492
FXUS65 KRIW 041729
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1129 AM MDT Tue Jun 4 2024

.KEY MESSAGES...

- Drier and warmer weather will arrive this afternoon and
  continue through at least Thursday.

- Windy conditions are expected today and tomorrow, with
  elevated fire weather possible on Wednesday afternoon.

- Warm temperatures will lead to high elevation snowmelt which
  could bring rising river levels and minor flooding late this
  week.

&&

.DISCUSSION...
Issued at 125 AM MDT Tue Jun 4 2024

Summer, at least weather wise, will be arriving, especially
starting on Wednesday. As for now, we still have some showers across
northern portions of the area in response to the Pacific trough
moving across the area and the left front quadrant of an 120 knot
jet providing some upper level divergence. These showers should
continue to decrease through the overnight but a few may linger into
the morning hours before everything ends by around 10 am or so. The
main concern then shifts to wind as we shift from the left front to
right front quadrant of the jet this afternoon, enhancing downward
forcing. Reasoning remains the same as yesterday. The 700 millibar
winds do not look sufficient for high winds, but gusty to strong
winds are certainly possible. Some windier areas, like Rock Springs,
have greater than a 1 in 2 chance of seeing wind gusts over 40 mph.
Temperatures today will average close to slightly above normal.
Humidity should remain high enough to prevent many fire weather
issues.

Wednesday also looks dry. This is where temperatures will begin to
rise, with many locations likely seeing their warmest temperatures
of the calendar year with lower elevations seeing highs well into
the 80s. This a day when elevated fire weather may be a concern. The
low that brought the rain will be held up by a blocking ridge over
eastern Canada, with the low spinning over Manitoba. A tight height
line gradient between the low and ridging building across the desert
southwest. In addition, the jet will be close enough to keep breezy
to windy conditions continuing. With relative humidity falling into
the teens at times, fire weather statements may be needed for
Wednesday.

Thursday looks dry and warmer as well, and probably the first
possibility to see high temperatures hit 90 in our warmer spots.
Also, with the ridge building northward, wind will decrease. The
heat really looks to peak on Friday, with the best chance of seeing
high temperatures in the 90s. This is also the day some mid level
moisture will be introduced to the area, bring a possibly, although
a small one (generally less than 1 out of 4 chance) of some
afternoon or evening convection. And, with the hot temperatures,
rising rivers will likely become a concern. A general rule of
thumb around here is three days with highs in the 80s is when
high level snowpack really starts to melt. So, we will have to
start watching for this, especially starting on Friday.

More uncertainty creeps into the forecast stating on Saturday. The
ridge looks to get suppressed just a bit with some shortwaves moving
into the area, bring chances of convection, mainly of the diurnal
variety. There are still differences in guidance in the timing of
the waves, so details are still hard to come by though. It does look
more active for the weekend and Monday as well. Nevertheless, I
think we can safely say, welcome to summer in western and central
Wyoming.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1130 AM MDT Tue Jun 4 2024

Yesterday`s weather system moved eastward overnight, bringing
strong northwest mid-level flow over western and central Wyoming
today. With some cumulus around 5-7K ft and high clouds
streaming toward the southeast, VFR conditions will dominate
today and remain through the forecast period at the TAF sites.
Biggest issue today is the WNW wind, with 15-25 kts and gusts
25-35/40 kts this afternoon and early evening. Far northwest WY
may see some localized MVFR conditions late this afternoon and
evening, but precipitation is not expected at any TAF sites.
Winds will decrease around sunset, but remain 8-12 kts. The WSW-
WNW winds will increase again between 05/15-17Z tomorrow as a
zonal/NW mid-level flow pattern continues with high pressure
building over the Great Basin. A weak wave in the flow will
bring increased clouds to northern WY from 05/06-18Z, with
decreasing clouds in the afternoon. Wednesday`s winds will again
be 15-25 kts with 20-30 kt gusts during the afternoon at most
TAF sites.

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...Hattings
AVIATION...McDonald