Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 222043

Area Forecast Discussion
National Weather Service Sioux Falls SD
343 PM CDT Wed Mar 22 2017

.SHORT TERM...(This evening through Thursday)
Issued at 342 PM CDT Wed Mar 22 2017

Light mixed precipitation moving quickly east of the area. Dry air
in the low levels really limited any amounts. Latest 1.61um visible
satellite has done a good job of delineating where precipitation
will fall by showing the ice based clouds aloft which correlated or
preceded the precipitation at the surface really well. The clouds in
the wake of the precipitation appear to be all water based so the
threat for additional precipitation should be pretty low with no
instability expected and mid level frontal forcing now out of the
area. Thus expecting dry conditions through the remainder of the
afternoon and night. Low level moisture currently over western parts
of Kansas will stream northward tonight and reach the southern CWA
by about 9z and the remainder of the area by about 15z, setting up a
pretty dreary Thursday. Lows tonight will be mild and in some cases
will be this evening as winds, moisture and low level temperatures
increase through the night.

Went ahead and lowered the chances for precipitation on Thursday as
saturation in the mid levels is pretty much absent and capping aloft
increases as well. Plenty of saturation in the low levels so about
the only chance for measurable precipitation will be with drizzle.
Could see a scattered shower near Huron as some warm advection in
the mid levels occurs just north of there and possibly late in the
afternoon in northwest Iowa as the deeper warm and humid air spreads
northeast. Temperatures a real trick with a balance between a lack
of warming because of the significant amount stratus but also that
the entire column of air will be warming through the day. Limited
highs a bit across southwest MN and far east central SD where the
warmer air will be latest to arrive. High should range from 45-50
across southwest MN to the mid 60s in south central SD.

.LONG TERM...(Thursday night through Wednesday)
Issued at 342 PM CDT Wed Mar 22 2017

Primarily followed a blend of the ECMWF and GFS for the passage of
the surface and upper lows for the rain event coming up Thursday
night through early Saturday. Both models are reasonably close with
their respective placements of the surface and upper lows, as well
as dynamics structure. Overall, mid level frontogenesis is rather
weak, but what there is of it does hookup with more robust
frontogenesis in the 850-800mb layer to help produce rainfall. The
frontogenetic band initially favors the northern half of our
forecast area Thursday night, then shifts slowly southward through
time from late Thursday night through Friday night across our
forecast area in a deeply saturated atmosphere.

There is a chance of convection through much of the forecast area
Thursday evening, elevated in nature. The chances for TSRA then
shift southeastward through time late Thursday night and early
Friday. The chances for severe weather is extremely remote. This is
because the soundings continue to show an inversion through the
lowest 1.5-2.0km, therefore strong winds aloft will have trouble
making it down to the surface. Following suit, the instability is
very limited until reaching 850 or 800mb. So for thunder chances,
followed a blend of the NAM and GFS 850mb lifted index values and
capes. Convective type rain will probably move northward Thursday
evening into our southern and southeast zones from the central
plains. This will produce the heaviest rainfall in a given 6 hour
period in our forecast area, maximized in extreme southeast SD. High
pops will linger through Friday for the area, then will begin to
decrease in our northern and western zones Friday night, and finally
in our southeast zones by Saturday afternoon as the upper low tracks
southeast of our forecast area via the central plains. All told we
are looking at a generalized rainfall ranging from near two tenths
of an inch in our northwest near Huron, to an inch or inch and a
half along and south of a Lake Andes, to Sioux Falls, to Jackson MN
line. This is all the way from Thursday through Saturday. The upper
low gets so wrapped up with little in the way of jet interaction,
that there may not be a lot of pockets of heavy rainfall other then
Thursday evening, and it should be more of a general rain which just
adds up over time.

After Saturday, the weather does look unsettled by mid week next
week. However confidence is low in the details in that deterministic
solutions are all over the place as well as ensembles. Overall,
chances for rainfall will increase Tuesday night and linger into
Wednesday. But given the temperature structure, it should be
primarily rainfall. In fact its doubtful that there will be any snow
accumulation over the next 7 days even though some chances for snow
exist on the north side of the rain shield late this week in our
northern zones, and again next Tuesday night, again in our north.

Highs look rather unexciting from Friday onward, with just a lot
of 40s and 50s.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1234 PM CDT Wed Mar 22 2017

VFR conditions through about midnight other than a fast moving
band of very light precipitation which should move through
southwest MN and northwest IA by 21z. After about 6-9z MVFR and
IFR ceilings will spread north and remain in place the remainder
of the period.




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