Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 190724
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
124 AM MDT Fri Oct 19 2018

.SHORT TERM...(Today through Sunday night)

The closed low that migrated up from the Desert Southwest has
weakened to an open trough and is exiting to the east. What was
left of the low produced some isolated shower activity over the
Uinta mtns around sunset yesterday evening. As a result,
northwest winds of 10 to 15 mph behind the trough has resulted in
many areas that favor nw winds such as RIW/PNA/BYG. Our northern
zones should run 5 to 10 degrees cooler today than Thursday east
of the divide behind this weak trough. Ironically, the strong
positively tilted trough responsible for the accumulating snow
last Saturday split with the southern piece of energy forming the
aforementioned closed low that just weakened into a weak exiting
trough. Well, this trough will again squeeze out another bubble of
cooler air beneath a resulting weak omega block. This cool pocket
of air aloft will be enough to spark off more isolated shower
activity in our extreme southwest CWA late Sunday. Other than
these innocuous events, we can expect dry weather with above
normal temperatures, in other words, wonderful Indian Summer
weather along with light winds. In fact, the weather has been so
tranquil during these last couple of days, the bursting of the
weather balloon was witnessed with the naked eye here at the NWS
RIW at an elevation of over 110,000 feet Wednesday and Thursday
evening of this week, as it reflected sunlight much like a
satellite does during twilight.

.LONG TERM...(After midnight Monday through Friday)

Upper low is still forecast to be over cntrl CA/wrn NV to start
this period and then gradually drift ne over us into Tuesday
night/Wed mrng before finally dying/exiting stage right. Shower
chances will increase in the far west by Monday afternoon,
especially in the mountains. Shower and possible isold tstms will
peak in the west on Tuesday as what`s left of the cold core moves
in. Not much instability showing up but wouldn`t be surprised to
see an isold tstm or two by Tue aftn along and west of the divide.
As the remnants of this upper low swing east of the divide, a few
showers will likely pop up but the best chance will be over the
mountains and higher terrain. Mid level temps are still quite mild
(+2 to +3C at H7) so temps will be cooler than what we`ll see
over the weekend but still not bad for late October with 50s
across the lower elevations and even some lower 60s east of the
divide. Depending on the exact timing, a few showers may linger
into Wednesday across the mountains but otherwise, just some
lingering clouds and still mild with 50s to lower 60s across the
lower elevations and 40s in the mountains. Brief shortwave ridging
is possible Thursday ahead of a fast moving system that will
likely impact us on Friday. Models are still struggling with this
system and how much of an impact it will have on us. The GFS
5-wave is holding a mean ridge over us through the week. It`s
weaker by Friday but still a mean ridge. The most likely scenario
is for a strong jet move across MT with most of the energy well to
the north. However, the new Euro is further south with the system
with colder temps, stronger front and a more qpf across the area
late Thu ngt and Friday. Not buying into this scenario yet
considering the big picture but worth watching. Otherwise, still a
shot for some strong to high winds in the Cody Foothills from
this system with fcst 40-50kt H7 winds in the Absarokas ahead of
the front. We could still see some light rain/snow showers in the
mountains up north but not looking great for pcpn chances further
south or across the lower elevations (per GFS). We will probably
see a cold front impact the north and far ern zones by Friday
night. Besides the strong to possible high winds in the Cody
Foothills Friday, the wind corridor and most mountain locations
will also see increasing wind Friday with some 40-50kt H7 winds
developing.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)

VFR conditions will occur through the period. Wind speeds are
expected to be less than 12 knots at the terminal sites.

&&

.FIRE WEATHER...
Issued AT 1055 PM MDT Thu Oct 18 2018

Dry conditions will continue into the weekend. Expect light winds
into the weekend. A dry cold front has moved mainly over NE WY
last evening, cooling this afternoon temperatures several
degrees over Northern Wyoming east of the divide Temperatures
will rebound by Saturday, with above normal temperatures returning
(especially east of the Divide) through the weekend.

&&

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

$$

SHORT TERM...Lipson
LONG TERM...Skrbac
AVIATION...Ross
FIRE WEATHER...Lipson


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