Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 180909
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
309 AM MDT Thu Apr 18 2019

.SHORT TERM...Today through Saturday night

Any showers should end by sunrise. This will be followed by two of
the more pleasant days we have seen in a while across western and
central Wyoming. High pressure will build into the area and bring a
good deal of sunshine to much of the area along with seasonal
temperatures. There will be a bit of a breeze around at times in the
favored areas through. In addition, Johnson County will be downright
windy with some 35 knot 700 millibar winds mixing to the surface.
These should subside late in the day though. A couple of models have
the stray dot of QPF over the mountains. These are usually not
believable though so we left it out.

Friday at this point looks to be the warmest day so far this year as
thicknesses rise and flow turns southwest. This could be the day of
the first 80 degree temperature in the County Warning Area, more
than likely in a place like Basin, Worland or Greybull. At this same
time, a cold front will begin sliding toward the area from the north
and west. This will tighten the pressure gradient across the area
and bring breezy conditions to the favored areas from the Red Desert
through Casper. This could bring elevated fire conditions to some
areas in the afternoon.

The aforementioned cold front will begin to slide toward Wyoming
Friday night. The models continue to slow the front down through. As
a result, we removed most of the POPS for Friday evening and even
later at night and showers would be confined to the far northern and
western Wyoming. This front will then slowly slide into the area
Saturday into Saturday night. With the slower movement of the front,
most showers and a few thunderstorms will be confined mainly to
northern Wyoming with most central and southern areas having a dry
start to the weekend. We ended up raising high temperatures as a
result. Saturday night at this point looks to be the wettest time
with the front settling over the area and some overrunning
conditions developing. As for precipitation type through this
period, with 700 millibar temperatures generally remaining at minus 4
or higher, the valleys and basins would be mainly rain. This would
put snow levels anywhere from 6500 to 8000 feet, depending on
location. At this time, we do not expect a lot of heavy
precipitation due to a lack of upper level dynamics, with the jet
energy remaining over Montana.

.LONG TERM...Sunday through Thursday

The surface cold front looks to be across much of the forecast
area by 12Z Sunday. Early Sunday morning models are showing
isentropic lift over the surface front with a decent precipiation
shield expected over the forecast area. The mid-level low
(700-500 MB) is progged to gradually push northeast from southern
Nevada to northeast Utah/southwest Wyoming by 00Z Sunday. As this
occurs some models are showing the 700 mb flow becoming a moist
easterly upslope flow for areas east of the Divide that lasts into
Sunday night. Other models continue the isentropic lift over a
shallow frontal boundary. Snow levels look to be 5000 to 6000 feet
over the Bighorn Basin and Johnson County, 6000 to 7000 feet over
Fremont and Natrona counties, and 8000 to 9500 over western and
southwest parts of the forecast area Sunday lowering a bit Sunday
night. The upper low will slowly push east Sunday night, before
pushing into the Plains Monday into Monday night. This system
could result in significant valley rain (0.25-0.75), and several
inches of snow in the mountains in the Saturday to Sunday night
time frame. The precipitation looks to end from west to east
Monday, but the overall intensity/amounts for Monday look to be on
the light side as the main energy should have shifted away.

The consensus of 00Z models are showing mainly dry conditions and
a quick warming trend Tuesday through Thursday. However
yesterday`s 00Z runs still had the possibility of a weak system
or two impacting the area mid to late next week. Therefore will
keep some PoPs mainly over the northwest for now.

&&

.AVIATION...12Z Issuance

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals

VFR conditions will occur at the terminal sites. A gusty wind will
occur at KCPR airport from 16Z until 01Z, then decrease.

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals

VFR conditions will occur at the terminal sites. A gusty wind will
occur at KRKS, KBPI, and KPNA airports after 18Z through 01Z, then
decrease.
&&

.FIRE WEATHER...

High pressure will bring drier and warmer conditions to the area
today. Windy conditions will occur across Johnson County. A gusty
breeze will also occur across portions of Sweetwater, Lincoln and
Natrona Counties. Relative humidity will remain above critical
levels today. Mixing and smoke dispersal will range from fair to
good in the west to very good in eastern areas, especially Johnson
County. Elevated fire conditions will be possible Friday with warm
temperatures and a gusty breeze in some locations.
&&

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

$$

SHORT TERM...Hattings
LONG TERM...Murrell
AVIATION...Ross
FIRE WEATHER...Hattings


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