Area Forecast Discussion

FXUS63 KFSD 180935
Area Forecast Discussion
National Weather Service Sioux Falls SD
335 AM CST Sun Feb 18 2018
.SHORT TERM...(Today and Tonight)
Issued at 335 AM CST Sun Feb 18 2018
Sunday will bring our last gasp of warmth for several days as an 
impressive low level jet gets going overnight. Winds have kept our 
temperatures from falling off tonight and will drive some vigorous 
mixing tomorrow to get us into the 40s and will bring some gusty 
winds to the surface, potentially gusting above 45 mph in parts of 
northwest Iowa and southwest Minnesota. Have thus opted to issue a 
wind advisory.
Late Sunday night brings the arrival of our long advertised extended 
period of snow and wintry mix as a longwave trough begins to dig in 
over the western CONUS while a series of disturbances in the flow 
translate across the northern Plains. The southerly flow earlier on 
Sunday will have brought in enough warm air aloft to lead to a 
wintry mix across northwest Iowa, while most of southeast South 
Dakota will receive light snow as the most of the column will be 
below freezing by the time precipitation starts. Northwest Iowa 
could get up to a tenth of an inch of ice Sunday night into Monday 
morning, so have issued a winter weather advisory. For the rest of 
the forecast area, snow amounts Sunday night look to be low, 
generally an inch or less.
.LONG TERM...(Monday through Saturday)
Issued at 335 AM CST Sun Feb 18 2018
Early Monday will likely see freezing rain and sleet continue in 
northwest Iowa as southwesterly flow aloft helps maintain a nose of 
warm temperatures around 850-800mb. Monday's precipitation type 
looks messy, to say the least. Anything from snow northwest of a 
Yankton - Windom line, to freezing rain/sleet southeast of a Sioux 
City - Spencer IA like with a mix of everything in between. The CWA 
will be in the right entrance region of the upper jet pretty much 
all day Monday, so have put in PoPs for the entire period.
By late Monday night, the warm nose aloft will have eroded and 
saturation will reach above the -12C level across nearly the entire 
CWA, so we should all be receiving snow by that time save for areas 
around Storm Lake and Ida Grove. Unfortunately, it looks like 
forecast simplicity will not result from this, courtesy of potential 
banded snowfall. GFS, NAM, and CMC all show moderate frontogenesis 
around the 700mb level with a weakly stable or even unstable layer 
above it as the main wave swings through. Have bumped up amounts 
slightly along a Bonesteel - De Smet line to illustrate some of the 
potential banding. Did not go all out with a QPF increase because of 
the uncertainty that always comes with potential banded snowfall. 
This will be something to keep an eye on as it comes in range of 
short term guidance. With more time to go before the main snowfall 
event, have opted not to issue any headline products at this time.
Opted not to focus too much on the extended forecast beyond Tuesday 
morning due to the larger impact weather all taking place during the 
first three days. Next chance for precipitation looks to be in the 
Thursday-Friday time frame.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 530 PM CST Sat Feb 17 2018
The main issue later tonight are winds. A very strong low level
jet will develop, most acute at KFSD and KSUX, but also windy at
KHON. Surface winds from the southeast and then south, will
frequently gust to 25 to 30 knots coupled with non convective low
level wind shear, as 50 knot winds exist not too far off the
surface between 1000 and 1500 feet AGL. The winds will first
subside at KHON Sunday morning, then across KFSD and KSUX Sunday
afternoon. A cold front will then move through KHON by mid
afternoon Sunday likely ushering in MVFR ceilings behind the wind
SD...Winter Weather Advisory from midnight tonight to noon CST Monday 
     for SDZ070-071.
MN...Winter Weather Advisory from midnight tonight to noon CST Monday 
     for MNZ081-090.
     Wind Advisory from 9 AM this morning to 2 PM CST this afternoon 
     for MNZ080-081-089-090.
IA...Winter Weather Advisory from midnight tonight to noon CST Monday 
     for IAZ002-003-012>014-020>022-031-032.
     Wind Advisory from 9 AM this morning to 2 PM CST this afternoon 
     for IAZ002-003-013-014-021-022-032.
NE...Winter Weather Advisory from midnight tonight to noon CST Monday 
     for NEZ013-014.
SHORT TERM...Ferguson
LONG TERM...Ferguson