Scientific Forecaster Discussion
fxus63 kfsd 240331
Area forecast discussion
National Weather Service Sioux Falls South Dakota
1031 PM CDT Tue may 23 2017
Short term...(this evening through wednesday)
issued at 258 PM CDT Tue may 23 2017
A weak shortwave embedded within a broad positive-tilt trough across
the upper Mississippi Valley will continue to shift south-southeast
this evening. This weak system will continue to bring scattered
light rain showers into late this evening. Quantitative precipitation forecast amounts will remain
on the light side, with just a tenth of an inch or less through
As the trough moves out of the cwa, skies will slowly start to clear
out from west to east. This will result in a mild night across the
region. Leaned toward the mosguidance for low temperatures tonight,
where areas west of the James River could see temperatures in the
upper 30s. Areas east of the James River will have temperatures in
the lower 40s. With decreasing cloud cover from west to east, and
light winds, patchy frost will be possible along and east of a line
from Lake Andes to Plankinton to Huron area.
Low clouds/stratus will stick around mostly east of the James River,
at least, through late Wednesday morning. Otherwise, an upper ridge
will begin to settle across the area, bringing a pleasant day with
mostly sunny skies and light winds on Wednesday. Highs will be from
the lower 60s across southwest Minnesota, to upper 60s across
southeast South Dakota.
Long term...(wednesday night through tuesday)
issued at 258 PM CDT Tue may 23 2017
A ridge of high pressure will quickly exit east on Wednesday evening
and will allow southerly flow to develop across the area overnight.
This will bring warmer lows with mid 40s in northwest Iowa and 50 to
55 in south central South Dakota.
Warmer air aloft will spread through very late Wednesday night
through early afternoon on Thursday. This may allow a few very
elevated showers to develop but at this time the lapse rates are
marginal and moisture is a bit marginal so the chances will remain
at 20 percent or lower. Otherwise temperatures will be warmer,
especially along and west of the James Valley where a weak trough of
low pressure should turn winds around to the west and northwest
which will allow for enhanced mixing. Will aim for highs in the 70s.
Troughiness aloft poised to settle into the northern plains again
this weekend into early next week. The models are a bit inconsistent
with this energy as the GFS has been more consistently deepening low
pressure aloft in Minnesota towards the Great Lakes on Sunday while the
Canadian and European model (ecmwf) are more open and only indicate some deepening
late in the period north of the Great Lakes. Still a little too
early to tell if the GFS is overdoing the deepening so for now will
just lean a bit against it. One of the bigger differences would be
much warmer highs on Sunday if the European model (ecmwf)/Canadian solution pans out.
For now can't really fight what guidance has handed ME which is
highs 65 to 75 and lows 45 to 55. As for pops we have entered the
time of year where it is tough to be too confident both on the low
side of pops and the high side of pops as skiddish convection and
timing differences cause problems. Until we have a better feel for
which pattern will evolve more closely there really is not a time
frame that looks better than any other Saturday through Tuesday.
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1026 PM CDT Tue may 23 2017
There will be the possibility of MVFR stratus developing in areas
from near the Interstate 29 corridor and eastward after 10z. If
low clouds develop, they will scatter out by mid morning on
Wednesday. Light northwesterly winds overnight will transition to
northeasterly on Wednesday, then southeasterly by Wednesday
afternoon and evening.