Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 200551
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1151 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 06Z TAFS through 06Z Saturday night)
Issued at 1148 PM MDT Fri May 19 2017

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

Isolated showers will linger from the southern end of the Wind
River Range to vicinity KRKS until around 09z, otherwise VFR
conditions will prevail through the early afternoon. An upper
level disturbance will dive south across western Montana Saturday
afternoon, across eastern Idaho Saturday night. Scattered showers
and isolated thunderstorms will develop ahead of this system
spreading south along and west of the Divide through the
afternoon, into vicinity KRKS by 00z Sunday. Brief MVFR conditions
will be possible with the stronger cells, along with occasional
mountain obscurations. This activity will dissipate from north to
south from sunset through late Saturday evening.

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

VFR conditions will prevail through early Saturday afternoon.  An
upper level disturbance will dive south into western Montana
Saturday afternoon, across eastern Idaho Saturday evening. This
system will spread widely scattered showers and possibly a few
thunderstorms vicinity of the Continental Divide into the central
basins Saturday afternoon evening, with some higher mountain
obscurations. VFR conditions will continue to prevail; however,
brief MVFR conditions are possible mainly vicinity KCOD-KRIW-KLND
and westward. This activity will dissipate from north to south at
sunset through Saturday evening.

&&

.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...Meunier
FIRE WEATHER...Baker



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