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Area Forecast Discussion
Issued by NWS Sioux Falls, SD
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FXUS63 KFSD 262008
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
308 PM CDT Fri Apr 26 2024

.KEY MESSAGES...

-  Showers and storms continue to expand in coverage early this
   afternoon. Strong to severe storms possible into this evening
   (greatest risk remains through (9PM). Rain chances decrease
   late tonight.

- Through Sunday night, an additional widespread beneficial
  rainfall of an inch or more is expected (>70% chance), with
  higher chances across northwestern IA. Low chances (40% or
  less) for an additional 2" in northwestern IA.

- Chances for showers and storms return late Saturday night
  through Sunday, with rainfall accumulations forecast to range
  between half an inch to an inch, though locally higher amounts
  may still occur. A few storms may become strong to severe.

- Unsettled pattern continues through next week, with periodic
  rain chances, though precipitation chances and temperatures
  are both low confidence forecast due to widely varying model
  solutions.

&&

.DISCUSSION...
Issued at 304 PM CDT Fri Apr 26 2024

REST OF TODAY AND TONIGHT: Convection has begun this afternoon, with
elevated hailers earlier this afternoon in northwestern IA. Elevated
instability is evident on satellite by the convective CU
developing over the stratus, even into south central SD. Further
to the southeast, convection is developing across eastern NE,
along the dryline and clearing. Instability, including surface
based CAPE, is beginning to increase in this area. Dewpoints are
increasing across eastern NE as well. Closer to our area,
clearing in the stratus has been noted in the more stable areas
of the James River Valley, although we are starting to see some
thinning via satellite of the lower clouds in western IA.
Continuing to monitor the clearing of the stratus in
northwestern IA this afternoon, as clearing soon rather than
later will help us destabilize, leading to an increasing
conditional severe weather threat.

Showers and storms will continue to develop across NE and move to
the northeast, entering our southern area by 21z/4PM based on the
latest timing of development and hi-res guidance. Large hail,
generally to golf ball size, remains the main threat with steep mid
level lapse rates over 7 deg C/km. Shear values within the 0-6 km
range remain high as well, 25 knots or more, and increasing as you
move to the east (with values from most of the deterministic
guidance and mesoanalysis over 40 knots in northwestern IA). Expect
supercells, or at minimum some rotation in the storms, which will
aid in the keeping the hail threat in play into the evening
hours across the area. Uncertain how far north storms will
maintain their strength, but can`t rule out a stronger storm or
two approaching/crossing the I-90 corridor.

Beginning to see that surface destabilization mentioned in the
previous paragraph via the SPC Mesoanalysis page, with values
increasing 400+ J/kg over the last couple of hours across
northeastern and eastern NE. LCL heights in this area are low
(less than 1500 ft), and SRH values are over 200 m^2/s^2. If we
can continue to see this trend over the next hour or so,
concerned with conditional tornado threat increasing across the
southern MO Valley into the Hwy 20 corridor in northwestern IA.

Strong wind gusts to 60 mph are possible with storms mixing down the
stronger winds in the low level jet. However, this is the lesser
threat, and looks more likely with linear mode of storms.

In summary, large hail to golf ball size is the main threat with any
strong to severe storm this afternoon and into the evening. If a
storm can stay discrete, 2" hail may be possible. If we can continue
to clear out stratus before 4PM or so, a few tornadoes may be
possible, mainly across the Hwy 20 corridor into northwestern IA.
Damaging wind gusts to 60 mph may occur as well - particularly if
storms are able to become more linear. Locally heavy rainfall is
expected, but flash flooding concerns remain low. Localized rises
and ponding are possible.

Severe threat diminishes after 8-9PM this evening, with some
lingering showers and isolated storms into the overnight hours.
Rainfall amounts this afternoon through tonight generally an inch to
1.5", although could see higher amounts within stronger
thunderstorms. Lows in the upper 40s/mid 50s. Breezy winds gust
around 20 to 25 mph tonight, and begin shifting from southeast to
northwest.

