698
FXUS65 KRIW 120736
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
136 AM MDT Sun May 12 2024

.KEY MESSAGES...

- A weak shortwave will bring isolated convection today,
  especially to Johnson and Natrona Counties.

- A couple of stronger waves and a cold front will bring more
  numerous showers and storms Monday through Wednesday. Details
  are still uncertain starting Tuesday.

- Drier, but not completely dry and warmer for the end of the
  workweek.

&&

.DISCUSSION...
Issued at 134 AM MDT Sun May 12 2024

After a beautiful day today, things looks to take a more active turn
starting today and then continuing into at least midweek. All is
quiet right now expect for a few mid level clouds, including here at
our office, which is hindering viewing of the northern lights. As
for today, the main culprit today will be a shortwave moving out of
Montana. Models are similar to yesterday with the best coverage of
showers and storms from the Bighorns and east, mainly Natrona and
Johnson Counties. But even here, other than the mountains, the
chances are 1 in 3 at best. Elsewhere, activity would be limited to
in or near the mountains with at most a 1 in 4 chance. It will be a
warmer day though, with some locations getting well into the 70s.
This should be a fairly early show, with dry conditions returning by
late evening. Even places that do get a shower or storm, most of the
day should be rain free.

A more potent trough then crosses the area on Monday and brings a
better chance of showers and storms. All models continue to zero in
on northern Wyoming with the best chance, averaging around 2 out of
5, with lesser POPs further south. As for stronger storms, there
will be some CAPE with values over 500 J/Kg at times. Lifted indices
top out around minus 2 though, so the chance looks low at this time.
This looks like the warmest day of the period, especially East of
the Divide where some of the warmer spots could reach 80. Showers
may linger through the night as well as the jet energy hangs around.

The second trough and associated cold front then approaches Tuesday
into Wednesday. There is still more uncertainty with this system
with more of a model spread on timing of the precipitation with as
much as 12 to 18 hours of difference. Placement of the heaviest
precipitation is also in flux. Some guidance shows a mid level low
forming over the Wind River Basin enhancing precipitation there with
some upslope flow developing, others have it further north. Some
models have the heaviest QPF Tuesday night, others on Wednesday. So,
although we have high confidence in a wet pattern over mainly the
northern two thirds of the state, confidence in details remains very
low. Cooler air will move in behind the cold front as well, bring
temperatures 10 to possibly 15 degrees below normal for Wednesday.
700 millibar temperatures also get chilly Tuesday night, falling to
around minus 1 which could bring snow levels down to around 8000
feet or so. Amounts look to remain light.

We should trend toward a warmer and drier pattern for the end of the
week. Models are not completely agreeing though. For now, we have
kept some mainly isolated diurnal POPs across the area. Most areas
should be dry a vast majority of the time though. Temperatures
should climb to near to above normal levels through the end of the
workweek.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1028 PM MDT Sat May 11 2024

VFR conditions will prevail across terminals through the period.
Isolated convection is again likely Sunday afternoon, but
confidence on any terminal impacts are low and will not mention
in TAFs. KCPR has the best chance at around 30 percent.

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

&&

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

&&

$$

DISCUSSION...Hattings
AVIATION...Myers