Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 251654

Area Forecast Discussion
National Weather Service Sioux Falls SD
1154 AM CDT Tue Apr 25 2017

.SHORT TERM...(Today and Tonight)
Issued at 420 AM CDT Tue Apr 25 2017

More challenging short term forecast today than the past few days,
with cooler temperatures, increasing rain chances, and potentially
some light mixed precipitation toward the latter part of the period

Early morning temperatures already a bit cooler than anticipated in
some locations, with leading band of mid-level based rain lifting
through eastern Nebraska toward the Missouri River. Lower levels
initially on the dry side, and this leading band may diminish some
as it lifts north. However, increasing lift from approaching wave,
with secondary band of showers developing near I-80, should serve to
enhance saturation, and models in fairly good agreement in showing
this southern rain band expanding in response to increasing 700mb
frontogenesis, and moving into our far southern counties by 12Z or
shortly after. This appears to become primary focus throughout the
day, as the mid-level boundary stalls across the southeast half of
the forecast area. Will continue to focus categorical pops in this
area, with potential rainfall in excess of a half inch through 00Z.
Lesser chance for rain across the western CWA, but should see at
least isolated to scattered showers as upper trough slides east
through the Dakotas, but amounts should be much lighter.

As far as temperatures today, do not expect them to climb too far
from where they are to start the day, with only a 3-5F diurnal range
expected for most areas. Much of this climb should occur during the
morning, with readings leveling off or falling back a bit as the
rain spreads in.

Mid level front weakens and shifts out of the eastern CWA by late in
the evening, taking the more persistent rainfall with it. Lingering
mid-upper trough will keep a chance of spotty light precipitation
around through much of the night, though, with the latter half of
the night bringing some uncertainty regarding precipitation type.
Deeper cool air pushes southward into the area, mainly near and west
of I-29, with surface temperatures falling into the lower-mid 30s.
Thermal profile largely supportive of some very light snow, except
that some model soundings depict drying in the mid-levels which
could cut off the introduction of ice into the deep stratus layer.
Given uncertainty regarding how much precipitation will still be
around in our western counties after 06Z, opted to keep potential
for some light snow mixing in. However, if the mid-levels do dry out
sufficiently, could be looking at more of a drizzle/freezing drizzle
scenario, and next shift will want to examine this in more detail.

.LONG TERM...(Wednesday through Monday)
Issued at 420 AM CDT Tue Apr 25 2017

On Wednesday the main upper level trough slides across the region
during the day. The better lift with the system, located across the
eastern portions of the CWA in the morning, translates to the
northeast through the day with precipitation following suit.
Thermal/moisture profiles will support the possibility of some mixed
precipitation or drizzle along the western edges of the
precipitation shield in the morning, which would include areas
generally west of Interstate 29. Only minor precipitation amounts at
that point as the precipitation ends, so not expecting much in the
way of accumulation. With cold air advection and only slowly
decreasing clouds in the afternoon, it will be a cold day, with
highs upper 30s through east central SD and southwestern MN, to mid
40s through the MO River corridor. It will be a windy day with
northwesterly winds of 15 to 20 kts.

Clouds will continue to decrease west on Wednesday night, though
will probably remaining mostly cloudy in our northeast where there
may remain enough moisture and lift to produce some sprinkles or
flurries overnight. Winds will be diminishing, and temperatures will
drop below freezing over most areas, with upper 20s possible from
south central SD into east central SD. Thursday looks to dry out as
weak high pressure builds into the region. With a little more sun
highs will climb into the upper 40s to mid 50s.

With the departure of the midweek system, a long wave upper level
trough will dominate across much of the CONUS for the end of the
week, with a more amplified upper level pattern developing by the
weekend as energy over the Pacific dives dives southeastward and
carves out a deep trough over the central CONUS by Sunday. What this
means for our area is below normal temperatures into the beginning
of next week. While it appears to be a fairly wet period, confidence
in precipitation timing and placement remains low with model
differences. A little more model consensus for precipitation exists
for Saturday and Sunday, so that may be our best chance in the
long term.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1153 AM CDT Tue Apr 25 2017

Widespread IFR and occasional MVFR ceilings are expected through
tomorrow morning. There will be some improvement tomorrow morning
from west to east from central into eastern SD. Rain will also be
likely across much of the area through the evening hours with some
mix of snow or sleet possible around KHON.




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