Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 231115

Area Forecast Discussion
National Weather Service Sioux Falls SD
615 AM CDT Mon Apr 23 2018

.SHORT TERM...(Today and Tonight)
Issued at 345 AM CDT Mon Apr 23 2018

Focus for today, and really much of this forecast period, will be on
temperatures. Still some decent snow cover in the higher elevations
of southwest Minnesota, and possibly a bit lingering between the
James and Missouri River Valleys, based on visible satellite imagery
yesterday afternoon. While effects of this will be diminishing, will
still hold highs today a few degrees shy of full potential in these
areas. Elsewhere, favored highs toward the higher end of guidance as
we have been trending warmer than forecast in areas where the snow
has fully melted and the ground is likely starting to dry out.
Fortunately, not much wind today with the weak surface ridge still
in the vicinity, so fire danger should be moderate at most.

Tonight will bring increasing clouds from west to east, with an area
of showers spreading into areas mainly west of the James River after
06Z, as an upper trough and associated cool front drop southeast
through the northern Plains. Temperatures will generally remain on
the mild side with lows in the 40s in advance of the front, though
eastern areas may see enough influence from the departing surface
ridge that temperatures could drop into the mid-upper 30s.

.LONG TERM...(Tuesday through Sunday)
Issued at 345 AM CDT Mon Apr 23 2018

Tuesday will be the coolest and wettest day of the forecast period,
especially for western portions of the forecast area, where rainfall
amounts of 0.25-0.50 inch or more will be possible late tonight into
Tuesday evening as a fairly tight mid-upper level circulation drops
south-southeast across areas west of I-29. Fortunately, we finally
seem to be in a springtime temperature regime, so the air mass looks
to remain warm enough to keep any potential for snow at bay. The
wave shifts into Nebraska early Tuesday evening, which should bring
a quick end to precipitation across our area after 00Z. Timing of
the front on Tuesday, along with the more widespread rain potential,
will limit the diurnal range to just a few degrees in our west on
Tuesday, with highs in the upper 40s-lower 50s there while southeast
areas should be able to again achieve lower 60s by early afternoon
before cold advection takes over.

Another weak wave could bring some spotty showers to the area on
Thursday, but otherwise the focus from the middle of the week into
next weekend will be on temperatures. Should temperatures hold on
the cool side of late-April normals through the remainder of the
work week, warmer Wednesday ahead of this next wave, followed by
slight cooling Thursday, and warming again on Friday.

The temperatures become more challenging by next weekend, as our
consensus blend is suffering from the inclusion of bias-corrected
grids which are still influenced heavily by the very cold start to
April in this region. Model pattern suggests a good potential for
above normal temperatures to close out April, with an upper ridge
building over the region, and an increasing southerly flow that will
help draw warmer air northward. Thus have nudged high temperatures
for the coming weekend upward toward a consensus of raw model temps
that does not include any bias-correction. This adjustment may still
end up too cool given the projected low-level model temperatures,
but it will at least start the trend in the positive direction.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 615 AM CDT Mon Apr 23 2018

VFR conditions will dominate through most of this period, though
patchy/shallow fog may be found in low lying areas through 13Z-14Z.
Thickening mid level clouds will spread into the region from the
west tonight, with ceilings lowering into the lower VFR-MVFR range
in areas west of the James River late in the period as rain moves
across central South Dakota.




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