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Area Forecast Discussion
Issued by NWS Riverton, WY
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FXUS65 KRIW 191720
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1120 AM MDT Fri Apr 19 2024

.KEY MESSAGES...

- Cool for most today, but temperatures warm Saturday, with
  above normal temperatures on Sunday.

- A weather system moves across northern Wyoming Sunday into
  Monday. Windy across western Wyoming, with precipitation
  chances for northern areas.

&&

.DISCUSSION...
Issued at 118 AM MDT Fri Apr 19 2024

Not much of a change today compared to yesterday. A strong low in
Canada, north of the Midwest, continues to bring northwest flow to
Wyoming. As a result, another day of weak instability develops
across the area. Snow showers begin developing late morning across
the central and northern mountains. Like yesterday, not much snow
expected, with only a 40% to 60% chance of more than half an inch
for the mountains, with about a 60% chance for more than an inch at
the highest peaks of the Absarokas, Winds, and Bighorn Mountains.
Outside these mountain locations, the area remains dry, with
afternoon cloud development due to the very slight instability (< 50
J/kg surface CAPE).

Temperatures today rise a little for the Sweetwater County area,
bringing the highs there near normal (mid 50s). Elsewhere, the
cooler air remains. Many lower elevation locations (not including
Sweetwater County) are forecast to be in the upper 30s to middle
40s. The Bighorn and Wind River Basins have a 70% to 80% chance to
see highs above 40, and a 10% to 20% chance to rise above 45; these
will be the warmest locations east of the Continental Divide.

A transitory ridge moves through the state starting Saturday. This
should help warm temperatures some, bringing most places around
normal. This drier air also keeps precipitation chances away, with
only isolated (15% or less) shower chances for the central
mountains.

The ridge axis crosses through for Sunday, with the warmest
temperatures for the next 5 days expected (90% confidence) this day.
High temperatures around the 70 degree mark look possible (40% to
60%) for much of the lower elevations. Jackson Hole will be notably
cooler, in the low to mid 50s. The aforementioned ridge is also
quick to move through on Sunday, with a trough moving through later
in the day. Precipitation chances increase from west to east through
the afternoon and evening, with chances mainly across the northern
half of the state. This system still does not look very impactful in
the precipitation department. However, wind may be another story.
The current NBM has mean wind gusts in the 30 to 40 mph range Sunday
afternoon for western Wyoming, and through the Wind Corridor to near
Casper. Will have to watch this system the next couple days to gain
better confidence in these winds.

Winds decrease for Monday, with lingering precipitation across
northern Wyoming. Temperatures also drop to around normal. As usual,
long range models begin to differ later in the period. Nothing
impactful stands out at this time, with some shortwave energy
occasionally passing through fairly zonal flow. A larger system
looks to approach around next Friday, but being about 8 days out,
would not put stock into any details.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1120 AM MDT Fri Apr 19 2024

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

VFR to prevail through the period. Gusty east-northeast surface wind
at KRKS slows for the afternoon and then increases to 15-25kts
tonight as surface high pressure slides south tightening the
pressure gradient. These speeds diminish just prior to sunrise
Saturday.

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

Lingering moisture in combination with jet dynamics has allowed for
low-end VFR and mid-cloud decks to persist across the Wind River and
Bighorn Basins late this morning. While ceilings rise this
afternoon, cloud cover is likely to remain through at least this
evening. Clouds dissipate around 12Z/Saturday as the moisture and
jet energy push east ahead of a shortwave in northwest flow aloft.
North to northeast surface wind will predominate for much of the
period. Mountain tops frequently obscured above 11K feet MSL.

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...Wittmann
AVIATION...CNJ