Area Forecast Discussion
Issued by NWS Riverton, WY

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290
FXUS65 KRIW 260832
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
232 AM 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.

&&

.AVIATION...12Z ISSUANCE

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

Decreasing cloud cover has led to VFR conditions across the western
terminals of KJAC, KBPI, and KPNA early this morning. Temperature-
dew point spreads favor the possibility of VCFG at KBPI and KPNA,
and to a lesser extent KJAC. Light rain and IFR/MVFR conditions will
wane at KRKS by 12Z/Sun with mountain top obscurations continuing
until that time. All locations to be VFR after 16Z/Sun 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 Sunday night, with pieces of energy ejecting
toward western Wyoming. Right now, it looks like this will result
in mainly increasing mid and high cloud Sunday night. KJAC may
flirt with some low end VFR by 12Z/Sun, but main precipitation
shield and lowering clouds appear to come past the end of this
forecast period.

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

Light overrunning precipitation still falling in portions of central
Wyoming early this morning. KCPR will remain the most likely location
for MVFR or IFR as low-level upslope flow will enhance the chance of
light rain and lower ceilings through about 12Z/Sun. Lingering MVFR
conditions will be possible until 15Z/Sun at KCPR as upslope flow and
overrunning is slow to clear central Wyoming with developing surface
low to the southeast. KLND and KRIW could see a brief period of VCFG
if cloud cover dissipates before sunrise. Overall, all other terminals
but KCPR should be VFR into Sunday morning. By 16Z/Sun, all terminals
will be VFR and these conditions will continue through the forecast
period. 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.

&&

.FIRE WEATHER...

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.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

Winter Weather Advisory until 6 AM MDT early this morning for
WYZ008-009.

&&

$$

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



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