Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 301636
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1136 AM CDT TUE AUG 30 2016

.UPDATE...
Issued at 1136 AM CDT Tue Aug 30 2016

Earlier morning activity has pretty much come to an end across
parts of southwest Minnesota and northwest Iowa. Currently see
surface boundary sagging slowly southward from east central South
Dakota through southwest Minnesota. Has broken out of cloudiness
quite effectively along I-90 and west of the James River in
southeast South Dakota, and will likely warm hourlies and highs
a few degrees over previous forecast in these locations. Likely to
find an increase in cumulus field near backing frontal zone by
the time temps reach the lower 80s. Otherwise, clouds will hang
tough across northwest Iowa with some thinning this afternoon, and
instability will be hampered a bit by loss of diurnal support.
Many CAMS still indicate potential for storms to develop near this
slowly backing boundary this afternoon, but don`t expect a perfect
performance due to the weakly forced environment. Did expand
isolated level pops back toward south central South Dakota where
will gradually work out the weak surface based cap by mid
afternoon. Overall, parameters of marginal instability and very
weak shear suggest a minimal severe threat. On occasion, these
weak deep shear setups will allow development for a few funnel
clouds near the slowly propagating boundaries. Otherwise, slow
movement to any isolated storms which manage to develop could
lead to very spotty, very heavy rainfall in parts of far southeast
South Dakota, northeast Nebraska and northwest Iowa.

&&

.SHORT TERM...(Today and Tonight)
Issued at 253 AM CDT Tue Aug 30 2016

A cold front continues to settle  into the northern portions of the
CWA very early this morning. At this time almost the entire area is
rain free, with earlier convection over our lower IA/NE zones
dissipating. The exception is some scattered thunderstorms brushing
our far southwestern MN zones near Marshall in an area of optimized
low level convergence. The cold front will continue to settle
southward through the morning hours, becoming situated through the
lower Missouri River corridor by late afternoon. With weak forcing,
precipitation trends through the day are rather tricky, with the
main focus for precipitation being low level convergence/confluence
as the front drops southward aided by day time heating. This will
place the better chances for showers/thunderstorms from the central
and eastern Interstate 90 corridor southward into the lower MO River
Valley/northwestern IA during the day. Severe storms are not
expected with limited instability and very weak shear. While
temperatures are also tricky dependent on cloud/precipitation
trends, at this point will go with highs in the upper 70s east of
Interstate 29 to the lower 80s to the west.

The front drops south of our CWA by early this evening, and with
this and loss of day time heating will see any remaining
showers/thunderstorms dissipate across our south. Clouds will be
deceasing overnight, with lowering dew points and cooling
temperatures on a east/northeasterly low level flow. Lows will be in
the mid 50s to around 60.

.LONG TERM...(Wednesday through Monday)
Issued at 253 AM CDT Tue Aug 30 2016

Rather pleasant conditions are expected from Wednesday through
Friday as high pressure over the Great Lakes influences the Tri-
State area. Temperatures will average near to slightly below
seasonal normals.  Dew points will be on the comfortable side, and
winds will remains light through at least Thursday. Breezy winds may
elevate the fire danger west of the Missouri River ever so slightly
on Friday.

The holiday weekend will be considerably more interesting
weatherwise, as southwesterly flow aloft moves into the Central US.
Rain chances will begin to increase later on Saturday as a series of
weak shortwaves lift through the region. Scattered late day
thunderstorms may become more numerous during the evening and
overnight hours. Several clusters of storms may form and lift
northeast through the area into Sunday morning. While the overall
severe weather risk due to the elevated nature of the activity will
be on the lower end, there could be a elevated risk of locally heavy
rainfall.

Considerable uncertainty remains for Sunday and Labor day with
details highly dependent on the mesoscale. Model trends continue to
suggest lingering morning convection, and potential for
destabilization rather quickly in the afternoon on Sunday. However,
far too many uncertainties to get too deterministic on the severe
weather risk.  It is a day to keep a closer eye on given the
increasing shear and instability potential and would not be
surprised to see severe weather convective outlooks introduced for
the region.

Lower confidence on forecast specifics as we move into Monday and
into next week with Labor day convection potential very dependent on
Sunday`s thunderstorms. The broad synoptic pattern continues to
indicate southwesterly flow aloft, typically keeping an elevated
thunderstorm risk into the middle of next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1136 AM CDT Tue Aug 30 2016

Potential for additional convection the more significant concern
as boundary drops southward through the afternoon. Convective
chances too low to mention for KFSD as will be near the most
possible northward extent of development, but a couple or three
hours around KSUX could manage a vicinity mention for the later
afternoon. Could potentially see brief IFR to MVFR conditions
within slow moving storms.  A little lingering low level moisture
may produce some MVFR visibilities near the Missouri River later
tonight due to light winds.

&&

.FSD Watches/Warnings/Advisories...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

UPDATE...Chapman
SHORT TERM...JM
LONG TERM...Dux
AVIATION...Chapman



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