Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 120916
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
416 AM CDT Tue Mar 12 2024

.KEY MESSAGES...

- Very warm temperatures (20-30 degF above normal) will continue
  today, dropping to be 15-25 degF above normal on Wednesday.

- Consistent storm track continues to show to higher probabilities
  of rain (as high as 80%) late Wednesday into Thursday, and
  meaningful rain potential. There remains considerable spread in
  where the highest rainfall amounts will fall.

- Cooler temperatures and breezy conditions are expected for the
  weekend, with highs closer to seasonal normals.

&&

.DISCUSSION...
Issued at 415 AM CDT Tue Mar 12 2024

Early morning satellite imagery shows some cirrus clouds aloft out
ahead of a weak and dry shortwave as it moves towards the region. At
the surface, temperatures behind the departing cold front and
approaching surface high pressure have dropped into the 30s and 40s.
As the surface high begins to move into our northern fringes, can`t
rule out a few locations in central and east central South Dakota
dipping down into the 20s, but as warm air remains aloft we`ll warm
up into the mid 50s by the late morning hours. In fact, ensemble
situational awareness tables (ESATs) show that temperatures at 850mb
continues to be just above the 90th percentile of climatology. While
winds will remain weak below the lowest 8000 feet, we will have no
problem mixing up to 850mb, allowing for those warm temperatures to
be brought down to the surface resulting in temperatures back up
into the mid 60s and lower 70s.

As the aforementioned shortwave and surface low move by to our south
as they travel eastwards, our next trough is strengthening over the
western CONUS, with leeside cyclogenesis creating a new surface low
over western CO/NM. As the surface low strengthens, the inverted
surface trough will extend up into the northern plains, though there
are is some uncertainty on just how far north and east it gets. The
further north it gets will bring warmer temperatures along with it,
and the further east it ends up will dictate how far west the
warmest air will be able to get. While winds aren`t looking to be
more than breezy with gusts into the lower 20s, the further east the
inverted surface trough the further east the strongest winds will
be. The NBM currently has this trough reaching up into the Mitchell,
SD area, so have left that unchanged given the uncertainty in exact
placement, but don`t be surprised  if temperatures end up
warmer/cooler based on the above discussion.

Throughout the morning and afternoon hours, the jet will eject onto
the central plains, sending the surface low northeastwards and up
towards the IA/NE/KS border. As warm-air advection (WAA) and
shortwaves aloft move overhead, chances for rain will begin from
southwest to northeast during the late afternoon hours into the
evening. As the surface low reaches the central plains, ample lift
from shortwaves, WAA, along with being in the left exit region of
the upper level jet, will lead to the majority of the precipitation
expected to fall overnight and continuing throughout the day time
hours on Thursday. Precipitation will be focused largely on and
southeast of the 850-700mb front, which is expected to be draped
from Windom, MN to Sioux Falls, SD and down towards Tyndall, SD.
Areas northwest of that line will likely see a sharp cut-off on the
highest rainfall amounts, but should still see amounts from a tenth
up to 3/4 of an inch. As there is some instability to work with
along and southeast of the 850-700mb front, rainfall totals are
expected to be higher ranging from 3/4 of an inch and up towards
1.25". Current forecast aligns fairly well with the GEFS mean QPF,
while the ECM solution is on the lighter side, reducing amounts by
roughly 25%. Ensemble clusters don`t offer much help trying to find
the most favored solution, as the four clusters share 30/26/22/22
percent of the members respectively. In addition to the rain
chances, the close proximity of the surface low will tighten our
surface pressure gradient, resulting in breezy winds gusting 35 to
possibly 45 mph before decreasing during the evening hours.

As the surface low is pushed eastwards starting Thursday evening as
the trough axis moves towards the area, a surface high is expected
to move down bringing cooler air along with it. This will bring some
low chances for snow as the system exits our area, mainly late
Thursday evening into the overnight hours on Friday, but with
temperatures in the mid 30s little to no accumulations are expected.
As the surface high slides down to off to our southwest, cooler
temperatures are expected to remain across the region with highs in
the upper 40s to lower 50s. Flow aloft remains active into the
weekend as north-northwesterly flow looks to set up, with a dry cold
front moving through on Saturday resulting in breezy northwesterly
winds. Cold air lags behind, but is brought down overnight into
Sunday, with highs on Sunday in the 30s and 40s.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1046 PM CDT Mon Mar 11 2024

VFR conditions are expected for the TAF period. The low level jet
(LLJ) has begun to strengthen this evening and is bringing low level
wind shear (LLWS) to parts of northwest Iowa, including to KSUX. The
LLJ will wane through the overnight hours and end the LLWS. A cold
front continues to push through the area late this evening and will
turn the surface winds to out of the northwest for the overnight
hours. Winds will turn out of the east/northeast for the day
tomorrow and will remain light at 5-10 knots. These light winds will
finish out the TAF period.

&&

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

&&

$$

DISCUSSION...APT
AVIATION...Meyers


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