Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 112023
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
223 PM MDT Wed Oct 11 2017

.SHORT TERM...(This evening through Saturday) Issued at 221 PM
MDT Wed Oct 11 2017

Imagery shows a broad trof/ridge pattern (west to east) across the
CONUS with WY/MT lying under/near the inflection point and WY under
swrly flow aloft. Jet (90 to 110 kts) in place in the trof from nrn
California to wrn WT and on up into Canada with a secondary but
strengthening jet to the south ovr cntrl California/cntrl NV. An
embedded small but strong shortwave associated with the more nrn jet
is currently coming through nrn California/srn Oregon. The SFC has a
long cold front stretching from Saskatchewan to cntrl MT and on
through cntrl NV/nrn CA. No precipitation currently falling in WY
with a few isolated light afternoon showers over cntrl ID.

Tonight, as the wrn trof slowly expands ewd with the jet(s) moving
over wrn/nwrn WY, light precip will begin to fall mainly over the
nwrn Mountains...becoming slightly enhanced overnight by low level
convergence associated by the SFC front, mentioned above, as it
moves through nwrn/nrn WY overnight. Liquid precip through the day
Thursday will only amount to a tenth or less form most of the far
nwrn portion of WY...with associated snowfall amounts remaining
under an inch. Otherwise, Thursday will become post frontal and dry
for most of the FA with gustiest winds (G15-30kts) west of the
Divide and over the Wind Corridor of srn/cntrl WY. Thursday night
will be dry and seasonal for the most part.

Friday becomes busy as an incoming nrn branch jet moves through the
w side of the main trof and begins to phase with the srn branch jet
now roaring overhead from the Great Basin through srn/sern WY and
off through the Plains and upper Midwest. Light areas of precip,
mostly as snow across the nwrn Mountains, will begin to fall under
divergent flow aloft while Cyclo- and fronto- genesis starts to take
place from ern ID to ern WY...with the newly formed SFC low pushing
into the cntrl/nrn Plains overnight while the associated front moves
through WY. With the FA being cut-off from moisture return out of
the e/se behind tonight`s/tomorrow`s front...a very dry atmosphere
across the swrn CONUS under the influence of a large EPAC High...and
only limited moisture encroaching with the upper trof...QPF values
from Friday afternoon through Saturday morning west of the Divide
will generally range from a trace to a quarter of an inch...perhaps
slightly higher across the far northwest. This will equate. with H7
temps cold enough to snow down to the valley floors from the
beginning of this event, to generally 3 inches (northwest mountains)
or less. Through the rest of the day Saturday, a secondary front of
sorts looks to kick through the FA with the upper trof
axis...bringing some modest chances for precipiation east of the
Divide...including light snow or afternoon rain/snow mixes. Snowfall
accumulation, through Saturday afternoon east of the Divide, looks
to remain low at generally less than inch inch at any given
location.

.LONG TERM...(Saturday night through Wednesday) Issued at 221 PM
MDT Wed Oct 11 2017

Synopsis...A dry, northwest flow will set up over the area Saturday
night, as the trough quickly exits into the Central Plains. A dry,
zonal pattern will then be in place through the rest of the forecast
period. A dry cold front will quickly pass through the area
Wednesday, ahead of a longwave trough beginning to make its way
onshore over the PACNW.

Discussion...Will have to keep an eye on temperatures in this
pattern next week, especially east of the Divide. Readings are
expected to be seasonal to slightly above normal, with above normal
readings east of the Divide possible on Tuesday.

&&

.AVIATION...(For the 00Z TAFS to 00Z Thursday evening) Issued at
221 PM MDT Wed Oct 11 2017

VFR conditions will occur through the period. Gusty winds will
continue at many terminal sites this afternoon, with the wind
decreasing after 00Z in most locations. A cold front over NW WY will
continue its eastward trek through the state through the overnight
hours. A few rain and snow showers will occur over NW WY from 00Z
through 12Z Thursday.

&&

.FIRE WEATHER...
Issued AT 221 PM MDT Wed Oct 11 2017

Fuels remain at critical levels across over Johnson and Natrona
Counties. (Please see the Fire Weather Forecast product for more
information).

...Elevated fire conditions this afternoon...

Today and Thursday will remain seasonally cool but relatively dry
with minimum RH values ranging from 15 to 25 percent across the
lower elevations and 20 to 30 percent over the mountains. No
precipitation expected today...with a few increasing chances for
snow showers across far northwest Wyoming tonight through Thursday
morning. Winds will become quite gusty from eastern Sweetwater
through Natrona Counties this afternoon and evening...then not so
gusty on Thursday. Today could see a few areas across Sweetwater
County seeing Red Flag conditions for a period this
afternoon...quieting down later this afternoon and into the evening.
Smoke dispersion will be good to very good this afternoon...good
Thursday afternoon.

&&

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

$$

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


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