Area Forecast Discussion
Issued by NWS Riverton, WY
FXUS65 KRIW 261844
Area Forecast Discussion...Update
National Weather Service Riverton WY
1245 PM MDT Sun Mar 26 2017
.SHORT TERM...Sunday through Tuesday night
There should be a drying trend through the day today as the trough
and cold front that is moving through the area slowly moves away to
the east. The drier air is slow to move in however, so some showers
will likely linger in eastern areas through midday. As for the
advisory, this still looks good at this point so we will let it ride
as is. Otherwise, expect increasing amounts of sunshine today with
temperatures fairly close to normal. A few showers will continue in
the northwestern mountains as well but should be fairly light.
Another shortwave will approach the northwest tonight and could
bring some light precipitation there. However, this wave is looking
weaker with each model run so any amount of precipitation tonight
looks fairly light. Another system will try to push toward Wyoming
on Monday, riding the left front quadrant of a jet streak moving
into Colorado. It does appear a bit slower than yesterday, so we
cut POPS in the morning. Precipitation should spread further
northward in the afternoon. However, most areas East of the Divide
should have dry conditions for a vast majority of the day.
There is some model disagreement for Monday night into Tuesday
however. Both models do show some northeasterly upslope flow
developing Monday night into Tuesday.The NAM has trended a bit
further south with the best energy and 700 millibar and limits
precipitation. The GFS is further north and brings a decent amount
of QPF to portions of central Wyoming, although exact placement of
it is probably off at this point. For now, we split the middle. With
temperatures falling toward freezing, some of the lower elevations
could wake up Tuesday morning to some snow. However, with the recent
warm weather and warmer ground temperatures, how much sticks,
especially to paved surfaces is still in question. Mainly lighter
precipitation will likely stick around through the day as well.
Given the northeasterly flow and cloud cover, we kept high
temperatures below guidance. Precipitation should then end Tuesday
evening as shortwave ridging builds across the area.
.LONG TERM...Wednesday through Sunday
Wednesday looks dry as does Wednesday night. There may be some
light precipitation developing over the far west late Wednesday
night and have a low chance there after midnight. The next weather
system dives southeast toward Nevada on Thursday. Moisture
increases over western and southwest WY Thursday with better
coverage of rain and high mountain snow. The rest of the region
will be dry Thursday. This weather system moves to the four
corners on Friday. Both the GFS model and the ECMWF model spread
rain and snow over much of the area Thursday night into Friday.
700MB temps are very close to see rain change to snow on the
valley floors Fri morning. Will need to watch this over the coming
days. Otherwise a damp and cold day to close out March like a
lion. The precipitation ends from west to east Friday night with
partial clearing in the west late Friday night. Any lingering
precip on Saturday morning in the south zones will end by late
morning. Otherwise a dry Saturday for the region. It looks like
next Sunday will be dry as well per the GFS model. The ECMWF model
wishes to spread some light precip into northwest WY Sunday PM.
Leaning toward dry weather as the ECMWF model may be too quick. As
for temps, milder Wed and Thurs, followed by colder highs on Fri.
Then a slow moderation next weekend.
WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES
Some relatively low based cumulus clouds have spread out into a
broken MVFR layer at KPNA but these clouds should lift and scatter
out by 20Z this afternoon. Otherwise, all locations to be VFR today
and likely to continue through at least 06Z/Mon. The next Four
Corners low will be diving southeast across the Pacific Northwest
and the Intermountain West tonight, with pieces of energy ejecting
toward western Wyoming. Right now, it looks like this will result in
mainly increasing mid and high cloud tonight. Lowering and
thickening clouds will move into KJAC by 10z Monday and 15z by at
KPNA and KBPI. Mountain snow and valley rain will move into Western
Wyoming from west to east with mvfr/ifr conditions and mtn
moving into KJAC before 18z Monday and mvfr conditions and mtn obscn
spreading to KPNA/KBPI after 18z Monday.
EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES
Except for a broken layer at 4500 feet over Eastern Natrona County
including KCPR, that will elevate and partially dissipate, all other
terminals, including KCPR, will be VFR today. Mid and high clouds
will increase after 06Z/Mon as moisture increases ahead of the next
Four Corners low dropping southeast to the west of Wyoming. A few
showers will move into the area after 20z from west to east,
affecting KLND first and then spreading east with associated lcl
Rain across areas East of the Divide will slowly end from west to
east with snow tapering off across the Big Horns this morning. This
afternoon should be mainly dry with only a few showers in the
western mountains. Winds should remain light to moderate today.
Mixing and smoke dispersal will be generally fair to poor. Another
system will spread rain into many areas late Monday with some snow
possible later Monday night.
Winter Weather Advisory until 6 AM MDT early this morning for