Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 172124
AFDFSD

AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
424 PM CDT Mon Jun 17 2019

.SHORT TERM...(This Evening through Tuesday)
Issued at 424 PM CDT Mon Jun 17 2019

Main surface boundary has cleared the area into central NE to
central IA, and the enhancement of precipitation near and behind the
front associated with support from leading wave/jet entrance pulling
away through IA. Another trough embedded in the wave to the north
will enhance the jet again tonight, likely spurring additional
convection beyond just the area working east/southeast from south
central SD/north central NE along the draped mid-level boundary.
Deeper mixed-layer instability is fairly limited to south of a KICR
to KSPW line at only 500-1000 J/kg, and weaker elevated instability
roughly that area to a bit north, so the prospect of much thunder as
far north as I-90 is small.  Have tried to trim back northern edge
of precipitation tonight and especially later tonight into Tuesday,
with really the only halfway decent chance for precipitation tied
toward Highway 20, and perhaps a bit better chance as inflection in
flow bulges the boundary a bit northward during the afternoon on
Tuesday. Nonetheless, there should not be any threat for severe
storms with surface-layer vorticity shifted southward along with
most of even the elevated instability.

Likely to see some greater sunshine north of I-90 to start the day,
but looks to be a very self-destructive day with likely cumulus
field developing. Not seeing indications of any appreciable
potential for CAPE in profiles, so likely just some modest cumulus
depth without threat for showers.

Lows tonight with northerly influx of drier air should allow some
lower to mid 50s in the far north, with mainly near 60 beneath
better clouds south.  Highs on Tuesday somewhat a reverse profile
based on clouds/precip threat, from near 70 far south to the mid to
upper 70s north.

.LONG TERM...(Tuesday Night through Monday)
Issued at 424 PM CDT Mon Jun 17 2019

Protective influence of the low-level ridging in MN and trough
digging south of the area should keep quiet weather prevailing on
Tuesday night, and lows just a touch cooler than tonight in the
lower to mid 50s.  Another trough digging into the northern Plains
on Wednesday will increase the return flow into the central Dakotas,
which will prime the pump with a little more moisture and set up
location of a better low-mid level boundary going into Wednesday
night as the next quick moving wave slips into the region from the
west.  A better surge of mid-level lapse rates will nose toward
southern/southeastern SD by late night, and increase in low-level
jet once again will increase the effective shear in 1-6km levels to
over 40 kts.  With this will come a marginal risk for a severe
wind/hail producing storm mainly west of the James River, limited by
the likely fairly skinny CAPE profiles.

As ridging aloft works to become more established on Thursday, the
wave is shunted northward during the day, with dynamics abandoning
the boundary working eastward which should fade as it settles across
the area. Will not take long for the return flow to redevelop later
Thursday night into Friday, which will bring with it another chance
for thunder, along with potentially some areas of heavier rainfall
as the better return moisture begins to advect in.

Will have to keep an eye on the severe potential for Friday given
the greater degree of instability expected with the duration of
return flow leading into Friday, along with the higher degree of
probability of a warm frontal boundary somewhere near the area.
While there would be a window for elevated storms earlier in the
day, those storms after the diurnal cycle late day and evening would
be likely more threatening.

By the weekend, there is a greater degree of variation in solutions,
mainly depending on how much the Friday trough amplifies as it
closes off, and how much energy is left behind across the
intermountain west.  The variations in solutions are appreciable,
very dry to very wet, and moderate to very warm.  Would tend to put
a higher degree of faith in the ECMWF which has less feedback from
convection, but even the convection in that model has some influence
on the progression of features. Again, likely too many precipitation
chances in the initial blends for the weekend, so the take away
should be not an all-day soaker, likely more dry than wet Saturday
and Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1214 PM CDT Mon Jun 17 2019

Primary aviation concern in the near term revolves around the
thunderstorm chances, currently most prevalent in NW Iowa. At this
point the thunder threat at KHON and KFSD looks fairly low with
generally just a hit or miss shower expected thru the afternoon.
KSUX will continue to see showers over the coming hours with the
potential for a few thunderstorms later this afternoon and thus
tried to show this potential in the latest set of TAFs. Could see
ceilings trend toward MVFR or even lower overnight depending on
precipitation coverage but kept this fairly limited for now.


&&

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

$$

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


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