Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 270545
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1145 PM MDT Sun Mar 26 2017

.SHORT TERM...(This evening through Wednesday) Issued at 141 PM
MDT Sun Mar 26 2017

Imagery shows very progressive 5 wave pattern over the HH with
kludgy embedded pattern. Troffing nrn/cntrl Rockies moving into the
central Plains west (CONUS) with SW ridging following. Upstream,
another trof resides just offshore PAC NW with lead portion of the
wave pushing into WA/OR. SFC has torn up cold front well out of WY
with modest but building high pressure across the forecast area.
Light precip dissipating, moving east and out of central WY.

Today, post frontal with weak ridging aloft ahead of the next
system/trof due to arrive Monday afternoon/evening across
western/southwestern WY. In the meantime from Sunday afternoon
through Monday morning...increasing modestly moist mid level west to
southwest flow will keep weakly forced showers a possibility across
the western mountains. Then, the nw coast trof makes its way across
the intermountain west and into wrn WY Monday afternoon...the bottom
portion of the trof will dig southward toward the Desert Southwest
and 4 corners area. The best energy with this system still looks to
stay south of the FA...but should be able to return moisture up
through east CO and into/across eastern WY Tuesday morning. With
frontogenesis going on west of and over southern WY Monday night and
early Tuesday morning, temperatures may be cold enough across the
area east of the Divide to change to snow at many locations by
around midnight Monday and continue into the late morning/early
afternoon Tuesday before changing back over to rain. Central and
eastern WY, including portions of Fremont and Natrona counties could
see a few inches of wet heavy snow through Tuesday morning...with
heaviest snow generally expected near the front. Winter Wx Advisory
Highlights possible zone 19 in addition to the eastern Bighorn
Mountains.

System exits Tuesday night into the CO high Plains and Central
Plains with high P and SW ridging and clearing skies returning to
the FA through the end of the forecast period.

.LONG TERM...(Wednesday night through Sunday) Issued at 141 PM
MDT Sun Mar 26 2017

Beginning of the fcst...exiting deep closed low trof continues to
head ewd into the Plains with building high P across the SFC over
the FA. Upstream, the next in a series of shortwaves moves into the
PAC NW. The jet associated with this trof looks quite strong and
able to help develop what looks to be a quite vigorous, digging
close low trof with cyclogenesis proceeding over the srn Rockies by
Friday. Frontogenesis with this system looks to develop a bit
earlier to the west and north of WY on Thursday...arriving as more a
Canadian type cold front with a slightly colder airmass
accompanying. Precip should arrive across western WY by Thursday
morning with the cold front moving east of the Divide by Thursday
night. It continues to look like possible "blizzard-like" conditions
for a period after midnight Thursday and into/through the Friday
morning period...especially across the southern zones. The system
should mostLY be out of the region late Friday night/early Saturday
morning. This system still has a lot of possible outcomes as the
closed, and possible near cut-off, nature of this system (over the
srn Rockies) could still produce some timing problems that could
affect location and subsequent impacts. Just saying. Interesting to
watch right now...and deal with later. Some hydro concerns a
possibility.

&&

.AVIATION.../06Z ISSUANCE/

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

Despite lowering mid-cloud deck invading from the west, VFR
conditions are anticipated through about 15Z/Mon. KJAC has the best
chance of low end VFR or MVFR conditions through early Monday
afternoon, mainly between 15Z-21Z/Mon. Moisture then begins to
spread across southwest Wyoming and left exit region of 90kt jet
will aid lift during the late afternoon in the vicinity of KRKS.
Precipitation will shift to this area during the late afternoon and
evening with gradually lowering ceilings and visibility. Heavier
precipitation and dynamic cooling will likely enable the rain to
change to snow at KRKS between 04Z/Tue and 06Z/Tue. KBPI and KPNA
may remain VFR, but have at least added MVFR ceilings during the
late afternoon and evening Monday.

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR conditions to prevail through 00Z/Tue before moisture begins to
overspread a southward moving cold front by around 03Z/Tue.
Upslope flow deepens and increases between 03Z-06Z/Tue in the
central basins. This should bring light rain and MVFR conditions to
KCPR, KLND, and KRIW by 06Z/Tue.

&&

.FIRE WEATHER...
Issued AT 141 PM MDT Sun Mar 26 2017

Fire danger will remain low through much of the week. A very
progressive and unstable pattern has taken over the forecast area
and will remain in place over the next week or so. Periods of
precipitation will move across WY every other day or so along with
several frontal passages. Temperatures will be seasonal or slightly
below seasonal for much of the time with gustiest winds accompanying
frontal passages. Smoke dispersion will be fair to good most
afternoons.

&&

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

$$

SHORT TERM...Braun
LONG TERM...Braun
AVIATION...CNJ
FIRE WEATHER...Braun



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