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Area forecast discussion...update 
National Weather Service Riverton Wyoming
1055 am MDT sun Apr 26 2015

Short through Tuesday night

Most of the state will see some measurable rain or snow today as a
large system moves across the region. Most of the elements come
together early in the period over central Wyoming with the focus
shifting more to central and eastern Wyoming by the afternoon and
evening. There is already some steady rain and snow developing in
the Wind River basin as of 2am...right on cue. DuBois was quick to
changeover to snow while Crowheart took a few hours longer. Lander
..Riverton and most of the Green River basin are still raining at
this hour. Dewpoints are also above freezing at this early hour as
well. However...the trend should call for modestly cooling
temperatures through the morning with most areas above 6500 feet
changing over to snow by morning...perhaps closer to 7kft in the
Upper Green...which is right around the elevation of Pinedale.

Kept the existing advisories and added the bighorns as they will
likely receive as much snow as the other mountain zones...they will
just start and end a little bit later.

No matter what the form of the precipitation...this could really be
a soaker for the upper Wind River basin including DuBois and for the
Lander foothills and for Fort Washakie. There could be a period of
steady rain and snow early this morning in these areas but it will
likely change back over to all rain at some point during the day
today...that combined with the warm Road temperatures...the impact
is not expected to be enough to warrant a highlight for the lower
elevations though some isolated spots could develop some slushy
roads if a changeover to snow occurs. Otherwise...looks like the
best chance for accumulation and travel impact will be in the
mountains...especially over South Pass and the DuBois side of
Togwotee Pass.

There could be one last hurrah over the i25 corridor Sunday night
before the system exits late but again temperatures will be
borderline but recent model trends have kept precipitation in the
area for about 6 hours longer than previous runs so that could lean
toward advisory level snows on Casper Mountain. Probably the main
impact will be on travel at that elevation as the Road surfaces are
cold enough to support accumulation not too long after the snow
begins to fall.

Most areas will be free of precipitation by Monday morning as a
warming and drying trend begins with the rising heights behind the
trough but Monday will still be on the cool and moist side with
patchy morning fog expected in any areas with saturated ground or
snow cover. Tuesday will be rather nice with temperatures rising
back into the 60s to low 70s...light winds and mostly clear skies.

Long term...Wednesday through Sunday

Wednesday looks to be dry with breezy to windy areas in the
afternoon and early evening. Warm day on Wednesday as well.
The next weather system moves across the northern rockies Thursday
pushing a cold front across the west in the late morning and east of
The Divide late afternoon or early evening. The GFS is 3 to 6 hours
quicker with the frontal passage and weather system than the European model (ecmwf)
model. Will keep the chance of showers and storms in the mountains
with isolated in the far north and far south zones Thursday
afternoon and evening. Showers will end late Thursday night. The
European model (ecmwf) is dry for Friday while the GFS implies isolated mountain
showers or storms. For now will have mainly isolated for the
mountains and some adjacent foothill locations. The GFS and European model (ecmwf)
models differ Saturday and next Sunday. The GFS has isolated
afternoon and evening showers or storms both days. The European model (ecmwf) brings
a weather system into the Pacific northwest Saturday night through Sunday.
This results in a moist SW flow over the region with a better chance
of showers and storms on Sunday versus Saturday. For now will keep
isolated to scattered showers and storms for the mountains and west
Saturday and Sunday with isolated activity for the lower elevations
east of The Divide. As for temperatures...will keep highs on the warm side
east of The Divide Thursday with slightly cooler highs in the west
as the cold front gets there sooner. Friday will be cooler all
areas. Next Saturday and Sunday will see seasonal highs for late


Aviation.../12z issuance/

A major Spring storm will result in widespread and persistent
IFR/MVFR conditions today. Snow levels will range between 055-075
kft mean sea level. The precipitation shield will be decreasing in the
afternoon...but enough precipitation coverage and cloud cover to
keep MVFR or low VFR ceilings at all terminals. Also...breezy to
windy north to east winds will occur in most locations.
Precipitation is expected to end over the west during the evening
with mainly VFR conditions but with ceilings remaining around
050-080 kft above ground level. However along and east of a krks...kriw to kwrl
line...areas of precipitation and low ceilings will continue
overnight...with a decent chance for continued MVFR and possibly IFR
conditions. Snow levels this evening are expected to drop to around
5000 kft above ground level. Mountains will be obscured through the forecast period.

Please see the aviation weather center for the latest information on
icing forecasts.

Fire weather...

It will be hard to avoid a wetting rain or snow today as a large
system affects the entire region. It will clear out by tomorrow
however with high rhs and cooler temperatures hanging around on
Monday. Tuesday will be warmer and drier but with no wind concerns.
Wednesday and Thursday will be warmer as well but there could be
another...much weaker and quicker...system grazing the area which
could increase winds to above 25mph on Thursday with some humidities
potentially into the middle teens across Rawlins and portions of Casper
dispatch...but it is still a bit early and uncertain to pinpoint any
areas of concern...if any.


Riw watches/warnings/advisories...

Winter Weather Advisory until midnight MDT tonight

Winter Weather Advisory until noon MDT today wyz016-025.

Winter Weather Advisory from 6 am this morning to midnight MDT
tonight wyz008-009.



Short term...Allen
long term...Arkansas
fire weather...Allen

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