451 
FXUS63 KFSD 181800
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
100 PM CDT Thu Oct 18 2018

.UPDATE...
Issued at 1015 AM CDT Thu Oct 18 2018

Went ahead and issued a wind advisory for the afternoon hours for
our south central SD counties. Latest 12Z data off the NAM12, and
also the RAP13, shows wind speeds of 40 knots in the 0-1km mixed
layer in those locations. Coupled with a decent pressure gradient
and daytime heating, a lower end wind advisory is needed for some
25 to 40 mph winds. There will probably be some gusts upward of 45
mph in the higher terrain locations. Wind direction means
everything in that area, and with directions from the south to
southwest instead of south to southeast, stronger mixing will 
occur with some westerly component to the wind. 

&&

.SHORT TERM...(Today and Tonight)
Issued at 411 AM CDT Thu Oct 18 2018

Mid-level shortwave ridge in control across the Northern Plains 
early this morning, displacing the deep trough of the last several 
days, and ahead of a trough of low pressure starting to pull away 
from the Great Basin. Return flow at and near the surface continues 
to strengthen early this morning, with warming (and stronger winds) 
seen at elevation per IR satellite and surface observations early 
this morning.

Today will be the day most have been waiting for, with temperatures 
above normal for all locations, expected to reach the mid 60s to 
lower 70s. Should have a strong support from mechanical mixing with 
gusty southwest winds 15 to 30 mph, stronger in south central SD, 
expected to expand off the early day higher elevations by mid to 
late morning. Sunshine will start the day, but as trough of low 
pressure begins to shear out of the southwest and move toward the 
region, will see an increase in mid- level clouds form the 
southwest.

This trough shears northeast and then becomes shunted more eastward 
tonight as a northern stream wave kicks the system out of the way by 
early Friday.  With an increase in mid-level moisture depth along 
with lapse rates a shade steeper than moist adiabatic, are a little 
more likely to find a few showers mainly east of I-29 tonight from 
03z-11z. The other factor tonight will be the winds, with a good 
signal for ridge wind enhancement, especially along and downstream 
of the Buffalo Ridge. 30 to 40 mph gusts in those typically windy 
spots is not out of the question.

.LONG TERM...(Friday through Wednesday)
Issued at 411 AM CDT Thu Oct 18 2018

That northern stream wave on Friday will push a cold front southward 
across the area during the morning and early afternoon. The 
strongest cold push will come in a bit lagging from the wind shift, 
with some warm air lingering near the wind shift likely allowing a 
mixing toward warmer end of solution distribution, especially south 
of I-90. Most areas will be in the 60s, at least until some drop 
later in the afternoon north of I-90, but not out of the question 
that could approach 70 in the lower Missouri valley.  Winds will 
start brisk southwest ahead of the boundary, but a well-mixed 
environment with deepening mixed-layer as temps aloft begin to fall 
in the afternoon will set up a gusty northwest wind from 25 to 35 
mph for most.

Saturday now looking even less pleasant, mainly a result of the 
strong secondary trough dropping into the long wave through eastern 
MN during the early part of the day.  A strong secondary cold front 
will push southward during the morning, accompanied by an increase 
in northerly winds, a drastic increase in clouds, and temperatures 
likely falling for a time. Thermodynamic profiles from KMML to KSPW 
exhibit a small capped positive area with the significant cooling 
aloft with temps dropping from around 0C, to -6 to -9C, suggesting 
potential for convective roll development behind the front before 
drying minimized the threat by early afternoon with sharper 
clearing. However, the depth of the unstable area does not really 
encompass a strong likelihood of efficient ice processes within the 
shallow cloud layer, and therefore do not expect measurable 
precipitation as the post-frontal convective rolls move through for 
a few hours during the morning. It is possible that a few highs may 
actually end up early morning, but for now have left room for some 
brief recovery in the afternoon in southwest MN into northwest IA.

A chilly night is in store Saturday night with most areas dropping 
back into the 20s to lower 30s. However, consensus of models kick up 
a return southerly flow a bit faster for all, and in fact get fairly 
breezy west of I-29 by late night. Therefore, should see mins occur 
earlier in the cycle with temps rising later into the night.  Weak 
wave/jet entrance spreads in by later Sunday, dropping a frontal 
boundary into the area.  Location ahead of the boundary with west to 
southwest flow, along with a growing consensus of a more significant 
eastward push to warmer air ahead of the front, suggests warmer 
numbers for Sunday. Ensemble guidance deviations also showing a 
strong signal in favor of a warm solution, so expanded warming 
considerably eastward over initial blend, and could end up being 
even a few degrees warmer for many locations.

Following the boundary early next week, cooler surface ridge drops 
in the northern Plains, with temps returning to the 50s for most. A 
difference in long wave patters develops across the model spectrum 
between the more progressive GFS types, and a more amplified ECMWF. 
Both show some evidence of some orientation of troughing back into 
the area around Wednesday, so the small chance of precipitation is 
justified at this time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1256 PM CDT Thu Oct 18 2018

Breezy southwest winds will increase in intensity throughout the
afternoon hours. These quickly relax after sunset. Overnight, a
few hours of light rain showers are likely for KFSD, KSUX, and
other areas south and east of KFSD. These are forecast to end
around sunrise, with clearing skies. During the day Friday, a 
cold front moves in from the northwest and will swing winds around
to the west and then northwest throughout the daytime hours.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 7 PM CDT this evening for SDZ050-052-057-058-
     063-064.

MN...None.
IA...None.
NE...None.
&&

$$

UPDATE...MJ
SHORT TERM...Chapman
LONG TERM...Chapman
AVIATION...VandenBoogart