Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 211121

National Weather Service Sioux Falls SD
621 AM CDT Thu Oct 21 2021

.SHORT TERM...(Today and Tonight)
Issued at 325 AM CDT Thu Oct 21 2021

Low pressure will continue to move east today as high pressure
builds into the Dakotas at the surface. Latest model soundings
indicate that cloud cover may be difficult to shake today. While the
cloud cover will not be as expansive and deep as yesterday any
heating may lead to additional cumulus development. This may aid in
keeping temperatures even a little cooler than expected, so maybe a
good swath of the area will not reach 50 degrees.

By tonight a fast moving upper level jet will swing southeast into
the area and allow mid level warm advection to develop. While
precipitation chances are small some light activity will be possible
north of Interstate 90 late tonight. The mid level forcing will be
fighting a significant dry layer below about 800 mb which may make
it difficult for precipitation to reach the surface. For now if
precipitation can make it to the surface it will likely fall as
light rainfall but not impossible to see a few flurries as well.
With the increased cloud cover the chance for frost will be a bit
lower, but still anticipating lows roughly 32 to 36.

.LONG TERM...(Friday through Wednesday)
Issued at 325 AM CDT Thu Oct 21 2021

Overall the better chances for sprinkles and light showers will be
on Friday as the main mid level wave moves through. Better chances
will be east of the James River. By afternoon the forcing will shift
east and more sunshine will make it through. A relatively cold
environment will only allow temperatures into the upper 40s to mid
50s in most locations, but a lighter wind should help take the edge

Saturday morning may see a little frost or freezing temperatures
with the lighter winds and mostly clear skies. The best combination
of these two will be in southwest MN. A fast moving upper level
ridge will move through as the next wave moves into the Northern and
Central Rockies. This should bring an increase in cloud cover
through the day, but temperatures and winds will be a little higher
than on Friday. Still only expecting highs in the 50s.

Warm advection in the mid levels will increase ahead of this wave
later Saturday night into Sunday. This will bring a good chance for
showers to the area, with the better chances across northwest IA.
The model soundings are indicating a little weak instability as well
so do have some thunder chances in the forecast over mainly
northwest IA and far southeast SD. Nothing severe with CAPE values
less than 500 J/kg. With the expected rainfall on Sunday and more
extensive cloud cover highs will take a dip with most location
topping out in the upper 40s to lower 50s.

This wave will move through quickly with upper level ridging building
in for Monday. This should support more sunshine and milder
temperatures. Highs mostly 50s with readings near 60s along the
Missouri River.

Upper level ridging will be exiting the northern plains on Tuesday,
bringing in the next upper wave. WAA at 850 mb will be increasing
throughout the day, resulting in above average temperatures. High
temperatures will likely be in the 60s and maybe a few locations can
sneak into the low 70s. The WAA will coincide with increasing cloud
cover through Tuesday due to increasing moisture aloft. The upper
wave will develop a Colorado Low that will intensify the surface
pressure gradient thanks to an expansive area of high pressure over
the Hudson Bay in Canada. Wind speeds could be 10-20 mph with gusts
into 30s. Rain arrives late Tuesday night into Wednesday. Currently
have 30-40% PoPs and may increase them as forecast confidence
increases. Models currently show stratiform precip but if
instability increases, there may be a few rumbles of thunder. High
temperatures look to be a bit cooler in the 50s and low 60s.
However, given forecast uncertainty, this may change with evolving
runs depending on how long the clouds and rain last. The upper wave
and rain moves out of the northern plains by early Thursday, leaving
cool and dry northwest flow in its wake for the rest of the day.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 619 AM CDT Thu Oct 21 2021

IFR conditions across parts of southwest MN and northwest IA will
persist through much of the morning. MVFR ceilings will move in
late morning through the afternoon, gradually becoming VFR this
evening. Eastern SD will see MVFR conditions gradually become VFR
through the morning. Some hints that some diurnally driven MVFR
cloud cover could linger into the afternoon, but for now not
thinking that it would produce a ceiling.




LONG TERM...08/Meyers
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