386 
FXUS63 KFSD 042344
AFDFSD

AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
644 PM CDT Sun Apr 4 2021

.SHORT TERM...(This Evening through Monday)
Issued at 252 PM CDT Sun Apr 4 2021

Another incredible day across the area today. Lighter winds, low 
humidity and very warm temperatures are found across the entire 
region. Winds will gradually turn more east and southeast through 
the night and likely average about 5 to 10 mph. Not overly strong, 
but enough to keep many locations from decoupling and tanking in 
this very dry air mass. However, because of this dry air mass a 
little concerned that forecast lows around 50 in most locations will 
end up being too warm, but any colder lows will quickly rebound when 
the sun comes up. Isolated showers and maybe a thunderstorm will be 
possible over mostly northwest IA tonight with a very steep EML. 
However not really sure we can get any moisture aloft below these 
steeper lapse rates to take advantage of these steeper lapse rates. 
There is some weak to moderate mid level warm air advection so some 
forcing to help out, just not confident on the moisture. So, will 
maintain only low chances.

Kept the very warm temperatures in place for Monday as the front 
does not appear as though it will impede warming. In fact looks like 
some nice enhanced mixing along and ahead of the incoming front 
which focuses most along and west of Interstate 29. May see our 
first 90 degree high temperature somewhere in there with widespread 
mid to upper 80s. Southwest MN and northwest IA likely topping out 
from 80 to 85. 

.LONG TERM...(Monday Night through Sunday)
Issued at 252 PM CDT Sun Apr 4 2021

Attention then turns to precipitation and thunder chances Monday 
night into Thursday morning. Low pressure over the Rockies cuts off 
from the main flow to the north and slowly drifts across the central 
Plains during this time. Strong to moderate warm air advection in 
the low to mid levels sets up across the are for about 24 to 36 
hours with some of the better synoptic scale mid level forcing over 
central SD into northeast SD. A little farther to the south across 
far southeast SD, northeast NE and northwest IA some slightly more 
unstable air will be in place and could serve as a secondary focus 
for development. Overall, a very good chance for a half an inch to 
an inch of rainfall for most locations with upwards of a couple 
inches possible if some of the better instability pairs up with the 
slow moving synoptic front.

On Monday evening a cold front will shift east through the area. 
Peak heating may allow a few thunderstorms to develop just to the 
north of the area, then shift southward near and after sunset. 
Isolated thunderstorms could actually develop anywhere along that 
front. For now will lean towards the drier low levels from the 
Rap/HRRR/GFS which limits CAPE potential. Still anticipate about 
1000 J/kg so some decent instability. Shear is a little messy. Just 
ahead of the front low level winds back just a touch, but are pretty 
weak and low to mid level winds all generally less than 30 knots so 
suspect any storms would be isolated to scattered and life spans 
would be fairly short. With that being said not out of the question 
to see an updraft strong enough to support some smaller hail, maybe 
up to dime size. Freezing level is up around 10 kft.

Ridging aloft moves across most of Monday night so suspect that 
other than any diurnally driven thunderstorms that develop activity 
should be pretty quiet. Warm advection does begin to increase late 
Monday night into Tuesday morning around the Missouri River, 
especially towards central SD, so will have some smaller chances for 
that. The better chances will be west of I-29 in the morning. By 
afternoon flow from about 850 mb to near the surface will increase 
from the south and southeast and bring in some more unstable air. 
Once again it appears that CAPE values will be near 1000 J/kg with 
very disorganized shear. Still a lot of question marks with boundary 
location and thus any severe threat. So very isolated severe threat 
right now. Do expect showers and isolated thunderstorms to expand 
across eastern SD into southwest MN on Tuesday afternoon and night, 
with northwest IA possibly struggling the most to get into the main 
precipitation. The better chances for northwest IA may come on 
Wednesday as the system is shifting east. 

Once this system exits mainly little to no precipitation into next 
weekend. The models are picking up on a fast moving northern stream 
wave Thursday night that will swing through a cold front and could 
produce some isolated showers, but we will see where that ends up 
going.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 643 PM CDT Sun Apr 4 2021

There will continue to be a little nocturnally driven low-level 
wind shear tonight around KSUX starting late evening, and with
this low-level jet there may be isolated showers or thunder in the
vicinity of KSUX, but below mentionable levels during the most
favored period from 05z-10z. Surface winds could again approach
some 25kt wind gusts ahead of a surface front slipping southeast 
through Monday, which should reach KFSD area toward 00z. VFR
conditions will prevail through 00z Tue.

&&

.FIRE WEATHER...
Issued at 252 PM CDT Sun Apr 4 2021

Another very dry day and a very high fire danger. Winds for the
most part have remained low enough to not need a red flag 
warning. However relative humidity is around 10-15 percent in most
locations. For now expecting relative humidity to increase a bit 
tomorrow ahead of the incoming cool front, but with trends 
pointing towards a drier than forecast air mass will need to 
monitor this for tomorrow. Humidity low enough in central SD 
Monday afternoon but winds not very strong. Strong winds in 
northwest IA and far eastern SD but humidity values a little too 
high. 

Right now leaning towards a very good chance for rain Tuesday into
Thursday so this should really aid in bringing the fire weather
concerns down and hopefully start the rapid green up into late
April.

&&

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

$$

SHORT TERM...08
LONG TERM...08
AVIATION...Chapman
FIRE WEATHER...08