Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 131922

Area Forecast Discussion
National Weather Service Riverton WY
122 PM MDT Tue Mar 13 2018

.SHORT TERM...(This evening through Friday)
Issued at 115 PM MDT Tue Mar 13 2018

We will continue to warm through Wednesday as temps continue to warm
ahead of our large ern Pacific upper low. Wednesday will definitely
be the warmest day this year as H7 temps warm well above 0C east of
the divide (+1 to +2C)) which translate to 60s for most areas. In
the far west, we`ll see mid 40s to mid 50s. An approaching
disturbance and associated jet streak, will likely aid in developing
showers/isold tstms hitting the far swrn corner late in the day and
lifting nwd through the evening. A couple healthier tstms may form
with some favorable low level wind turning (se-sw and increasing
rapidly). This weather system will lift nwd overnight through the
evening spreading showers/isold storms nwd from swrn WY into north
central WY. Some concern for rain on snow in the southwest including
the Star Valley late Wed/Wed evening. Otherwise, many of the wrn
mountains will receive 3 to 6 inches of snow with locally higher
amounts due to the showery nature. An even more interesting system
is forecast to move just to our south on Thursday with an upper low
forming off to our se (over ne CO and nw KS) Thursday night. An
inverted trough axis (and associated jet streak) extends nwwd into
our ern zones. A swath of showers will likely form and lift nwd
across our ern zones later Thursday afternoon through Thursday
night. Some locally heavy showers are possible, especially in
Natrona and Johnson Counties. The lower elevations will be mostly
rain initially with lowering snow levels overnight. The rain will
likely change to snow in Johnson County after midnight Thursday
night with some snowfall continuing through Friday. Natrona County
is even more of a challenge depending on where our inverted trough
axis remains and our jet streak. It`s a rather complex pattern and
there is some potential right entrance region jet streak support in
our ern zones Thu ngt through Fri. We will just have to watch this
very closely for some eventual accumulating snow across our ern and
nrn zones Thursday night into Friday.  The north and west half looks
most unsettled through Friday (after the initial convective pcpn
Thursday aft/eve lifting nwd across the area) with snow showers and
chilly temperatures. Can`t rule out significant snow across
especially Johnson County the the showers turn to snow later
Thursday night and potentially continue through Friday afternoon.
The winter wx desk is giving widespread warning amounts to the lower
elevations of Johnson County Thursday night and Friday with advisory
amounts in Natrona. The sw will be the driest. Quite the
interesting and challenging pattern the next several days.

.LONG TERM...(Friday night through Tuesday)
Issued at 115 PM MDT Tue Mar 13 2018

At this point we did not make a lot of changes to the long term.
Some lingering showers will be found across portions of northern
Wyoming as low pressure pulls away to the east. Expect a brief break
then before the next Pacific trough moves into western Wyoming with
the next shot of mainly snow moves in. At this point, the steadiest
and heaviest precipitation will likely hold off until the afternoon
and more than likely at night. This precipitation may then spread
East of the Divide Sunday into Sunday night. This the models agree
on. However, they continue to disagree on pinpointing the areas of
heavier precipitation with the GFS having more in northern Wyoming
and the European a bit further south with the heavier precipitation.
For now, we gave everyone at least slight POPS and hope that there
will be more agreement as we move closer to the event. This
precipitation will begin to end later Sunday night into Monday as
low pressure moves into the Plains states and high pressure builds
into the area. High pressure will then bring dry and settled weather
from later Monday through most of Tuesday night before the next
system approaches western Wyoming on Wednesday.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday afternoon)
Issued at 115 PM MDT Tue Mar 13 2018

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

VFR conditions will hold through around 18Z Wednesday. Marginal wind
shear may develop in spots tonight, especially in vicinity of KJAC
as a Pacific system approaches. Showers with possible local MVFR
conditions will move into all TAF sites with exception of KRKS,
where dry conditions should hold through the period. Thunderstorms
are possible in some areas after 22Z Wednesday, but not enough
confidence to pinpoint at this time.

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

VFR conditions are expected through 00Z Thursday. A southwesterly
breeze will develop in vicinity of KCPR after 17Z Wednesday.


Issued AT 115 PM MDT Tue Mar 13 2018

Seasonal to above seasonal temperatures expected across the the
region today through at least Wednesday. It will be dry all
locations today through most of Wednesday morning. Then the effects
of the next weather system begin to be felt west of the Continental
Divide with a little everything - from rain and snow to
Thunderstorms with small hail possible. Up to 6 inches of new wet
snowfall will be possible above 8000 feet...with rain/snow mixed
and only local accumulation below that level. Another system will
spread an increasing chance of showers and higher elevation snow
across especially the eastern and northern part of the area later
Thursday afternoon and Thursday night. The rain will change to
snow later Thursday night into Friday. Strong and gusty winds are
most probable across the Wind Corridor from eastern Sweetwater
through Natrona Counties both Wednesday and Thursday afternoons.





LONG TERM...Hattings
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