Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 282031

Area Forecast Discussion
National Weather Service Sioux Falls SD
331 PM CDT Tue Mar 28 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 331 PM CDT Tue Mar 28 2017

Showers located over western SD this afternoon are expected to
remain mainly west of our CWA through the early evening. This in
part due to a dry easterly low level flow keeping moisture at bay.
Otherwise, a shortwave will eject northward out ahead of the large
upper level low over eastern NM/western TX overnight, leading to an
increasing chance of rain through the Missouri River Valley. Dry air
will remain entrenched back to the north and east, and tightened up
the pop gradient over those areas overnight. Skies will be cloudy
tonight, and temperatures will be milder with lows in the upper 30s
to lower 40s.

The aforementioned upper level low drifts into the Central Plains on
Wednesday. Strongest forcing, in the way of midlevel isentropic lift
and frontogenesis will be located across our southeast, so have
highest pops through the lower MO River Valley/northwestern IA/and
portions of our lower MN zones. Again, tightened up the pop gradient
back to the north and west where it looks like dry air will win out.
With the clouds and shower it will be generally cooler on Wednesday,
with highs in the upper 40s over northwestern IA to the mid 50s
through the Chamberlain to Huron corridor.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 331 PM CDT Tue Mar 28 2017

Upper and surface low pressure will continue to track across the
central plains Wednesday night and Thursday. The limiting
streamlines at 850-800mb pretty much tell the whole story by these
two periods. Weak high pressure develops north of this low in
Minnesota and noses back into our forecast area, therefore the
trajectory of the streamlines is fairly dry. The only hookup with
the central plains low encompasses our southeast zones in northwest
IA, with rapidly decreasing pops heading north and northwest of
there. Superblend pops displayed too broad of a gradient Wednesday
night and Thursday, so tightened the gradient from northwest to
southeast by following the ECMWF and GFS. Superblend was influenced
by the NAM which is likely a bit too far north with its QPF output
given the amount of dry air which is streaming into the lower layers
from the east. After non eventful lows Wednesday night, the
atmosphere mixes to about 900mb on Thursday producing highs of 45 to
50 along and east of I 29, and in the 50s west of I 29.

After that, we have a very persistent flow of east to southeast
winds in our area day after day with high pressure in the northern
MS valley and Great Lakes area, which is an extension of a very
large high pressure system over the Hudson Bay. The wind speeds are
not very strong either which will keep fire weather concerns muted
over the next several days at least. Another strong low tracks
across the central and southern plains once again this weekend,
which will produce chance pops mainly over northwest IA Saturday
afternoon through Sunday. The way it looks now, only light amounts
of rain are possible in our southeast zones because the trajectory
of the streamlines are not favorable for deep moisture.
Interestingly, this low then strengthens to the southeast of this
region and there is some agreement in that between the deterministic
solutions of the GFS and ECMWF. Therefore at this time, there is
decent chances of widespread light rainfall at the tail end of the
extended period next Tuesday. There is also agreement in chilly
850mb temperatures beyond the extended forecast later next week, so
something to watch for.

Friday onward, there will be a lot of 50s for highs. Next Tuesday,
there could be an error of being too warm if the aforementioned
strengthening low pans out which will drain down cold air from the
northeast, especially if it rains.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1145 AM CDT Tue Mar 28 2017

VFR conditions expected through this evening, then rain will
develop through the Missouri River corridor after 06z tonight.
Ceilings will lower into the MVFR range with this activity. Rain
chances will continue over that area through Wednesday afternoon.




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