Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 010835
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
235 AM MDT FRI JUL 1 2016

.SHORT TERM...Friday through Sunday night

The plume of deepest monsoonal moisture is slowly exiting the county
warning area stage east. There are still some showers in Natrona
County and the western Mountains but these are slowly weakening. The
models still indicate some showers in the east in the morning but
the NAM is wetter than the GFS. For now, we will go with isolated
POPS in the morning. In addition, with the low temperature/dew
point and rain spreads we did add patchy fog to some areas the
models do indicate somewhat drier air spreading across the area
today with precipitable water about 0.40 inches less than
yesterday, generally in the 0.50 to 0.90 inch range. This will
still be enough for isolated to widely scattered convection this
afternoon and evening, but coverage should be less than on
Thursday. Locally heavy rain is still possible though as steering
flow remains weak and an storm that forms will be slow to move.
Temperatures should be a couple of degrees warmer but still fairly
comfortable for this time of year.

Convection looks to reach a minimum on Saturday as heights rise
across the state with ridging building a bit.Some very dry air will
move in west of the divide so we removed POPS in that area. Most
convection on this day should remain over the mountains and some of
the adjacent foothills as steering winds will remain weak. With
more sunshine and fewer clouds temperatures should rise once again,
but likely only back to near normal levels.

Coverage could increase again for Sunday however. The models are
showing some deeper moisture moving into the state. In addition, a
shortwave will be moving by to the north of Wyoming, helping to
increase instability a bit. At this point, the threat of
thunderstorms would be restricted to the west most of the day. As
the shortwave passes east of the divide the best chance would be
across northern areas. As a result, we did add some slight chances
across the Big Horn Basin for Sunday evening. High temperatures
should be fairly similar to Saturday, near to slightly above average
for the first part of July.

.LONG TERM...Monday Through Friday

Still quite a few differences in the models from midweek onward.
Big picture still has mean upper ridge redeveloping ewd over the
Southern High Plains but exactly how the energy between 180w and
the Gulf of Alaska comes into play varies widely in location and
timing. The GFS is almost back to where it was two nights ago with
a fairly significant upper low lifting newd from Eastern Oregon
into Wrn MT between 00z and 12z Thu. This is currently the system
on the west end of the Aleutian chain. The Euro has this same
system in Ern OR around 00z Thu but it weakens it more and pushes
it ewd across Srn MT and Nrn WY on Thu. The GEM is further north
than both moving the system from Ern WA into Wrn MT during about
the same time. The change in the upper high position as we`ve been
saying for four nights still opens the door for one of these
systems to impact at least our wrn or nrn sections and we`ve made
sure that at least some pops cover this region later Wednesday
into Thursday. The GFS also has a secondary shot of energy coming
down from the nw on Friday that the other models do not. Have some
isold mtn pops in now but certainly nothing the the GFS would
indicate since confidence is just too low this far out.
Backtracking to the beginning of this period, the current Gulf of
Alaska low opens up and moves east well north of our area with
just the nrn part of our area open to potential moisture/forcing
and front in the area. If the midweek system does setup right,
there will still be the potential for some stronger storms in the
west and north as trough dynamics/jet streak and front potentially all
come into play. Timing may hinder this if it`s more towards Wed
ngt but we`ll just have to wait and see since it`s still 5 days
out. Generally very warm to hot ahead of this midweek system with
most areas dry but still a few ripples in the w-sw flow to act on
what moisture we do have around to produce isold storms in and
near the mountains. Dying ex-Gulf of Alaska system may also push a
front near the nrn border for early in the week to potentially be
a focus.

&&

.AVIATION.../12Z ISSUANCE/

VFR conditions will prevail through tonight. Isolated showers and
storms this morning. Then new showers and storms will form after 18z
across the region. This activity will decrease after 02z with
lingering showers or storms after 06z Saturday. Local MVFR
conditions will occur due to lower visibilities and ceilings in
areas of heavy rain. Wind gusts to 35 knots may also occur near
storms.
&&

.FIRE WEATHER...

Fire danger should remain fairly low today. Relative humidity will
remain below critical levels with winds generally light to moderate
outside of any thunderstorms. A few showers may linger this morning
in the mountains and in Johnson and Natrona Counties but most
showers and thunderstorms will be during the afternoon and evening
hours. Smoke dispersal and mixing will be generally fair to good for
most areas in the afternoon.
&&

.RIW Watches/Warnings/Advisories...None.

&&

$$

SHORT TERM...Hattings
LONG TERM...Skrbac
AVIATION...AR
FIRE WEATHER...Hattings


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