SATURDAY: Some lingering showers are possible early in the day
and especially along the Hwy 14 corridor as the low pressure
pivots off to the northeast, but otherwise a mostly dry day is
expected. Cloud cover remains in place, with highs in the 50s
and 60s. Warmest conditions will be along and southeast of IA/MN
Hwy 60, where flow looks to take the longest to switch to the
northwest. Winds shift to the northwest then northeast as the
low moves away. We`ll be a bit breezy, with gusts 20 to 25 mph
at times.

SATURDAY NIGHT THROUGH SUNDAY: Rain chances return to the forecast
Saturday evening as a pronounced upper level low near the Rockies
edges closer to the region. Despite the model variability that still
exist, most guidance generally suggest that showers/storms will
begin along the MO River Valley prior to midnight, then continue to
lift northeastward throughout the day Sunday as the aforementioned
low moves over western SD/NE. Do think it`s worth noting however,
that the sfc low low will be a bit more displaced from the upper
low, so not expecting the system to become as stacked at Friday`s -
at least for the time being.

As alluded to in the previous discussion, the severe threat will
largely depend on track of this complex in addition to where any sfc
boundaries set up. Timing could also be a limiting factor, as this
system is progged to reach our area during the late morning/early
afternoon, limiting the opportunity to tap into our diurnal
heating. Nonetheless, sounding profiles shows ample shear (40+ kts),
instability (~1000J/kg), and steep mid level lapse rates (7-8
degC/km) ahead of the wave. Thus, can`t completely rule out the
possibility of seeing a few severe storms, which would be capable of
producing large hail, damaging winds, and isolated tornadoes. SPC`s
latest Day 3 Outlook does include a small portion of our area in a
Marginal Risk (Level 1 of 5) for severe weather, mainly across NW
Iowa - so will continue to monitor trends. In any event, we strongly
encourage you to have multiple ways to receive warnings. Lastly, in
regard to rainfall totals, expect widespread amounts between half an
inch to an inch across our area, with isolated pockets near 1.5
inches also possible.

MONDAY: Upper level flow turns quasi-zonal Monday as the low lifts
northeastward towards the International border. As a result, should
see dry conditions prevail across the region, with highs ranging
from the mid 50s across SW Minnesota to mid 60s along the MO River
Valley. Winds during this time look to remain primarily out of the
west, with gusts between 20 to 25 MPH possible in areas east of I-29
through the afternoon.

TUESDAY THROUGH THURSDAY: Scattered rain chances return for the
remainder of the period as multiple shortwaves push eastward across
the Northern Plains. Still a bit of model variability exist
concerning the timing of these waves, though most generally agree
that showers will be possible throughout the daylight hours Tuesday,
with a relative lull Wednesday, followed by another round of showers
Thursday. Again, too much uncertainty still exist to put confidence
behind any one solution just yet. Otherwise, look for highs to rise
into the 60s to lower 70s, with lows generally in the 40s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1227 PM CDT Fri Apr 26 2024

Showers and storms are expanding in coverage early this
afternoon, with strong to severe storms possible into the
evening hours. Large hail is the main threat between 26.20z and
27.02z. Expect locally heavy rainfall, which may further reduce
visibility. Storms are most likely this afternoon and evening,
although an isolated rumble of thunder is possible into the
overnight hours.

MVFR/IFR and lower conditions continue through much of the
period as low pressure keeps stratus and precipitation in the
area. There may be some breaks or brief improvements to lower
end VFR conditions, but confidence is too low for that much of
an improvement.

Breezy southeasterly winds continue this afternoon and into the
evening, with gusts near 30 knots (stronger possible in storms).
Otherwise, winds will shift through the period as the low
pressure swings across the forecast area, becoming northwesterly
by Saturday morning. Winds tonight through tomorrow morning may
gust around 20 knots.

&&

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

&&

$$

DISCUSSION...SST/SG
AVIATION...SG
National Weather Service Regional Headquarters
