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Area forecast discussion 
National Weather Service Riverton Wyoming
357 am MDT Monday Sep 22 2014

Short term...Monday through Wednesday night

A pinwheeling low is now moving north northeastward out of Nevada
and toward southern Idaho. The initial band of precipitation is now
lifting northward through northern Wyoming but is having trouble
hitting the ground with dry conditions at the surface. Radar also
shows a well defined dry slot moving through southern portions of
the County Warning Area. Meanwhile...across the west some fog has
formed where the rain had fallen so we will add some patchy fog to
to the grids late tonight and early this morning. Showers appear to
be reloading across northeastern Utah however so another round looks
likely in the west. The dilemma for today is that the models have
trended a bit drier today with only isolated to scattered activity.
There is a good amount of moisture around however...although the GFS
has trended downward with precipitable water values. With the
falling heights and the low expected to track over Wyoming this
afternoon and evening we have maintained the chance of convection
for the entire area this afternoon and evening. Temperatures will be
tricky since a lot depends on sky cover so for now we left them

Conditions will improve late tonight as low exits to the east. There
could be just enough moisture and instability leftover tomorrow for
some isolated thunderstorms across the higher elevations. Models are
drier but left them in for now. After Tuesday evening...a ridge will
build northward across Wyoming for Wednesday and bring a nice early
autumn day with plenty of sunshine...warm temperatures and dry

Long term...Thursday through Monday

A Dry Ridge will be exiting to the east to start the period on
Thursday. This looks to bring very warm conditions in the middle to
upper 80s...and some 90s...east of The Divide Thursday afternoon.
Some breezy conditions will also be possible across the Rock Springs
to Casper wind corridor for Thursday...and possibly again Friday. A
brief thought of adding some isolated thunderstorms for Thursday
afternoon across the west was a developing jet
streak...and moderate shear values...will approach the west.
However...with lack of instability...and very warm 700 mb
temperatures...let dry conditions prevail for Thursday.

GFS has slowed slightly on the progression on the large trough for
the weekend. This will keep warm conditions for Friday...with a few
isolated to scattered showers and thunderstorms across the western
areas. Timing of this system still remains uncertain. GFS and
European model (ecmwf) do not want to budge from their tracks. GFS continues to be
progressive and brings widespread showers and thunderstorms as
early as Saturday. European model (ecmwf) holds on to the ridge across the northern
plains...which delays this storm system until late Saturday
night...with the better chances of precipitation coming Sunday and
Monday. Decided to put at least slight chance to chance probability of precipitation in
for Saturday...especially across the west...with increasing probability of precipitation
Sunday through Monday. Mostly showers and thunderstorms will be both solutions lack ample cold air for lower
elevation snow. GFS hints some higher elevation snow could be
possible Sunday and again Monday morning. An European model (ecmwf) could also give
snow to the higher elevations Monday morning...and possibly a cold kicker system potentially pushes through.
Another concern to monitor with either solution are high quantitative precipitation forecast
amounts that most areas could receive...especially if the GFS
solution comes true.


Aviation.../12z issuance/

A weather system will move into northwest Wyoming this afternoon and
into northeast Wyoming tonight. This system will bring scattered
showers and isolated thunderstorms to the region through this
evening. Areas of MVFR conditions will occur today...mainly west of
the Continental Divide due to lower clouds and lower visibility in
rain showers or storms. Mountains will be frequently obscured today
into the evening hours. Conditions will be improving after 01z this
evening across the area as showers and storms decrease to isolated
by 05z Tuesday.


Fire weather...

An upper level low will cross the state today and bring isolated to
scattered showers and thunderstorms. Wetting rains are possible for
many areas...especially in the western mountains. Expect a drying
and warming trend from Tuesday through much of the week as a ridge
builds northward across Wyoming. Although relative humidity will
lower starting Wednesday...winds are expected to remain light to
moderate and as a result critical fire weather is not expected.


Riw watches/warnings/advisories...


Short term...hattings
long term...Anglin
fire weather...hattings

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