Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 182308

Area Forecast Discussion
National Weather Service Sioux Falls SD
608 PM CDT Tue Apr 18 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 241 PM CDT Tue Apr 18 2017

Latest water vapor loops show the nice, compact wave that brought
showers and thunderstorms to the area moving east. The next wave/s
of interest were moving into the four corners region early this
afternoon and are expected to bring another round of showers and
thunderstorms to the area.Late afternoon into the evening however
should see nothing more than increasing clouds and mild temperatures
as winds gradually turn from the north to the east by late tonight.
This will drag in a little dry air in the 925mb to 850mb layer which
might hold off shower and thunderstorm activity for a little while,
but with the strength of the wave expect any developmental issues to
be overcome.

First off the right entrance region of the upper jet will move from
the central Rockies into North Dakota late tonight into Wednesday
morning. This is expected to allow a mid level band of rain to
develop in southern and central SD after about 6z and shift north
through Wednesday morning. The band does not appear to have much if
any instability to work with, and with the drier air in the 925mb to
850mb layer intruding to the region, may have a little more trouble
getting rainfall to develop. Still expecting a very good chance from
about Chamberlain to Brookings north with this band from 6z-15z, but
to the south of there precipitation may struggle.

Late tonight, likely 9z or so, the southern branch of the upper
level jet will spread into Nebraska and will interact with a strong
low to mid level boundary. At this time the surface to about 850mb
layer looks, but we should see development of showers and
thunderstorms in about the 800mb-750mb layer where enough CAPE
exists, about 500-1000 J/kg. Expect this area of showers and
thunderstorms, not expected to be severe, to lift off to the
northeast through the day wit the main wave and dry punch aloft
shifting into the area in the afternoon. This dry punch and slightly
cooler air aloft, as well as potentially much cooler if saturated,
might allow development closer to the 925mb boundary. If this can
happen there could be a few strong to severe storms south of a Dixon
Neb to Spencer IA line. With about 1500 J/kg CAPE and 40 knots of
bulk shear an isolated storm could produce golf ball sized hail. A
lot will depend upon how far north the near surface warm sector can
shift north.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 241 PM CDT Tue Apr 18 2017

Wednesday night will see showers and thunderstorms shift east with
only a very small chance for showers in southwest MN early Thursday
morning. Thursday through Sunday continues to look dry and seasonal
with lows 35 to 45 and highs 55 to 65 as a broad trough of low
pressure spreads across the area and keeps the strongest jet energy
to the south. If there were a morning with a chance for a little
frost it would be Saturday morning as a ridge of high pressure
settles into MN and eastern SD.

Monday into Tuesday brings back the potential for a busier pattern
with the chance for showers and possibly thunderstorms both days.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 602 PM CDT Tue Apr 18 2017

MVFR ceilings will continue to affect locales through the Highway
14 corridor into the evening. Otherwise, showers and isolated
thunderstorms with lowering ceilings will develop over south
central SD after 09Z tonight, then spread eastward through the
morning hours of Wednesday.




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