Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 241126

Area Forecast Discussion
National Weather Service Sioux Falls SD
626 AM CDT Fri Mar 24 2017

.SHORT TERM...(Today and Tonight)
Issued at 259 AM CDT Fri Mar 24 2017

Rain continues to pivot across the CWA early this morning.  Axis of
precipitation has narrowed and shifted slightly further south since
midnight, as a weakening MCV works across eastern Nebraska and into
northwest Iowa. Instability has really waned as expected after
midnight, with observed lightning down to minimal values.  Radar
estimating upwards of 1 to 2" along an axis from Vermillion
northeast through Sioux Center, which seems match reasonably well
with observations.

Today: Concentrated areas of moderate rains will continue to pivot
northeast through this morning as shortwave/MCV pulls away from
the area. Best guidance overnight has been the GFS, NAMNest, with
slight input from the HRRRs. That said, all guidance has been
about 25-50 miles too far to the north. Guidance is hinting at a
relative break in any steady rainfall through the late morning and
early afternoon hours as upper lift really weakens and shifts
eastward. Increasing flow of slightly drier air in the low-
levels from the north will work to really narrow the deformation
band later this afternoon as the larger upper trough ejects
eastward. Thus, have pulled PoPs further south, and really tried
to narrow up the northern PoP gradient. Increasing dynamics
should aid in developing renewed light to moderate rain with a low
end risk of an isolated rumble of thunder, mainly along a line
from Vermillion to Storm Lake.

Tonight: Steady shower activity should remain in place for the
southern zones of the CWA from Vermillion to Storm Lake into
Saturday morning.  Further north, stratus that never really leaves
the area, will try to expand through the night, with indications
that, especially along the edges, fog may try to develop as stratus

.LONG TERM...(Saturday through Thursday)
Issued at 259 AM CDT Fri Mar 24 2017

Saturday: The large upper low will slowly pivot eastward into the
Mississippi river valley through the day.  However, low level flow
from the East will only work to maintain an increased RH field over
the eastern half of the CWA through the day. Would not be surprised
to see a few spits of rain or even drizzle east of I-29 for much of
the day.

Sunday: A kicker wave moving through the Central Rockies will
finally provide enough of a push to nudge the upper low eastward
into the Great Lakes on Sunday. Flow in general over the area is
rather weak and disorganized, which may only serve to keep clouds
and a produce a few spits of rain during the day.  Temperatures
Sunday will climb near or into the lower 50s.

Monday-Friday: A fairly energetic flow pattern persists through
next week, with medium and extended models continuing their
disagreements in solutions. Edging towards dry conditions for
Monday-Tuesday as favored by the GFS, and a stronger influence
from brief mid-level ridging and dry northeastern flow from
surface high pressure in Manitoba.

The most uncertainty and lowest forecast confidence develops from
Wednesday through Friday.  Still significant differences in the
track and depth of an upper trough expected to cross through the
Four Corners region into the Southern Plains. GFS remains stronger
and further south, with less influence to the local area, while
ECMWF is weaker, more phased with northern stream energy and does
provide at least a glancing blow of light precipitation for
Wednesday and Thursday. The GEM and the GEFS support the GFS
deterministic soln, and have tried to trend the forecast towards a
bit less impact. Temperatures will begin to climb through the
week, with 60s possible for the second half of the week.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 621 AM CDT Fri Mar 24 2017

Widespread IFR to low MVFR ceilings to impact the terminals
through the day. It`s possible to have a few pockets of slightly
improved ceilings, but given the short duration of these windows,
will continue to advertise the broken lower deck at FSD.

Showers may continue at Sioux City on and off through the day,
with the highest concentrated risks this morning, and then again
later this afternoon. It`s possible Sioux Falls could be impacted
by a few showers later this afternoon, but confidence too low to
go any further than a vicinity wording.

Up at Huron, it`s possible that ceilings may try to lift briefly
through the day. However, anticipating a return of stratus
overnight as flow turns easterly. This IFR stratus should remain
at all the terminals into Saturday morning. Fog may become
problematic for Huron overnight, and later TAFs may need to
address the risk.




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