Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 142058

Area Forecast Discussion
National Weather Service Riverton WY
258 PM MDT Sat Oct 14 2017

.SHORT TERM...(This evening through Sunday)
Issued at 106 PM MDT Sat Oct 14 2017

Synopsis...Building high pressure, as the trough responsible for
this morning`s snow quickly exits into the Central Plains. The
flow aloft will turn NW over the area through Tuesday, before a
more zonal pattern sets up.

Discussion...Snow has ended across the forecast area, with skies
continuing to clear across Johnson/Natrona. Some CU has developed
this afternoon across the west, as well as eastern Sweetwater
County. With mainly clear skies expected by sunset, fog will be
possible in the Wind River Basin and the western valleys. However,
gusty winds near Dubois and along the Cody Foothills are expected
to increase this evening. The winds near Dubois will translate
down the basin toward Crowheart, with gusts of 45 to 55 mph
expected. These winds could be just above the inversion near KRIW
from 05-11Z tonight, either helping to erode the inversion away or
keep fog from developing altogether. Have left fog in the forecast
for now, mainly impacting the low lying areas. The aforementioned
winds along the Cody Foothills are also expected to quickly
increase after sunset this evening. Wind gusts of 70 to 80 mph
will be possible in the favored areas along Highway 120 between
Clark and Cody. Chief Joseph Highway has already gusted to 59 mph
just before 3pm. The local models depict 40-50kt boundary level
winds in this area through 16Z Sunday, before quickly dropping off
to 15-25kt by 18Z. Have issued a High Wind Warning for this area.

Otherwise, dry and warm conditions are expected through the rest
of the period. Model guidance is still too low for high temps
Monday and Tuesday and have bumped up accordingly, especially east
of the Divide. Elevated fire weather conditions will be possible
Tuesday, as gusty SW winds return to the Wind Corridor as well.

.LONG TERM...Tuesday night through Saturday night
Issued at 106 PM MDT Sat Oct 14 2017

Mean longwave pattern shows us transitioning from a flat ridge
overhead to a mean trough along the West Coast by Friday which moves
inland some Saturday. Overall, the end result is mild, above normal
fall period Wednesday through Friday (except starting to
deteriorate far west Friday) before another trough swings through
Friday night and Saturday. The far west will likely start to cool
Friday, already with increasing clouds and a chance of showers
developing. East of the divide, it will remain mild, but with
increasing wind. The wind corridor will be quite windy Friday with
increase H8-H7 flow and surface low likely developing to the
northeast. But temperature-wise, it will remain quite mild.
Otherwise, the medium range period starts with a dry Wednesday and
Thursday for all areas with highs in the 60s to possibly even some
70s east of the divide (especially by Thursday) with generally 50s
to around 60 west of the divide. The high country will see 40s and
50s overall. Ahead of the main trough, we may get a shortwave in the
southwest flow riding up on a jet streak. This system may get some
light pcpn going in the west during the day Friday. The main trough
then swings across on Friday night into Saturday with much
cooler/colder temps. Overall, this system doesn`t look as cold as
the current system (especially central and srn zones) but it`s still
looks cold enough for some rain/snow or snow showers east of the
divide Saturday with a period of snow in the west Friday night/early
Saturday before shifting east of the divide. System could lay down
some decent snowfall west of the divide, so we`ll have to watch this
with time. Quick hitter like the current system but could be an
intense period of heavy snow. Current thinking is that this system
will come through fairly quickly with clearing showing up from west
to east Saturday night. The GFS is also showing a rapidly
intensifying nw flow Saturday night into next Sunday so some strong
west to northwest winds may rapidly follow our Saturday system. The
warm advection pattern may also return some snow to the northwest
mountains next Saturday night. Until then, though, several mild/warm
days for late October!


.AVIATION...(For the 00Z TAFS through 00Z Sunday afternoon)
Issued at 106 PM MDT Sat Oct 14 2017

VFR conds will cover the entire area then through Sunday. The one
exception to that will be the potential for patchy fog across the
low lying areas of the central and the far western valleys from
10-15z Sunday. West to southwest winds will increase along the
east slopes of the Divide and along the southern wind corridor,
50SM NE KRKS-KCPR, and between KCOD and Clark after 03z Sunday.
The west wind between KCOD and Clark could be in excess of 60 mph
with LLWS also possible from 03z through 12z Sunday.


Issued AT 106 PM MDT Sat Oct 14 2017

Snow has ended across the area this afternoon, with clearing
skies. Winds remain gusty behind the front across western and
southern portions. Strong winds are expected to quickly develop
this evening, along the Cody Foothills to the Upper Wind River
Basin and continue through late Sunday morning. These winds are
expected to quickly diminish by the noon hour. High pressure will
then bring dry and mild weather starting Sunday and lasting into
much of next week. A gusty wind will blow at times across the
areas favored by southwest flow, mainly from Rock Springs through
Casper. Elevated fire conditions will be possible at times,
especially Tuesday.


High Wind Warning from 9 PM this evening to 10 AM MDT Sunday for



LONG TERM...Skrbac
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