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000
FXUS65 KRIW 242302
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
502 PM MDT Wed Apr 24 2024

.KEY MESSAGES...

- Some isolated rain showers and a few rumbles of thunder  possible
  over the western mountains this afternoon.

- More widely scattered rain showers and isolated thunderstorms
  Thursday associated with a cold front.

- Main system pushes through late Friday and over the weekend
  with ample QPF for much of the area to include mountain snow.

- Ridging and warming trend for next week with another system
  late week into the weekend.

&&

.DISCUSSION...
Issued at 1211 PM MDT Wed Apr 24 2024

IR currently depicts southwesterly flow aloft pumping in Pacific
moisture to the western mountains into this afternoon. An upper
level low sits off the Pacific northwest coast with little
southeasterly movement. Weak surface high pressure sits over the
Yellowstone area and will weaken throughout the day with
decreasing convergence aloft. Radar shows some light sporadic
rain showers across Sweetwater County and will pick up in
coverage over the Winds and south of the Rattlesnakes this
afternoon. Little movement expected under weak 700mb steering
flow but will remain light in nature. An isolated rumble of
thunder is possible as instability values are decent enough over
100 to close to 150 J/kg, but just little to no shear or
diffluence aloft.

Overnight, the aforementioned upper level low will deepen and
elongate southward with increasing divergence pushing into the
western Rockies as it nears the CWA. This will support a cold
front to push through northwest to southeast from mid to late
morning and into the afternoon hours. Timing and speed of the
front will determine afternoon high temperatures but looks to be
slow enough to allow warm temperatures once again east of the
Divide. HiRes models indicate a pretty fair alignment with one
another, even though the Nam Nest looks to have the best handle
on current conditions and into this Wednesday afternoon.
Regardless, a more widely scattered showery afternoon is in
store for Thursday with a more thunderstorm activity east of the
Divide with the warmer unstable air for the cold front to
collide with. Better steering flow and a more enhanced
instability range will allow for a few more isolated
thunderstorms to be more likely to start by early afternoon from
Thermopolis to Riverton and points eastward as the day
progresses into the evening hours before losing to the cooler
air depressing any higher sustained updraft activity. These
cooler and more seasonable temperatures will expand through
Friday and over the weekend as well.

The main through will push through late Friday with more potency
due to stronger difluent flow aloft expanding over the western
CWA and especially for the Winds and to a lesser extent the
Absarokas. These will most likely need winter storm watches at
some point but with uncertainty still ahead with this part of
the main storm, will put this off until incumbent shifts. For
the most part, the more mid term model data is mostly in
agreement with near similar initializations of the 12Z data in
terms of timing. However, QPF is somewhat in more of
disagreement not handling this type of system for late April too
well. Probabilistic data indicates a wider range of
possibilities with the higher snowfall amounts over at least 8
inches to ping greatest over the Winds and Absarokas to near 100
percent and lesser for anything over a foot (around 60-70
percent, moreso for the Winds). The Bighorns have indicated a
hint at the higher snowfall amounts, but as past storms have
signified, these are overdoing it as well. Time will tell, but
it should be an all around good event for snowfall for these
ranges.

Points east of the Divide will mainly be in the form of liquid
precipitation being an overall stratiform type of rain in the
cooler air for the lower basins and valleys. The Wind River
Basin should be the area of most "concern" with the highest QPF
probability but all areas should get a decent amount
regardless. Even the Bighorn Basin and points east of the
Bighorns will get a more than measurable amount IAW the longer
term models with a decent grasp on the system setup. The trend
has been a bit southward, which is why some of the northern
zones will see less but the difluent flow will continue to push
around the low with its eastward progression. Stay tuned for
updated forecasts in the coming days.

Beyond the weekend, ridging builds back in across the northern
Rockies and the CWA with a warming trend in store into much of
next week. Long term outlooks show another system that could
affect the area and region but late in the work week and into
the following weekend. Regardless, there are really good chances
for substantial moisture in the near and longer term future
that much of the state needs at this point in time.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 501 PM MDT Wed Apr 24 2024

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals.

Terminals remain VFR through the forecast period, although ceilings
will lower steadily through the day Thursday. Convection across
mainly southwest Wyoming wanes between 01Z-03Z/Thursday. Impacts
would be brief and generally related to gusty and erratic outflow
wind. Shortwave and associated moisture reaches KJAC 12Z-
16Z/Thursday with -SHRA beginning by 18Z. It does appear VFR will
prevail at KJAC as ceilings drop to around BKN040-050. Cold front
pushes across the southwest terminals Thursday mid-afternoon with
scattered showers and gusty northwest wind to follow. Mountain tops
occasionally obscured after 09Z/Thursday.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals.

VFR to prevail at all terminals through the forecast period.
Scattered showers and isolated thunderstorms over central and
southern Wyoming persist until around 02Z/Thursday, although
isolated showers linger through 06Z/Thursday east of KRIW to KCPR.
Gusty outflow wind around 30kts would be the primary hazard with
convection. Surface cold front pushes through KCOD and KWRL Thursday
morning, surging into the central terminals by mid-afternoon.
Favorable dynamics for widespread showers appear to come together
just beyond this forecast period. Northerly wind shift and VCSH are
the main concerns at this range. Mountain tops occasionally obscured
after 21Z/Thursday.

&&

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

&&

$$

DISCUSSION...Lowe
AVIATION...Jones