Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 101056
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
356 AM MST Wed Jan 10 2018

.SHORT TERM...(Today and tonight)
Issued at 328 AM MST Wed Jan 10 2018

The splitting full latitudinal Pacific trough appears to be
located over Central Idaho ATTM. A heavy band of snowfall ahead of
this feature in Eastern Idaho is poised to hit far Western
Wyoming. About 4 hours of heavy snow is expected for far West
Wyoming from now through 8 to 9 am. This will help us catch up on
our expected snow totals approaching near a foot in the Western
Mtns and 2 to 4 inches in the western valleys. Will let the
western winter weather hilites ride through 12 noon today. In the
meantime, a strong cold front will be tracking south from Northern
to Central Wyoming east of the divide through the course of the
day today where lighter snowfall amounts are expected. Snow and
blowing snow is expected in Johnson County today where sfc
pressure rises of 8 to 9mb in a 3 hour period are expected after
the fropa. This will result in north winds of 30 to 50 mph which
will toss the snow around significantly for considerable blowing
and drifting snow that we handled with an SPS. Strong pre frontal
west winds of 30 to 50 mph are expected in Sweetwater County
today.

Then on Thursday, the next significant trough in the nw flow will
deliver more snowfall to the far west with up to at least 15
inches of additional snowfall expected in the far western mtns
Thursday afternoon through Friday. Thursday night will be a very
windy period for the southern wind corridor and for the foothills
east of the Continental Divide with 60 knot 700mb anticyclonic
winds surfacing and 5 decameter height lines over Wyoming spaced
apart every 30 decameters expected.

.LONG TERM...(Thursday through Tuesday)
Issued at 328 AM MST Wed Jan 10 2018

Strong upper ridge holds along the Pacific Northwest Coast over
the weekend with potential strong arctic cold front dropping south
later Sunday into Monday east of the divide. This system
originates from the far northern reaches of Canada up near 80N and
then drops swd along the west side of the Hudson Bay low (which
shifts off to the east by the weekend). The airmass is quite cold
and if this system is truly this far west (The Euro and GEM are
stronger/colder) it could be a fairly potent arctic front with
strong north wind, rapidly falling temperatures and a period of
light to locally moderate snow for several hours later Sunday in
the north and Sunday night/early Monday further south. Bumped up
pops into the chance category for starters across central WY for
now and will see if it still looks good again tonight. Still some
concern with the mean ridge onshore over the PacNW that the main
energy could be just a little further east in the plains leaving
us with a fropa but with limited snow chances but as of now all
the guidance has at least some snow chances across much of central
WY during this time period. Monday could be quite cold east of
the divide, especially in the far nrn and ern sections. Lowered
temps some with this system but no where near as much as it could
be if the colder Euro/GEM are more right. Cold start Tuesday
morning east of the divide behind this system. A weaker system may
try and undercut the ridge with a little moisture/mtn
flurries/very light snow in the far west later Tuesday into
Wednesday but just keeping some 20-30 pops out west for now. The
Euro and GEM have a small closed low passing overhead (GEM) or
just south (Euro) vs a much weaker wave passing to the north on
the GFS. Confidence low at the end of this period attm.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 328 AM MST Wed Jan 10 2018

West of the Continental Divide...KJAC, KBPI, KPNA and KRKS

Rain and snow will change to all snow by 14Z in the valleys. The
mountains will see snow through this afternoon with snow showers
lingering into this evening. MVFR to IFR conditions will prevail
through most of the day. KJAC will stay in the MVFR conditions
through 06Z Thursday. Mountains will be frequently obscured. KRKS
will have a brief period of MVFR to IFR conditions today when the
cold front moves through that area.

Please see individual terminal sites for more details.

East of the Continental Divide...KCPR, KCOD, KRIW, KLND, and KWRL

VFR conditions will prevail through 12Z. A cold front will move into
northern WY this morning after 14Z. This front pushes into central
WY 18Z to 19Z, and then into the southern portion by 00Z. Some snow
will occur along and behind the front creating MVFR to IFR
conditions for a 4 to 6 hour period. Then conditions will return to
VFR. Please see individual terminal sites for more details.

Please see the Aviation Weather Center for the latest information on
icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued AT 328 AM MST Wed Jan 10 2018

Today through the end of the work week, a couple of strong winter
weather systems will impact the forecast area with periods of
heavy snow and blustery winds at times west of the Divide. Lighter
snowfall amounts and gusty north winds will combine today east of
the divide. As much as 1 to one and a half feet of snow will be
possible in the mountains of the west above 7500 feet through 12
noon today, with more to follow later Thursday and Friday. Areas
east of the Divide will see much lighter accumulations. Smoke
dispersion will be fair to good today and good to very good on
Wednesday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon MST today for WYZ001-002-014-
015-024.

Winter Storm Warning until noon MST today for WYZ012.

&&

$$

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



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