Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 222002
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
202 PM MDT Sun Oct 22 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 201 PM MDT Sun Oct 22 2017

A Pacific low pressure trough and cold front will bring widespread
snow to the western mountains this evening tapering off through the
night.  Strong winds will accompany the snow.  The strongest
winds will be over and near the east slopes of the mountains and
through the wind corridor from Northern Sweetwater county through
Natrona county this evening. Behind the cold front strong north
winds will blow on Monday across northern Johnson county.
Temperatures will cool on Monday behind a cold front with
decreasing winds.  Dry and warmer conditions are then expected
through mid week with lighter winds as a large high pressure
ridge builds over the western U.S.

.LONG TERM...(Wednesday night through Sunday)
Issued at 201 PM MDT Sun Oct 22 2017

After a warm day Wednesday, many areas are going to be in for a slap
in the face as we head into Thursday. A strong Canadian cold front
will drop into northern portions of the state Wednesday night and
continue to sweep southward through the night and into Thursday. As
for precipitation, it should move into the north before midnight and
move across most areas East of the Divide by Thursday morning. With
the Canadian origin of the system, there is not a tremendous amount
of moisture associated with it. However, there will be some decent
upper level forcing in the form of a 110 knot jet streak moving in
behind the front. The precipitation would likely start out as rain
but then change to snow quickly as the front passes through. And the
timing of the snow could have some concerns for the morning commute
on Thursday if the snow is heaviest at that time. It is too early to
talk about amounts however. In addition, it will be windy behind the
front. This pattern is a good one for strong and possibly high winds
in areas favored by strong cold advection with north to northwest
flow, mainly the northern Bighorn Basin as well as northern Johnson
County. With the quick movement of the system, most steady
precipitation should end by Thursday afternoon and all by Thursday
night. We kept temperatures below what forecaster builder loaded in
since the models usually do not capture this very well. Out west,
other than the north, most areas should remain dry from this system.

Quieter weather should be the rule after that. At this point, Friday
looks to be dry but cool day. Both the GFS and European have come
into better agreement as well for Saturday with keeping the area dry
and shifting another system further to the east. We maintained some
slight POPs in the north and east put nothing more. The area should
continue to see a warming trend with near to possibly above normal
temperatures by Sunday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday)
Issued at 201 PM MDT Sun Oct 22 2017

Occasional light snow and lower elevation rain will continue through
03Z in the northwestern mountains, mainly in vicinity of KJAC. A
cold front dropping southward will bring a few showers further south
in areas West of the Divide, mainly around KBPI and KPNA through
00Z. Areas of wind shear will be found around the mountains, mainly
in vicinity of KCOD, although this will end after the frontal
passage. Winds in most areas should decrease after around 06Z
tonight though. The exceptions will be near KRKS. Strong winds will
likely develop north of a line from KGEY to 20 miles south of KBYG
after 06z tonight and continue into 18Z tomorrow. VFR conditions are
expected for all TAF sites East of the Divide through the period and
after 06Z West of the Divide.

&&

.FIRE WEATHER...
Issued AT 201 PM MDT Sun Oct 22 2017

A Pacific low pressure trough and cold front will bring widespread
snow to the western mountains this evening tapering off through the
night.  Strong winds will accompany the snow.  The strongest
winds will be over and near the east slopes of the mountains and
through the wind corridor from Northern Sweetwater county through
Natrona county this evening. Behind the cold front strong north
winds will blow on Monday across northern Johnson county.
Temperatures will cool on Monday behind a cold front with
decreasing winds.  Dry and warmer conditions are then expected
through mid week with lighter winds as a large high pressure
ridge builds over the western U.S.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until midnight MDT tonight for WYZ002-003-015-
016.

High Wind Warning until 6 PM MDT this evening for WYZ018>020.

High Wind Watch from midnight MDT tonight through Monday morning
for WYZ010.

Winter Weather Advisory until 9 PM MDT this evening for WYZ001-
012.

&&

$$

SHORT TERM...Baker
LONG TERM...Hattings
AVIATION...Hattings
FIRE WEATHER...Baker



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