Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 222156
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
357 PM MDT Fri Jun 22 2018

.SHORT TERM...This evening through Monday
Issued at 230 PM MDT Fri Jun 22 2018

Low pressure system has moved across MT yesterday and today, and
will progress into western Dakotas by tonight. Result has been
somewhat unstable northwest flow over the area, and has brought
scattered showers and isolated thunderstorms along and east of the
divide along with breezy to windy conditions. Isolated showers to
continue through midnight as boundary layer stabilizes and low
moves further east. Model guidance is suggesting and area of
showers to impact YNP and northern Absarokas after midnight.

Another shortwave trough will move into western and SW MT
Saturday, helping to again destabilize atmosphere and increase
showers and thunderstorms across the area. This system looks to
bring another cool front down east of the divide by midday
Saturday as the upper level low moves SE. Area of showers and
thunderstorms then will increase Saturday afternoon and evening.
Some of the thunderstorms in central WY could bring heavy rain.
Some favored upslope areas are expected to to see a half inch to
1.5 inches of precipitation by Sunday morning. Flood watch out for
central WY highlights possible concerns with the increase
precipitation. NAM has upper level low slowly moving over NE WY by
Sunday morning, continuing cool wet conditions. Sunday could see
some moderate rain in eastern Johnson and Natrona counties before
moves into western NE. With 700mb temps and precipitation,
Saturday and Sunday highs in the lower elevations to only reach
low 70s.

Upper level low then moves off into the plains Monday and a
shortwave ridge over the Great Basin moves eastward over WY.
Monday to clear out considerably and return temperatures and
humidities to more seasonable conditions. Breezy dry conditions to
return to SW WY.

.LONG TERM...Monday night through Friday
Issued at 1242 PM MDT Fri Jun 22 2018

A quieter period of weather is forecast for Tuesday through
Wednesday with most areas seeing dry conditions and warm
temperatures. A cold front pushes into northern WY thursday morning.
A few showers and storms are possible along the Montana border into
the Northern Bighorn mountains, and in northern Johnson county. GFS
model is indicating isolated showers and storms Thursday and Friday
across the area. The ECMWF model is drier with very isolated
activity over the region. Will take the GFS model for now and have
the isolated showers and storms in the forecast for Thurs and next
Fri. High temps still warm Thurs, then slightly cooler next Fri due
to more cloud cover.

&&

.AVIATION...For the 00Z TAFS through 00Z Saturday afternoon
Issued at 357 PM MDT Fri Jun 22 2018

Conditions will be VFR through 19Z/Saturday. Low pressure over
Montana will cause convection to continue this afternoon and into
the evening. This activity will be mainly east of the divide with
the exception of KJAC. The best chance for localized MVFR conditions
with the strongest storms will be along and east of a line from KCOD-
KHSG-KCPR between now and 03Z Saturday. The main hazards with this
convection will be heavy rain and small hail. Winds will be gusty
but not as strong as seen Thursday. Convection and cloud cover will
largely dissipate at all terminals between 05Z-08Z/Saturday. Another
round of showers and thunderstorms expected in the north Saturday
afternoon.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.


&&

.FIRE WEATHER...
Issued AT 230 PM MDT Fri Jun 22 2018

Current low pressure system over SE MT will continue scattered
showers and thunderstorms across much of the area into the evening
hours, with isolated to scattered showers through midnight.
Exception is SW WY where conditions will remain more clear,
warmer, and drier. Breezy to windy northwest flow to also continue
through 8pm or so. As low pressure system moves into plains and
another moves into SW MT on Saturday, isolated showers possible
over YNP overnight then increase across northern and western WY
from 6am-12pm Saturday. Showers and thunderstorms to develop
Saturday afternoon, primarily along and east of the continental
divide with dry breezy NW flow in far SW WY. Low pressure system
to move over the area late Saturday into Sunday, providing
conditions for moderate to heavy rain in central and eastern WY.
Certainly wetter and cooler through Sunday. Heavy rain could cause
minor flooding by Sunday morning. Sunday to dry out some but
remain cooler. High pressure to move in Monday, increasing
temperatures and wind, and decreasing humidities.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Saturday evening through Sunday afternoon for
WYZ005>011-017-019-020-022.

&&

$$

SHORT TERM...McDonald
LONG TERM...Hulme
AVIATION...Hulme
FIRE WEATHER...McDonald


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