Area Forecast Discussion
Issued by NWS Riverton, WY

Current Version |  Previous Version |  Text Only |  Print | Product List |  Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
108
FXUS65 KRIW 201023
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
423 AM MDT Sat Jul 20 2024

.KEY MESSAGES...

- The weather pattern will keep the same weather conditions
  across the Cowboy State through this weekend into next week.
  This means hot, afternoon showers and storms, and fire weather
  concerns.

- Saturday looks to be a more active convective day with
  widespread rain showers and thunderstorms across the area.
  The main threat will be gusty wind from outflow boundaries and
  downdrafts, but brief heavy rain and frequent lightning will
  be threats as well.

- In terms of temperatures it has been hot, but not oppressively
  hot. This will continue to be the case as high pressure
  remains centered over Nevada through this weekend.

- A shift in the ridge/high will occur by the middle of next
  week, which means temperatures will, once again, jump up near
  triple digits east of the Continental Divide and near 90
  degrees F west of the Continental Divide.

&&

.DISCUSSION...
Issued at 149 AM MDT Sat Jul 20 2024

With the high centered over Nevada the Cowboy State remains on the
periphery of its effects. This has allowed for subtle shortwaves to
drop down from the north. This is especially true for today
(Saturday) as model guidance is depicting a little more
consequential shortwave dropping down into the Cowboy State.
Subsequently, model guidance shows more coverage of convection
compared to the last few days. As such, expect numerous outflow
boundaries to form as convection gets going late in the morning in
the mountains thanks to the added lift from the shortwave and
diurnal upslope flow. PWAT`s are respectable around 0.75"-1"
across the area, so there will be sufficient moisture for heavy
rainfall with the strongest storms, but overall the atmospheric
profile doesn`t look conducive for flash flooding. Forecast
soundings show too much dry air in the column and (no surprise)
show moderate inverted v signatures. Wouldn`t be surprised if
there were a couple of gusts close to 50 knots this afternoon.
It certainly doesn`t take much here to get that kind of wind,
especially this time of year. The shortwave will also bring
northerly wind to the area this afternoon, which combined with
more cloud cover/convection will limit high temperatures this
afternoon. Expect, on average, around 5 degrees F cooler than
yesterday.

The pattern shouldn`t change much into next week as the dominant
high slowly shifts east by the middle of next week. There will be
continued chances for isolated to scattered rain showers and
thunderstorms each afternoon and some pockets of mid-level energy
move through the Cowboy State. Gusty wind will be the main threat
with any convection that develops. By Wednesday model guidance is
showing 700 mb temperatures approaching/reaching 20 degrees C over
the area. With that kind of warmth moving overhead it is almost a
certainty that several locations east of the Continental Divide will
rise back into the triple digits. The good news is this looks to be
temporary as model guidance has a trough pushing the high to the
south down into the Desert Southwest late in the week. Don`t get
your hopes up, however; getting a dominant high/ridge to move that
much in the peak of summer is no easy feat, so model guidance may be
overestimating the response of the high as the trough tries to push
it south. Regardless, heading into the middle of next week fire
weather concerns will increase as temperatures rise, RH drops, and
isolated storms bring more lightning.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 420 AM MDT Sat Jul 20 2024

Prevailing conditions will remain VFR through the TAF period,
although brief reductions to MVFR are possible with the
strongest convection this afternoon. A weak shortwave will drop
down into Wyoming this afternoon, which will aid in the
development of convection. This should result in more widespread
rain showers and thunderstorms than the area has experienced
the last few days. In addition to this, a shift in wind
direction becoming northerly/northeasterly will occur this
afternoon.

To account for the convection there are PROB30 groups with VRB gusty
wind and -TSRA at all terminals Saturday afternoon. The timing is
subject to change and very difficult to pinpoint as numerous
outflow boundaries will interact causing rain showers to develop
erratically and possibly linger at certain terminals well into
this evening before ending after midnight.

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

&&

.FIRE WEATHER...
Issued at 149 AM MDT Sat Jul 20 2024

Convection will be the driving factor behind fire weather concerns
in the short-term. Fire starts from lightning have been cropping up
over the last couple of weeks as fuels have been drying thanks to
mostly dry conditions and hot temperatures. Wind is not a primary
concern in the sense that synoptic flow will remain weak, but
plentiful outflow boundaries from convection will continue to pose a
risk to ongoing and new fires. This will be the main threats through
this weekend into early next week, but temperatures will rise, which
will result in falling RH by the middle of next week. Wind will be
the saving grace, again, since high pressure that is bringing the
hotter/drier air will keep wind light in general. Convection will
decrease in coverage, but is not likely to cease altogether, so new
fire starts from lightning will remain a threat through next
week.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Air Quality Alert until 1 PM MDT this afternoon for WYZ001-012-
013.

&&

$$

DISCUSSION...Rowe
AVIATION...Hattings
FIRE WEATHER...Rowe