Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 141741
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1141 AM MDT Sat Oct 14 2017

.SHORT TERM...Today through Monday night

Some snow is currently ongoing west of the Divide as a cold front
and 700 millibar low begin to work their way into the state. It is
banded though so it will be on and off. A few locations could see
advisory level amounts across the west but at this point it would be
the exception rather than the rule. The snow in this area should end
fairly quickly after mid morning with dry weather the rule the rest
of the day.

We have a bit of a dilemma East of the Divide however. Most snow
should hold off until after dawn. However, the position of the mid
level low and a period of upslope could bring a period of moderate
to occasionally heavy snow in spots. Both the NAM and GFS are in
decent agreement in bringing that area of snow to eastern Fremont
and western Natrona Counties, possibly including Casper. As a
result, we upped POPS and QPF in this area. 700 millibar
temperatures at this point look to be plenty cold enough for the
precipitation to fall as almost all snow, especially during the
heaviest period when evaporational and dynamic cooling will be at
the peak along with decent northerly upslope flow. At this point,
this looks to be between 9 am and 1 pm. This will be a quick hitting
system however, with the steady precipitation over by early
afternoon and all precipitation over by evening. We are on the fence
of an advisory for Natrona County, this will likely be a game time
decision. Otherwise, expect a chilly and breezy day, although
sunshine will return from west to east in the afternoon.

High pressure will then bring dry weather from tonight through
Monday night. Temperatures should recover to near normal levels
Sunday and then above normal for many areas on Monday. A gusty
southwesterly breeze will develop across the southwestern wind
corridor as well starting Saturday night and then continuing through
Monday as well.

.LONG TERM...Tuesday through Saturday

A mild and dry zonal flow will occur Tuesday and Wednesday with
breezy conditions in the wind corridor. On Thursday, a digging
Pacific trough will approach the West Coast with the flow backing
to the southwest, but the forecast area remaining dry with mild to
warm temperatures. The 00Z ECMWF and GFS show the trough pulling
across the West Coast into the Great Basin Thursday night/Friday,
and then across the Rockies Friday night and Saturday.
Precipitation, based on current timing, looks to begin out west
Thursday night spreading east of the Divide Late Friday/Friday
night especially as the cold front pulls across the region in the
Friday night/Saturday. Looks like the precipitation would end from
west to east during the day Saturday. This is a warmer system than
the current one, so it looks the precipitation will be a valley
rain/mountain snow even out west until a change over occurs with
frontal passage Friday night/Saturday.

&&

.AVIATION...18Z Issuance

The tail end of a weather system will keep some MVFR/IFR conds a
cross the area from Jeffrey City to KCPR through 20-21z before
VFR conditions return. 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
southwest basins and far western valleys early 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.

&&

.FIRE WEATHER...

A Pacific cold front will move across the area early this morning
followed by a period of snow, possibly mixed with rain, steadiest in
the morning hours. Temperatures will be below normal with relative
humidity remaining well above critical levels. A gusty north wind
will blow at times however. 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 with elevated fire
conditions possible at times.

&&

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

&&

$$

SHORT TERM...Hattings
LONG TERM...Meunier
AVIATION...PS
FIRE WEATHER...Hattings



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