Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 160951
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
351 AM MDT Tue Jul 16 2019

.SHORT TERM...(Today and tonight)
Issued at 317 AM MDT Tue Jul 16 2019

Strong to severe thunderstorms are again possible along and east
of the Continental Divide. The best chance of severe weather will
be across Johnson County followed by the Bighorn Basin. Expecting
a late show as the area will be capped with a loaded gun
sounding. Once the cap is broken between 2 and 4 PM expect
thunderstorms to quickly go strong to severe. Across the north,
models show 1000 to 2000 J/kg of Convective Available Potential
Energy (CAPE) and effective bulk shear of 40 to 50 knots. The
Significant Hail Parameter (SHiP) is between 1 and 2 with the
largest values over Johnson County. This would indicate the
potential for very large hail around 2 inches if not a bit larger.
Also precipitable water values remain relatively high so
torrential rainfall in a short amount of time could cause
localized flooding.

The first wave of thunderstorms should exit the area between 6 PM
and 9 PM. Except for Yellowstone, the far west looks to be dry
during the day, but an approaching trough is expected to initiate
showers and thunderstorms across eastern Idaho spreading into the
far west during the early to mid evening. This activity will then
spread east/northeast during the night, before exiting by around
12Z Wednesday.

Wednesday looks to drier with thunderstorms more isolated in
nature. However some of these storms could be quite strong over
the east. Winds across Natrona County look to become southwest
during the afternoon which would curtail the chances of robust
convection. The same cannot be said for Johnson County.

Elevated fire weather conditions are expected over the southwest
today and Wednesday. For more details please see the fire weather
discussion below.

.LONG TERM...(Wednesday through Monday)
Issued at 317 AM MDT Tue Jul 16 2019

Hot, dry, and windy will be the story for Thursday and Friday. Low
humidities and gusty afternoon winds will spread across southern and
central Wyoming Thursday and continue into Friday. On Thursday
westerly winds will be widespread 20 to 25 mph with gusts of 30 to
35 mph. The wind corridor from South Pass to Natrona County could
see winds around 30 mph with gusts into the 40 mph range. friday`s
winds do look slightly lower due to a loosening gradient but will
still be high enough to cause problems. Fire weather concerns will
have to be closely monitored through Saturday.

Saturday will see an influx of moisture and humidities will rebound
a bit east of the Divide. Saturday afternoon looks like our next
good shot at thunderstorm activity across the north. Models are
still in partial agreement on this next system, so confidence
remains low on how impactful it will be. Early next week looks like
a return to high pressure ridging with convective activity in the
north as shortwaves move through. Only minor changes to the forecast
at this time.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 317 AM MDT Tue Jul 16 2019

Isolated showers will occur over the region until 15Z. New showers
and storms will develop over the region after 19Z and continue
through 02Z. The Isolated showers and storms will linger until 04Z
from KBYG to KCPR. Outflow wind gusts between 30 and 40 knots will
occur with some storms. VFR conditions will prevail and the terminal
sites. However, MVFR conditions will occur in stronger storms.

&&

.FIRE WEATHER...
Issued AT 317 AM MDT Tue Jul 16 2019

...Elevated Fire Weather Conditions over Southwest Wyoming over
the next several days...

Breezy westerly wind in combination with low afternoon relative
humidity will result in elevated fire weather conditions over
southwest Wyoming for much of the week. Critical fire weather
thresholds will likely be met at times in this area with the worst
conditions occurring Thursday and Friday. Wednesday still looks
quite winds, but relative humidity is expected to be higher than
what was forecast yesterday.

Isolated to scattered afternoon and evening thunderstorms are
expected across central and northern fire zones while southwest
Wyoming will remains dry. The best chance over the north. Showers
and thunderstorms will last well into the night. Isolated
afternoon and evening thunderstorms are expected along and East of
the Continental Divide.

&&

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

&&

$$

SHORT TERM...Murrell
LONG TERM...Hulme
AVIATION...LaVoie
FIRE WEATHER...Murrell


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