Scientific Forecaster Discussion
fxus63 kfsd 211135
Area forecast discussion
National Weather Service Sioux Falls South Dakota
635 am CDT Sat Sep 21 2019
Short term...(today and tonight)
issued at 318 am CDT Sat Sep 21 2019
Strong shortwave pivoting northeast through the western Dakotas
continues to force a linear area of convection into central South
Dakota early this morning. Convection continues to struggle as it
reaches a more stable environment, but can't rule out a few gusty
winds over 40 mph in the immediate MO River Valley through 4 or 5
am. Further east, widespread stratus continues to develop
under the low-lvl stable inversion. Weak lift in the layer has
already produced a few sprinkles and woulnd't be surprised to see
patchy drizzle develop by daybreak.
Today: frontal boundary will very slowly drift eastward today.
Anticipating an area of showers and embedded thunder ahead of
this boundary to reach the I-29 corridor after daybreak and slowly
drift eastward. Given saturated soundings below 800 mb, could
also see drizzle break out in lower stratus. The actual front
itself may not reach the I-29 corridor until mid-day, which gives
some outside risk for minor redevelopment along the boundary as
mid-lvl lapse rates sharpen slightly and stratus clears ahead of
the boundary. While low, not a zero percent risk of a strong storm
with some gusty winds early this afternoon across SW Minnesota
and northwest Iowa.
Tonight: cold air advection settles into the area tonight, which
should clear most of the cloud cover out of the area. Temperatures
will fall into the lower 50s, a considerable change from the lows
the past week.
Long term...(sunday through friday)
issued at 318 am CDT Sat Sep 21 2019
Sunday: a large upper trough continues to pivot through the northern
plains on Sunday. Latest guidance hinting at a narrow band of light
rain developing by daybreak Sunday near or just south of the area,
as some enhanced 700 mb frontogenesis develops. Will bump up cloud
cover slightly through the day Sunday, while holding temperatures
in the upper 60s to lower 70s.
Sunday night and monday: upper troughing passes east of the region
Sunday night, with low temperatures falling towards normal levels by
Monday morning. Monday is shaping up to be a great day across much
of the region as upper ridging increases and low-lvl warm advection
begins. Temperatures will warm back above normal in most locations.
Tuesday-wednesday: mid-lvl flow turns a bit more westerly and
progressive for the middle of the week. No big changes to the
forecast in the medium range, but after another very nice day on
Tuesday, anticipating a bit more cloud cover Tuesday night and
Wednesday. A weak frontal passage Tuesday night will cool
temperatures for Wednesday, with trailing mid-lvl moisture keeping
a chance of very light rain north of the County Warning Area on Wednesday.
Thursday-friday: upper pattern buckles once again by the end of next
week with indications pointing to an extended period of high
amplitude trough/ridge pattern across the Continental U.S.. precipitation
chances will increase by the very end of the forecast as energy
ejects out of the southwestern US. Temperature outlooks favor above
normal temperatures through the end of the week and at least next
weekend if not longer.
Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 633 am CDT Sat Sep 21 2019
Scattered convection moving through the I-29 corridor this
morning will continue to slide east into Minnesota after daybreak.
Frontal boundary behind convection lingers significantly, and
will keep MVFR stratus in the area through mid-morning.
Ceilings will improve through the morning, with VFR conditions by
mid-day. Frontal boundary moves through turning winds more
westerly to northwesterly by the afternoon. Occasional gusts over
20 knots are expected.
VFR conditions continue overnight.