Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 252029

Area Forecast Discussion
National Weather Service Riverton WY
229 PM MDT Sat Mar 25 2017

.SHORT TERM...(This evening through Tuesday) Issued at 223 PM MDT
Sat Mar 25 2017

Imagery shows very progressive but kludgy pattern with troffing west
(CONUS) and ridge ovr closed low east. Entrance region to exiting
jet near northern WY. SFC has a weak cold front through WY from
ncntrl to sw with weak high(er) P off to the west. Current ongoing
light precip along and post frontal with mainly virga north and
light snow/rain across swrn WY.

As the trof moves through the wrn CONUS, the lead portion of the
wave and moisture is currently moving into/across wrn/swrn WY.
Another round of moderately unstable conditions producing periods of
both rain and snow. Accumulating snow levels across wrn WY, while
near 6500 feet this morning, have saturated and warmed some...with
snow levels now rising above 7000 feet. The trof axis will cross the
western border tonight...with clearing from west to east behind the
front as it pushes south and east. Current snow amounts look to
remain below Advisory criteria fro most locations west of the
Divide...with AOA Advisory criteria above 7500 feet being met over
the Bighorn Mountains which will remain closer to the best upper
level forcing from the jet. Otherwise east of the Divide, there will
be a period of frontally forced and focused precipitation tonight.
QPF values will be greatest just to the east of the central Basins
across Johnson and Natrona counties with a changeover to snow
possible after midnight tonight. Most of this should be of the wet
type with little accumulation on roadways (perhaps a bit of
slush)...and perhaps a half inch to locally two inches on grassy

Sunday will be post frontal with weak ridging aloft ahead of the
next system/trof due to arrive Monday afternoon/evening across
western/southwestern WY. In the meantime from Sunday afternoon
through Monday morning...increasing but modestly moist west to
southwest flow will keep showers and possibility across the western
mountains. As the trof begins to bump up over western WY...the main
portion of the trof will dig southward across the Desert Southwest
with the best energy staying south of the FA...but still able to
return moisture up through east CO and into/across eastern WY by
Tuesday morning. With frontogenesis going on over central to
southeastern WY early Tuesday morning...temperatures may be cold
enough across the much of the area east of the Divide to snow in
some fashion into the late morning/early afternoon before changing
back over to rain later. ATTM...central WY...including portions of
Fremont, Natrona and Johnson counties could see a few inches of wet
heavy snow through the end of the forecast period...with heaviest
snow generally expected near the front over Natrona and southern
Johnson counties. Highlights possible...not probable at the moment.

.LONG TERM...(Tuesday night through Saturday) Issued at 223 PM
MDT Sat Mar 25 2017

Beginning of the fcst...exiting deep closed low trof continues to
head ewd into the Plains while the aforementioned front pushes out
of WY by Wednesday morning. Wednesday, shortwave ridging gets
squeezed into/over the FA ahead of yet another, and what looks to be
quite vigorous, shortwave trof racing toward the central and
northern Rockies and arrive across the western forecast zones
Thursday night. This system, while also plunging into the Desert SW
and srn Rockies, looks to have a Canadian type cold front already i
n tow which may end up providing snow chances for the entire FA from
nearly the get-go. However, it does look quite progressive, so other
than a brief "blizzard-like" period (hope not) it should mostLY be
out of the region by Saturday morning (hopefully). This final system
still has a lot of possible outcomes as all early maturing closed
upper systems do and will have a lot of mountains to traverse and
cause problems or mutations of sorts. Interesting to watch right
now...and deal with later.


.AVIATION...(For the 00Z TAFS through 00Z Sunday night) Issued at
223 PM MDT Sat Mar 25 2017


Areas of rain and snow and the associated MVFR/IFR conditions will
continue through about 03Z. Then precipitation will be ending after
03Z with VFR conditions prevailing by 06Z. Expect mountain
obscuration through this evening. Clouds will be decreasing after
08Z with patchy fog possible in the western valleys through mid
morning Sunday, with local MVFR/IFR conditions. Then VFR conditions
to prevail after 18Z Sunday.


Scattered showers will occur through this evening. The cold front
will continue to move south and east through the region into the
evening hours with a wind shift to the north or northwest. Areas
of MVFR conditions will develop late this afternoon and evening due
to low clouds and rain. Precipitation will be ending between 09Z
and 12Z. Expect some mountain obscuration. Ceilings will be rising
over the north to VFR by 07Z. Ceilings in the central and south
will rise toward 12Z Sunday with VFR conditions prevailing by 16Z
Sunday. Please see individual terminal sites for more details.


Issued AT 223 PM MDT Sat Mar 25 2017

Fire danger will remain low through much of the week. A very
progressive and unstable pattern has taken over the forecast area
and will remain in place over the next week or so. Periods of
precipitation will move across WY every other day or so along with
several frontal passages. Temperatures will be seasonal for slightly
be low seasonal for much of the time while winds remain in check,
relatively speaking. Smoke dispersion will be fair to good most


Winter Weather Advisory until 6 AM MDT Sunday for WYZ008-009.



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