Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 181954
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
154 PM MDT Fri May 18 2018

.SHORT TERM...(This evening through Monday)
Issued at 113 PM MDT Fri May 18 2018

A large Pacific low pressure trough over the northern Rockies
and Great Basin spreading moisture and instability across
western, northern and central Wyoming will continue to produce
showers and thunderstorms with small hail, strong gusty winds and
local heavy rain tonight, then decreasing through Friday.
Temperatures will cool with increasing relative humidity. Showers
and isolated thunderstorms spreading east will linger into Saturday
then decrease as the trough moves east and high pressure moves in from
the west. Enough heating is expected to keep some showers over the
west and north on Sunday and Monday with warming.

.LONG TERM...(Monday night through Friday)
Issued at 113 PM MDT Fri May 18 2018

BY MONDAY NIGHT THE NEXT CLOSED LOW TO OUR WEST IS PROGGED TO DRIFT
SOUTHEAST TO SOUTHERN CALIFORNIA, THUS INCREASING THE SOUTHERLY
DIFLUENT FLOW OVER OUR CWA AHEAD OF THE LOW. THE MOST UNSTABLE
CONDITIONS APPEAR TO BE OVER JOHNSON COUNTY MONDAY EVENING. THE
HIGHEST SCATTERED POPS WILL BE OVER THE NORTH AND WEST. THIS
SOUTHERLY DIFLUENT FLOW WILL CONTINUE THROUGH TUESDAY AS THE CLOSED
LOW MIGRATES ACROSS THE GREAT BASIN SO ANOTHER DAY OF ACTIVE
AFTERNOON AND EVENING CONVECTION IS ANTICIPATED TUESDAY, ESPECIALLY
FOR CENTRAL AND EASTERN ZONES. JOHNSON COUNTY IS AGAIN PEGGED TO
RECEIVE THE MOST SIGNIFICANT CONVECTION AND RESULTANT RAINFALL
TUESDAY NIGHT. ON WEDNESDAY, THE MODELS BEGIN TO DIVERGE. THE EURO
PULLS THE H5 LOW TO NORTHWEST WYOMING WHERE AS THE CANADIAN AND THE
GFS KEEP IT SPINNING OVER THE GREAT BASIN. ANOTHER ROUND OF
CONVECTION IS SLATED, MAINLY FOR CENTRAL AND NORTHERN WYOMING FOR
WEDNESDAY AFTERNOON AND EVENING. FREMONT COUNTY IS SLATED TO HAVE -6
LIFTED INDICES SO FREMONT COUNTY COULD BE UNDER THE GUN WEDNESDAY.
THEN BY THURSDAY, THE THE CANADIAN AND EURO IS RELATIVELY QUICK TO
TRACK THE ASCT TROUGHPA ACROSS WYOMING WHERE AS THE GFS IS THE
SLOWEST, BRINGING IT THROUGH FRIDAY. IN ANY EVENT, CONVECTION
APPEARS MOST LIKELY NORTH AND WEST OF WHAT IS LEFT OF THE CLOSED LOW
WITHIN THE TROUGH ACROSS NORTHERN AND WESTERN WYOMING ON THOSE DAYS.
THE GFS IS ALREADY INDICATING -7 LIFTED INDICES FOR JOHNSON COUNTY
FOR THURSDAY. TEMPERATURES WILL GRADUALLY WARM THROUGH MID WEEK,
THEN LEVEL OFF, WITH THE FAR WEST COOLING OFF ON THE BACK SIDE OF
THE SLOW MOVING TROUGH LATER NEXT WEEK.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday)
Issued at 113 PM MDT Fri May 18 2018

Scattered thunderstorms with gusty winds and some with small hail
expected to develop between 20Z- 00Z across central and southern WY
as northerly flow strengthens east of the divide and runs up against
southerly flow in southern WY. By 00Z- 02Z/Sat widespread rain
showers expected across central and southern WY, especially in
upslope areas like vicinity KLND and KCPR. Heavier precipitation
moves to SE WY after 06Z/Sat. Mountains to be generally obscured
after 00Z/Sat, and VFR/MVFR mix could also see localized IFR
conditions near and around heavier precipitation this evening.
Prevailing MVFR conditions, local IFR conditions with areas of light
rain and fog are expected across central areas into SW Wyoming 06z-
18z Saturday. Mainly MVFR conditions are expected along and east of
the divide 18z Saturday through 00Z Sunday where we are expecting
rain showers/low cigs to occur. West of the divide, MVFR with some
VFR conditions are expected with scattered thunderstorms expected to
develop resulting in local IFR conditions 18Z saturday through ))Z
Sunday.

&&

.FIRE WEATHER...
Issued AT 113 PM MDT Fri May 18 2018

A large Pacific low pressure trough over the northern Rockies
and Great Basin spreading moisture and instability across
western, northern and central Wyoming will continue to produce
showers and thunderstorms with small hail, strong gusty winds and
local heavy rain tonight, then decreasing through Friday.
Temperatures will cool with increasing relative humidity. Showers
and isolated thunderstorms spreading east will linger into Saturday
then decrease as the trough moves east and high pressure moves in from
the west. Enough heating is expected to keep some showers over the
west and north on Sunday and Monday with warming. Mixing heights will
lower Saturday with general good smoke dispersal in the afternoon.
Areas with lower clouds and heavier precipitation will have poor
smoke dispersal.

&&

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

$$

SHORT TERM...Baker
LONG TERM...Lipson
AVIATION...Lipson
FIRE WEATHER...Baker


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