Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 251005
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
305 AM MST Sun Feb 25 2018

.SHORT TERM...Sunday through Tuesday night
Issued at 230 AM MST Sun Feb 25 2018

With the contrast in the weather, we will again split the discussion
into West and East of the Divide.

West of the Divide...Once again, the main concern here will be snow.
There was some mainly light snow last night but it is in the process
of tapering off. Today looks to be the meat in between the pieces of
bread with mainly light snow through most of the day with only light
accumulations expected. The next trough and cold front approaches
late tonight and will bring the next round of snow. This is not the
strongest system we have seen. However, there will be enough for the
issuance for some highlights. As a result, we will issue some winter
weather advisories for the western valleys and mountains starting at
5 pm this evening. As for the heaviest snow, it looks to fall from
late Sunday night through around noon on Monday with the best
jet dynamics and trough axis passing through. Snow should then taper
off fairly quickly later Monday afternoon before ending Monday
night. At this point, most of Monday night into Tuesday looks
mainly dry with some ridging in place. The models are showing some
light QPF for Tuesday night but this can be overdone so we kept any
POPS in the slight range. With the Pacific origin of the air mass,
temperatures will be cool but not cold.

East of the Divide and Sweetwater County...Again, the main concern
here is wind. We have had a couple of isolated gusts over 50 mph
this evening. However, we still feel the strongest winds will be
tonight as the pressure gradient continues to tighten and 700
millibar winds increase to 50 to 60 knots. So, we will hoist a high
wind watch across the favored areas, otherwise known as the
Absarokas and Cody Foothills in the north and from the Red Desert
through Natrona County in central Wyoming. One good side effect of
the breeze was it mixed out some of the inversions so temperatures
will moderate today and possibly bring some melting of the snow.

On Monday, the cold front and trough will move across the area.
However, both the NAM and GFS are showing the system splitting and
shearing apart. And as a result, we do not expect a lot of snow with
it has it moves through. The best chance would be across northern
Wyoming where there will be a bit of right rear quadrant jet
dynamics to enhance lift. We can`t rule some out anywhere but again,
amounts should be fairly light. This also looks to be the warmest
day of the three before the front slides through.

All snow should be done by Tuesday as high pressure builds into the
area. Temperatures will cool a bit, but as stated above, with the
Pacific origin of the air, it will cool but not cold. In addition,
with sunshine expected in most areas, it will feel warmer as we will
only be a couple of days away from March at that point.

.LONG TERM...Wednesday through Sunday
Issued at 230 AM MST Sun Feb 25 2018

Wednesday will be dry for most places. Lingering light snow in the
higher mountain peaks cannot be ruled out. High temps will be in
the 20s and 30s. The weather pattern becomes more complex Thursday
into the weekend. A storm system slides south into the Pacific
Northwest states Thurs night through Friday and then lifts
eastward into the Northern Rockies Friday night through Saturday
night. The system winds up in the northern plains or southern
Saskatchewan, Canada next Sunday. However, we stay in the trough
next Sunday. Western WY will see an increase in snow Thursday
afternoon through Friday night with the potential for a significant
snow event. The snow in the west decreases Saturday morning with
lingering mountain snow showers Saturday afternoon. Will need to
keep an eye on this as the week unfolds. East of the continental
divide, Thursday looks mostly dry as does Friday. Friday night and
Saturday would see the best chance for snow in the Bighorn
mountains. The lower elevations east of the divide would see a
chance of snow Fri night into Saturday morning, but the track of
the storm would likely dry slot some places. One can expect windy
conditions at times with this storm as well. Plenty of time to
watch changes in storm track and adjust things as needed. High
temps Wed and Thurs will be in the 30s to lower 40s ahead of the
storm. Then colder highs Saturday and next Sunday.

&&

.AVIATION...12Z Issuance
Issued at 230 AM MST Sun Feb 25 2018

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

Snow showers will be on the decrease overall early this morning as a
upper level low pressure system dives SE across the Four Corners
area. Snow showers will mainly be confined to the mountains above
8500 feet from 12z-21z Sunday.  The next Pacific system will bring
increasing snowfall to the western mountains and far west (KJAC-
KAFO) 21z Sunday-03z Monday with mountains becoming mostly obscured
and prevailing IFR conditions expected at KJAC Sunday night. KPNA
can expect MVFR conditions in light snow late Sunday evening.
Additionally, southwest winds at mountain top level will increase
substantially Sunday night with areas of LLWS possible.

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

VFR conditions will prevail at all terminals through 12z Monday.
Southwest surface winds will increase Sunday afternoon and evening
along the east slopes of the Divide and in the wind corridor from
KRKS-KCPR.  Some gusts over 50 knots are possible vicinity KCPR 00z-
12z Monday, while areas of LLWS will develop Sunday night vicinity
KCOD-KDUB-KLND.  These strengthening winds may also result in
patchy blowing snow and partial terrain obscurations.

&&

.FIRE WEATHER...
Issued at 230 AM MST Sun Feb 25 2018

Occasional light snow will continue in the western mountains tonight
before steadier and heavier snow returns tonight and especially for
Monday. Mainly dry conditions are expected East of the Divide. Many
areas will see breezy conditions with windy conditions in the Lee of
the Absarokas and from the Red Desert through Casper where high
winds are possible tonight. Mixing and smoke dispersal will range
from poor in the Bighorn Basin to good in the mountains and breezier
locations.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

Winter Weather Advisory from 5 PM this afternoon to 5 PM MST
Monday for WYZ001-002-012>014-023-024.

High Wind Watch from 5 PM this afternoon through 8 AM MST Monday
morning for WYZ003-019-020.

&&

$$

SHORT TERM...Hattings
LONG TERM...AR
AVIATION...Meunier
FIRE WEATHER...Hattings



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