717
FXUS63 KFSD 020346
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1046 PM CDT Wed May 1 2024

.KEY MESSAGES...

- Additional rainfall is expected tonight across the area with
  the highest amounts from a half an inch to an inch expected
  along and southeast of a line from Slayton, MN to Canton, SD
  to Vermillion, SD. Severe weather is not expected but minor
  flooding is possible.

- Another chance for rain is possible Friday night into
  Saturday. The probability is moderate to high (50-80% chance)
  for rainfall amounts exceeding a tenth of an inch.

- A strong low pressure system looks to bring renewed storm
  chances on Monday but details are uncertain as of now.

&&

.DISCUSSION...
Issued at 334 PM CDT Wed May 1 2024

High pressure dominates the area this afternoon along while cloud
has expanded aloft. Outside of a few sprinkles across the area, high
temperatures have warmed to the upper 50s to low 60s while winds
remain light beneath the surface high. The surface high will push
off to the east this evening, turning winds easterly. A mid/upper
level wave will push into the Northern Plains this evening, setting
the stage for another round of rain. Yesterday`s surface front
resides well south of the area in Kansas. However, the front will
push northwards in response to the incoming wave. The low level jet
(LLJ) will strengthen which will strengthen warm air advection (WAA)
across the area and kick off rain after midnight. The LLJ will also
push the 850 mb boundary across northwest Iowa while also tightening
the thermal gradient. This will create a solid area of frontogenesis
(FGEN) which will also for a band of rain to develop. With the right
entrance of an upper level jet overhead, negative equivalent
potential vorticity (EPV) is possible above the frontal circulation
which could allow for the band of rain to be a bit more narrow and
intense. This will result in the strongest lift and bulk of the rain
falling approximately between 4 am to 8 am Thursday morning. Any
chance for rain will push east of the area come noon, allowing dry
conditions to prevail for the rest of Thursday. Rainfall amounts
between a half an inch and an inch are expected along and southeast
of a line from Slayton, MN to Canton, SD to Vermillion, SD. Isolated
higher amounts are possible in this area. Lower rainfall amounts
from a tenth to a half an inch are expected northwest of the line.
Rainfall rates do not look impressive with this system which should
prevent any flash flooding from occurring. However, ponding on
roadways along with minor flooding on some streams and rivers is
possible.

With rain finally east of the area, Thursday will be a much quieter
and cooler day. High temperatures will only warm to upper 50s to 60s
during the afternoon and lows down to the upper 30s to low 40s
overnight. A surface ridge will be passing through the forecast area
during the overnight hours. Clear skies will accompany the ridge`s
passing which suggest that fog may be possible. Latest HREF
probabilities only show a 20-30% chance for fog development. As
such, have kept any mention of fog out of the forecast but will
continue to monitor this potential.

An active pattern continues aloft on Friday, brining another chance
for rain. This chance for rain looks to come Friday evening and
night as a strong cold front pushes through the northern and central
Plains. Good news is that the daylight hours on Friday will be dry
with seasonal high temperatures into the 60s. The bulk of the rain
looks to be tied to the front itself, especially as this front will
lie again in the right entrance region of an upper level jet. As
such, negative EPV above the frontal surface is possible, thus
increasing confidence in a tight band of rain passing through the
area. Ensembles support this as they show a broad 50-80% chance for
rainfall totals to exceed a tenth of an inch. Low temperatures will
fall to the 40s overnight.

The weekend will be dry as shortwave ridging takes over aloft. High
temperatures will remain seasonal in the 60s and 70s with mostly
sunny skies. With only marginally breezy winds expected, the weekend
looks like a great time for outdoor activities!

The pleasant conditions will end on Monday though as medium range
guidance is very consistent in a strong upper level wave ejecting
off the Rockies and into the Plains. While there is agreement in the
overall synoptic setup, mesoscale details remain uncertain at this
time. Have left model blended PoPs due to this uncertainty. Severe
weather may also be possible but again, too much uncertainty to say
for sure at this time. Rain chances will continue through the middle
of next week along with near seasonal temperatures.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1032 PM CDT Wed May 1 2024

Although ceilings are remaining at VFR levels longer than
anticipated, expect MVFR/IFR conditions to advect in with
showers and thunderstorms from NE through the overnight hours.
Reduced visibility has been observed this evening with locally
brief and heavy rainfall. This looks most likely along and east
of I-29, especially over northwestern IA. Stratus with MVFR/IFR
ceilings continue through the early afternoon Thursday, with
widespread rainfall ending through the morning hours. However,
latest guidance this evening shows the potential for isolated
showers through Thursday afternoon, as well as patchy drizzle
with the low cloud deck. Have not included any afternoon showers
in the TAFs, as confidence in coverage is low at this time.

Winds increase overnight with gusts around 20-25 knots. Evening
model runs have backed off with the potential for LLWS across
northwestern IA as the LLJ increases; however, have continued to
include at KSUX through 02.09z as gusts have currently dropped
off. Wind direction varies through this forecast period, becoming
northwesterly to westerly by late Thursday morning/early Thursday
afternoon.

VFR conditions are currently expected to return by the end of
the period.

&&

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

&&

$$

DISCUSSION...Meyers
AVIATION...SG