Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 171710
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1110 AM MDT Mon Jul 17 2017

.SHORT TERM...Monday through Wednesday night
Issued at 225 AM MDT Mon Jul 17 2017

As for the weather today, it will be described in four words. And
those words are, more of the same. The radar is quiet right now.
However, more showers and thunderstorms are on the way. In the
morning, a weak system will pass across southern Wyoming and may
bring a few showers this morning. However, the main event will be
this afternoon as second, more potent shortwave approaches the
region. All areas will have a chance of at least an isolated
thunderstorm with the best chance across northern areas. The
stronger storms would more than likely be across the north as well
with the best shear and forcing. One difference is that this should
be a later show as the atmosphere may need more time to reload. The
NAM, which has been doing the best job lately with the convection,
shows a complex developing across the western mountains and then
moving across the north through well after midnight. We adjusted
POPS tonight to show this as well. And again, for around the tenth
day in a row or something, I don`t know it`s been so many I`ve lost
count, the main threat will be strong outflow winds. These will move
out by sunrise Tuesday. As for high temperatures, the GFS has been
more reliable than the NAM so we kept temperatures warmer, although
a few degrees cooler than recent days.

With rising heights and temperatures aloft for Tuesday, along with a
drier air mass moving in, Tuesday looks drier. Actually, it looks
dry for almost everyone. The NAM is dry and even the GFS has trended
away from it`s constant thinking the Absarokas and Bighorn Ranges
are wetter than the Olympic Mountains in western Washington. As a
result, we have removed POPS from all areas and went completely dry.
With more sunshine and higher thicknesses, temperatures will once
again begin to warm with 80s and 90s widespread across the lower
elevations.

On Wednesday, we see may see the beginning of the arrival of a
seasonal friend. That friend is the monsoon with some moisture
starting to creep in from the south as the ridge axis shifts to the
east. For now, we kept the convection mainly across the south but
this may need to be adjusted with time. As for temperatures, what a
surprise, in keeping with recent days, temperatures should be
above normal for most locations once again.

.LONG TERM...Thursday through Monday
Issued at 225 AM MDT Mon Jul 17 2017

The GFS and ECMWF models have a decent weather disturbance moving
around the western periphery of the upper high on Thursday into
late Thursday night. Provided the cloud shield associated with
this weather system is not too thick, a better chance of showers
and thunderstorms would occur. Far northern WY would be on the
fringe of this activity per the models. Storms would produce
locally heavy rain in places, but as with any given summer day,
not everyone will see rain. High temps Thurs would be slightly
cooler most areas. In the southern zones, the cooling will be more
noticeable due to the expected cloud cover and made adjustments
to reflect this thinking. Friday looks mainly dry with isolated
thunderstorms in the far south. Very warm to hot high temps.

The GFS model Saturday has a weather system dropping into Montana
and then this system passes across WY on Sunday. It has a cool
front with it and generates some showers and storms Saturday night
into early Sunday in the northeast and east zones. The ECMWF
model is farther northeast with this feature. Thus, much less
impact on the area and less cooling. Have went with isolated
showers and storms Saturday night from Buffalo to Casper and dry
elsewhere. Behind this system on Sunday, conditions look to be
dry. Have cooled high temps a few degrees east of the divide for
Saturday with little change in the west and southwest. High temps
Sunday will be similar to Saturday and possibly a few degrees
warmer in places. Next Monday looks dry with very isolated
thunderstorms over the mountains. Temps will be very warm to hot
once again.

&&

.AVIATION...18Z Issuance

VFR conditions will prevail through the forecast period.  Isolated
to widely scattered showers, with possibly a thunderstorm or two,
continue across the southwest, vicinity KRKS-KBPI-KPNA, and have
now moved toward KLND-KRIW. An upper level disturbance will bring
a round of widely scattered showers and thunderstorms across the
area this afternoon and expected to exit the area by midnight, or
primarily from 22z Mon-06z Tue. A few storms could be marginally
severe with wind gusts 40-50 knots and hail. The strongest storms
are expected vicinity and north of a KJAC- KWRL- KCPR line. Some
lingering showers will be possible vicinity KRKS-KCPR between
06z-09z Tuesday.

&&

.FIRE WEATHER...
Issued at 225 AM MDT Mon Jul 17 2017

Expect another warm day today although a few degrees cooler than
over the weekend in many locations. A couple of upper level
disturbances will move across the state from the west and bring
another round of isolated to widely scattered showers and
thunderstorms to the area. And again, the main threat will be
strong outflow wind gusts. Thunderstorms will be mainly later in
the day and could last through the night across portions of the
northern zones. Relative humidity will fall into the teens for
many of the lower elevations. However, wind should remain below
critical levels outside of any shower or thunderstorm. Mixing and
smoke dispersal will range from fair to good in the Basins East of
the Divide to excellent in the western mountains.

&&

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

$$

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



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