Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 292318

Area Forecast Discussion
National Weather Service Sioux Falls SD
618 PM CDT FRI JUL 29 2016

.SHORT TERM...(This evening through Saturday)
Issued at 317 PM CDT Fri Jul 29 2016

A rather pleasant Friday for much of the region, with light winds,
highs near 80, and low humidity. A few diurnally driven showers and
thunderstorms have formed over North Central Iowa and Northern
South Dakota this afternoon. These showers may brush with the edges
of the CWA border near Huron and Storm Lake/Spencer, but
generally are  not expected to have a large impact.

These pleasant conditions will continue into the overnight hours, as
high pressure settles into the region.  We`ll watch a weak shortwave
currently over Montana/Wyoming dropping southward later tonight.
Reasonable chances for a few showers or thunderstorms along an
advancing low-lvl moisture gradient, mainly focused over central and
western South Dakota. Elsewhere, light winds and boundary layer
moisture may lead to fog over northwest Iowa and adjacent areas of
Minnesota and Nebraska overnight. More likely is an increase in
stratus which will attempt to advect northwest.

Outside of a morning risk for showers and isolated thunderstorms
west of the James River, Saturday looks quiet.  Temperatures, as
winds turn southerly, will rise into the middle 80s west of
Interstate 29, with highs in the upper 70s to near 80 east of
Interstate 29.

.LONG TERM...(Saturday night through Friday)
Issued at 317 PM CDT Fri Jul 29 2016

The two features of the Saturday night through Monday time will be
steady warming...and a chance of storms mainly during the night.
Conditions for storm initiation from daytime heating Sunday and
Monday do not look favorable with the warming taking place stronger
upstairs and a cap in place. Some degree of low level jet develops
during the nighttime hours as MUCAPE slowly increases from the west
to 2000-3000 J/kg over the area. The Canadian border system
approaching the Dakotas Sunday night is tabbed in the SPC day 3
outlook to produce a convective system that could move into the area
Sunday night and bring a little risk for severe storms. For
Monday...a separate weak short wave is progged by models to break
across the developing upper ridge and could help activity linger
Monday, at least east of the James River.

The warming will give rise to 80s highs Sunday, with 90 possible
west of the James, then a little more warming to highs in the mid
80s to lower 90s is in store for Monday. During this time moisture
levels including surface dew points will be increasing, and this
could make for around 100 heat indices along the Missouri River
Monday afternoon. Low temperatures of course will be warming with
60s Saturday night and around 70 Sunday night.

Tuesday through Friday will see hot weather cooling back to normal
as a moderately strong Pacific wave drives a surface cold front
across the Dakotas by Thursday. Storm chances of course will
accompany the system with the threat peaking Wednesday night.
Extended guidance slowly abates the threat after the front goes
through, leaving a little chance in northwest Iowa through Friday,
otherwise the trend near the end of the week will be to dry weather.

One interesting facet of the extended guidance is that on the
projected hottest day, Wednesday, Surface dew points are slipped
back into the 60s, keeping the heat index below triple digits. Given
that the upper ridge over the area is less strong and further south
than during the somewhat recent hot spell, some mixing down of dew
points could happen and will leave alone. However, given the
terrible performance of some models, especially the GFS, on gouging
dew points during that hot spell, suspicions are there. In any
event, models seem to be consistent on flattening the upper ridge
and bringing the cooling late in the week, so if Wednesday turns out
to be stickier than now forecast, the heat should abate by the
next day.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 616 PM CDT Fri Jul 29 2016

Generally VFR through the period. Will need to watch parts of
mainly northwest Iowa late tonight and early Saturday morning for
the potential for MVFR fog. This area is on the back edge of the
low level moisture which may allow for fog development as
temperatures and winds drop tonight.


.FSD Watches/Warnings/Advisories...


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