793
FXUS63 KFSD 081123
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
623 AM CDT Wed May 8 2024

.KEY MESSAGES...

- Showers and isolated storms expected today. Some storms could
  be strong to severe and bring another round of meaningful and
  locally heavy rainfall. Confidence is low in severe weather
  threat as well as location of heaviest rainfall.

- Warmer and mainly dry conditions move in for the weekend.
  Continued warm with renewed rain chances by mid week.

&&

.DISCUSSION...
Issued at 334 AM CDT Wed May 8 2024

CURRENTS: Pleasant conditions this morning with calm to light winds
and some clouds across the Hwy 20 corridor and south central SD. A
few weak echoes are visible on radar in these areas as well, but dry
low levels is precluding any measurable precip. Temperatures through
08z/3 AM CDT are in the 40s to mid 50s, and expect widespread 40s by
daybreak. Surface low is located over north central NE, with upper
low across northwestern SD/southeastern MT.

TODAY AND TONIGHT: Some uncertainty today in the forecast, as models
disagree on where exactly the stacked low pressure meanders and
where the associated fronts are. This will impact everything from
rain chances to winds to severe weather potential through today.
Guidance shows the surface low by 18z/1 PM CDT anywhere from
northeastern NE to over Sioux Falls to over IA/MN border. By this
time, the mid and upper low are located in central and southwestern
SD, respectively, with roughly the same amount of variability as the
surface low. All this to say the subtle differences are leading to
lower than average confidence in precipitation forecast today.

Overall, trends in the hi-res and other guidance show showers
developing by late morning into the early afternoon hours, generally
isolated at first becoming more widespread through the later
afternoon and early evening hours. Although risk is low, we could
see a few strong to severe storms. Instability increases fairly
quickly this morning into the early afternoon to around 1000 to as
high as 1500 J/kg. Steep mid level lapse rates over 7 deg C/km with
this instability and increasing bulk shear would support some large
hail of quarter to half dollar sized. Think that damaging wind gusts
to 60 mph are less of a concern with DCAPE at or less than 500 J/kg,
but can`t entirely be ruled out. As we sit under the upper low,
funnels and/or landspouts are also possible. Landspout/non-supercell
tornado threat is additionally supported by 0-3 km MUCAPE and 0-1 km
MLCAPE both over 500 J/kg and steep low level lapse rates (over 8
deg C/km). This threat will also be variable in location depending
on where the warm front ends up, which would provide another
focus. Folks should stay weather aware today and this evening.

Regarding heavy rain potential, with the variance in model
solutions, it is difficult to say exactly where the highest QPF will
be realized and how much. Taking a look at the 08.00z deterministic
guidance, the axis of heaviest precip ranges from the Hwy 14
corridor to north central IA. Ensemble guidance (outside of the HREF
and GFS) shows a less than 10% chance of any portion of our area
seeing over 0.50" of rain. However, the GFS ensemble paints a 50%
chance over the MN/IA border stretching east. The HREF is the most
bullish - with most locations across southwestern MN and
northwestern IA having a 60-90+% chance of over half an inch of
rain. Think that some folks will see 0.50-0.75" through Thursday,
with locally higher amounts possible in thunderstorms. This could
lead to localized ponding and some small rises on local
creeks/streams if the heavier precip falls in our more saturated
areas.

Otherwise, highs today in the 60s to lower 70s with increasing
clouds. Winds will be variable as the low moves across the area,
with sustained winds 5-15 mph and gusts to 20-25 mph. Showers and
isolated storms continue to slowly sink south during the overnight
hours. Lows fall into the 40s.

TOMORROW THROUGH THE WEEKEND: Our persistent stacked low pressure
system is shoved out of the way Thursday as another wave drops
south, keeping scattered shower/isolated storm chances in play.
We`ll see drier weather for Thursday night into Friday. We`ll remain
in northwesterly flow with another wave or two skirting by to the
east over the weekend which could bring the return of low end shower
and storm chances. Still some variability in the timing/location of
the wave(s), so have left the NBM for now. Periodically breezy winds
expected. A warming trend is also expected, with highs warming into
the 70s by the weekend and lows in the 40s and 50s. Some 80 degree
highs are possible by Sunday.

EARLY TO MID NEXT WEEK: More zonal flow is progged to move over the
Plains by early next week, with models varying widely on the tracks
of waves/troughs. Generally expect near to above average
temperatures to continue. Rain and storm chances also return,
greatest currently expected in the middle of the week with a more
robust trough.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 614 AM CDT Wed May 8 2024

Outside of convection, expect VFR conditions to prevail for much
of the period. Showers and storms may reduce category to MVFR or
IFR for brief periods. Guidance is continuing to poorly handle
the isolated to scattered convection beginning late this
morning/early this afternoon through much of the period, but
tried to average the timing within the latest guidance for
convective PROB30 groups. More widespread precipitation is
possible toward the end of the period along and south of I-90,
which could bring a period of more widespread near MVFR
ceilings.

Winds will be variable in direction today as low pressure slides
over the area. Expect gusts at times around 20 knots.

&&

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

&&

$$

DISCUSSION...SG
AVIATION...SG