Scientific Forecaster Discussion
fxus63 kfsd 211700
Area forecast discussion
National Weather Service Sioux Falls South Dakota
1100 am CST Tue Nov 21 2017
Short term...(today and tonight)
issued at 321 am CST Tue Nov 21 2017
The main impacts in the short term will be the gusty winds and a
strong push of cold air advection. Trough digs southeast across the
upper Midwest this morning, with much drier and colder air filtering
southwest. Tight pressure gradient and strong unidirectional low and
mid level winds will lead to a blustery day. Used the consmos wind
guidance to produce sustained winds of 20 to 30 mph with gusts to 40
mph through late morning, with the Buffalo Ridge area and Iowa Great
Lakes likely to see sustained winds at Wind Advisory levels at times
with a few gusts topping 45 mph. Went ahead and added Lincoln Minnesota,
Murray, and Clay Iowa counties to the advisory, with the potential for
winds briefly reaching criteria through early afternoon.
Temperatures will continue to fall this morning as the cold air
advection arrives. Late morning/midday temperatures will stabilize
and rise a few degrees, however, mid afternoon readings will be much
colder than previous days in the mid 20s to lower 30s. Much drier
airmass will allow skies to become mostly sunny by midday. Clear
skies continue into the overnight hours. The gusty northwest winds
diminish quickly in the early evening, turning southerly late
tonight. Low temperatures will rapidly drop into the teens
overnight, dropping to near 10 degrees in east central South Dakota.
Long term...(wednesday through monday)
issued at 321 am CST Tue Nov 21 2017
Drier and milder air return into the area on Wednesday as the high
pressure moves southeast and flow shifts to a southerly component.
Clouds will be increasing by mid-morning as southerly flow/warmer
air starts to spread some mid to high clouds back into the area.
Highs will be ranging in the upper 30s to near 40, except west of
the James River Valley where more sunshine is expected. These areas
could see temperatures in the upper 40s to lower 50s. Impulses of
energy aloft will bring shortwaves ahead of the next upper wave
approaching by Friday. By later Wednesday night, this weak
shortwave will accompany the next upper jet diving southeast
through early Thursday morning. No impacts are expected on
Thanksgiving day other than a few clouds and well above normal
The aforementioned strong upper wave moves north of the region
Thursday night into Friday, with the warm front sliding east into
the area. The main impact on Friday will be strong winds in the wake
of the frontal boundary. GFS shows a strong mixed layer from 35 to
over 40 knots. Guidance suggests strong winds, but have also
increased winds by using a blend between superblend and consmos. At
this point, areas west of the I-29 could get the strongest winds.
Warmer than normal temperatures are still on target for Friday.
Questions arise on when the warmer air will arrive into the area and
how much cloud cover will there be, impacting highs. Models continue
indicating a warm 925 mb layer of 10+ to 15+ c by early afternoon
supporting highs in the upper 50s and lower 60s. More cloud cover is
expected across southwest Minnesota where spotty rain/sprinkles will
be possible behind the front.
Looking ahead for the remainder of the extended, the weekend is
shaping up to be dry and cooler than normal but warmer temperatures
return on Monday.
Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 1058 am CST Tue Nov 21 2017
VFR conditions through the period. Northwest winds will gust to 35
mph at times today, but gradually diminish through the afternoon.
Expect stratocumulus to move in on Wednesday morning around 7000