Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 281730
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1130 AM MDT Tue Mar 28 2017

.SHORT TERM...Tuesday through Thursday night

Quite a difficult forecast for today as the systems is throwing some
curveballs. Precipitation is spreading across the area, especially
in the Wind River Basin in association with a jet streak moving
north across the area. Satellite imagery shows another surge of
colder cloud tops moving across border from Colorado. The models
show the area fairly well but look to be overdoing the QPF a bit.

The mashing of teeth is in regards to the precipitation type. As of
now, snow levels look to be running near 6500 feet. The webcam
around Beaver Rim is showing snow for example. In most lower
elevations, dew points remain rather high with wet bulb
temperatures above zero. There will be some further cooling
through this morning so there could be some mixing with snow or
even a changeover at times but with warm ground temperatures most
accumulation would be limited to non paved surfaces. And with the
high late March sun angle, snow would have a tough time sticking.
We gave serious thought to cancelling Winter Weather Advisories
except for the Big Horns but we let them ride at issuance. The
remainder of the day will be rather cloudy in the morning.
However, there could be some afternoon clearing the further west
you go. Most precipitation should end by dark. All in all, any
amounts in the lower elevations will likely end up low and mainly
on grassy surfaces. Another story will be the wind as the pressure
gradient tightens. Areas prone to gusty north winds like the Big
Horn Basin, Johnson County and even portions of Fremont County
will see gusty winds that will make it feel rather chilly.

A transitory ridge of high pressure will build across the area for
late tonight through Wednesday night and bring mainly dry conditions
and seasonal temperatures with light to moderate winds. All in all,
this looks like the nicest of the next three days. This means
seasonal to somewhat above normal temperatures, light to moderate
winds and a partly to mostly sunny sky.

The next shortwave then moves into the west later Wednesday night.
As a expected, the models have trended a bit slower so we cut POPS
on Wednesday night as the bulk of the precipitation looks to hold
off until Thursday morning. At this point, it looks to bring light
to moderate precipitation to areas West of the Divide. With
downsloping flow, areas east of the Divide will have a mainly dry
day, although a bit breezier. The fun may start later Thursday
night though, as an upper level low moves out of the Great Basin
and turns the flow upslope across many areas. This could bring the
s word back into the forecast for areas, although the worst would
be would be on Friday. My esteemed colleague will have more on
that.

.LONG TERM...Friday through Tuesday

The GFS and ECMWF models are still robust with liquid precipitation
in parts of central and southern WY Friday into Friday evening.
Then they hang on to lighter precip in the east Saturday morning,
then drying Saturday afternoon. Forecast 700MB temps would support
a change to snow in the Wind River Basin and long the Cody Foothills
Friday morning and then into Friday evening. Casper looks to be
rain at this point while Sweetwater county may be a mix of rain
and snow. The far west and parts of the Big Horn Basin will see
lesser precip from this storm Friday. Will see how the models
handle this in the coming days. Saturday will be dry for most
places except for the morning precip in the east zones. Model
differences come into play Sunday through Tuesday. The GFS model
is dry Sunday and Monday with a few showers making it into NW WY
by 00Z Tue. Then the GFS brings a weather system across the region
Monday night and Tuesday. Meanwhile, the ECMWF model has a weather
system moving through the area Sunday into Monday with a weaker
system on Tuesday. This would lead to a chance of precip all three
days. Each model has been consistent in their last few runs, so
deciding which way to lean is difficult that far out. For now will
go with a mostly dry day Sunday with a few showers in NW WY. Then
isolated to scattered rain and snow Monday through Tuesday. As for
temps, cool day Friday, then warmer Sat and Sun, then slightly
cooler Mon and Tue.

&&

.AVIATION...18Z ISSUANCE

Low clouds with rain and snow will continue from around KLND to KCPR
and south to KRKS through about 21z except to around 00z around and
west of KRKS. Snow and low cigs will keep KRKS IFR through 22z
before improvement to MVFR thru 02z. Ocnl MVFR cigs/vsbys will occur
from KLND to KCPR through 21z before improvement begins. Most areas
will be VFR tonight through Wednesday. However, patchy fog and low
clouds will develop where recent rain and snow has fallen mainly
near and south of a line from KLND to KCPR south to KRKS. Sweetwater
County and the KRKS area will likely have the most potential for IFR
cigs/vsbys later tonight and Wednesday morning.

&&

.FIRE WEATHER...

A front and upper level disturbance will move across the today and
bring some rain and snow to much of the area, with the steadiest
precipitation in the morning hours. A gusty north wind will
develop across the Bighorn Basin, Johnson County and portions of
Fremont County. Mixing and smoke dispersal will range from poor in
the west to fair to good East of the Divide. Mainly dry weather
will return late tonight through Wednesday before the next system
moves into the west later Wednesday night and Thursday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

Winter Weather Advisory until 6 PM MDT this evening for Wyz008-
009-019-028>030.

&&

$$

SHORT TERM...Hattings
LONG TERM...AR
AVIATION...PS
FIRE WEATHER...Hattings


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