Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 052254
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
354 PM MST Fri Mar 5 2021

.SHORT TERM...(This evening through Saturday night)
Issued at 150 PM MST Fri Mar 5 2021

Today will continue to be a gorgeous early spring day across the
region. Some breezy southwest winds will continue this afternoon
across the Casper area, but otherwise, not much to talk about
regarding today or tonight`s forecast. Lows will be similar to the
past few nights with basins radiating out.

Cloud cover will be slightly more dense than previous nights, but
will remain scattered to broken high clouds, which won`t be enough
to prevent radiational cooling in most areas. Clouds continue to
increase through the day Saturday as the next system pushes into the
west. Models continue to weaken this system, thus PoPs and QPF were
significantly decreased from guidance. The HRRR has backed off on
the shortwave completely, keeping any precip to the north of the
region. Went more with the GFS solution which keeps some light
precip across the western mountains, but is not as bullish as the
NAM solution. Timing of the system will bring any precip that does
fall, across the western mountains Saturday afternoon and move out
by later Saturday night. Precip will be confined to the western
mountains and Yellowstone Ntl Park. The Canadian solution brings
precipitation across the southwest, but with the current flow
pattern and the nature of the system, we threw that solution out.

The other concern for tomorrow is the gusty winds across the usual
areas, especially Natrona County. With low RH and near 60 degree
temps, this could lead to some elevated fire weather conditions
across that area. RHs do not look to be critical so will hold off on
any highlights. The winds may be SPS worthy, but will let the mid-
shift make that call.


.LONG TERM...(Sunday through Friday)
Issued at 210 PM MST Fri Mar 5 2021

Weak high pressure builds back over the forecast area Saturday
night into Sunday as the weekend wave moves into the northern
Plains. Moderate southwest flow will prevail for the rest of the
weekend as mean high pressure is over the southern plains and a
trough is along the west coast. Clouds will slowly increase on
Sunday as moisture start moving up from the southwest.
Temperatures should be around normal and winds will be breezy.
Monday will see the trough slowly move eastward and develop over
the Intermountain West and northern Rockies as a lee-side surface
low develop over eastern WY. Winds will increase somewhat and
clouds and moisture will increase over western WY. Models are in
good agreement showing an elongated surface low from western SD
into NE CO and a short wave trough moving from NV into easter ID.
This trough will help in pushing a cold front west to east across
the forecast area from early Tuesday morning into Tuesday. The
western mountains and valleys should see moderate precipitation
(rain turning to snow in the lower elevations, and snow in the
mountains) on Tuesday. Additionally, as the surface low over NE CO
deepens, the cold front will wrap through MT southeastward into
NE WY, helping enhance precipitation around the Bighorn Mountains
and increase NE wind behind the front. With the secondary push
from the norther, upslope conditions are expected to develop
across central WY early Wednesday morning through mid-day,
bringing snow to much of the precipitation-starved area. Moist
unstable NW flow remain for Wednesday. Some model guidance is
showing another weak trough moving southeastward in the northwest
flow Thursday, though the GFS and ECMWF are not capturing the
feature. Have allowed higher NBM PoPs to remain in the forecast.
Cool NNW flow then remains from Thursday into Friday, with high
pressure possible late Friday. Overall, an active pattern from
late Monday through the rest of the week for below normal
temperatures and a good chance of precipitation to the entire
forecast area.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday)
Issued at 345 PM MST Fri Mar 5 2021

VFR conditions will occur through 00Z Sunday. Breezy conditions will
subside early this evening at KCPR. A system will approach NW WY
Saturday, with clouds increasing over western WY Saturday. Scattered
snow and rain showers are to impact NW WY late Saturday afternoon,
and perhaps bringing some light precipitation to KJAC early Saturday
evening. Ahead of this system, southwest winds will strengthen at
most TAF sites, with gusts 25 to 40 kts likely.

&&

.FIRE WEATHER...
Issued AT 150 PM MST Fri Mar 5 2021

Saturday will be a breezy to windy day across much of the region,
especially during the afternoon. RHs will be low, but not critical,
so we do not plan on issuing a Rangeland Fire Danger statement,
despite the wind and well above normal temperatures. Greatest
elevated fire threat will be across eastern Sweetwater county and
Natrona county during the afternoon. Precipitation chances will
increase tomorrow afternoon across the northwest and western
mountains. Snow/rain amounts look to be minimal with the Saturday
cold front. The next more significant chances of precipitation will
be Tuesday and Wednesday across the region.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Fisher
LONG TERM...McDonald
AVIATION...McDonald
FIRE WEATHER...Fisher



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