176 
FXUS63 KFSD 231103
AFDFSD

AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
603 AM CDT Fri Apr 23 2021

.SHORT TERM...(Today and Tonight)
Issued at 408 AM CDT Fri Apr 23 2021

Water vapor imagery early this morning shows a strong shortwave 
trough tracking slowly east through the Dakotas and into Minnesota. 
Elevated, weakly unstable warm air advection showers should taper 
off by sunrise as the better forcing for ascent progresses
eastward into MN and IA. However cloud cover will linger east of 
I-29 this morning as low level warm air advection continues and 
cumulus development occurs ahead of and behind the approaching sfc
trough. Should see sunshine peek through across much of the 
region this afternoon with drier air aloft, helping temperatures 
rise into the mid 50s to mid 60s - warmest in northwest Iowa.

Southwest winds will turn west and northwest with the passage of the 
sfc trough today. Despite post-frontal strong mixing, mid level 
winds mixing down are relatively weak so should see winds remain 10 
to 20 mph sustained with gusts up to 25 mph, generally weaker than 
yesterday. Although winds will weaken briefly after sunset, the 
pressure gradient doesn't weaken much until the upper trough axis 
tracks through late tonight through early Saturday. Thus will 
maintain a sustained north wind overnight. 

Model soundings and the latest hi-res guidance support increased 
cloud cover with the upper trough axis passage late tonight, as 
well as introduction of a slight chance of rain or snow. The best 
chance for precipitation resides south of I-90 along the SD/NE 
border late tonight through Saturday morning, though it cannot be 
ruled out further north. Most guidance supports very light 
amounts, if any, but more robust mid level Fgen in NAM based 
solutions supports potential for 1 to 2 inches of snow in south 
central SD or north central NE late tonight. Even if this worst 
case scenario did occur, impacts would be minimal due to the warm 
ground.

.LONG TERM...(Saturday through Thursday)
Issued at 408 AM CDT Fri Apr 23 2021

Saturday will be notably cooler as an unseasonably cold sfc high 
digs into the Northern Plains. Despite 850mb and 925mb temps dipping 
below 0C, clearing clouds should allow for decent diurnal 
insolation with daytime temperatures rising into the 40s and 50s.

Quiet weather is short-lived as Saturday night's broad ascent
regime associated with strong warm air advection prompts a chance
of precipitation late Saturday night through Sunday. Temperatures
should dip to near freezing in southwest MN and east central SD
Saturday night, bringing potential for another round of snow 
accumulations along and northeast of a line from Worthington MN 
to Madison and Huron SD. Ptype and impacts will be highly 
dependent on how warm temperatures can climb in this region on 
Sunday, and ensemble guidance shows potential for highs to perhaps
not even rise out of the 30s. With strong mid level Fgen forcing,
a narrow band of heavier pcpn is certainly possible north of I-90
as well. Rain is the most likely ptype along and south of I-90, 
but further north nearing the Buffalo Ridge in MN, potential 
scenarios could range from one third inch of rain with a little 
snow mixed in, to one to three inches of snow accumulations with 
isolated higher amounts. At this point, a warmer solution is 
favored, but will continue to monitor potential for Sunday snow 
accumulations in southwest MN.

For Sunday through at least Monday night, the pattern becomes much 
warmer and breezier as heights build and strong warm air advection 
develops ahead of a strong Colorado Low ejecting from the Rockies 
and a deep upper trough digging into the West. On Sunday, highs in 
central SD will rise to the 70s, and for Monday, many will easily 
see 70s for highs and 80s are likely for locations south of I-90. 
The strengthening sfc pressure gradient will yield breezy south 
winds with peak gusts in the 30s Sunday and Monday. Bumped up wind 
gusts to the NBM 90th percentile Monday, when deep mixing is likely. 
Additionally bumped up Monday's highs to the 50th percentile of 
model guidance to account for 850mb temperatures approaching the 
90th percentile of NAEFS climatology. Enhanced fire danger is 
possible during this period of stronger winds and much warmer air.

The approaching upper trough supports periods of rain chances Monday 
night through Wednesday. Ensemble guidance favors most locations 
seeing less than an inch of new rain through this period, unless 
isolated thunderstorms can develop at some point. Little confidence 
in the details at this range, particularly regarding the period 
with the highest rain chances and Tuesday's temperatures. However, 
upper trough should be well east of the forecast area by Thursday,
lending support to drier weather late week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 555 AM CDT Fri Apr 23 2021

Fragmented back edge of some MVFR ceilings currently sits over
KSUX and very well may linger for another couple/few hours this
morning. The other location to watch for potential aviation
concerns in the near term is KHON. An area of fog and low stratus
is sinking southeastward out of north central SD although the soon
arrival of sunrise and solar insolation may slow its progress
before reaching the terminal. Will leave out restrictive mention
at KHON for the time begin but not out of the question to see its
necessity over the coming hours. 

Otherwise, look for veering surface winds from southerly to 
westerly to eventually northerly through the daytime hours. 
Tonight will bring a chance for additional MVFR ceilings along 
with a hit or miss rain/snow shower.

&&

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

$$

SHORT TERM...BP
LONG TERM...BP
AVIATION...Kalin