Area Forecast Discussion
Issued by NWS Riverton, WY

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683
FXUS65 KRIW 171937
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
137 PM MDT Tue Apr 17 2018

.SHORT TERM...(This evening through Friday) Issued at 130 PM MDT
Tue Apr 17 2018

Imagery shows ridge/trough/ridge/trough pattern across the CONUS. A
rather strong trough is currently moving across WY with its
associated jet (100kt +/-) moving over the southern Rockies then up
through the western Central and Northern Plains. The trough`s axis
cuts southeast from north central MT, through WY and on into the
Four Corners region. The surface shows a developing low pressure
center over east central CO with an inverted trough up through
central/northern WY. Nearly stationary fronts extend around this
low,  one from central WY down through western CO...the other from
central WY through northeastern/eastern CO.

The low in eastern CO continues to strengthen and move into the
Central Plains with the slow moving front pulling completely out of
the forecast area by this evening. Heavier rain/snow/rain-snow mixes
will taper off later this afternoon leaving areas/patchy but
decreasing showers behind the front. SPSs are in place supporting
todays activity. Still, brief periods of heavy snow with visibility
less than a mile will be common from time to time. Additionally,
accumulations under the stronger portion of the deformation band
aloft will see up to 3 inches of snow on grassy areas through the
rest of the afternoon (including some of the Wind River Basin).
Later tonight, ridging will begin to overtake WY, continuing through
Thursday morning. Warming/drying trend both Wednesday and Thursday
with very dry air infiltrating portions of south-central WY by
Thursday along with moderately gusty south winds.

Thursday afternoon through Friday, rapidly developing cyclogenesis
will be taking place, starting over the Great Basin, moving
toward/across the Four Corners region by Friday morning, then
continuing eastward toward the Central/Southern Plains and starting
a period of instant occlusion cyclogenesis that goes beyond this
forecast period. As the trend over the last several days has slowed
slightly and taken this system further south, there is also a delay
in tapping into Gulf moisture and instability...so much so that it
will take longer for moisture to work its way back into the
southern/southeastern/central CWA...if at all. Other than isolated
to widely scattered rain/snow showers and/or some gusty north or
northeast winds, the overall impact should be low.

.LONG TERM...Friday night through Tuesday night
Issued at 130 PM MDT Tue Apr 17 2018

An upper low over the Four Corners, will continue its eastward
trek toward the Central Plains. Eastern and southern portions of
the forecast area will remain on the northern fringe of this
system, with precipitation ending Friday night.

A warming trend with mainly dry conditions is expected over the
weekend. Cannot rule out an isolated mountain shower over the
north. Temperatures look to be 5 to 10 degrees above average.

Both the ECMWF and GFS are showing a weak wave pulling across the
northern Rockies Monday and Tuesday, which could give the area
some valley rain/high mountain snow.

&&

.AVIATION...For the 00Z TAFS through 00Z Thursday
Issued at 1123 AM MDT Tue Apr 17 2018

West of the Continental Divide...KJAC, KBPI, KPNA, and KRKS

Isolated to scattered snow showers, with mountain obscurations,
will end this evening. VFR conditions will prevail at the
terminal sites, with clearing skies after 06Z Wednesday. Gusty
west to northwest wind will also be subsiding after 01Z, with
several sites becoming light and variable between 09Z-12Z
Wednesday.

East of the Continental Divide...KCPR, KCOD, KRIW, KLND, and KWRL

A band of snow continues over eastern WY, with isolated to
scattered snow showers over central WY. These lingering snow
showers will continue through 03Z Wednesday. MVFR to IFR
conditions will occur during the snow showers, before returning to
VFR conditions once the snow ends. Mountains will be frequently
obscured at times. VFR conditions will prevail at the terminals
after 02Z Wed, with clearing skies after 06Z Wednesday.

&&

.FIRE WEATHER...
Issued AT 130 PM MDT Tue Apr 17 2018

A strong upper level disturbance and associated cold front continue
across Wyoming today, and will clear out of the forecast area from
northwest to southeast by this evening. Light to moderate rain or
snow with occasional bursts of heavier precipitation will occur
into/through this afternoon with a few light instability rain or
snow showers following the heavier snowfall into this evening.
Blustery north to northwest wind will continue into the early
evening period with gusts 35 to 50 mph at times. Then, it will be
dry and warmer Wednesday and Thursday with low relative humidities
making their way back into Wyoming from the south.

&&

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

$$

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



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