Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 132025

Area Forecast Discussion
National Weather Service Riverton WY
225 PM MDT Fri Apr 13 2018

.SHORT TERM...This evening through Monday
Issued at 1257 PM MDT Fri Apr 13 2018

Cyclogenesis has taken shape over the CO/KS/NE triple point. The
anticipated stronger nnw winds that have been expected to develop
on the backside of this low and asct upper trough has been delayed
in some areas, but should pick up at least for a few hours later
this afternoon as the low center continues to bomb, and the asct
trough moves off to the east, allowing the tighter gradient west
of the trough to works its way into the area. Also, temperatures
have been slow to warm as weak convection has taken place just
beyond the outer reaches of the higher clouds more directly
related to the storm complex where more solar insulation has taken
place. This convection has been producing more clouds and light
snow showers over Central Wyoming which has delayed the warming,
albeit, only into the 40s east and 30s west. Rain and snow showers
have been taking place on both sides of the divide.

The wind and weak convection should die off around sunset this
evening as a positively tilted ridge builds in from the west with a
confluent flow. Thanks to the area of high pressure, a warming trend
along with mostly dry weather is expected for the weekend. After a
chilly end to the work week, we are looking at high temperatures in
the 50s Saturday at the lower elevations east of the divide and 40s
west. Then on Sunday, highs in the 60s east and 50s west. Occasional
periods of light rain and snow will occur in the far west Saturday
night through Sunday night as a series of weak vort lobes track
across the area from the west northwest. High temperatures should
climb to near 70 Monday in the east but will remain in the low 50s
west as a sharp catafront type cold front begins to overtake
Northwest Wyoming from the northwest. This will result in widespread
rain and snow showers in the far west by Monday afternoon due to
the increasing southwest flow with increasing diffluence. Winds
will increase across the CWA Monday.

.LONG TERM...Monday night through Friday night
Issued at 1257 PM MDT Fri Apr 13 2018

A strong cold front that will enter western portions Monday
afternoon, will continue to progress eastward through the overnight
hours before clearing the forecast area by midday Tuesday. Very high
to strong SW winds will continue Monday evening across the Wind
Corridor ahead of the front. The trough supporting this front will
be in two parts: the first being an upper low that move NE into N MT
by 12Z Tue and the second being the main trough axis that will swing
through by 18Z Tuesday, as it become negatively-tilted.
Precipitation amounts will generally be light, with a band
developing along the front Tuesday morning. Scattered showers will
then be possible across much of the area during the day Tuesday, as
the trough passes through. Windy conditions will occur across much
of the forecast area, with very high winds returning across southern
portions Tuesday afternoon. A transitory ridge will then build over
the area Wednesday and continue eastward over the Plains Thursday.
Models differ on the height of this ridge, which could affect high
temperatures for Wednesday. A digging trough will move onshore S CA
during the day Thursday, which will bring warmer temperatures aloft
and SW winds to the forecast area. Again, how warm the area gets
Thursday will depend on how strong the ridge builds. For now, H7
temps of 0C to +1C are expected across southern portions. The low
continues to track over the Four Corners region during the day
Friday. This system has the potential to tap into Gulf moisture as
it begins to exit over E CO Friday night. This moisture could be
pulled across central and southern portions Friday and Friday night.
The extent of this will all depend on the track of the low. This
system will certainly be one to watch.


.AVIATION...For the 00Z TAFS through 00Z Sunday
Issued at 1257 PM MDT Fri Apr 13 2018

West of the Divide...KBPI/KJAC/KPNA/KRKS Routes

Isolated snow showers will continue through this afternoon over
the Wind River mountains and the Absaroka mountains, with mountain
obscurations over the highest peaks. Isolated showers will also be
possible this evening vicinity KRKS. Will put VCSH at KRKS
airport from 00Z to 06Z Saturday. MVFR conditions will occur in
the snow showers. Skies will begin to clear across the area after
00Z Saturday, before BKN-OVC FL120-200 return from the NW after
12Z. Gusty wind will occur at most terminal sites through 02Z

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Routes

Isolated rain and snow showers will gradually end this evening.
Brief MVFR conditions will occur in these showers. Gusty north-
northwest winds will also gradually subside this evening. VFR
conditions are expected through the TAF period, with BKN-OVC
FL120-200 clouds returning across the area during the day


Issued AT 1257 PM MDT Fri Apr 13 2018

Clearing skies and diminishing winds will take place tonight as a
strong low pressure center tracks east and away from the area.
Temperatures will warm through the weekend along with mainly dry
weather. However, periods of light rain and snow showers can be
expected in the far west from Saturday night through Sunday. Winds
will gradually increase through Monday. Widespread precipitation
will develop in the far west by Monday evening. Much stronger
winds can be expected by Monday. High temperatures will likely
warm to near 70 by Monday at the lower elevations east of the
divide and will remain in the 50s west. Central Wyoming east of
the divide and zone 279 could have a critical fire weather day
Monday, as the minimum RH dips to the low to mid teens in zone
283 with increasing wind and highs near 70s along with even
stronger winds from Rock Springs to Casper and a minimum RH in the
mid to upper teens in those locations.




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