Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 141658
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
958 AM MST Tue Feb 14 2017


.SHORT TERM...Today through Thursday night

Imagery shows split flow across the west with a closed low and
associated trof, helping in separating air-masses, centered over
northern New Mexico with an upstream ridge now along the CONUS west
coast with the ridge center over the PAC NW. SFC has high pressure
across most of the western CONUS,including WY, with low pressure
generally over the southernmost portions of the USA. No precip
currently anywhere in WY.

Most of the forecast will remain seasonal or to the cool side of
seasonal, with light SFC winds through today in addition to light
flow aloft. Patchy morning fog a possibility mainly west of the
Divide and over the central and northern basins east of the Divide.
Otherwise, with little available moisture or forcing at any
level...few clouds and no precipitation will be expected through
Thursday morning.

Tonight through Wednesday night, upper level ridging and building
deep high pressure at the surface will be in place across the Great
Basin and Intermountain West with lower pressure off to the north
and east of the FA. These conditions will slowly increase the P GRAD
at the SFC between the two pressure zones along the Continental
Divide and may induce some gusty southwest winds across the usual
areas (Cody Foothills and Wind Corridor) beginning tonight and
lasting through Thursday morning. Nothing special here except that
some lee side foothills may be able to take advantage of their
location and associated breezes to occasionally gust near high wind
a few times (particularly Wednesday night) and warm up enough
to reach seasonal average temperatures.

Thursday night, the upper ridge axis passes to the east over the
Plains States with the first hints of an oncoming upper trof/SW/jet
moving toward/into western WY. Although moisture will be somewhat
limited with this first part of the system, the western mountains
will be close to an entrance region of the jet...combining with
terrain lift to produce precipitation. Currently H7 temps associated
with this trof will represent snow even to the valley bottoms by the
time precip starts...except for perhaps a short period at very
beginning of the event. Overall light snowfall accumulation by
Friday morning should generally range up to a couple of inches at
best...with a trace to a tenth or two over the northern Bighorn
Basin/Foothills.

.LONG TERM...Friday Through Tuesday

Mean ridge will be overhead or slightly to our east to start this
period with weakening shortwave moving through this ridge. The best
chance of lingering snow will likely be in the nw corner of the
state near right entrance region jet streak dynamics. The Euro and
GEM weaken this system more than the GFS and may be more right with
the mean ridge overhead. Either way, no significant pcpn on Friday
as this weakening system moves e/ne across the area. The next
system is still poised to split with the bulk of the energy diving
well south and the northern piece lifting into MT later Saturday
into Sunday. Weak shortwave ahead of this splitting trough is
expected to produce some mainly light snow lifting n/ne across the
far west Saturday. Light snow is likely across the west on Sunday
as the energy in the split moves east across the area mainly in
the west with a chance in the south with weak frontal passage.
Some of the guidance even has a little in the north and eastern
portions so left in the slight chances there. Pattern becomes more
and more active early next week as mean trough develops over the
western U.S and shortwaves lift ne across Wyoming. However, the
more significant storm indicated by the models will be just beyond
this period as the mean upper trough moves closer the middle of
next week. More on this potential storm tonight. Snow will remain
likely most of the period in the far west with a chance in the
south. Limited chances east of the divide except perhaps where
shortwave energy and frontal boundary intercept which is mainly
forecast to be in the far ern or nern zones. Temperatures will
generally be above normal through the period but cooling to near
normal by Tuesday.

.AVIATION.../18Z ISSUANCE/

Patchy fog will be the main aviation concern again in the valleys
and basins later Tuesday night and Wednesday morning. Boundary
layer moisture is on the dry side, so not expecting widespread
fog. Otherwise, VFR conditions with mainly be SKC, and light
winds today. A leeside trough developing Tuesday night will
result in winds at KCPR picking up and continuing through the day
Wednesday, and some marginal low-level wind shear at KCOD after
06Z Wednesday.

.FIRE WEATHER...

Fire Danger low for all of WY through the next week as a good
existing snow pack will combine with seasonal to below seasonal
temperatures and less wind to keep fire danger low for most of the
next week. Smoke dispersion poor to briefly fair through Thursday
night. Light snow to return to the region Thursday night.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Braun
LONG TERM...Skrbac
AVIATION...LaVoie
FIRE WEATHER...Braun



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