154
FXUS63 KFSD 261120
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
620 AM CDT Fri May 26 2017

.SHORT TERM...(Today and Tonight)
Issued at 353 AM CDT Fri May 26 2017

Weak frontal boundary draped near the I-29 corridor will continue to
track east this morning. Winds will likewise shift to the northwest
and increase to around 10 to 20 mph behind the front. Watching a
pair of mid level shortwaves impacting the region today. The first
is quickly shifting east through western Iowa through the next few
hours, with a few isolated high based rain showers possible through
shortly after daybreak. It is likely that very little of this
activity, if any, will reach the surface. A second mid level trough
trailing the surface front will ride along the Nebraska and South
Dakota border through around midday. Again, low level moisture is
quite limited, with mainly just some high based clouds tracking
through the area this morning. HRRR and RAP paint a narrow band of
scattered weak showers tracking east through southeast South Dakota
this morning before dissipating near the South Dakota and Iowa
border around noon. Did boost pops to just below mentionable levels,
but expect mainly virga.

Mid and high clouds will clear out by midday with surface high
pressure arriving. With ample afternoon sunshine and decent mixing,
temperatures will be quite pleasant. Followed the BCCONSMOS guidance
with highs in the 70s.

Tonight, we start seeing some mid level frontogenesis nose into
south central SD and north central Nebraska late. Mid and high
clouds again increase from the west, with additional high based
showers developing mainly west of the James River late tonight.
Forecast soundings suggest there will not be enough instability for
thunder mention.

.LONG TERM...(Saturday through Thursday)
Issued at 353 AM CDT Fri May 26 2017

Saturday seems to be trending toward a somewhat higher precipitation
threat as jet dynamics appear fairly favorable around closed upper-
level low moving north of the International Border. More favorable
thermodynamic fields bottled up closer to I-80. Despite this,
northern edge of MCS along with a bit of elevated thunder could
creep fairly close to the KSUX area during the morning, and further
north the strong jet entrance region interacting with mid-level
frontal feature will likely spread a band of lighter precipitation
from south central toward east central and southeast South Dakota.
This latter area will struggle somewhat with drier air toward lower
levels heading toward southwest MN, but should still see as least
some isolated to scattered light showers/sprinkles push into
southwest MN as main precipitation threat focuses mainly across
northwest Iowa in the afternoon and very early evening.  Possible
that with enough clearing behind precipitation area and with
westerly flow taking hold, some slightly warmer air will push into
lower Brule to mid James River valley locations late day, but
generally should see highs vary from upper 60s to lower 70s.

Frontal zone sweeping southward as strong lobe wraps across
northern Minnesota during Saturday evening could spread a few
showers and perhaps even a rumble of early evening thunder north of
the area, but mainly a small shower threat as diurnal cycle weakens
any activity into the Highway 14 corridor. Otherwise, will see winds
shift from west and southwest to a more brisk northwest by later
night at least as far south as a bit past I-90.

Sunday will start out with some sunshine, but winds will rapidly
increase and become gusty from the northwest. With the diurnal
heating and deeper cyclonic vortex east, should eventually be able
to overcome subsidence forcing during the morning hours to generate
a few afternoon pop-up showers. While not high on the likelihood
scale, the potential deeper cloud depth to around -20C means a small
chance for a few of the diurnal showers Sunday afternoon to yield a
rogue lightning strike or two as temps reach 70 to 75. Continued
influence of the cyclonic pattern over the northern plains on
Monday, but a little less potential for developing deeper MLCAPE
profiles suggest more in the way of just a few showers, and brisk
northwest winds again ushering in just a little bit cooler air for
early week, mainly mid 60s to lower 70s.

Differences in ECMWF and GFS in that ECMWF pulls a stronger wave
around the vortex through Minnesota on Tuesday and delays the exit
of the feature by at least a day over the GFS, which shears that
impulse more eastward toward the Great Lakes.  At this point, did
not alter any of the minimal precipitation chances from Wednesday
into Thursday, but would generally be much less prevalent in ECMWF
solution type which suppressed the main synoptic boundary southward
through the period vs. the GFS which allows return of instability
boundary northward around later Wednesday and Thursday, although
most of the ensembles would be not so much in favor of that trend.
Temps will probably remain fairly close to seasonal "normals" mid to
late week, but starting to look like there is room to begin a shift
back toward above normal beyond the period.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 613 AM CDT Fri May 26 2017

VFR conditions are expected through the TAF period. The exception
will be some low end VFR or MVFR ceilings building into the lower
Brule region of south central SD after 09z Saturday morning.
Scattered rain showers will also be possible late tonight in south
central SD.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...
LONG TERM...Chapman
AVIATION...