Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 101114

Area Forecast Discussion
National Weather Service Riverton WY
514 AM MDT Sat Jun 10 2023

.DISCUSSION...(Today through Friday)
Issued at 145 AM MDT Sat Jun 10 2023

Today will once again be wet, with areas along and east of the
Continental Divide being most favored to see showers and
thunderstorms. The driving weather feature for today will be a
backdoor trough and associated weak cold front. Current water vapor
imagery shows this feature well, with a drier air mass traveling
from northeast to southwest, the front boundary of it currently
moving through northern North Dakota and Minnesota. As the front end
of this trough approaches northeastern Wyoming through the day
today, moisture convergence will aid in showers and thunderstorms
for the eastern half of the CWA, mainly for Johnson and Natrona
Counties. The eastern half of the Bighorn Mountains and Casper
Mountain are favored upslope for this pattern, so higher
precipitation chances for those locations. Precipitation will likely
begin this morning, with the best chances beginning over the Bighorn

Precipitable water (PWAT) values had decreased across the area
Friday, but as this system pushes in, PWAT values are expected to
increase, with values again reaching 150% to 175% of normal. These
higher values will mainly be confined east of the Divide. The
Weather Prediction Center (WPC) has Johnson and portions of Natrona
Counties in a slight risk for excessive rainfall as a result, with
the rest of locations east of the Divide in a marginal risk. This
has been a common theme for this area of the state over the past
week or so, therefore the threat for any storms to drop heavy rain
will be the main concern today. Forecasted CAPE values are showing
roughly 300 to 800 J/kg for the Johnson/Natrona County area, so an
isolated stronger storm is not out of the question. Cloud cover may
limit that slightly. West of the Divide, less boundary support will
result in less widespread showers/storms. However, less cloud cover
and a generally moist atmosphere will likely bring afternoon
convection, although more isolated.

High temperatures for the day west of the Divide will be very
comparable to yesterday, with highs generally around 70F. East of
the Divide, highs will be a bit cooler, thanks to that weak cold
front moving through. Highs will generally be in the middle 60s to
lower 70s. The Bighorn Basin sees upper 70s.

Rain will likely persist for many of the areas east of the Divide
Saturday night into Sunday. Sunday is looking a repeat of Saturday,
with the best shower/thunderstorm chances east of the Divide. The
boundary does look to shift slightly more east/southeast, so PWAT
values may not be as high Sunday. High temperatures Sunday will be
comparable to those Saturday.

Monday, an upper low tracking northeastward will be centered over
southern Nevada. Through Tuesday, models are showing it track along
the southern boarder of Wyoming. This will continue the wet pattern
through mid-week. A pattern shift finally looks to take shape in the
Wednesday/Thursday timeframe. A low near the Montana/Canada border
will bring down a trough into Wyoming. Exact timing and placement of
this low is still uncertain at this range out, but this low looks to
finally push that persistent high out of the plains. It would also
bring a more westerly/northwesterly flow to the state.
Interestingly, the ECMWF brings slight ridging over Wyoming next
Saturday (June 18th), meaning perhaps a day without widespread
convection. The GFS does not have this solution, bringing down
another Canadian low instead. Although it is all far out, a glimpse
of a changing weather pattern is indeed on the horizon.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 510 AM MDT Sat Jun 10 2023

VFR conditions to persist at all terminals through 06Z/Sunday, with
a chance for MVFR at KCPR after 08Z/Sunday. Lingering convection has
finally waned and is mainly confined to central Wyoming early
this morning. A frontal boundary pushes through areas east of the
Continental Divide from late morning into the early afternoon as
shortwave energy backs into the region from the north and east.
Showers and isolated thunderstorms increase steadily from late
morning through the afternoon. Weak upslope leads to persistent
showers for many eastern terminals, while western convection will
be more diurnally driven. Brief MVFR ceilings and wind gusts
around 30kts will be the primary hazards. Showers linger after
sunset and prevail longest across the east. A moistening boundary
layer and the weak upslope combine to bring the chance of MVFR
ceilings to KCPR late in the period. Other eastern terminals can
expect lowered mid- cloud decks. Mountain tops occasionally
obscured after 00Z/Sunday along and east of the Divide.

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


Issued at 145 AM MDT Sat Jun 10 2023

A weak, backdoor cold front will push into northeast Wyoming
today, moving to the southwest. With it, high temperatures will
generally be 5 to 10 degrees cooler east of the Divide today.
Upper level flow will shift northeasterly. Gusts of 20 to 25 mph
are possible east of the Divide. The most likely effected
locations are zones 280 and especially 281. Showers and
thunderstorms will again occur today, favored for locations east
of the Divide and along with the weak cold front. Moderate to
heavy rain are the main threats with storms today. Relative
humidity values will be notable higher today, especially east of
the Divide. Cool and wet conditions continue into Sunday.





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