Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 131127
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
627 AM CDT Wed Mar 13 2024

.KEY MESSAGES...

- Another nice and warm day for today with temperatures running
  15-25 degF above normal.

- Chances for rain Wednesday night through Thursday continue to
  shift southeastwards, highest chances (80+%) for measurable
  precipitation occurring across northeast NE and northwest IA.

- Cooler temperatures and breezy conditions are expected for
  the weekend, with highs at or below seasonal normals Sunday
  and Monday.

&&

.DISCUSSION...
Issued at 414 AM CDT Wed Mar 13 2024

3 AM satellite imagery shows ample cirrus clouds moving overhead,
with surface temperatures in the mid 30s to mid 40s. The cirrus
clouds are a result of upper level moisture moving across the region
out ahead of a soon to be ejecting upper level wave, with the
associated surface low pressure currently forming in SE CO. As the
jet streak begins to round the base of the trough during the morning
hours, the inverted surface trough will be extending up into a weak
surface low pressure currently residing in our western counties.
This will act as a focus area for warm-air advection (WAA), and
combined with temperatures at 850mb remaining just about the 90th
percentile of climatology (per the ensemble situational awareness
tables(ESATs)), we are looking at another rather pleasant day with
temperatures in the mid to upper 60s. Winds throughout the boundary
layer look to remain on the weaker side, though a few gusts into the
upper teens can`t be ruled out. So, while we are again expecting
minimum relative humidity values in the mid 20s to lower 30s, fire
danger will be confined to the moderate and high category, largely
due to our dry antecedent conditions.

By the afternoon hours, the jet will eject onto the central plains,
though as the previous discussion mentioned, the upper level jet is
now oriented more east-northeasterly rather than the previously
expected north-northeasterly direction. For us, this shifted the 850-
700mb front southeastwards, now expected to reside from Windom, MN
and down towards the Sioux City, IA area. So, while areas northwest
of the aforementioned line will still have a chance for seeing some
rain, probabilities for a tenth of an inch are in the 60-80% range
under the front, dropping to 20-30% range for areas along and near
the highway 18 corridor. This is due to the 850-700mb front keeping
moisture from traveling further northwestward, and as the high
resolution models show us, will likely result in waves of rather
weak showers starting to move across the area later this evening
into the overnight hours as weak forcing moves through.

Areas along and southeast of the front have much better chances for
rain, with the ESATs showing precipitable water values approaching
3/4 of an inch, which is above the 90th percentile of climatology.
As the surface low moves towards the region overnight into the
morning hours, isentropic lift and positive vorticity advection
(PVA) from the main shortwave should result in a couple hours of
light to moderate rainfall. In addition, while most models show
instability has similarly shifted southeastwards, the HREF mean
shows 100 J/KG of CAPE remains across the area, which will further
act to create locally higher rainfall totals. Probabilities for this
region for a quarter inch are in the 60-80% range, probabilities for
half an inch in the 50-70% range, dropping down into the 20-30%
chance for an inch of rain.

As chances for rain start to dwindle Thursday morning for areas in
central South Dakota, this is when the highest rainfall totals are
expected for areas along and southeast of a line from Sioux City, IA
and up towards Windom, MN. As the proximity to the surface low has
increased, the previously expected stronger winds have come in
weaker, and now look to remain confined into the 25-35 mph range.
Winds and rainfall chances decrease throughout the afternoon hours
as the low moves off to the east, with northerly winds starting to
bring in some cooler temperatures as a surface high moves
southwards. By early morning Friday, temperatures in the upper 20s
to lower 30s are expected.

As the surface high slides off to our southwest by Friday morning,
cooler temperatures are expected to remain across the region with
highs in the lower to mid 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 morning 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,
bumping up slightly into the 40s by Monday. As ridging forms again
out west, warmer temperatures look to work their way back into the
region by middle of next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 627 AM CDT Wed Mar 13 2024

VFR expected at least through the early evening hours, likely into
the early overnight hours. After starting with light and variable
winds this morning, expect a few more wind shifts throughout the TAF
period, with south-southwesterly winds this morning becoming
northerly through the evening hours. Scattered showers will become
possible throughout the afternoon hours for those along the SD/NE
border, but better chances for scattered showers arrive overnight
into Thursday, with best chances across northwestern Iowa. MVFR cigs
and visby`s look to remain confined to the Storm Lake, Cherokee, Ida
Grove area.

&&

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

&&

$$

DISCUSSION...APT
AVIATION...APT


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