Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 251715

Area Forecast Discussion
National Weather Service Sioux Falls SD
1115 AM CST Sun Feb 25 2018

.SHORT TERM...(Today and Tonight)
Issued at 308 AM CST Sun Feb 25 2018

Not a lot going on in the short term but there are a couple of
concerns. In the near term this morning, there is an area of stratus
currently located in central ND and extreme north central SD oozing
southeastward. The RAP does bring some of this stratus south this
morning into our northern zones, in fact nearly to Sioux Falls,
before dissipating between 18Z and 21Z as it mixes out. However, the
boundary layer to 925mb winds are out of the west all morning so
there is also a chance the stratus may dry up before it gets to our
CWA, or divert off more to a straight easterly direction eventually.
For now, just kind of hedged with a partly cloudy wording in some of
our northern zones this morning. Secondly, am a little concerned
about fog development late tonight. Winds become light southerly as
a trough of low pressure moves into the western plains, and the
surface dew point depressions are very small. With a cold ground,
will have to keep an eye on this but indications are now that it is
pretty dry just barely above the surface. So if fog does form, it
may be pretty shallow.

Concerning temperatures, highs today will be in the upper 20s to mid
30s. Lows tonight could get pretty chilly in the low lying areas,
therefore blended some ARW and NMM values into the consensus which
lowers temperatures in low lying terrain.

.LONG TERM...(Monday through Saturday)
Issued at 308 AM CST Sun Feb 25 2018

A mainly dry pattern is setting up for the first half of the week as
westerly flow aloft persists across the region. At the surface,
warm air advection will take place on Monday ahead of a weak and dry
frontal system moving over the Dakotas. Low to mid level moisture is
limited; therefore only a few clouds will be possible with the
passage of this front, along with warmer temperatures. Highs will
range from the upper 30s to lower 40s. Temperatures on Tuesday will
be back down to near average as a surface high moves in and winds
turn to the northwest.

By Wednesday night into Thursday, a closed upper wave will be
located over the western CONUS and will track northeast into the
Rockies/Central Plains. This system could bring precipitation
chances across the forecast area. It is still far out and confidence
remains low given differences between models. The GFS is more robust
than the ECMWF, bringing the highest QPF amounts over northwest
Iowa. Conversely, the latest ECMWF run brings the core of the system
far east into central/eastern Iowa, keeping the forecast area dry.
The main concern with this system will be precipitation type, as
warm air advection surges northward, allowing warmer temperatures
aloft. That said, snow/rain will be possible, especially over Iowa.
As for now, have kept PoP as guidance suggested, with precipitation
likely over northwest Iowa. Strong pressure gradient will be
expected with the passage of the system. Given this, have increased
wind speeds for Wednesday and Thursday, mainly along and east of I-

For the remainder of the extended, upper ridging builds over the
region, keeping the area dry through the end of the week.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1115 AM CST Sun Feb 25 2018

Patch of low MVFR-IFR stratus drifting east-southeast across from
east central SD into southwest MN to start the period. This should
exit eastern portions of the forecast area by 20Z. Gusty westerly
winds, especially along and east of the Buffalo Ridge in southwest
MN, could result in drifting snow and patchy blowing snow which
may reduce visibility at times. The winds gradually subside after
sunset, but could increase again by mid-morning Monday, so will
have to watch for similar conditions across parts of southwest MN
on Monday.

Remainder of the forecast area should see VFR conditions prevail
through the period, though may have to watch some valley areas for
patchy fog late tonight/toward sunrise Monday.




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