.
Fuels remain relatively green though which preclude much of a fire
weather concern.  Much cooler temperatures and some chances of
showers/rain are on tap for Friday into Saturday.




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