Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 182006
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
206 PM MDT Sat Mar 18 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 153 PM MDT Sat Mar 18 2017

Lots of lee enhanced clouds off the divide today but temps are still
rising fairly quickly early this afternoon. Cold front is still a
long way off. Weak initial front looks to be in wrn ID early this
afternoon and will not arrive until later this evening. It still
looks like there will be enough instability and possible jet support
for a line of showers and a few thunderstorms moving into the far
west, especially wc/nw as the evening wears on. The actual shortwave
doesn`t arrive until early Sunday. The `nrn` front will then arrive
Sunday afternoon and be aided by shortwave passing to the north and
building surface high to the nw. Front looks like it will make a
push up against the hills in central Wyo Sunday night. The bigger
question is will it wash out in the srn part Monday afternoon. The
NAM/WRF say yes and the GFS no (at least for Natrona and the nrn
part of the Wind River Basin). Will have to watch this closely.
Counting on it mixing out somewhat especially around here but will
need to watch it closely. The far north will be quite cool if not
chilly with potential for some cold rain or even rain/snow mixture
Monday but definitely sharply cooler/colder with low clouds. The
somewhat unstable sw flow will continue in the west through the
short term with embedded shortwaves and periods of valley mostly
rain showers and some mountain snow. Nothing significant in any
short period of time but still unsettled with a few inches every 12
hours possible in the especially the nw mtns with some isold late
day thunder still possible into Monday. Some limited instability
near the nrn border Sunday with front so that`s worth watching and
also in the south where I`m keeping my isold storms going. Still
some weak instability in the far west/sw Monday so isold storms
still ok there. Brief shortwave ridging Tuesday but still embedded
moisture and ripples for some showers around the higher
terrain/mountains, especially west.

.LONG TERM...(Tuesday night through Saturday) Issued at 153 PM
MDT Sat Mar 18 2017

By Tuesday night, the mean trough axis will be located along the
Pacific Coast. The shortwave that this trough will eject toward the
Canadian Rockies by mid week will tighten the southwesterly gradient
and draw in Pacific moisture ahead of it, resulting in snow showers
in the far west Tuesday night through Wednesday night with snow
levels starting out at around 7K Tuesday night, with the snow mixing
with rain on the valley floors out west by 00Z Thursday.

Then by later Wednesday night, the precip will decrease in the west
as the trailing northern stream shortwave exits the area and the
focus shifts to the southern stream energy that will break off the
aforementioned main trough along the Pacific Coast. This low will
close off Thursday and track northeast to the CO/KS/NE triple point
by 00z Friday. The GFS is farther north with the track of this low
than the Euro, even though the Euro extends the northwest back edge
of the primary area of precip farther northwest. For now will keep
the idea of the northwest back edge of the main area of precip
extending roughly from RKS to CPR Thursday and Thursday night. The
rain from this weather feature will mix with snow at the lower
elevations in our southeast zones east of the Divide Thursday
evening. This low pressure center will be more or less vertically
stacked so if this weather feature decides to track farther north
than what is currently indicated, it will have to be watched
closely.

After this weather feature exits the region, Friday should be mainly
precip free. Than the next upstream Pacific trough will approach the
area with the southwest flow increasing and drawing in more Pacific
moisture, once again increasing the chances of precip in the far
west by Saturday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday afternoon)
Issued at 153 PM MDT Sat Mar 18 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 for the rest of
this afternoon vicinity KJAC.  Surface south to southwest winds will
increase to 15-25 knots prevail across the area for the rest of this
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 this 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. Another area of precipitation will approach the far west
including the vcnty of KJAC by 22z Sunday.


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

VFR conditions will prevail through the period.  South to southwest
winds will continue across the area for the rest of this afternoon
along with areas of LLWS.  Winds will remain gusty tonight 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. Southwest winds will
increase once again after 15z Sunday.

&&

.FIRE WEATHER...
Issued AT 153 PM MDT Sat Mar 18 2017

Critical to near critical fire conditions will continue into the
early evening hours for fire zones 280, 281 and 282 where min rh`s
are in the 15 to 20 percent range and windy are gusting from the
south and southwest at 25 to 35 mph. Many areas will be breezy to
windy into the evening hours as a cold front moves in from the west
overnight. Areas west of the divide will be cooler and more moist
the much of the week with low fire danger although isolated
thunderstorms are possible the next couple days in the far west. A
cold front will move down from the north Sunday afternoon making
that area cooler and more moist with time, gradually spreading
into all of central Wyoming Sunday night and hanging around into
at least Monday for much lower fire danger as min rh`s will be
much higher and some showers will be around.

&&

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

Red Flag Warning until 7 PM MDT this evening for WYZ280>282.

&&

$$

SHORT TERM...Skrbac
LONG TERM...Lipson
AVIATION...Lipson
FIRE WEATHER...Skrbac



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