Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 231812

Area Forecast Discussion
National Weather Service Cheyenne WY
1200 PM MDT Wed May 23 2018

Issued at 1117 AM MDT Wed May 23 2018

Latest radar loop was showing the showers starting to develop over
the Laramie and Snowy Mountain ranges due to orographic effects
and weak cap. LAPS data is not showing much CINH over the forecast
area. As a result, we would expect the convection to be more
widespread today compared to yesterday. Storm motion will also be
a bit faster at speeds of 20 to 30kts with some gusty winds
possible on the leading edge of these convective cells with even
damaging winds possible with the stronger storms where the low
level flow parallels the stronger winds aloft. Steeper lapse rates
will also provide stronger updrafts/downdrafts which will also
yield to some hail producers up to golf ball size perhaps larger
if the effective shear is realized.


.SHORT TERM...(Today through Friday)
Issued at 250 AM MDT Wed May 23 2018

Main concerns this period will be with convection today, some of
it possibly being severe.

Skies have cleared over southern parts of the CWA early this
morning as a modest impulse is lifting northward into northern Wy.
Should see at least some sunshine this morning into this
afternoon over most of the CWA as drier air and subsidence
continues over the area behind the departing impulse.
convection should then begin firing over the mtns by mid-afternoon
as another weak wave lifts northeast across the CWA around a
weakening upper low over Montana. Decent instability should exist
over the plains this afternoon /about 1000-2000 J/kg/ and with a
belt of stronger mid level winds moving across should see better
organized storms over the far eastern Wy plains into the Panhandle
mid-afternoon into this evening. Large hail and strong wind gusts
expected to be the main threats from any storms. Convection should
weaken some and exit the CWA this evening with a weak surface
trough working eastward across western Neb.

Thursday and Friday looking warm and mainly dry as upper ridging
builds over the Rocky Mtn chain and drier air spreads over the
area on westerly winds. Could even see some max temperatures
surpass 90F over the Panhandle Friday.

.LONG TERM...(Friday night through Tuesday)
Issued at 250 AM MDT Wed May 23 2018

Unsettled weather returns Sunday evening into Monday as another
low pressure system moves into the central Rockies. Slow moving
low will keep chance for showers and thunderstorms at least
through Tuesday as downstream blocking ridge very slow to move
east. Southeast low level flow should bring Gulf moisture into
the area. Looks like a pretty good setup for another round of
heavy rain and severe thunderstorms.


.AVIATION...(For the 18Z TAFS through 18Z Thursday morning)

Thunderstorms are currently developing across the Laramie Range and
areas west of Interstate 25 early this afternoon. This activity will
become more widespread and stronger as thunderstorms move northeast
into western Nebraska late this afternoon. KCYS should see VCTS over
the next few hours while the western Nebraska terminals will begin
to see some activity as early as 21z to 23z. VFR conditions will
prevail, but MVFR VIS are expected around the heavier showers and
thunderstorms through early this evening.


Issued at 250 AM MDT Wed May 23 2018

Fire weather concerns expected to remain low for the rest of the
week with fuels non-critical due to greenup. Min humidities do
fall to around 15% out west Friday afternoon and 10% Saturday
afternoon but winds should remain in the 10-20 mph range overall.




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