Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 180555
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1155 PM MDT Fri Mar 17 2017

.SHORT TERM...(This evening through Monday)
Issued at 146 PM MDT Fri Mar 17 2017

Tail end of yesterday`s shortwave/front are still affecting our nrn
and ern zones. Weak frontal boundary is keeping temps down across
the north and east and some moisture/upglide in the nw is generating
some very weak mainly flurries. Otherwise, ridge axis will be moving
in tonight for a dry period into Saturday afternoon. Next system off
the West Coast will begin approaching the far west late Saturday
into Saturday night. Frontal boundary will likely still be west of
the border at 00z Sunday with a area/line of showers/isold thunder
ahead of it moving towards or into far wcntral Wyo. Winds will be on
the increase ahead of this system for many areas and showers/isold
thunder in the far west will just aid to gusty/strong wind potential
late Saturday into Saturday evening. Pacific frontal boundary will
then sweep east across the area Saturday night/early Sunday before
nrn front pushes into the nrn zones Sunday morning. A couple jet
streaks, one across MT and another moving in from the west may
provide some jet support on top of this frontal area for developing
rain, mtn snow in the nrn Sunday with more isold coverage south.
Frontal sags further south Sunday night into Monday as passing
shortwave to the north aids in a building high into MT Monday.
Frontal boundary will likely sag all the way to the continental
divide along and east of the divide. Much colder north of this
boundary in the far north especially where rain could change to snow
by Monday morning. Lowered temps quite a bit with that thinking in
mind.

.LONG TERM...(Monday night through Friday)
Issued at 146 PM MDT Fri Mar 17 2017

The beginning of the work week looks to start off fairly seasonable,
with weak high pressure over the southern Rockies and a Canadian
push in the Northern Plains.  The result is kind of messy for WY
with a boundary draped across the central part of the state in a WNW
to ESE fashion.  Warm SW surface wind looks to dominate southern WY
on Tuesday with cooler SE flow across NE WY.  Models indicate
showery precipitation along the boundary, although there is
uncertainty on the placement, with the ECMWF trending more to the
north Monday night.  As the ridge amplifies somewhat on Tuesday, the
potential areas of precipitation move to the northeast.  All medium
range models are in agreement with the general pattern; the main
differences are the surface variables like precipitation and wind,
based on the varying weak shortwave troughs moving through the area
in general SW mid level flow.  Looks like a more dominant wave will
move into western WY Wednesday morning through.  Expecting snow in
the higher elevations, with a rain/snow mix in the lower elevations.

From late Wednesday through Friday however, the models are not in
good agreement.  The general pattern is for the high pressure to
move to the central plains allowing for a deep trough to move
through the western US.  The models are indicating good genesis to
the lee of the Sierras from the Las Vegas area into southern Utah,
but there are timing differences as well at latitudinal variations
which make confidence in the specifics difficult at this time.
Either way, later in the week from late Wednesday to early Friday
appears to turn cooler, with a chance of widespread precipitation,
and potentially breezy NW wind later Thursday.  The GFS, ECMWF, and
Canadian global models are all different though, so hopefully a
better consensus will develop over the weekend.  Later Friday though
does look like high pressure over the area before move unsettled
weather moves in Saturday and Sunday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday)
Issued at 1146 PM MDT Fri Mar 17 2017

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

VFR conditions will prevail through 00z Sunday. Increasing
southwest flow aloft will result in areas of LLWS developing
vicinity KJAC Saturday morning. Surface south to southwest winds
at 15-25 knots prevail across the area Saturday afternoon.

A Pacific cold front will move east across the area 03z-09z
Sunday. Scattered showers and isolated thunderstorms will develop
ahead and along the front Saturday evening, mostly concentrated
from southeast Idaho and along and north of vicinity KAFO. Rain
and snow showers will become more numerous with increasing
mountain obscurations 06z-12z Sunday with snow levels lowering to
near 8KFT. Most of the activity will remain along and north of a
vicinity KAFO-KPNA line. Expect areas of LLWS ahead of and with
the frontal passage through 12z Sunday.


EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR conditions will prevail through the period.  South to southwest winds will increase across the area Saturday afternoon along with areas of LLWS.  Winds will remain gusty Saturday night with a Pacific cold front moving east across the area 08z=12z Sunday.  Most precipitation with this front will remain along and west of the Continental Divide with mainly some passing mid and high clouds along the front across central Wyoming.



&&

.FIRE WEATHER...
Issued AT 146 PM MDT Fri Mar 17 2017

...FIRE WEATHER WATCH IN EFFECT FOR ZONES 280...281 AND 282 FOR
SATURDAY AFTERNOON AND EVENING...

Low fire danger through tonight as high pressure builds over the
area. Expect dry conditions with winds remaining light to moderate
in a vast majority of the area. Mixing and smoke dispersal will be
generally fair to poor. Fire danger will increase on Saturday as a
combination of gusty southwest winds, warm temperatures and relative
humidity falling into the teens in some areas. Critical fire
conditions are possible across the lower elevations of Natrona...
Johnson...Hot Springs and Washakie Counties. Therefore, the Fire
Weather Watch will continue. Isolated late day thunderstorms are
possible along the western border. Elevated fire conditions
elsewhere across the lower elevations of Central Wyoming due to
warm and windy conditions with min rh`s in the 20s to locally
upper teens.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Saturday afternoon through late Sunday night
for WYZ013-023-027.

Fire Weather Watch from Saturday afternoon through Saturday
evening for WYZ280>282.

&&

$$

SHORT TERM...Skrbac
LONG TERM...McDonald
AVIATION...Troutman
FIRE WEATHER...Skrbac



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