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Area forecast discussion
National Weather Service Riverton Wyoming
1545 PM MDT sun Sep 15 2019

Short term...this afternoon through Monday

Summer holds on for another day across the cowboy state this
afternoon. Dry, hot and gusty conditions will continue across the
area, leading to elevated to critical fire conditions.
Temperatures will be well above normal, staying just a few degrees
shy from setting any records. Gusty southwest winds this afternoon
will quickly subside this evening by sunset. High cirrus clouds
will increase from Sweetwater to Natrona counties later this
afternoon, into the evening hours. This will be a precursor of
increasing moisture tonight. As a result, milder temperatures are
expected. Cold-prone locations will still drop to near freezing
temperatures, due to mainly clear skies.

The weather pattern becomes more active Monday, as winds increase
across the area, along with chances for precipitation. This will
be due to an approaching cold front, that is associated with the
storm system that has been discussed in the long term for the last
few days. As mentioned earlier, moisture will increase from the
south tonight, raising dewpoints into the upper 30s and 40s. This
will push any fire weather concerns to the northern zones, where
relative humidity values will be critically low. This will mainly affect Johnson
County and eastern portions of the Bighorn Basin. Temperatures
will be well above normal in these areas, with upper 80s and lower
90s. Showers and thunderstorms will develop across areas west of
The Divide Monday afternoon. No major threats are expected with
these storms at this time. Cape values will range between 200 to
600 j/kg and lifted indexes around minus 2. Storm motion will be a
bit fast (given the overall wind field of 15-20 mph), so wind
gusts of 40 to 50 mph will be possible. Dewpoint depressions do
not look large enough for severe wind gusts to occur.

Long term...Monday night through Sunday

Longwave trough still expected to sweep eastward across the Pacific
northwest early in the week, as the overall pattern begins to buckle
significantly. Monday night will see the shower activity across
western Wyoming continue through Tuesday morning. Tuesday the beginning
piece of the 500 mb trough races across WY, with a much better chance
for rainfall pushing eastward across the rest of the forecast area. Colder
temperatures will be sweeping into the state as well, with highs
Tuesday 10 to 20 degrees lower than Monday. Wednesday will be a
drier day in the wake of he first trough, before the second trough
slowly meanders across The Rockies. This will keep temperatures
below normal into the upcoming weekend, with a chance of rain
continuing each day.


Aviation...for the 00z tafs through 00z Monday
issued at 1545 PM MDT sun Sep 15 2019

Minimal impacts to terminals through Monday early afternoon. Skies
remain mostly clear though a broken high cloud deck will begin to
enter from the south. Winds will be gusty west of The Divide and at
kcpr through Sundown. As inversions set up overnight low level wind shear is likely
at many locations west of The Divide until around 15-18z Wednesday.
Kcpr will see gusty winds return around 15z Monday. Monday afternoon
will see showers and thunderstorms move into the area west of The
Divide. These will be fairly isolated so we only went with vicinity
showers for the time being. East of The Divide should remain dry
through the period.


Fire weather...

Red flag warnings remain in effect for zones 277, 279, 280 and 300
through 7 PM this evening. Gusty winds and critically low relative humidity
values will continue this afternoon, before improving after
sunset. Moisture will increase across the area starting this
evening and continuing tonight. Temperatures will be milder
tonight, compared to the last several nights. A cold front will
approach the area Monday, bringing gusty winds to the area once
again. Temperatures will not be as warm Monday afternoon, for all
but Johnson County and eastern portions of the Bighorn Basin.
Conditions in the latter areas will have near critical relative humidity values
and temperatures in the upper 80s to lower 90s. Showers and
thunderstorms will occur across areas west of The Divide Monday
afternoon. Chances for wetting rain will be low.


Riw watches/warnings/advisories...
red flag warning until 7 PM MDT this evening for wyz277-279-280-



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