Area Forecast Discussion
Issued by NWS Riverton, WY

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937
FXUS65 KRIW 280556 AAA
AFDRIW

Area Forecast Discussion...UPDATED
National Weather Service Riverton WY
1156 PM MDT WED JUL 27 2016

.UPDATE...added 06z aviation discussion.

&&

.AVIATION.../06Z ISSUANCE/

West of the Continental Divide...KJAC/KBPI/KPNA/KRKS

Scattered showers and isolated thunderstorms will continue across
yellowstone national park with a few showers vcnty KJAC until 9z.
Smoke from the Cliff Creek Fire near Bondurant may bring MFVR vsbys
to vcnty KBPI-KPNA 12z-16z Thursday.  Otherwise, drier air will
bring VFR conditions and unlimited ceilings to all terminal sites
12z thursday through 12z friday with some west to northwest breezes
in the afternoon.  A dry cold front will result in a wind shift from
the NE along the Interstate 80 corridor, vcnty KRKS, Thursday
evening.

East of the Continental Divide...KCOD/KCPR/KLND/KRIW/KWRL

An upper level disturbance will continue to bring scattered showers
and thunderstorms vcnty and north of a KCOD-KWRL-KCPR line through
12z.  A decrease in this activity will occur 12z-20z, then showers
and thunderstorms will blossom across most areas Thursday afternoon
and early evening.  The strongest storms are expected along and east
of the Interstate 25 corridor where isolated storms may produce
large hail and wind gusts over 40 knots.  Most of this activity will
move out of the area by 03z Friday.

&&

.PREV DISCUSSION... /issued 241 PM MDT WED JUL 27 2016/

SHORT TERM...TONIGHT THROUGH SATURDAY

LAPS data is showing capes of 1400 in Johnson County and decent
lifted indices, with these mesoscale dynamics decreasing from
northeast to southwest across the CWA with areas west of the
divide devoid of much in the way of any convection potential at
the moment. We already have seen a few small convective cells
march east across Johnson County. The first disturbance in the
west northwest flow will produce an increase in thunderstorm
activity, mainly in our north and east zones for the rest of this
afternoon and evening. Considering the large hail that fell in
Johnson County late yesterday afternoon with a similar shortwave,
would not be surprised to see similar activity for the rest of
today in the northeast where they are in a marginal risk. Then
after midnight, the next disturbance and associated with tonight`s
cold front will keep the convection going east of the divide with
the most widespread activity expected in Johnson County. This
activity should spill over the divide toward the southwest
tonight. With the higher dew points spilling in behind this
front, plus whatever rainfall this front decides to doll out, this
added moisture will lay the ground work for the ingredients for
the thunderstorms expected Thursday associated with the strongest
shortwave/cold front expected this week, which we expect to come
through Thursday night, along with significant activity expected
out ahead of this weather feature by Thursday afternoon. Johnson
County could once again be under the gun for the potential for
strong thunderstorms by Thursday afternoon, with the northeast
portion of the county in "marginal risk." The convection Thursday
afternoon and evening should be more widespread than what we
witness this evening along with the best shot of a wetting rain
anywhere in the CWA this week. Again, we expect some of this
activity to spill over the divide. Much of this activity will
continue through the night Thursday night as this next stronger
shortwave will also be coming through around 12z Friday. Then one
more shortwave/southwest bound surface boundary to push through
late friday with more convection expected Friday afternoon with
the previous night`s influx of moisture to work with once again,
with most of the activity expected east of the divide. By Saturday
the high will begin to spread east from the desert southwest
toward the Southern Plains, thus backing the west northwest flow,
with any additional shortwaves being held at bay well to our north
for a dry day everywhere Saturday. One side note, Sweetwater
County will experience fairly brisk west winds of 20 to 30 mph
along with an RH of 10 percent Thursday but fuels are not
considered critical there yet.

LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY

Ridge axis moves from the Desert SW area to the Southern Plains
during the period turning flow more wsw/sw which will likely bring
up a little monsoonal moisture during the period. Models vary on how
much with the Euro keeping most of it south of the area after an
initial surge Saturday night and Sunday. Will hit much of the area
with at least isold showers/tstms with the initial surge Sat ngt
into Sunday but other than that will keep it mainly near the srn
border. Otherwise, hot and breezy at times with a few shallow fronts
impacting the nrn and ern zones early next week with passing
shortwaves to the north.

AVIATION.../00Z ISSUANCE/

A couple weather disturbances will impact the area for the rest of this
afternoon through tonight. The first one will aid in isolated to
widely scattered thunderstorms from around KCOD to KCPR while a
second disturbance will aid in evening and overnight showers and
thunderstorms from about KJAC to KCPR that as it moves east across
the area. A few stronger storms with hail, wind and frequent
lightning are quite possible late this afternoon and evening
northeast of a line from KCOD to KCPR. A new batch of showers and
thunderstorms will move into Northwest Wyoming later this evening
and move east across areas east of the divide during the early
morning hours. Generally along and north of a line from KJAC to
KCPR for these nocturnal showers/storms.

FIRE WEATHER...

Afternoon showers and thunderstorms with threats of gusty wind will
continue for the next few days. A near continuous threat is
anticipated for Natrona and Johnson counties, with showers
potentially lingering through the overnight hours. A cold front will
sweep through northeastern Wyoming tonight, helping to cool off
temperatures Thursday. Additionally, this front will increase
instability for areas east of the divide on Thursday, resulting in
a threat for some stronger storm activity Thursday afternoon.

&&

.RIW Watches/Warnings/Advisories...
None.
&&

$$

SHORT TERM...Lipson
LONG TERM...Skrbac
AVIATION...AEM
FIRE WEATHER...Lipson



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