Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 240441
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1040 PM MDT Tue May 23 2017

.SHORT TERM...(This evening through Friday)
Issued at 132 PM MDT Tue May 23 2017

A dry high pressure ridge aloft will bring mostly clear and cool
conditions with light winds to western and central Wyoming tonight
and Wednesday Morning. Then a Digging Pacific trough tracking
across southwest Canada and the Pacific Northwest will push into
the Northern Rockies spreading clouds and scattered showers to the
western and northern mountains in the afternoon with isolated
thunderstorms. West to southwest winds will develop ahead of the
low pressure trough becoming windy across the south and over and
near the east slopes of the mountains. Part of the trough will dig
south into the northern Great Basin while the main closed low
circulation tracks east across the Canadian Prairies. This will
keep some showers, mainly over the mountains, Wednesday night with
a cold front moving into the north. The Canadian portion of the
low pressure trough will stall out over southern Saskatchewan
as a second cold front dives south across Montana into northern
Wyoming on Thursday with increasing showers and isolated afternoon
and evening thunderstorms. Cooling will be widespread as the cold
fronts move through the state. Thursday night and Friday northeast
upslope flow will extend across the area with low stratus and
showers expected to be rather widespread with snow above 7500
feet. Isolated thunderstorms cannot be counted out Friday
afternoon. Much of the lower elevations will have highs in the
50s, with lower to mid 60s over the Bighorn basin. The mountains
will have highs in the 40s with 30s above 9000 feet.

.LONG TERM...(Friday night through Tuesday)
Issued at 132 PM MDT Tue May 23 2017

The weekend looks to kick off with scattered showers and isolated
thunderstorms with near or just below normal temperatures, with
warmer conditions southwest of the continental divide, and cooler
air east of the divide.  Good forecast guidance agreement at this
time with a shortwave trough continuing Friday evening to push down
from the north and over the CO Front Range Saturday morning.  The
GFS has another trough moving down Saturday afternoon, while the
ECMWF keeps this feature more over western SD, so a bit of some
uncertainty about how Saturday will play out over the area.  Mostly
unsettled northerly flow though.  As a result, Sunday ends up being
much the same difficulty with the GFS keeping more of the main
northern plains trough over eastern WY, while the ECMWF allows a bit
more ridging to develop from NV into OR and warm things up.  Have
continued to go with scattered showers in the afternoon and evening
with near seasonal temperatures.  Memorial Day continues in much the
same pattern, although the models are in more agreement with the
primary ridge and trough agreement from the western to central US.
Biggest weather impact across the area on Monday look to be breezy
northerly flow and scattered showers from Johnson into Natrona
County.  As the ridge over the western US builds somewhat Tuesday,
warmer air should move in over WY and push temps to the mid to upper
70s which is slightly above normal, and just in time for diurnal
thunderstorms to develop over the higher elevations.

Overall, the 2017 Memorial Day weekend should see near normal
temperatures with a slight chance of showers and thunderstorms due
to a disturbance moving south out of Canada.  The SW part of the
state should remain more clear, with the NE part more stormy and
cooler.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday evening)
Issued at 1040 PM MDT Tue May 23 2017

VFR conditions will prevail through 06Z Thursday. A gusty wind will
develop at most terminal sites Wednesday ahead of a cold front. This
cold front will push through the north Wednesday afternoon and
across the central and south Wednesday night. Isolated showers and
thunderstorms will occur in the west and far north Wednesday
afternoon. Scattered showers and storms will occur in the south
Wednesday night with local MVFR conditions near storms. KRKS and
KCPR airports may be impacted by this activity. A few showers will
linger after 06Z Thursday. The wind will gradually decrease after
00Z Thursday. Please see terminal forecasts for more details.

&&

.FIRE WEATHER...
Issued AT 132 PM MDT Tue May 23 2017

A dry high pressure ridge aloft will bring mostly clear and cool
conditions with light winds to western and central Wyoming tonight
and Wednesday Morning. Then a Digging Pacific trough tracking
across southwest Canada and the Pacific Northwest will push into
the Northern Rockies spreading clouds and scattered showers to the
western and northern mountains in the afternoon with isolated
thunderstorms. West to southwest winds will develop ahead of the
low pressure trough becoming windy across the south and over and
near the east slopes of the mountains. Part of the trough will dig
south into the northern Great Basin while the main closed low
circulation tracks east across the Canadian Prairies. This will
keep some showers, mainly over the mountains, Wednesday night with
a cold front moving into the north. The Canadian portion of the
low pressure trough will stall out over southern Saskatchewan
as a second cold front dives south across Montana into northern
Wyoming on Thursday with increasing showers and isolated afternoon
and evening thunderstorms. Cooling will be widespread as the cold
fronts move through the state. Thursday night and Friday northeast
upslope flow will extend across the area with low stratus and
showers expected to be rather widespread with snow above 7500
feet. Isolated thunderstorms cannot be counted out Friday
afternoon. Much of the lower elevations will have highs in the
50s, with lower to mid 60s over the Bighorn basin. The mountains
will have highs in the 40s with 30s above 9000 feet. Mixing
heights should be high enough in the afternoons for generally
good smoke dispersal Wednesday and Thursday but should be poor
on Friday with more widespread clouds and precipitation and
colder temperatures.

&&

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

&&

$$

SHORT TERM...Baker
LONG TERM...McDonald
AVIATION...AR
FIRE WEATHER...Baker



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