442 
FXUS63 KFSD 060341
AFDFSD

AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
1041 PM CDT Tue Oct 5 2021

.SHORT TERM...(This Evening through Wednesday)
Issued at 328 PM CDT Tue Oct 5 2021

Diurnally driven cumulus across parts of northwest IA continues to 
dissipate this afternoon, but that may not be the last that we see 
of it. With low level flow remaining from an easterly direction, a 
much larger and deeper area of cloud cover across central and 
eastern IA will likely slowly advect to the northwest through the 
night and expand into the area, possibly into eastern SD. The better 
chances for this will be late tonight into Wednesday morning. If not 
a more solid deck overnight into Wednesday morning with layer of 
moisture should provide a better environment for diurnally driven 
cumulus from late morning into Wednesday afternoon. There will also 
be a chance for a little fog on the western edge of the incoming 
moisture, maybe near I-29, but confidence not high enough to include 
in the forecast. Low temperatures tonight should mostly be in the 50 
to 55 degree range but some 40s are still possible where winds 
diminish. As south to southeast flow increases through the night we 
will actually see a bit of cooling aloft as we wrap some cooler air 
in from the east. This should result in highs a couple of degrees 
lower than today. Expecting gust about 15 to 20 mph with highs in 
the 70s.

.LONG TERM...(Wednesday Night through Tuesday)
Issued at 328 PM CDT Tue Oct 5 2021

Wednesday night into Thursday will see south to southeast flow 
continue and we will still see the threat for the cooler air aloft 
and an increased chance for a more widespread cumulus cloud cover. 
These two factors point towards milder low temperatures in the mid 
and possibly upper 50s. Highs Thursday should mostly be in the lower 
to mid 70s but if the cloud cover is thick enough some locations may 
struggle only into the upper 60s. The only other concern during this 
time will be the potential for a few showers and possibly an 
isolated thunderstorm east of I-29. For now only extremely skinny 
CAPE so nothing more than light to possibly moderate showers.

Thursday night into Friday we start to shake off the easterly 
component and go more south to slightly southwest, which should 
allow for better mixing and warming. Raised lows a touch as the 
stronger southerly flow and mild 925 mb temperatures may keep 
temperatures from falling below 60 in many locations, so shooting 
for mid to upper 50s. Low level temperatures increase through the 
day so highs should be from the upper 70s to lower 80s. While windy 
conditions are not expected we should see a pretty consistent 10 to 
20 mph.

Friday night into Saturday night an upper level wave is expected to 
pass to the northwest and then north of the area, which should 
leave us in mostly a dry slot position. As the warm advection 
surges north Friday night into Saturday we may see a threat for 
showers and isolated thunderstorms, but for now the models are far
too dry below about 700 mb to allow any elevated activity to 
develop. There are also some timing issues between the models so 
will wait until further runs come in to determine if there will be
a shower and thunderstorm threat. One other thing to watch once 
confidence in timing and location of the wave increase will be 
winds. The northwest flow should be fairly stout if something 
closer to the GFS/Canadian pans out.

Cold air advection will work its way into the region as the wave 
departs to the northwest. With strong northwest winds at 850mb along 
with a mainly unidirectional wind profile, gusty winds will be 
possible. Models handle the dew points quite differently with the 
Euro having the highest Td with 50°F+ while the GFS mixes more 
aggressively and has Td’s in the upper 20’s to mid 30’s. Still 
thinking that Sunday has the potential for fire weather concerns, 
but confidence is too low to elaborate any further on specifics. 
Shortwave ridging develops on Monday, continuing dry conditions for 
the day. With light surface winds in place, Monday could be another 
warm, diurnally driven day. Most models have a longwave trough 
moving through the 4 corners region throughout Tuesday. This 
longwave trough will generate a Colorado low resulting in a 
tightening of the surface pressure gradient and strengthening of the 
surface winds. The wind direction will also turn to a warm southerly 
wind. Despite the warmth, confidence is far too low to determine if 
strong enough moisture return will occur. Have left 20-30% pops in 
place to account for any precipitation uncertainty. 

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1041 PM CDT Tue Oct 5 2021

Stratus approaching Hwy 71 corridor from KSLB-KSPW as of 0330Z
still largely VFR with ceilings 3500-4000ft AGL, with hints of
thin moisture layer as far west as KSXK-KSHL with reports of 
cloud layer, though nothing apparent on satellite imagery. Still 
looking for ceilings to lower into MVFR range as stratus expands 
westward into northwest Iowa/southwest Minnesota overnight into 
early Wednesday, but potential for IFR ceilings seems less likely.
Diurnal heating should allow any MVFR ceilings to rise back into
the lower VFR range as any strato cu approaches I-29 corridor by 
midday, so will stick with 3500-4000ft BKN clouds for KFSD/KSUX 
during the afternoon, with western edge of this cloud shield
expected to clear with loss of heating by 07/00Z.

Could possibly see patchy fog on the western edge of the advancing
stratus tonight/early Wednesday, but latest high res models have 
been backing off on this potential with visibility trending higher
in recent runs.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.

&&

$$

SHORT TERM...08
LONG TERM...08/Meyers
AVIATION...JH