436
FXUS65 KRIW 211703
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1103 AM MDT Sat Sep 21 2024

.KEY MESSAGES...

- A cold front is passing through early this morning, with
  increased northerly wind behind the front through Friday
  evening east of the Continental Divide down into Sweetwater
  County.

- It will be cooler today behind the cold front and remain cool
  through Tuesday as another weather system brings a cold front
  through on Monday.

- A dirty ridge will bring back above normal temperatures by the
  middle part of next week.

- Very little precipitation is on the horizon for WY, which will
  exacerbate drought conditions across the state.

&&

.DISCUSSION...
Issued at 1256 AM MDT Sat Sep 21 2024

A loosely coupled upper-low currently located over central CA and a
trough in western MT will continue to slide eastward today. The
shortwave trough has already passed north of WY this morning and the
upper-low will pass to the south tonight, which means most of the
area will miss out on any precip chances as the weather systems
split the state. Some rain drops may fall across far southeastern
Sweetwater/Natrona County tonight as the upper-low passes to the
south. A strong cold front is sweeping through the area this morning
and will bring much cooler temperatures today into tonight. This
cold front is also bringing strong wind to northern portions of the
area east of the Continental Divide. A peak wind gust of 62 mph was
measured at Buffalo - Johnson County Airport around 11 PM. Windy
conditions will push south through this morning with the cold front,
but gusts that high are not expected. Gusts of 30 to 50 mph will
occur early this morning as this cold front shifts south. Overnight
lows tonight will be chilly in the mid to upper 30s for lower
elevations east of the Continental Divide. Wouldn`t be surprised if
there was frost in low spots Sunday morning. For those who still
have a garden it doesn`t look like this will be a freeze event, so
impacts should be minimal to vegetation.

A brief ridge moves overhead on Sunday in between weather systems,
which will allow for temperatures to rebound a bit, back to about
seasonal averages for this time of year. Another trough surges down
from the northwest very quickly on Monday. Very light precip
accumulations are possible (30%) with this weather system as it
really won`t have enough time to drop more than a few hundredths of
liquid for any location. Model guidance has come into better
agreement on the weather pattern for the middle part of the week.
Model guidance now shows a substantial ridge developing by Wednesday
and remaining in place until, at least, next weekend. This will
result in temperatures that are well above normal and no
precipitation. With no meaningful precipitation in sight drought
conditions will worsen. Also, fire weather season looks like it is
trying to hold on a bit longer.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1102 AM MDT Sat Sep 21 2024

With a cold front having passed from north to south east of the
continental divide this morning, and a cutoff low over Arizona
moving NE to the Four Corners area, the surface pressure
gradient over much of WY will increase NE winds from northeast
to central to south-central WY this afternoon. KRKS and eastern
Sweetwater County could see gusts over 30 kts, with gusts 15-20
kts in the Bighorn Basin, Johnson County, and Wind River Basin.
Partly cloudy skies over northern WY will decrease through the
day, with clouds increasing over southern WY due to the cutoff
low. VFR conditions are expected at all TAF sites through the
next 24-30 hours. A couple of high resolution models are
indicating some weak convection over SE Sweetwater County as
well as the southern parts of the Wyoming Range late this
afternoon and early evening, but chances are quite low. Primary
impact from the low pressure system over UT/CO the next 36
hours will be the gusty NE winds and increased clouds over
southern WY through early Sunday afternoon. Skies then become
mostly clear Sunday afternoon from the west to east. Clouds will
increase over northern WY Sunday night into Monday morning due
to a weak system moving through MT.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on smoke, icing, and turbulence
forecasts.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

DISCUSSION...Rowe
AVIATION...McDonald