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000
FXUS65 KRIW 142052
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
252 PM MDT Sun Apr 14 2024

.KEY MESSAGES...

- Another day of warm/dry conditions across the forecast area
  today. This ends tomorrow as an approaching cut-off low
  begins traversing to the south through the Four Corners
  Region. Isolated showers and an isolated thunderstorm possible
  (20%) this afternoon/evening for far western WY.

- It will remain mild on Monday, but a bit cooler as the low
  brings in clouds/rain/thunderstorms to the area. Most
  thunderstorm activity will be restricted to Johnson and
  Natrona Counties late in the afternoon/evening. Heavy rain
  appears to be the main threat at this time.

- The first upper-low moves out by Tuesday afternoon, with mild
  temperatures expected again ahead of a second upper-low/strong
  cold front Tuesday night into Wednesday

- The weather pattern then remains unsettled through the rest of
  the week as persistent energetic westerly flow drapes over the
  Cowboy State. This means rain/snow chances and cooler
  temperatures.

&&

.DISCUSSION...
Issued at 251 PM MDT Sun Apr 14 2024

Today will be another beautiful warm Spring day across the Cowboy
State, but the warm temperatures and dry conditions will keep
elevated fire weather conditions around this afternoon. Wind will be
a bit breezier today compared to yesterday as well. A cut-off low is
approaching from the west and the center of circulation is over
Central CA at this time based on current WV satellite imagery.
Isolated lower elevation rain showers and higher elevation snow
showers will develop this afternoon in southerly flow on the east
side of this low. Isolated thunderstorms are possible as well as
model guidance does show some weak instability this afternoon,
especially in YNP and the Tetons/Jackson Valley. Overall, the better
forcing does appear to be just to the west of our forecast area (in
ID) this afternoon, so coverage will be limited.

It starts to get interesting tomorrow as the cut-off low slides
eastward into the Four Corners Region to the south of the forecast
area. Southeasterly flow will bring up good moisture into eastern
portions of the forecast area (namely Natrona/Johnson County), which
combined with warm temperatures will result in decent instability.
CAPE values look to be anywhere from 500-1000 J/kg in that area late
Monday afternoon. Shear will be minimal, which is the big limiting
factor for severe thunderstorms. With the moisture (PWATs around
0.75") and weak steering flow the main threat would be heavy
rainfall and Flash Flooding. Will have to keep a close eye on this
as model guidance really increased QPF Monday afternoon/evening for
Johnson and Natrona Counties. The low is expected to strengthen
rapidly as it moves into the Plains, which will result in a
tightening pressure gradient Monday night into Tuesday morning. Most
notably across Johnson County where wind may reach High Wind
criteria. Am going to issue a High Wind Watch for both of the
Johnson County zones for Monday night into Tuesday morning. Wind
should decrease steadily Tuesday morning into Tuesday afternoon as
the low progresses east and the pressure gradient weakens
proportionally.

This initial Cut-off low exits into the Plains on Tuesday and it
will be cooler after it passes, but only slightly. High temps are
looking like upper 50s to middle 60s for most of the forecast area.
A larger upper-low then drops down into southern Canada Tuesday
night/Wednesday morning. This looks like a more widespread precip
maker for the forecast area. A strong cold front will be associated
with this low, so a major cooldown is coming by the middle of this
week. The northern half of the forecast area at least has a chance
for a trace of snow or more from Tuesday night through Wednesday
night. That looks like the best window of precipitation, but the GFS
keeps light to moderate rain/snow ongoing through Saturday for the
mountains, mainly. This seems like an outlier at this point, but the
trend is for it to at least stay cool through Saturday.


&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1158 AM MDT Sun Apr 14 2024

VFR conditions are expected to prevail through the period. Wind will
be the main impact at terminals in southern and central Wyoming,
especially at KRKS which will see gusts to around 30 knots. Wind
will subside after sunset. Otherwise, models have been hinting at a
few showers developing this evening in and around the western
mountains. This is most likely between 00-06z; the latest HREF run
has a 30 to 40 percent chance of precipitation during this period.
Given the uncertainty we will leave any impacts out at KJAC for now.
Lower clouds and precipitation chances will begin to increase late
in the period as a stronger system approaches Wyoming.

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 251 PM MDT Sun Apr 14 2024

Another warm day with well above normal temperatures continues. It
is also very dry across the area with RH values in the low teens for
most locations east of the Continental Divide. So, elevated fire
weather conditions continue for most locations. Critical fire
weather conditions are occurring in zones that have critical fuels.
The Red Flag Warning continues until 7 PM this evening for Natrona
County zone 280. South/southwest wind gusts of 20 to 30 mph will
continue this afternoon before decreasing this evening. RH recovery
will be poor for 280, 281, 283, 285, and 289 tonight. Tomorrow will
not be as warm, so RH values do not drop as low as today. Values
will be 20-30% for most zones.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Tuesday evening through Wednesday
evening for WYZ002.

High Wind Watch from late Monday night through Tuesday morning
for WYZ010-011.

Red Flag Warning until 7 PM MDT this evening for WYZ280.

&&

$$

DISCUSSION...Rowe
AVIATION...Myers
FIRE WEATHER...Rowe