Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 142047
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
347 PM CDT Fri Jul 14 2017

.SHORT TERM...(This evening through Saturday)
Issued at 347 PM CDT Fri Jul 14 2017

Surface high pressure off to the east of the area is having a direct
impact on our temperatures today, with the rather light
southeasterly flow not allowing temperatures to climb.  Temperatures
in fact may end up being a bit below normal in a few locations.

Quiet conditions are expected again tonight. With the surface high
drifting further southeast overnight, the turning of the boundary
layer winds to the south and southwest should allow slightly higher
dew points to lift northward by Saturday morning. Patchy valley fog
may be possible in the far eastern zones.

Bit of a tricky forecast for Saturday despite the dry conditions
expected. Weak shortwave dissipating in the morning may bring some
enhanced mid-level cloud cover in the morning. Meanwhile a surface
boundary settles into the region by mid-day, and could have an
impact on temperatures and dew points. Anticipating that
temperatures will end up a few degrees cooler behind this boundary,
across the northern and northeastern CWA. The warmest conditions
will be across south central SD where highs under the thermal ridge
axis could push 100 degrees. The other impact of the front may be
pooling of moisture along and especially behind the boundary. This
could push dew points into the upper 60s. Resultant heat index
values may challenge the 100 degree mark, but with fairly marginal
heat advisory conditions, will allow the next shift to better
examine numbers and impact of front to determine if an advisory is
needed.

.LONG TERM...(Saturday night through Friday)
Issued at 347 PM CDT Fri Jul 14 2017

As weaker wave continues to push into the Great Lakes on Saturday
night, boundary will continue to wander southward, and should drop
south of the Highway 20 corridor by later in the night or early
morning.  Will likely have some issues with surface-layer moisture
pooling below inversion to make for a fairly humid evening, and
enough could linger with weak flow around the boundary to bring some
areas of shallow fog into northeast Nebraska, far southeast South
Dakota and northwest Iowa toward Sunday morning.

Frontal boundary will likely stall out early Sunday before creeping
back slowly northward through Sunday night. Again, may be dealing
with a situation where dewpoints are underestimated and could be
enough moisture to bring at least a scattered flat cumulus scenario
by midday/early afternoon around the location of the boundary and
toward the more stable areas to the north. Overall, expect will be
capped off as ridge axis aloft builds across the area. Cannot say
with 100 percent certainty there will not attempt to be a rogue
storm near the front, but fairly close to that with stout capping
indicated in models. May be a bit overdone in event of greater near-
surface moisture, however, still enough wiggle room to maintain cap
at this point. Will see most areas maintaining an east of south
component to restrain temps in the 80s across most areas east of I-
29, with warmest readings sneaking back into areas west of the James
River, especially toward south central SD where a few readings near
100 possible.  More muggy Sunday night as warm front lifts northward
and southerly flow increases considerably, with return of lows to
the upper 60s to lower 70s for most.  Wave begins to flatten ridge
during the day Monday, with cold front arriving in the central and
northeast sections of SD late day.  Cap strength would suggest
virtually no chance for convection, but a very low potential for
very late afternoon thunder wandering toward K9V9 or KHON area.
Surge of warmer air ahead of the boundary with southwest component
suggests we all share in 90s, expect those locations likely to
exceed 100 degrees toward south central.

Wave pushing over ridge Monday night suggests that may get enough
dynamic support along with the boundary presence to finally get some
higher chance for convective development on Monday night.  In fact
at this range, do exercise a cautious optimism that pattern will
become more favorable toward precipitation as flow flattens and
boundary potentially remains in the neighborhood through the
upcoming week.  Models pick on different times/places to lose their
collective convective mind, but treating this more of an idea of
broad agreement of potential rather than details. For this reason,
most PoPs remain in the chance level at this point, and temperatures
gradually slide back into a lower diurnal variability (lows mainly
mid 60s to around 70, highs mainly 80s to around 90).  Will still
remain some challenge to precipitation given the remaining warmer
temps aloft through the period, but should generally be a more
nocturnally favored pattern with best chances, but confidence
generally low on details.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1152 AM CDT Fri Jul 14 2017

VFR conditions expected into Saturday. Southerly winds will turn
light overnight, and as a front approaches Saturday morning, may
again turn variable or even northerly by the end of the taf
period. A few mid-level clouds will drift across the TAFs through
Saturday morning.

&&

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

$$

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



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