Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 122250
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
550 PM CDT Tue Mar 12 2024

.KEY MESSAGES...

- Above normal temperatures and low humidity continue into
  Wednesday, but lower winds reduce fire danger risks.

- Rain risks Wednesday night through Thursday remain uncertain,
  but trends today support lowered risks and potential amounts.

- Confidence continues to grow that we`ll see a couple of days
  of below normal temperatures Sunday and Monday.

&&

.DISCUSSION...
Issued at 229 PM CDT Tue Mar 12 2024

THIS AFTERNOON:  A chamber of commerce day across the region as
temperatures continue to rise through the 60s, winds remain light,
and we have plenty of sunshine.  Only drawback are the critically
low relative humidity values that have again fallen into the teens
to 20 percent range. However, given the light winds and
reasonable mixing heights, fire weather conditions remain
favorable in most areas.

TONIGHT:  A large plume of cirrus is expected to spill east of the
Rockies later this evening and continue to move into MN/IA after
midnight.  This cirrus may provide some blanket to overnight low
temperatures, but even utilizing some of the bias-corrected data
still suggests lows above freezing.

WEDNESDAY:  There`s been a lot of discussion about the upcoming rain
risks for the second half of the work week.  An upper trough
continues to move into the West Coast today,  with energy digging
into the Four Corners on Wednesday.  Increasing southwest mid-lvl
flow will lead to an increase in mid-lvl clouds through the day on
Wednesday.  However it`s likely that with any wind, temperatures
will climb into the 60s.  The residual low-lvl dry air will lead to
lowering afternoon dew points slightly in most areas.

WEDNESDAY NIGHT-THURSDAY:  Once again, there have been substancial
shifts in the deterministic and ensemble guidance over the past 24
hours. Latest guidance continue to indicate the upper trough digs
just a bit further southwest, southeastern ridging is slightly
weaker, northern stream steering trough is slightly faster and
stronger.  This results in the wave that is ejected into the Plains
late Wednesday potentially taking a bit more of an easterly track
before pivoting northeast. Also, the slight eastward shift of
the low-lvl moisture transport may signal less moisture within
the elevated frontal zone. Both the GFS/EC ensemble
probabilities have come more into alignment keeping the highest
probabilities of >0.10" of QPF (70-90%) across northeast
Nebraska into northwest and into central Iowa, and shifting the
highest probabilities of 0.50" (50-60%) southeast of a Sioux
City to Storm Lake line. However, there remains at least a third
of both ensemble solutions suggesting that a more northwest
track (and deeper wave) solution could still be possible. ECM
plume data suggests a large QPF range for Sioux Falls (0-1.25",
but much more clustering below 0.10"). The spread for Sioux City
is slightly higher (0-1.75"), but there is also a high
distribution of ensemble members between 0.10-1.0" suggesting
that meaningful rain may still be possible in NW Iowa areas.
However it is becoming more apparent that a SW to NE oriented
low-lvl trough through Kansas into Iowa should allow for a sharp
northern QPF cutoff.

All that said, very broad warm advection and weak dPVA could result
in widely scattered showers developing by Wednesday evening, though
low-lvl dry air may limit what reaches the ground.   As the primary
lobe of vorticity arrives early Thursday, rain may become a bit more
pronounced and focused in areas south of I-90 and especially
towards Highway 20 on Thursday as low- lvl frontogenesis
increases. The area of rain may also tighten significantly,
meaning a larger portion of the forecast area may remain dry.
Meanwhile as the surface low moves into southern Iowa on
Thursday, we should see steady increases in the SPG and
resultant increase in sustained winds through the day. Low-lvl
flow northeast flow of 35-40 knots should mix-down to increase
overall gust potential over 30 knots at times into Thursday
evening. Generally though, as the surface low tracks further
southeast, and upper wave doesn`t deepen as further, winds may
trend lower in future forecasts.


FRIDAY: The upper wave pulls away quickly Thursday night, with high
pressure sliding through the Plains by Friday. A secondary northern
stream trough quickly races through the Northern Plains on Friday,
pulling warm advection eastward, leading to an increase in westerly
surface flow, and resulting in temperatures warming back towards the
50s.

SATURDAY-MONDAY: Medium range models and ensembles support a larger
trough dropping southward out of Canada and into the Great Lakes
this upcoming weekend. The biggest question will be when a cold
front will pass through on Saturday and how warm the afternoon will
end up with as cold advection aloft intensifies.  A series of waves
will travel around the backside of the larger trough into early next
week bringing reinforcing shots of cold air. Temperatures
Sunday and Monday remain in the 30s to lower 40s, with ensemble
data suggesting at least some probabilities (20-40%) that we may
struggle to reach 32 in a few areas.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 549 PM CDT Tue Mar 12 2024

VFR conditions are expected for the TAF period. Light easterly winds
will persist for the entire TAF period with speeds up to 5-10 knots.
Cloud cover will slowly increase through the day tomorrow but
ceilings remain well into VFR levels to end the TAF period.

&&

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

&&

$$

DISCUSSION...Dux
AVIATION...Meyers


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