136
FXUS63 KFSD 030812
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
312 AM CDT Fri May 3 2024

.KEY MESSAGES...

- Rain returns late this afternoon/evening and continues through
  Saturday morning. Rainfall amounts between a quarter to up to
  a half an inch are expected. Ponding on roads along with minor
  stream and river flooding are again possible.

- Dry through the weekend with temperatures at or just below
  normal for this time of year.

- A strong low pressure system looks to bring renewed storm
  chances and moderate to heavy rain on Monday but details
  remain uncertain as of now.

&&

.DISCUSSION...
Issued at 310 AM CDT Fri May 3 2024

Look for a quiet start to the day before a cold front/inverted
surface trough encroaches on the area by late afternoon/evening.
Although skies are clear very early this morning, clouds will
increase during the day as the system approaches. Warm air advection
overspreading the region will allow 850 temperatures to climb to 8-
10 degrees C over the southeastern CWA, and this will result in
highs climbing into the upper 60s to lower 70s over that area. Back
to the west where clouds will be increasing and warm air advection
is less pronounced on the back side of the inverted trough, highs
will only reach the upper 50s to near 60 from east central SD back
into south central SD. By late afternoon and early evening, a
shortwave lifts into the area in a southwesterly upper level flow,
as the inverted trough/frontal boundary begins to push to the east.
Models indicate strong mid/low level frontogenesis developing
through central SD during this time frame - with upper level lift
increasing as a jet streak streams from west/central SD into MN.
With that, a band of rain will develop in our far west around 22Z,
then move eastward across the CWA during the overnight period.
Models indicate any significant instability remaining bottled up
over NE, so precipitation should be primarily in the form of rain,
with only a low chance of isolated lightning strikes. Latest
guidance would suggest rainfall amounts of a quarter to half an inch
across the area through early Saturday morning.

The majority of the CAMs have the band of rain to the east of our
CWA by 12Z on Saturday morning. With the departure of this system,
we look on track for a dry weekend as surface high pressure settles
into the Northern Plains. The 850 mb thermal trough drops across the
area on Saturday, and with cold air advection highs will fall back
to the lower to mid 60s. By Sunday the surface ridge shifts into the
Mississippi Valley, and in a returning southerly flow, temperatures
will warm into the the mid and upper 60s.

Our next significant chance of rain comes into the forecast for the
beginning of next week. Models continue to indicate a strong upper
level low ejecting out of the Rockies and into the Northern/Central
Plains by Monday. Still seeing model differences with regard to the
evolution of this low, with the GFS/Canadian swinging the low into
the Central Plains initially, then into the Northern Plains by
Tuesday. The ECMWF offers a more northerly solution, taking the low
directly into the Northern Plains on Monday - so there does remain
some uncertainty in the details. While there will be the potential
for thunderstorms with the system, confidence in severe chances is
low. Both the GEFS/GEPS ensembles indicate moderate probabilities (40-
50%) of CAPE exceeding 1000 J/KG on Monday afternoon, though the ENS
ensembles indicate only a 10-20% - again a reflection of differences
in how the system evolves. As mentioned in the previous discussion,
CIPS analogs do have low probabilities of severe storms in our area -
the higher potential definitely remains to the south of our area -
through the Central and Southern Plains. What does look more certain
is the potential for at least moderate rain, with ensembles showing
a 80-90% probability of at least a quarter inch of rain for the
period Monday into Tuesday - and even a 40-50% probability of
receiving at least a half an inch during the same time frame.

Models indicate the upper level low remaining stagnant and rotating
over the Northern Plains, albeit weakening, through the middle and
end of next week. This will keep at least some chance of showers
over our area through the period. Temperatures look to be just
either side of normal.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1043 PM CDT Thu May 2 2024

Latest observations across the region show mostly clear skies and
light winds. Should see VFR conditions prevail for much of the
period, with southwesterly winds forecast to gradually shift
northwesterly during the afternoon/evening in the wake of an
advancing cold front. As alluded to in the previous discussion, this
front is expected to bring showers back to our area, which may
result in brief periods of reduced vsbys/cigs toward the later half
of the TAF cycle. Gusts up to 20 MPH may also be possible with
FROPA.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...SST