Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 230932

Area Forecast Discussion
National Weather Service Riverton WY
332 AM MDT Mon Oct 23 2017

.SHORT TERM...Today through Wednesday night
Issued at 330 AM MDT Mon Oct 23 2017

Synopsis...A cold front is quickly surging southward east of the
Divide Sunday night, with +3 to +6mb pressure rises occurring
over N WY and E MT. Apart from some light showers currently over
northern and central WY, this front will be dry through the day
today. A ridge over the EPAC will build into Northern Canada and
the Yukon Territory through the day today. At the same time, the PFJ
will be over northern and eastern WY and remain in place through the
day today. Strong winds are expected through 2am this morning, but
could continue through 6am over northern Johnson County, in the
wake of the cold front. As the ridge continues to build, this will
cause a longwave trough to dig and move over the Great Lakes. This,
in turn, will cause the PFJ to shift eastward over the Plains and NW
flow over the region Monday night through Tuesday night. The ridge
will flatten, as the next major trough (originating from the Gulf of
Alaska) dives southward along the Canadian Rockies through the day
Wednesday. The trough and associated cold front, will quickly make
their way over central WY by 12Z Thursday. Although temperatures are
not as cold as previous model runs have indicated the last few
days, this will be strong cold front that will bring sharply colder

Discussion...Light showers will gradually end this morning across
northern and central WY. Winds also remain gusty and high, with a
few isolated spots still blowing strong. Overall, this trend will
decrease through the morning hours as the front continues its
southward trek and the winds aloft weaken and shift eastward along
the jet. At the same time, strong winds will occur briefly
through 12Z this morning over northern Johnson County. However, winds
will remain high today with northwest wind gusts of 45 to 55 mph.
Otherwise, expect dry conditions and relatively calmer (finally!)
winds Monday night through Wednesday morning. The fast-
approaching cold front will cause winds to return to the wind
prone locations Wednesday afternoon, along with temperatures
rising well above normal but not record-breaking. Elevated fire
conditions across Johnson & Natrona counties, with Min RH values
dropping below critical thresholds. Scattered rain showers will
develop along and behind the cold front Wednesday night over
northern and central portions. Some of these showers could change
over to snow before sunrise, but any accumulation will be light
due to the abnormally high temperatures on Wednesday.

.LONG TERM...Thursday through Monday
Issued at 330 AM MDT Mon Oct 23 2017

The light snow will occur mainly along and east of the continental
divide Thursday morning and then decrease from north to south in
the afternoon. West of the divide, the coverage of light snow will
be less and mainly in the mountains. Colder high temps all areas.
Any lingering snow Thursday evening will end quickly followed by
decreasing clouds. Cold low temps Thurs night. North flow aloft
Friday with dry weather high temps in the mid 40s to lower 50s. A
north northwest flow aloft Saturday with dry weather expected and
high temps in the 50s. A northwest flow aloft on Sunday with dry
weather once again and seasonal high temps in the 50s to near 60.
Next Monday will be dry during the daytime hours with similar
highs to Sunday.


.AVIATION...For the 12Z TAFS through 12Z Tuesday
Issued at 330 AM MDT Mon Oct 23 2017

Isolated valley rain/mountain snow showers will come to an end,
from north to south, between 09Z and 14Z. Otherwise, dry
conditions are expected with decreasing cloudiness today with VFR
conditions. Winds will be breezy from the west/northwest in most
locations today with the exception of the middle of the central
basins where lighter winds are expected. Winds are expected to
subside around sunset with light winds tonight.


Issued AT 330 AM MDT Mon Oct 23 2017

A cold front will have passed through much of the state by sunrise
this morning. High winds will occur through the day today across
northern Johnson County. Otherwise, winds will be breezy for most
areas, but not nearly as strong as the last couple of days.
Conditions will be dry for the next couple of days, with
temperatures rising above normal Tuesday and Wednesday. Elevated
fire conditions will return Wednesday across Johnson and Natrona
counties, with Min RH values dropping to critical values, along
with gusty southwest winds in the afternoon. A strong cold front
will impact the state Wednesday night into Thursday, with sharply
colder temperatures.





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