Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 200501
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1100 PM MDT Sat May 19 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 216 PM MDT Sat May 19 2018

A Pacific low pressure trough extending south from the Pacific
Northwest into the Great Basin will spread moisture and instability
across the area producing scattered showers and isolated thunderstorms
with small hail and gusty winds this evening and again on Sunday.
Temperatures will begin to warm with favorable relative humidity.
Convection will increase on Tuesday as the trough shifts east.
Run off from recent heavy rainfall and snow melt will likely cause
rising river levels through Tuesday.

.LONG TERM...(Tuesday night through Saturday)
Issued at 216 PM MDT Sat May 19 2018

A weakly defined upper level low over the Great Basin Tuesday night
will be in a position to where we will be under a backing,
predominantly southerly difluent flow. This will fuel late day
convection Tuesday evening, especially over Natrona and Johnson
Counties where lifted indices will be down to -5 along with decent
capes. Currently, the GFS is indicating over two inches of precip in
this area for a six hour period. Convection, overall will be fairly
widespread. In addition, we will be underneath the LFQ of the jet
max. On Wednesday and Wednesday night, the low will become more well
defined and track east across Southern Montana. Based on the timing
of this low, it will come close to Northwest Wyoming late Wednesday
during the favorable time for convention, so the most convection will
likely occur over Northwest Wyoming where the GFS indicates a six
hour period of 1.46 inches. Behind this low/trough, the steering
flow will go northwest with slightly cooler temps Wed/Thu,
especially in the west where some additional convection will occur
through Friday. Northern Wy will also see convection Thu/Fri. By
Saturday of next week, convection is progged to be a bit more
widespread.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday)
Issued at 1100 PM MDT Sat May 19 2018

Low end VFR or occasional MVFR ceilings anticipated Saturday night
in several basin locations, mainly near the foothills. It would
appear that after 10Z/Sun all terminals should rise to VFR for the
remainder of the forecast period. The exception will be KCPR where
IFR ceilings and/or fog could settle in early Sunday morning.
However, surface wind should be from an unfavorable southeast
direction and around 10kts as the night wears on. Looks like
afternoon convection is most likely to affect KJAC after 21Z/Sun.
Have indicated VCSH in terminals west of the Divide between about
23Z/Sun and 05Z/Mon.

&&

.FIRE WEATHER...
Issued AT 216 PM MDT Sat May 19 2018

A Pacific low pressure trough extending south from the Pacific
Northwest into the Great Basin will spread moisture and instability
across the area producing scattered showers and isolated thunderstorms
with small hail and gusty winds this evening and again on Sunday.
Temperatures will begin to warm with favorable relative humidity.
Convection will increase on Tuesday as the trough shifts east.
Run off from recent heavy rainfall and snow melt will likely cause
rising river levels through Tuesday. Mixing heights will be favorable
even with relatively light transport winds to produce good or
better smoke dispersal each afternoon through Tuesday.

&&

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

$$

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



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