Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 191710

Area Forecast Discussion
National Weather Service Sioux Falls SD
1210 PM CDT Wed Oct 19 2016

.SHORT TERM...(Today and Tonight)
Issued at 424 AM CDT Wed Oct 19 2016

Split flow regime will influence the weather today across the
forecast area. A short wave will move across Nebraska through the
day, most evident in the 700-500mb layer and shows up well with the
mid level QG forcing fields. But to the north, our area is largely
influenced by a subtle wave dropping southeastward on the southwest
periphery of an upper low in southeast Canada. This northern stream
wave will bring an associated surface cold front southward with it,
evidenced by falling 925-850mb temperatures through the day. The
atmosphere is moisture starved below about 750mb in our extreme
southern zones, with the moisture even higher based as you approach
I 90. The frontogenetic forcing is fairly strong in the 750-700mb
layer, but remains to our south. Due to the proximity of the
southern stream wave, have some likely pops in our extreme southern
zones, from southern Gregory county to near Yankton for light
rainfall. Measurable pops decrease rapidly heading north and
eastward from that axis, although some sprinkles could fall out of
the mid deck of clouds as far north as I 90 during the middle of the
day. Another item to watch at least this morning is the massive
stratus deck in ND and northern MN. Based near 925mb, the current
NAM and GFS do not have a very good handle on it, but the RAP does.
The RAP brings it down into our extreme northern zones this morning,
generally from northern Beadle county to near Marshall before it
mixes it out by midday. This should not have a major influence on
our highs as we will have abundant mid and high level clouds with
the two short waves anyway. Because of the cloud cover and cold air
advection, lowered highs a bit based on 925mb temperatures, ranging
from the mid 50s in our north, to lower 60s in Sioux City and Storm

Tonight, the main feature to watch is another very weak mid level
wave moving down the northwest flow aloft, which primarily affects
our western zones. The wave should be enough to give mostly cloudy
conditions along and west of I 29, with a small chance for light
rain in our far west. Lowered a few lows in our extreme east from
Windom MN to Spencer IA below consensus temperatures, where sky
cover should be clearer coupled with light northerly winds.

.LONG TERM...(Thursday through Tuesday)
Issued at 424 AM CDT Wed Oct 19 2016

Main trough will continue to dig toward to mid and southern
Mississippi valley early Thursday, but a secondary bit of northern
stream energy falling into the Dakotas will keep a good deal of
clouds along with a low threat for light showers going across parts
of southeast South Dakota near and south of I-90 early in the day.
Cold advection will continue with greater focus into areas along and
east of I-29. Models, other than ECMWF or WRF-ARW, are not very
enthusiastic about stratus potential within zone of more northerly
flow. Historically, predictions of stratus fields generally far from
a strong point in the models. Have hedged in a greater degree of
cloud coverage in the afternoon over the initialization blend,
especially across southwest Minnesota and into northwest Iowa, but
would not be surprised in the least to get a far greater coverage of
stratus even westward from there.

Diurnal cycle and proximity of surface ridge should help to flush
out lingering clouds by early evening, and with light winds and
clear skies should get a few lows down toward the freezing point
across northwest Iowa.  Building ridge aloft will start to increase
high- and a few mid-level clouds, and increasing southerly flow will
slow or halt the fall in temps later in the night.

Large scale upper ridge will continue to build across the area, with
likely enough influence from wave traversing ridge along the
international border to push a weak boundary across the area Friday
night. However, a rapid return to warm advective patterns Saturday
with a bit breezier south winds developing. Will certainly be above
normal tempwise, but perhaps by quite a bit as warmer air noses up
into southeast South Dakota ahead of next frontal boundary to our

Models working to resolve some timing discrepancies from Saturday
onward, but generally that is the only significant difference with
the stronger upper ridging over the area until the axis shifts
eastward early next week. Increasing southerly flow at low levels
will bring greater moisture, along with threat for stratus
developing around Monday night or Tuesday. There will also come the
start of a precipitation threat by Tuesday with warm front lifting
into the area, but greater precipitation/thunder threat just beyond
the forecast period as jet energy pushes out across the plains and
cyclogenesis occurs over the plains.  Temps will continue above
normal through the end of the forecast period, with an abundance of
60s for highs, and lows moderating from 30s to lower 40s, into the
mid 40s to around 50 by the time southerly flow Monday and Tuesday


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1206 PM CDT Wed Oct 19 2016

Areas of stratus continue to develop just on the northern edges of
the CWA this afternoon behind an advancing cold front. Further
south, very light rain/sprinkles persist in areas south of I-90.

Through the upcoming 12 hours, will include a brief period of MVFR
ceilings at HON through the evening, with VFR conditions at the
other main TAF locations. Models are again struggling with
redevelopment of stratus overnight, primarily over the Missouri
River valley. While confidence is on the lower end, feel the
highest risk of lower end stratus will occur away from the TAF
sites, with general VFR ceilings elsewhere into Thursday morning.




LONG TERM...Chapman
AVIATION...Dux is the U.S. government's official web portal to all federal, state and local government web resources and services.