Scientific Forecaster Discussion
fxus63 kfsd 222252
Area forecast discussion
National Weather Service Sioux Falls South Dakota
552 PM CDT sun Sep 22 2019
Short term...(this evening through monday)
issued at 206 PM CDT sun Sep 22 2019
Quiet weather expected for the next 24-36 hours, with surface ridge
moving across the forecast area tonight, followed by light southerly
return flow Monday into Monday night. Upper trough responsible for
spotty afternoon sprinkles/showers in central South Dakota, and
possibly into the lower Missouri River valley, will rotate east
this evening, leaving mostly clear skies and light winds within
the surface ridge axis overnight.
Should be another comfortable night, with lows in the upper 40s to
lower 50s. Warm advection will bring temperatures back above normal
for Monday, with abundant sunshine expected to help push readings
into the mid-upper 70s. Dew points begin to climb slowly with the
light southerly flow Monday, and this should hold overnight lows
Monday night in the mid-upper 50s.
Long term...(monday night through sunday)
issued at 206 PM CDT sun Sep 22 2019
Mid-long range portion of the forecast begins with long-wave trough
swinging through the northern plains Tuesday/Tuesday night. Models
showing some differences in timing the associated cold front pushing
through the forecast area Tuesday afternoon/evening, and this will
play a role in determining location of potential severe threat.
Ample instability near/ahead of the front, with increasing deep
layer shear as 90-100+ kt jet dives into the base of the trough
Tuesday evening. As is often the case with cold front scenarios,
strongest shear lags behind the pre-frontal instability, with may
limit areal extent of severe threat to near vicinity of the front
itself. That said, storms that are able to punch through the weak
capping inversion could grow quickly given steep lapse rates above
the cap, so tough to argue with Storm Prediction Center day 3 outlook in our southeast
counties. Strong thermal ridge ahead of the boundary should allow
for a warm day, and like previous shift, nudged blended highs up
toward 90th percentile of guidance given potential for mixing into
lower-mid 80s most areas.
Reinforcing shot of cold air dives southward across the area later
Tuesday night/early Wednesday, which should lead to a chillier day
with highs only in the mid 60s-lower 70s and breezy west-northwest
winds. Winds should decouple quickly in the evening, with light
winds and the cooler air mass allowing for lows in the 40s most
areas Wednesday night.
Late week will see another surge of warmer air and moisture lift
into the region Thursday and Thursday night. Followed by the cool
front pushing through on Friday. This will bring our next potential
for rain/storms, which at this time appears to remain focused across
the southeast half of the forecast area late Thursday night/Friday.
Still uncertainty in timing/placement of the front, though, so will
be able to refine timing a bit better in later forecasts. Late week
temperatures look to remain fairly close to late September normals
for highs, with readings in the upper 60s-70s, though a little more
for Friday given differences in timing of the cold front.
Temperature roller coaster continues next weekend, starting off on
the cooler side Saturday in the wake of friday's cold front, but
consensus currently showing another strong surge of warmer air for
Sunday. Not seeing any strong precipitation systems for the weekend
ahead, but with continued southwest flow aloft, cannot rule out some
Aviation...(for the 00z tafs through 00z Monday evening)
issued at 551 PM CDT sun Sep 22 2019
VFR conditions expected through the taf period.