Area Forecast Discussion
Issued by NWS Riverton, WY
FXUS65 KRIW 231735
Area Forecast Discussion
National Weather Service Riverton WY
1135 AM MDT Sun Oct 23 2016
.SHORT TERM...Sunday through Tuesday night
All in all a pretty nice end the weekend. The so called cold front,
a rather wimpy one, has now moved out of the area. High pressure
will control the weather for one more day today and bring another
day of warm temperatures. The difference being that there will be
less wind so fire danger will be less. There will be more high
clouds through as high level moisture streams in from the west ahead
of a system moving in from the southwest. A few showers will move
into southwestern Wyoming late tonight. At this time, we feel the
models are rushing the precipitation in too quickly since it appears
to be outrunning the upper level forcing with a jet streak. As a
result, we held most POPS off until after 3 am tonight.
Monday at this point looks like a period of upslope / downslope.
Showers will be found across the west with the most numerous over
the western mountains with orographic enhancement and the south with
some upper level forcing. With the southwest flow and source region
of the system, it is a warm system with 700 millibar temperatures
remaining above zero, only falling down to plus 1 at the coldest. As
a result, any snow would remain above 9500 feet with any
accumulating snow well above pass level. However, there is not a ton
of moisture with the system so accumulations would be light.
Meanwhile, East of the Divide, downsloping flow will keep thing
mainly dry and mild. A gusty southwest wind will redevelop from Rick
Springs through Casper. However, upper level winds do not support
high winds. In addition, with more humidity any fire concerns should
remain fairly low.
Another shortwave will then swing across the area on Tuesday. And it
looks fairly similar to the previous one with most precipitation
remaining to the west of the Divide except for perhaps the Big Horn
Range. There are differences in QPF though with the GFS drier and
the NAM having more. For now, with the differences we made few
changes to continuity. This system looks a little colder but again
the valleys should be mainly rain with snow levels around 8000 feet.
There will again be the gusty wind in the above locations. Winds may
increase in the lee of the Absarokas bit low level winds do not look
strong enough to for high wind highlights at this time. Temperatures
will once again remain above normal for most locations.
.LONG TERM...Wednesday Through Sunday
Models are in good agreement through the extended with longwave
troughs on each Coast with ridging of varying intensities in
Wednesday and Thursday look to be dry with above average
temperatures. Although a bit slower tonight, global models
continue to show a shortwave trough ejecting out of the longwave
trough into the West Coast Thursday night, and then northeast
across the Great Basin/Northern Rockies Friday into Friday night.
The 00Z GFS shows the track farther west with only a glancing
blow, while the ECMWF continues to show a track across the
Northern Rockies. The Canadian solution is somewhat in the middle
of those two. Due to the slower timing, have warmed temperatures
considerable east of the Divide. For now will have slight to
chance PoPs across the west Fri/Fri Night with some slight PoPs
east of the Divide for a potential front Friday night.
Upper ridging takes hold again for next weekend with mainly dry
conditions and above average temperatures expected. Will have
some slight PoPs across the extreme west Sat/Sun as models show a
relatively moist atmosphere remaining in place.
Temperatures are expected to be above to well above average
through the extended. Thursday and Friday are expected to be the
warmest days. Casper could see a record high one if not both of
those days. Record highs for October 27th and 28th are 74 and 75,
Elevated fire weather conditions are possible Thursday and Friday
across Natrona County.
West of the Divide...KBPI/KJAC/KPNA/KRKS Routes
Conditions will be VFR through 09Z/Mon as mainly mid-high level
clouidness stream across southwest Wyoming. Moisture will gradually
increase overnight as a weather disturbance pushes across the Great
Basin toward Wyoming. Showers will develop around 09Z/Mon and
increase in coverage and intensity by 14Z/Mon. Depending upon
precipitation intensity, snow levels could drop to the valley floor
around KBPI and KPNA early Monday. Otherwise, temperatures remain
warm for late October and snow levels will increase to 8000 ft MSL
or higher by 18Z/Mon. Deepening moisture will bring lowering cloud
heights and some localized MVFR conditions between 14Z-18Z/Mon. Have
left low-end VFR ceilings in the forecast at KJAC, KBPI, and KPNA,
while drier conditions prevail at KRKS. Mountain top obscurations
will be widespread by 12Z/Mon continuing through 18Z/Mon. Wind
speeds will be less than 12kts through the entire forecast period.
East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Routes
Conditions will remain VFR through the forecast period. Southeast
wind 10-20kts will feed into Johnson County and northern Natrona
County this afternoon. Southwest wind will increase in the wind
corridor including KCPR between 19-20Z/Sun, but have brought speeds
down to 10-18kts as winds have been slow to develop. KLND will see
some LLWS develop late Monday evening and continue into early Monday
as southwest winds top the Wind River Range and cascade down the
east slope. Moisture in warm, southwest flow aloft will bring
increasing cloud cover tonight. Mountain top obscurations will
become widespread over the Wind River Range between 12Z-18Z/Mon as
moisture in southwest flow aloft moves over the range.
Fire concerns should remain low to moderate today. Today will be
another mild to warm day. However, with light to moderate wind and
higher relative humidity fire concerns will be less. Mixing and
smoke dispersal will be generally poor but fair across southeastern
areas. Showers an isolated thunderstorms will return to the west on
Monday. A gusty wind will redevelop in spots east of the divide but
with higher humidity fire concerns should not become elevated.