417 
FXUS63 KFSD 060339
AFDFSD

AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
939 PM CST Tue Nov 5 2019

.UPDATE...
Issued at 936 PM CST Tue Nov 5 2019

Have expanded the winter weather advisory a bit further south with
small warm layer on the southern edge of the band creating a
wintry mix of precipitation. Warm nose is expected to linger 
through midnight or so near Sioux Falls, at which time prevailing 
precipitation type should change to snow. 

UPDATE Issued at 754 PM CST Tue Nov 5 2019

With wave now working into forecast area, it appears heavy band of
snow is setting up slightly south that previously thought. Have
raised snow amounts, and expanded winter weather advisory. Still
looks like a quick hitting system with band of snow leaving the
area in the early morning hours on Wednesday.  

&&

.SHORT TERM...(This Evening through Wednesday)
Issued at 353 PM CST Tue Nov 5 2019

Focus for today has been on impending snow event across our northern 
forecast area. While high-res models displayed strong agreement in 
producing a heavier band of snow from east central South Dakota into 
southern Minnesota, they have had extreme difficulty capturing the 
earlier saturation which has already resulted in some very light 
snow accumulations toward and north of the Highway 14 corridor thus 
far this afternoon.

Looking at radar trends, appears there may be a break between this 
initial development along the mid level warm front, and the more 
robust development expected later this evening/tonight in response 
to low level warm advection and the approaching wave, which is now 
producing a second area of snowfall in western South Dakota. Next 
shift may have to adjust precip timing/trends to account for this, 
but overall, would expect to see light snow or flurries across our 
northern counties into the early evening, with intensity ramping up 
mid-late evening into the overnight, as the wave moves east and 
interacts with a fairly strong 850-800mb front located north of the 
I-90 corridor. By 03Z-06Z, both the GFS and NAM indicate pockets of 
weakly stable to unstable EPV* positioned above this front as well. 
At the same time, these models show pockets of strong lift within 
the dendritic growth zone. Both of these features could provide 
enhanced lift and tighten the overall banding from east central 
South Dakota into southwest Minnesota, potentially resulting in 
tighter gradients in snowfall on the north/south side of the band, 
as well as producing locally higher amounts than currently forecast 
at some locations within the band.

Per coordination with neighboring offices and WPC earlier today, 
bumped up QPF and snowfall amounts in response to above-mentioned 
dynamic features. A Winter Weather Advisory from Brookings, to 
Marshall and Jackson, was issued at that time, and to this point, 
that area still looks like the main focus. However, if the wave were 
to track slightly farther south as it moves across South Dakota, 
this area may need to be adjusted.

Cold air begins to settle into the region behind this wave for 
Wednesday, with areas north of I-90 likely remaining below freezing, 
while far southern areas climb toward the upper 30s, possibly near 
40. A weak trailing wave slides into western Nebraska on Wednesday, 
and that combined with a weakly unstable layer as the cold air pours 
southward behind the front, could produce areas of light snow or 
flurries. Cannot rule out some light snowfall accumulations in our 
southwest counties, but at this point, it appears that most areas 
would see a few tenths at most.

.LONG TERM...(Wednesday Night through Tuesday)
Issued at 353 PM CST Tue Nov 5 2019

Expected snowfall tonight will have an impact on temperatures in the 
coming days, especially Wednesday night/Thursday as a cold surface 
high moves across the area. Light winds/clearing skies will allow 
for optimal radiation over the fresh snow cover at night, followed 
by high albedo reflection during the day. Thus lowered temperatures 
in these areas closer to the 10th percentile of guidance. Elsewhere 
it will still be cold, with only our far southwest corner showing 
much hope of climbing above freezing on Thursday. 

Little time was spent adjusting the forecast beyond Thursday with 
the greater focus on the near term system. However, looks as though 
temperatures may attempt to rebound Friday/Saturday as the mid-week 
trough shifts east into the Great Lakes. 850mb temperatures warm to 
near/above 0C, which should translate to surface temperatures at 
least warming into the 40s, though again the snow cover will keep 
things cooler across our northeast at least into Friday.

The latter half of the weekend and into next week will feature 
another strong push of cold air into the region, and this looks to 
be colder, and last a bit longer, than the one on tap for Thursday. 
Similar to tonight/Wednesday, we may see an area of snow develop 
Saturday night into Sunday during the transition time, but far too 
much uncertainty in timing/placement to alter blended low pops at 
this time. Greater confidence in the very cold air slated to move in 
Sunday through Tuesday, when daytime temperatures may only climb 
into the teens-mid 20s, with lows in the single digits-lower teens 
for multiple nights in a row.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 454 PM CST Tue Nov 5 2019

Snow will increase across the area this evening as wave moves from
western South Dakota into eastern South Dakota. Ceilings will fall
into the low MVFR to IFR range within the band, and visibilities
will fall to a mile or less between 2-8Z. The heaviest snowfall
 is expected to fall north of I-90. Lower ceilings will linger
after the heavier snow shifts east. 

Cold front will surge south Wednesday morning with lower ceilings
moving south. Could be some light precipitation associated with 
lift along the front, but should be short lived. 


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory until 6 AM CST Wednesday for SDZ039-040-
     055-056-062.

MN...Winter Weather Advisory until 6 AM CST Wednesday for MNZ071-072-
     080-081-089-090-097-098.

IA...NONE.
NE...NONE.
&&

$$

UPDATE...BT
SHORT TERM...JH
LONG TERM...JH
AVIATION...BT