Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 140057
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
657 PM MDT Sun Oct 13 2019

.UPDATE...
Issued at 654 PM MDT Sun Oct 13 2019

Upgraded the Fire Weather Watch this evening to a Red Flag
Warning. Added zone 278 (Sublette County) to the warning, as gusty
winds will affect most of this zone Monday. However, far northern
portions of the zone will have RH values in the lower 20s.

&&

.SHORT TERM...(This evening through Monday)
Issued at 137 PM MDT Sun Oct 13 2019

H5 ridge continues to slowly progress east during the next 24
hours, being slowed down by the large storm finally exiting the
Great Lakes Region. Clear skies and light winds continue for the
region overnight, with lows right around freezing. A shortwave
sweeps into the northern Plains starting tomorrow morning, just
barely clipping the NE quarter of WY during the afternoon. With
the main lift confined to MT/ND during the day, the wave will pass
pretty innocuously, with increased cloud cover across the north,
but bringing minimal to no precipitation. But with a surface low
passing to the east, the pressure gradient will tighten
considerably, bringing breezier conditions to a larger portion of
the state. Highest winds will be across the Rock Springs/Casper
corridor. Sweetwater County will also have low humidity and
critical fuels, so the Fire Weather Watch continues for Monday
afternoon.

.LONG TERM...(Monday night through Sunday)
Issued at 137 PM MDT Sun Oct 13 2019

The cold air will be advecting into the area behind the strong
but dry backdoor cold front Monday night. 700Mb temps will bottom
out to -8C over Johnson County by 12Z Tuesday, but will only reach
-5C in the northwest, and will remain above zero in the
southwest. As a result, the high at BYG, according to the MEX MOS
guidance, will only reach 46, 15 degrees cooler than the projected
high for Monday and Casper will be 12 degrees cooler. Lander and
Riverton will see a cooling of 5 to 7 degrees. Except for an
increase in wind and some clouds, for areas west of the Divide,
the front will come through relatively transparently, with only
slight burp in the warming trend.

Then the front will retreat to the northeast by Wednesday. High
temperatures will shoot right back up to around 70 at lower
elevations east of the Divide and into the 60s west, as a
flattening ridge approaches from the west. We may need fire
weather hilites for eastern Sweetwater County for that day with
RHs in the low teens, borderline wind criteria, and critical
fuels. Wednesday will be the warmest Indian summer day of the
week.

Thursday will mark the beginning of a gradual trend to cooler and
wetter weather, which will take us through next weekend. A long
wave trough off the Pacific Coast will eject a couple of
shortwaves in our direction. The first weak low amplitude/vort
lobe will come through Thursday per the GFS with the first chance
of showers in the northwest. Then the next one comes through
Friday per the GFS/Euro/Canadian, when the environment becomes
weakly unstable. Then the long wave trough budges east and this is
where the models really have begun to diverge. After the GFS
moves this trough through Saturday night, it tries to close it off
over Eastern Colorado by Sunday. The Euro did close it off along
the Wyoming Montana border by Sunday on the earlier run, which is
where the GFS had it before. But now, like the GFS, the Euro
closes off the upper low over Eastern Colorado by 12Z Sunday. The
Canadian closes the low off way down along the Arizona/Utah border
and actually splits the long wave trough. The Canadian would be
the outlier. So, all we can say at this point is that the weather
will turn cooler by next weekend along with an increasing chance
of rain and snow, becoming more widespread by Saturday and Sunday,
but as far as exactly where the focus of any sensible weather
will be, the crystal ball needs a little polishing right now.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday)
Issued at 430 PM MDT Sun Oct 13 2019

VFR conditions continue through the period. The gusty wind at KCPR
will subside after 00Z this evening. Monday will become breezy over
most the central and southwest with a gusty west to southwest wind
from morning through 00Z Tuesday. A cold front will move into the
north after 18Z and push southward through 00Z Tue. Areas of gusty
north to northwest wind will be observed.


&&

.FIRE WEATHER...
Issued AT 137 PM MDT Sun Oct 13 2019

Dry weather will continue for the rest of the afternoon. Relative
humidity will fall to around 10 percent at times in southern
Wyoming. Wind should remain light to moderate though. Mixing and
smoke dispersal should range from poor in most of the basins to
good in the south. A combination of low humidity and gusty winds
may bring critical fire conditions to southern Wyoming Monday
afternoon ahead of a cold front passage. Tuesday will feature
cooler weather east of the Divide behind the front, with
temperatures west of the Divide unchanged. Wednesday will be
warmer and dry and will be the warmest day of the week. Next
Thursday through next weekend will feature a trend toward cooler
and more unsettled weather.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 7 PM MDT Monday for WYZ277>279.

&&

$$

UPDATE...LaVoie
SHORT TERM...Straub
LONG TERM...Lipson
AVIATION...Straub
FIRE WEATHER...Lipson


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