Area Forecast Discussion
Issued by NWS Riverton, WY

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038
FXUS65 KRIW 240536
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1136 PM MDT Fri Aug 23 2019

.SHORT TERM...(This evening through Saturday)

Potentially strong thunderstorms will continue to develop ahead
of a cold front and associated well defined shortwave through
this evening. Lifted indices down to minus 6 extend in areas
across Johnson and Natrona Counties and then shoot west all the
way into the Lander area in places, as do capes of 2000+ J/K in
some of these same areas. Wind directional shear increases as one
heads east to our eastern zones as well. Currently, a severe
thunderstorm watch is in effect through 10 PM this evening for
Johnson, Natrona, Washakie, Hot Springs and Fremont Counties,
although any severe weather will likely occur across the eastern
portion of the latter three counties mentioned. A mid and upper
level circulation trying to close off will track east across
Northern Wyoming through this evening, adding to the wind
directional shear component. In contrast, very little convective
activity is expected west of the Divide, except for perhaps in
portions of Yellowstone Park where the low will track part of the
time.

Then on Saturday, behind the exiting shortwave, our attention
begins to focus more on fire weather, as the weather pattern
shifts and we get underneath a stronger zonal west northwest flow
pattern. The only zone that appears will receive marginal critical
fire weather conditions will be fire weather zone 279 in
Sweetwater County. Decided to issue a Rangeland Fire Danger
Statement for this zone. Other areas will simply experience warmer
and drier weather.

.LONG TERM...(Saturday night through Friday)

Humidity will rebound a bit Saturday night, and then a cold front
will move across the area on Sunday. It has very little moisture
associated with it, so just isolated PoPs in the forecast for now.
The main factor with this front will be a tight pressure gradient
for a rather windy day on Sunday. Not looking at any wind
highlights at this time, but the Fire Weather conditions, mainly
in central and southern areas, will be elevated to critical with
the gusty northwesterly winds and low humidity. We will be
monitoring 700 mb for any indications of stronger winds.

Northwesterly flow will continue on Monday with the a ridge settling
in along the west coast. It will be cooler during the week with
temperatures in the 60s at higher elevations and 70s elsewhere.
Models are indicating at a an eastward shift of the ridge mid week
and a shortwave moving across the northern half of the state Friday.
This may bring a few showers for the higher elevations on Friday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1132 PM MDT Fri Aug 23 2019

VFR conditions will prevail through the forecast period at all of
the sites. The exception could be patchy morning fog where
significant rainfall occurred yesterday, including the KCPR
terminal. Saturday will see the westerly winds increasing across
the region with gusty conditions from 20Z to around 03Z. Mainly
scattered mid and high clouds are expected.

&&

.FIRE WEATHER...

Scattered thunderstorms ahead of a cold front, mainly east of the
Divide, some of which could be strong or severe across the more
eastern zones, will occur through this evening.

Then on Saturday, behind the exiting shortwave, our attention
begins to focus more on fire weather and even more so on Sunday as
the weather pattern shifts and we get underneath a stronger zonal
west northwest flow pattern. The only zone that appears will
receive marginal critical fire weather conditions will be fire
weather zone 279 in Sweetwater County. Decided to issue a
Rangeland Fire Danger Statement for that zone to differentiate the
more potentially extreme critical fire weather conditions
expected on Sunday, despite the critical fuels in that zones. On
Sunday, the critical fire weather conditions will likely become
more severe and widespread as we get underneath a right exit
region pulling down the 40 knot winds at 700mb closer to the
surface. Thus have issued a fire weather watch for a large area of
Central and Southern Wyoming valid from 10 am Sunday morning
through 9 pm Sunday evening.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Sunday morning through Sunday evening
for WYZ277>280-283-289-300-414-415.

&&

$$

SHORT TERM...Lipson
LONG TERM...Swanson
AVIATION...Swanson
FIRE WEATHER...Lipson



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