Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 131749
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1048 AM MST Tue Feb 13 2018

.SHORT TERM...Today through Thursday night
Issued at 300 AM MST Tue Feb 13 2018

Region continues to be split, as an upper low over CA weakens.
Upper level wind flow will be weak, as the trough axis becomes
centered over WY. This will shear out during the day today, with
the southern branch of the jet moving over the Four Corners and
Central Plains. This will gradually push northward on Wednesday,
but stay confined over SE WY. The next storm system will begin to
push over the PACNW by this time, with snow possible across the
far west by 00Z Thursday. This system remains somewhat
disorganized, with northern and southern components. The northern
component looks to be the most influential for the area, as the
southern component digs over the Great Basin and Four Corners. The
associated cold front will quickly move through the area, starting
early Thursday morning.

Timing of the winds along the Cody Foothills may start a little
later Tuesday night and could last during the day Wednesday. Even
though there will be a tight temperature gradient Tuesday night
into Wednesday morning, H7 winds look to be relatively light
(20-30kt). As the gradient slackens by 18Z Wednesday, the winds
increase to 40-50kt. So, this looks like it could be a localized
event for the Clark area with gusty winds across the rest of the
zone. Likewise for the Wind Corridor, H7 winds start 30-40kt
during the day today and increase to 50kt by 12Z Wednesday over
northern Sweetwater to southern Natrona counties. These winds
continue until the passage of the cold front. At this time, it
will get windy tonight over this area with the strong winds
impacting later during the day Wednesday. The strong damaging
winds may stay confined to Outer Drive/Wyoming Blvd on the south
side of Casper, with isolated strong gusts elsewhere across the
city.

Kept the snow forecast relatively unchanged, with 4 to 8 inches
remaining possible across the western and northern mountains and 1
to 2 inches over Johnson County and the Big Horn Basin. Snow will
taper off by Thursday evening, with lingering light snow across
the west during the overnight hours.

.LONG TERM...Friday through Tuesday
Issued at 300 AM MST Tue Feb 13 2018

NW flow aloft Friday into Saturday with enough moisture in the flow
for some snow in the NW WY mountains and a little bit of snow in the
valleys at times. The rest of the region will be dry Friday and
Saturday. Breezy areas Fri afternoon and night. Then breezy to windy
over more of the region Saturday afternoon and night. High temps
will be milder Fri and Saturday. The GFS and ECMWF models are
developing a deep trough over the NW United States Saturday night
through at least Monday. Details differ on the orientation of this
trough Sunday through Monday night. The ECMWF model is much deeper
with the trough over the Western U.S. The GFS model confines its
trough to the Pacific NW states through the central Rockies. Cold
air from Canada sinks south into WY Sunday into Sun night. The ECMWF
model is much colder than the GFS model for highs Sunday and Monday
over the north and central zones due to its orientation of this
trough. Models in the past week or two have been having issues with
the flow pattern that far out. Even the model blends are swinging
back and forth with little consistency. I am taking a middle ground
approach with temperatures Sunday and Monday as well as with the
chance of snow. Plenty of time to watch how this pattern plays out.
Next Tuesday looks drier at this time and still cold.

&&

.AVIATION...For the 18Z TAFS through 18Z Wednesday
Issued at 1048 AM MST Tue Feb 13 2018

Weak high pressure over the area continues today, with mostly VFR
conditions expected at all TAF sites.  Lingering MVFR conditions
with low ceilings may continue around KJAC (and near K46U and KAFO)
for the next couple of hours.  Wind speeds will increase throughout
the afternoon at about half the sites, especially KCOD and KCPR,
with strong gusts over 35 kts and LLWS.  Wind expected overnight and
into Wednesday morning, with KLND possibly seeing gusts over 25 kts
after 15Z/Wed.  Slight increase in moisture in SW flow mid day
Wednesday will bring lowering ceilings and vicinity showers from
KJAC to KPNA after 18Z/Wed, along with obscured higher terrain.

&&

.FIRE WEATHER...
Issued at 300 AM MST Tue Feb 13 2018

Winds will be on the increase again across the Cody Foothills
today into Wednesday and also across the Wind Corridor from
Jeffrey City to Casper. The lee of the mountain ranges and also
the area from Dubois to near Riverton will also likely see
increasing wind today and tonight. The light snow will return to
the northwest Wednesday and spread east of the divide Wednesday
night into Thursday morning with a gusty north to northeast wind.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

High Wind Watch from this afternoon through Wednesday afternoon
for WYZ019-020.

High Wind Watch from this afternoon through Wednesday morning
for WYZ003.

&&

$$

SHORT TERM...LaVoie
LONG TERM...AR
AVIATION...McDonald
FIRE WEATHER...LaVoie



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