Area Forecast Discussion
Issued by NWS Riverton, WY

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155
FXUS65 KRIW 290858
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
258 AM MDT Sat Apr 29 2017

.SHORT TERM...(Today through Monday night)
Issued at 157 AM MDT Sat Apr 29 2017

Imagery shows longwave trof across the CONUS with closed low in base
of trof centered over the 4 corners. Strong 120 to 160 kt jet
associated with the LW trof stretches from the west coast down
through the Desert SW...across the srn Rockies then out through the
cntrl Plains/Great Lakes/New England. Wind speeds are minimal at jet
level over WY. SFC has a cold front well south of the region across
the srn Rockies/srn Plains with high P building into/across the nrn
tier of states including WY. Weal inverted trofs extending from swrn
CO into scntrl/cntrl WY and another through UT and into sern ID.
Current decreasing (mainly) snow rotating from e to w across the srn
half of the FA.

Upper closed low continues to slip s/se along with the cold front,
moisture return and associated precipitation. A few lingering
terrain/ll boundary forced snow possible this morning over s/cntrl WY
...with a couple terrain induced showers this afternoon will be
about all in the way of precipitation chances as shortwave ridging
aloft begins to overtake the FA from the southwest. These general
conditions will last well into Sunday before an upstream sw trof
rides through the nw flow aloft and into wrn WY with late
afternoon/evening showers breaking out west of the Divide...with an
associated cold front and some precipitation moving east of the
Divide before sun-up Monday morning. Light non-highlight snow
amounts expected with this system into early Monday afternoon.

The next and somewhat more significant Wx system will then follow on
the heals of Monday`s system...sparked by the approach of yet
another sw trof (with jet and associated cold front to follow just
beyond this fcst period) entering the FA from the NW later Monday
night. Precip chances will increase accordingly west of the
Divide...especially over nwrn WY...with light snow expected to begin
around midnight Monday, spreading to the south and east through the
end of the fcst period.

.LONG TERM...(Tuesday through Saturday)
Issued at 157 AM MDT Sat Apr 29 2017

A quick moving shortwave trough in the northwest flow will push
across the Cowboy State Tuesday with scattered to locally numerous
mountain snow, valley rain and snow showers. The main energy looks
to slide along the Divide with the best chances of precipitation
occurring along and east of the Divide, as well as far western
Wyoming. Looks like snow levels will vary from 5000 to 6500 feet.
Overall precipitation amounts look to be on the light side with
some convection giving pockets with heavier amounts. Could even
see a few thunderstorms Tuesday afternoon, but not enough
confidence to include in forecast at this time.

Upper level ridging builds into the area Wednesday and Thursday
with mainly dry conditions and a warming trend. Global models show
the ridging flattening, or at least the ridge axis shifting east
into the Plains ahead of a potential trough pushing/digging into
the Western U.S. Either way looks like the area will remain in
the warm sector with perhaps enough moisture and instability to at
least mention convection over the west on Friday and then across
the entire area Saturday.

Temperatures will be below average Tuesday with a warming trend to
above average temperatures by Thursday and lasting through
Saturday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning) Issued
at 157 AM MDT Sat Apr 29 2017

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

VFR conditions will prevail through the period at KPNA, KBPI, and
KJAC airports. KRKS will see MVFR/IFR conditions until around 12Z
before becoming VFR after 12Z.

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

In Central WY, areas of MVFR to IFR conditions will gradually lift
to VFR by 15Z in most locations. Then VFR conditions will prevail in
Central WY the rest of the period. In Northern WY, VFR conditions
will occur through the period.

&&

.FIRE WEATHER...
Issued AT 157 AM MDT Sat Apr 29 2017

Fire danger low across the forecast area through the next week. All
fuels currently in green-up. Periods of isolated to widely scattered
light rain and/or snow showers will occur Sunday afternoon into
Monday afternoon...and again late Monday night through Tuesday
night...with heaviest and most widespread precipitation occurring
Tuesday afternoon and evening. Winds will be relatively light for
the most part for the next several days...with brief gusty periods
near any frontal passage (along with a wind shift). Smoke dispersion
fair to very good this afternoon...good to excellent Sunday and
Monday afternoons.

&&

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

&&

$$

SHORT TERM...Braun
LONG TERM...Murrell
AVIATION...Ross
FIRE WEATHER...Braun



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