FXUS65 KRIW 182019

Area Forecast Discussion
National Weather Service Riverton WY
219 PM MDT Mon Mar 18 2019

.SHORT TERM...This evening through Tuesday night
Issued at 214 PM MDT Mon Mar 18 2019

Another weak upper level disturbance will move across Wyoming
tonight. Once again it will increase cloud cover and maybe a slight
increase in wind speeds in the east. Cloudiness in the southwest
will slow radiation a bit overnight but there should be enough
cooling to bring another round of patchy fog to the Green River
Basin as well as the western valleys Tuesday morning. Skies will
begin clearing from the north Tuesday morning and progress southward
through the day. The Bighorn Basin will receive the longest period
of heating and thus should be our warmest area tomorrow. We dropped
low temps a bit across the area Tuesday night with clear skies
allowing greater radiational cooling.

.LONG TERM...Wednesday through Monday
Issued at 214 PM MDT Mon Mar 18 2019

On Wednesday, we will see a jump in the high temperatures as the
Alberta Clipper exits tot the southeast and the narrow ridge of high
pressure builds in from the west. Highs will be well into the 50s in
the Big Horn Basin Wednesday and the 40s most everywhere else with
stable air in place minimizing the potential for reaching the max
potential high temps if otherwise totally mixed, along with snow
cover cooling areas that would otherwise mix like Casper. With the
sfc still high over Southwest Wyoming Wednesday morning remaining in
place, would expect to see a repeat of patchy fog along portions of
the Interstate 80 corridor through Sweetwater County, extending up
into the adjacent Upper Green River basin as well.

Then all eyes turn south toward the southern stream energy. Last
night’s 06Z model run differ from yesterdays 12Z run which indicated
a col region separating the ridge building in. Also, earlier runs
had the other solns siding with the GFS punching the southern stream
low through the “weakness” in the ridge bringing the vertically
stacked weak low right across Central Wyoming. Lat nights 06Z run
wanted to keep the track of the low to the south over Utah and Co
once again with the ridge in tact. The model waffling continues with
this mornings 12Z run showing the GFS soln of tracking the low
northeast across Southeast Wyoming, the Euro actually taking it
northeast into Montana, and the Canadian taking the main low across
southeast Colorado, with a second circulation across Southeast
Wyoming. With all this uncertainty and lack of , along
with the GFS bias of bringing the system in too fast, will keep low
pops across the southwest and south for now for Thursday through
Friday, with low pops extending as far northeast as the Wind River
Mtns. Then on Friday night, the next upstream Pacific shortwave will
move in from the west and will weaken as it encounters the ridge and
combine with the weak southern stream system to keep chc pops over
the far west as well as the Big Horn Mtns Friday night through
Monday. The level of certainty as to how these two weather systems
track and interact is low at this point in time. Any precip that
does fall will likely be snow in the mtns along with rain/a rain
snow mix/wet snow in the lower elevations.


.AVIATION...For the 00Z TAFS through 00Z Tuesday afternoon
Issued at 214 PM MDT Mon Mar 18 2019

VFR conditions will occur at the terminal sites through 18Z
Wednesday. Patchy mid level clouds will track southeast across
Northern and East Central Wyoming through Tuesday morning. Patchy
fog is possible at KBPI and KRKS late tonight and Tuesday morning.


Issued AT 214 PM MDT Mon Mar 18 2019

Mainly dry and settled weather will continue. A weak weather system
will continue to move through o Wyoming tonight. However, it has
little moisture to work with. As a result only light mountain
showers are expected and even these will be few and far between.
Wind should remain light to moderate with relative humidity
remaining above critical levels. Mixing and smoke dispersal will be
generally fair to poor. Mainly dry weather should continue for most
locations through Wednesday. Patchy fog is expected during the
morning hours in Southwest Wyoming Tuesday and Wednesday.




LONG TERM...Lipson
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