Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 300345

Area Forecast Discussion
National Weather Service Sioux Falls SD
1045 PM CDT Thu Sep 29 2016

.SHORT TERM...(This evening through Friday)
Issued at 315 PM CDT Thu Sep 29 2016

Very little has changed in the larger scale weather pattern as upper-
level low pressure remains on a wobbly sit `n spin in the Ohio
Valley with a sharp ridge aloft back across the Dakotas.  The
reality of the situation is that change will be slow to occur, and
not more than subtle changes are expected over the next 24 hours.
Therefore, as midday cumulus continues to mix out, the evening
should become mainly clear with the surface ridge axis holding near
a northeast Minnesota to eastern Nebraska line.  Likely to have
areas of lower clouds and fog redevelop later in the night with low-
level moisture levels a touch higher than 24 hours previous. At this
point in time, anywhere near and east of the surface ridge axis
where easterly component to near/off-surface flow has increased
moisture would be prime for fog and stratus, mainly again shallow
fog and not terribly widespread. Exception could be some areas near
the Buffalo Ridge later tonight and early Friday morning that hints
in hi-res solutions to higher threat of widespread lower clouds and

Any fog and lower clouds will again undergo mixing process, thinning
or dissipating toward midday. Ridge aloft will narrow somewhat on
Friday as upper low starts to wobble back toward the northwest, and
wave pushes into upper ridge in the northern high plains.  Low level
ridge will remain in place, and southerly gradient increases just a
bit across the James valley. As low nudges back a bit toward the
region, easterly trajectory will spread another more organized area
of clouds which will push toward northwest Iowa by early evening.

Temps tonight with a bit more moisture in the mix should be mainly
lower to mid 40s, perhaps near 40 in some lower elevation locations.
There should continue to be a couple degrees moderation to temps
Friday, meaning upper 60s to lower 70s.

.LONG TERM...(Friday night through Thursday)
Issued at 315 PM CDT Thu Sep 29 2016

Upper low in the Ohio Valley drifts a little westward Friday night,
which results some increased cloud cover working into area along and
east of I-29 Friday night to Saturday night. This should counteract
radiative cooling within the surface ridge, keeping overnight lows a
bit warmer than recent nights, closer to 50 or even lower 50s. High
temperatures Saturday will likewise be held a little cooler in our
MN/IA counties, though still looking like upper 60s are reasonable,
with lower-mid 70s west of I-29. Despite the increased cloud cover,
little if any support for precipitation and will keep the forecast
dry through the weekend and into early next week.

Pattern breaks Sunday as the eastern upper low moves east through
the Great Lakes and an upper ridge briefly builds over the northern
Plains. This allows for a nice warmup into the mid 70s-near 80 for
most of the forecast area on Monday. The warmer temperatures linger
into Tuesday, though could start seeing spotty showers/storms work
into areas west of I-29 by Monday night/Tuesday as another strong
upper low begins to swing east through the Rockies.

Evolution of this upper low is primary challenge for the middle part
of next week. Differences between GFS/ECMWF/Canadian are primarily
centered on how far south the low digs into the Plains, and thus how
quickly precipitation will spread northward into our area. At this
point, appears as though Tuesday night would be most favored time
for rain across most of our area, but with timing/placement of the
driving features still uncertain, did not deviate from blended PoPs
in the higher end chance/low likely range. Most significant effect
of this system will be cooler air which will spill into the region
as it lifts north late next week. Currently still holding on to
highs in the lower-mid 60s for Thursday, but some models pointing to
a shot of much colder air affecting the region late next week, so
will have to monitor trends over the coming days.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1044 PM CDT Thu Sep 29 2016

After perusing over the 00Z NAM model data, it still appears the
main thing to watch for is late night and early morning areas of
fog. With an easterly fetch of air tonight, the most organized fog
still looks to be along the upslope side of the Buffalo Ridge in
southwest MN. However, certainly cannot rule out patchy low lying
fog at KHON, KFSD, KSUX, especially since these sites reside at or
near rivers. If the airports receive shallow fog, short term
conditions could be worse then what is reflected in the TAFs.
However due to the nature of shallow radiational fog, it is quite
unpredictable in how long it will last or how much area it will
cover. Therefore do not want to convey any IFR or LIFR conditions
at this time.




SHORT TERM...Chapman
AVIATION...MJ is the U.S. government's official web portal to all federal, state and local government web resources and services.