Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 191958
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
158 PM MDT Fri May 19 2017

.SHORT TERM...(This evening through Monday)
Issued at 150 PM MDT Fri May 19 2017

Cool brisk north northwest flow will spread from northwest to
southeast across western and central Wyoming tonight through
Monday. A series of weak low pressure short wave troughs and
associated Canadian cold fronts will bring scattered, mainly
mountain, snow showers with isolated afternoon and evening
thunderstorms to the area. Some areas over and near the mountains
may see half inch rainfall amounts with snow generally above 8500
feet with local 5 to 10 inch snowfalls along the continental
divide and over the backbone of the Bighorn mountains.
Temperatures will slowly rise Sunday and Monday.

.LONG TERM...(Monday night through Friday)
Issued at 150 PM MDT Fri May 19 2017

The last visages of the mean trough over the east half of the U.S
will be affecting us Monday evening as the northern stream shortwave
tracks to our south southeast and another weak vort lobe follows
behind. We can expect lingering shower activity Monday evening with
snow levels between 7000 and 8000 feet with the lowest snow levels
over the Big Horn Mountains closer to the cold core trough. Not much
in the way of precip is expected however due to the short residence
time with this fast moving system. Skies will clear after 06z
Tuesday with the potential for a frost/freeze event Tuesday morning,
with the coldest temps in the western valleys and basins. On
Tuesday, expect mostly to partly sunny skies as the ridge eventually
builds in from the west and high temperatures warm to the 70s at the
lower elevations east of the divide to the 60s west with the "dirty"
NNW flow loosening up. Then, we can expect a pattern change as the
ridge continues to build into the area from the west, with h7 temps
rising to between 10c to 11c with highs in the 80s east and 70s west
Wednesday and Thursday with increasing snow melt expected. By
Thursday, the ridge will begin to flatten out as the next next
upstream shortwave approaches from the west. This will result in an
increasing chance of late day thunderstorms in the west and north
Thursday through Friday with temps beginning to cool Friday. The
ECMWF appears to the outlier keeping the ridge axis to our west
until this next shortwave approaches.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 150 PM MDT Fri May 19 2017

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

The upper low pressure system over Colorado will slowly lift into
the High Plains this evening along with low clouds along the
Interstate 80 corridor and the Upper Green River Basin and
surrounding mountains dissipating and lifting for the remainder
of the afternoon. Elsewhere, the highest ridges will be
occasionally shrouded in cumulus clouds 4k above the valley
floors. Elsewhere, expect mainly VFR conditions. Slight
instability for the remainder of this afternoon will result in
scattered rain and snow showers developing over the high terrain
and moving southeast, vicinity KJAC-KPNA-KBPI, possibly pushing
south into vicinity KRKS this evening. Brief MVFR conditions are
possible with these showers. This activity should dissipate from
NW-SE 03z- 09z Saturday. Another round of showers and a few
thunderstorms will develop after 18z Saturday.

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

An upper low pressure system over the central Rockies will slowly
lift into the High Plains this evening. Areas of MVFR ceilings
should begin to lift and dissipate after 22z leaving prevailing
VFR conditions for the rest of this afternoon with some higher
mountain obscurations. Clearing from northwest to southeast is
expected this evening and overnight with some patchy valley fog
possible early Saturday morning. Another round of showers and a few
thunderstorms will develop after 18z Saturday, mainly in the
mountains.

&&

.FIRE WEATHER...
Issued AT 150 PM MDT Fri May 19 2017

Cool brisk north northwest flow will spread from northwest to
southeast across western and central Wyoming tonight through
Monday. A series of weak low pressure short wave troughs and
associated Canadian cold fronts will bring scattered, mainly
mountain, snow showers with isolated afternoon and evening
thunderstorms to the area. Some areas over and near the mountains
may see half inch rainfall amounts with snow generally above 8500
feet with local 5 to 10 inch snowfalls along the continental
divide and over the backbone of the Bighorn mountains.
Temperatures will slowly rise Sunday and Monday. With some
clearing mid day Saturday, mixing heights will lift with warming
and northwest winds mixing down from aloft to produce fair to
good smoke dispersal Saturday afternoon. With more heating and
increased low level instability, mixing heights will continue to
increase from late morning through the afternoon hours Sunday and
Monday for good to very good smoke dispersal most areas. Heavier
areas of precipitation will significantly lower mixing heights
producing local poor smoke dispersal.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

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



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