Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 202044

Area Forecast Discussion
National Weather Service Sioux Falls SD
344 PM CDT TUE SEP 20 2016

.SHORT TERM...(This evening through Wednesday)
Issued at 344 PM CDT Tue Sep 20 2016

Early this afternoon, a weakly organized sfc low over south central
SD will continue to drift slowly southeast as a warm frontal
boundary is beginning to take shape across the northern and
northeastern portions of the CWA. The minor shortwave which brought
scattered thunderstorms to the area this morning has shifted
eastward into eastern Minnesota and western Wisconsin. The primary
concerns in the short term will be convective redevelopment later
this evening and into the overnight hours.

This Evening and Overnight: Models suggesting the LLJ should begin
to increase fairly quickly this evening, with isentropic lift along
the 310K sfc suggesting that showers and thunderstorms may break out
along the Buffalo Ridge by or likely after 03z.   With the LLJ
veering rather quickly tonight, most of the low level convergence
should begin to focus well east of the CWA after midnight. That
said, as we`ve seen in the past, couldn`t rule out an isolated
shower forming further west along the I-90 corridor.

Wednesday: With the warm front settling near or just south of the
Interstate 90 corridor, and the surge of increased low level
moisture, would not be surprised to see stratus/fog or even minor
drizzle form along and north of the boundary into the mid-morning
hours of Wednesday.

Models are in a bit of disagreement in the timing of the initial
wave of energy lifting northeast into the CWA by the afternoon. The
broad consensus is that is that elevated thunderstorms may begin to
develop by mid-late afternoon north of the frontal boundary, with
the warm sector remaining subtly capped.  North of the boundary,
there will be upwards of 1000 J/KG CAPE, and while shear is
marginal, couldn`t rule out a strong storm. However the highest rain
chances won`t arrive until the evening.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 344 PM CDT Tue Sep 20 2016

Active forecast to begin the long term with remnants of tropical
storm Paine lifting toward the region.  Warm front is expected
remain in the neighborhood, but may shift slightly east extending
from approximately from Vermillion to Windom tomorrow evening.  PWAT
values ahead of the front are in the vicinity of 1.5 in, which is
above the 90 percent moving average. Shortwaves are expected to
train across the region from the southwest to the northeast from
late afternoon Wednesday through mid day Thursday.  SB CAPE values
are initially in the 1500-2000 j/kg range and 0-6 km bulk shear is
around 30 knots. Can`t rule out a severe storm or two, but the main
issue will be the potential for flooding with primed environment.
Went ahead and issued a Flash Flood Watch for northwest Iowa into
southwest Minnesota.  It is possible this watch may need to be
expanded slightly depending on the location of the front; however,
12z GFS/ECMWF suggested that the front may try to shift further
south and east than previous runs indicated.

Have some brief upper level ridging that develops on Thursday ahead
of a large upper level trough that develops across the west.  The
trough appears to be composed of two phased waves, one of which
becomes orphaned across the dessert southwest while the other lifts
north through the weekend across the Northern Plains.  Much of the
upper level forcing appears to be focused north of the forecast
area, but still could see some periodic rounds of storms with weakly
capped environment and lingering front remaining around the area.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1221 PM CDT Tue Sep 20 2016

VFR conditions expected into the overnight hours. Will monitor
for mid-lvl cloud development by this evening, with showers and
thunderstorms forming east of I-29 towards and after midnight.

With a frontal boundary sagging near the I-90 corridor by
daybreak, we`ll also watch for the potential development of MVFR
or lower stratus/fog, especially for the HON/FSD terminals.

If stratus/fog develops, it will likely linger into the morning


.FSD Watches/Warnings/Advisories...
MN...Flash Flood Watch from Wednesday evening through Thursday
     evening for MNZ081-089-090.

IA...Flash Flood Watch from Wednesday evening through Thursday
     evening for IAZ001>003-012>014-020>022-031-032.



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