Weather Service Report


280 
FXUS65 KRIW 150850
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
250 AM MDT Mon Oct 15 2018

.SHORT TERM...(Today through Wednesday night) 

With the fold over ridge moving down from the north, a classic
radiation fog pattern is currently in place along with clear skies,
light winds, and fresh snow cover for the Wind River and Big Horn
Basins as well as for the area along the North Platte River in 
Natrona County this morning as most of the snow fell yesterday 
east of the divide. In addition, warm bodies of water in the area
lakes will clash with this cold air where original dew points 
will be well above these colder ambient air temperatures, also 
helping to produce the fog. Temp/Dew point spreads are finally 
closing in. This morning will feature the coldest temperatures of 
the season thus far with many areas east and west of the divide 
expected to dip to 5 to 10 degrees above zero, with isolated 
readings around zero this morning. Some Mountain locations are 
already reporting temps between one below zero and 5 above, but 
these temps should begin to rise for the rest of this morning. But
temps in the valleys and basins should continue to drop until a 
little after sunrise this morning. One other fly in the ointment 
this morning is a weak weather feature diving southeast across the
Northern Plains which could produce a few isolated snow showers 
across the Northern Absaroka/Northern Big Horn Mtns this morning 
although the better isentropic lift appears to be relegated 
farther north in Montana from this feature. Southwest winds 
between South Pass and Casper will increase this morning in 
response to the relatively brief tightening of the gradient due to
this weather feature, but will diminish this afternoon. These 
southwest winds will help warm highs today in the 40s. Tuesday 
will be even warmer with highs in the 50s expected and well up 
into the 50s Wednesday with continued dry weather with the high 
still overhead.

The trough that delivered the snowfall to the area Saturday has 
exited off to the east, however. Although a piece of this energy 
will break off this positively tilted trough and form a closed 
low that will spin over the Desert Southwest and actually move 
northeast toward Wyoming and threaten far Southwest Sweetwater 
County with some isolated rain or snow showers Wednesday night.

.LONG TERM...(Thursday through Monday)


A seasonably mild and dry pattern will prevail Thursday 
through Monday.

Most of west and central Wyoming will be in between two weather 
systems on Thursday and Friday.  The first will be a cutoff 
southwest low that should be over Utah that is expected to at least 
partially shear out northeast over southern and eastern Wyoming 
Thursday morning.  We continue to keep chances of precipitation out 
of the area with this system, mainly spreading some mid and high 
clouds across the southeast half of Wyoming. The second system will 
be a clipper diving southeast out of central Canada into the 
northern Plains on Friday.   A weak, dry cold front is expected to 
clip northern and eastern Wyoming with this system, bringing 
slightly cooler highs roughly along and north of a Cody to Casper 
line.  Upper level high pressure is then expected to build into the 
area over the weekend with temperatures expected to warm to near 5F-
10F above normal on Sunday and Monday.  

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning) 

VFR conditions will occur through the period. Patchy fog is 
possible in the Big Horn and Wind River Basins, as well as parts 
of Natrona County until 16Z. Local MVFR/IFR conditions are 
expected. Will keep VCFG in some of the terminal sites. 
One side note...some isolated snow showers could occur in the
northern Absaroka and Big Horn Mountains this morning.

&&

.FIRE WEATHER...
Issued AT 212 AM MDT Mon Oct 15 2018

A combination of a clear sky and fresh snow will bring a cold 
start to the day this morning. Expect patchy fog in the basins and
valleys east of the divide this morning. Otherwise, today looks 
to be a dry day with temperatures not as cold as on Sunday. A weak
weather system moving across Montana will bring breezy conditions
from South Pass through Casper at times today. No rain or snow is
expected though, except some isolated snow showers are expected in
the northern zones this morning from a weak weather feature. Relative
humidity will remain above critical levels. Mixing and smoke dispersal
will be generally fair to poor.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

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

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Western Regional Climate Center, wrcc@dri.edu