FXUS65 KRIW 172135

Area Forecast Discussion
National Weather Service Riverton WY
235 PM MST Sat Nov 17 2018

.SHORT TERM...(This evening through Sunday)
Issued at 1248 PM MST Sat Nov 17 2018

Low clouds are taking their time dissipating and sliding off to
the southeast as the trough that delivered the substantial snow to
the area last night exits to the southeast. Without anymore QG
forcing, isentropic lift, and jet dynamics to work with, its just
a matter of a couple of hours before drier air works its way into
the area in the first couple of thousand feet from the nw, which,
according to the fcst soundings, will be around 00Z. This will be
a classic set up for at least patchy fog in the basins and
valleys that received snowfall last night and this morning as with
skies clearing right at sunset resulting in good radiational
cooling while retaining our sfc moisture. Except for increasing
southwest winds in Casper later tonight, coincident with the
development of a lee side sfc trough, winds will be light tonight
and Sunday morning. Tonight's temps will be comparable to what
occurred last Monday morning, with some of the cold spots in
protected areas west of the divide approaching 10 below. With
increasing winds expected from South pass to Casper Sunday,
expect blowing snow to occur in those areas, especially before
temps warm up above freezing in the lower elevations as this area
mixes out Sunday. Temperature inversions will be prevalent in the
basins and valleys through Sunday.

.LONG TERM...(Sunday night through Saturday)
Issued at 107 PM MST Sat Nov 17 2018

The end of the weekend will see some increasing cloudiness from
the north as a weak shortwave trough moves from southern Canada
into the northern plains. Winds across Johnson county should
become more northerly with some low to mid-level clouds during the
night, but not expecting any precipitation along the Bighorns with
the weak instability from SE MT into NW SD. The cloudiness and
cooler mid-level temperatures should weaken any basin inversions
and warm low temps Monday morning. Monday will then see clearing
from west to east as high pressure builds over the Intermountain
West. Nightly inversions are expected to build Tuesday and
Wednesday mornings as the mid-levels warm and skies clear out.
Exceptions might be from eastern Sweetwater county NE into Casper
area where SW wind could keep the lower layers mixed overnight.
Afternoon temperatures will warm through Wednesday as well,
depending on the amount of snow melt that occurs under the mostly
sunny skies. The upper level ridge axis is expected to move
eastward Wednesday night as strong shortwave troughs move from the
Pacific onto the west coast. Clouds will increase over western WY
Wednesday night, and by Thursday morning some snow showers could
been seen in the western mountains. The first shortwave trough is
forecast to eject off the main PacNW low into the western US on
Thursday bringing moist zonal flow into western WY. This pattern
will bring some good snowfall to western WY as well as increase
winds across southern into central WY. This first trough move
quickly through the state by Friday morning with a brief reprieve
on Friday. The larger trough then slides eastward into the
northern Rockies bringing more zonal moist flow into western WY
Friday night into Saturday. Still seven days out, but Saturday
looks to cool down a bit with the trough passage and more
widespread precipitation.

Overall, Sunday night through Wednesday night looks rather mild
over the area, with a more active and snowy pattern from Thursday
morning into the weekend.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening

Expect occasional MVFR ceilings through 21Z in the vicinities of
KBPI, KPNA, KLND, KRIW,KCPR, and KWRL. VFR conditions are
expected at KJAC, KRKS, and KCOD before clouds dissipate and move
off to the southeast by sunset.

Clear skies will prevail 00z-12z Sunday with some patchy fog
partially obscuring lower river valleys, and vicinity lakes and
reservoirs. Have indicated VCFG at KRIW,KWRL, and KPNA.

Occasional blowing snow could occur from 15Z to 18Z Saturday at
KCPR before temperatures rise above freezing there after 18Z,
during which time winds will blow at 22024G34kt. These winds will
continue through Sunday afternoon at KCPR.


Issued AT 1248 PM MST Sat Nov 17 2018

Periods of light snow will end from north to south across the
area through the rest of the afternoon with all areas largely dry
by sunset. Tonight looks to be mainly clear and cold with patchy
fog. Relative humidity will remain well above critical levels.
Wind will be light to moderate in most locations but locally gusty
across Natrona County Sunday. Some blowing snow is expected mainly
from Beaver Rim to Casper Sunday. Mixing will be generally fair
to poor. Inversions are likely across the basins and deeper
valleys on Sunday.





LONG TERM...McDonald
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