433 
FXUS63 KFSD 161801
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1201 PM CST Wed Jan 16 2019

.SHORT TERM...(Today and Tonight)
Issued at 253 AM CST Wed Jan 16 2019

Colder air continues to sink southward into the area this morning, 
marking the beginning of an extended period of near to below normal 
temperatures through the upcoming 7 day forecast.  In addition to 
the colder temperatures, there's no shortage of impactful weather 
through the forecast, with at least three chances for snow ahead. 

Today: Stratus will attempt to clear the CWA this morning, but
should be replaced by mid and upper clouds through the day. Most
should at least see filtered sunshine. Temperatures will only 
reach near or just below the seasonal normals. The good news at 
least is that winds will be diminishing slightly through the day.

Tonight: A nuisance wave emanating out of northern Utah will 
drift eastward overnight quickly pushing stratus back northward
this evening.  Models have trended towards a slightly stronger 
700 mb wave, with most models showing a period of saturation in 
the soundings later this evening and into the early overnight 
hours. QPF amounts won't be very high, but consensus suggests the 
possibility for a quick dusting up to an inch of snow. A little 
bit of freezing drizzle may mix with the snow at times, especially
on the back edge of the shortwave. Have boosted PoPs in most 
areas. 

.LONG TERM...(Thursday through Tuesday)
Issued at 253 AM CST Wed Jan 16 2019

Thursday-Thursday Night: Despite the lingering cloud cover, temperatures
may climb back near or slightly above the seasonal normals. It's 
possible to have a bit of fog early Thursday. Another surge of dry
and cold air arrives Thursday night, setting the stage for a 
widespread snow on Friday.

Friday-Friday Night: Overall, minimal changes to the ongoing 
forecast as model guidance remains consistent in bringing a 
progressive wave through the Central Plains on Friday. This wave 
will track eastward out of the traffic jam of disturbances visible
on  WV satellite imagery over the Pacific this morning. Warm 
advection associated with this wave is expected to begin early 
Friday morning over western and central South Dakota, slowly spreading
eastward by daybreak Friday as dry air is overtaken. 

Confidence is a bit higher on a few items for this event.

1. There will be a very sharp northern and northeastern snow 
gradient due to the influence of cold and dry air. 

2. Despite the broad nature of the warm advection, there will likely 
be a more narrowed and focused corridor of moderate snows on Friday. 
Soundings within this band suggest a rather deep dendritic layer, so 
when it snows, it will be efficient. Not a ton of instability within 
the soundings, but certainty something to monitor. 

3. SLR will be increasing as Friday wears on, and influence of 
colder air arrives. Snow should trend towards the lighter and 
fluffier variety. 

4. Driving around the region on Friday, will be messy. 

Regarding QPF, in coordination with surrounding offices have used a 
50/50 blend of WPC guidance and Superblend.  This does a bit better 
job accounting for the higher ensemble numbers, but won't go as far 
as the much higher ECMWF QPF. 

The end result is a fairly wide area of 2-6" snowfall, with the 
potential for locally higher amounts, especially in the initial 
development areas of central South Dakota, where amounts closer to 5-
8" may be possible. A fairly small winter storm watch could be 
considered later today for central South Dakota, if confidence in
higher amounts grows.

Saturday-Tuesday:  After the snow, a burst of arctic air is expected 
to move southward bringing very cold temperatures to the area for
Saturday along with wind chill advisory conditions. However this 
morning, we're seeing signs that the extreme drop in temperatures 
Saturday night into Sunday may be subdued a bit by increasing 
warm advection aloft, mid-level cloud cover and even a bit of 
light snow. Lows may still fall into the teens below zero, but 
they may also warm through the night from west to east. 

Rather extreme differences in extended guidance develops after 
Sunday, so confidence remains low.  The GFS/GEM both bring a more 
developed upper trough through the Northern Plains Monday. The ECMWF 
on the other hand drops most of this energy into the Southwestern 
US. Both camps would suggest at least some snow chances early next 
week, but to varying degrees.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1200 PM CST Wed Jan 16 2019

IFR ceilings which have backed west of the James River valley will
begin to spread ever so slowly eastward this afternoon, as a weak
system begins to expand light snowfall of MVFR to IFR visibility
eastward out of southwest SD toward mainly areas near I-90 and
southward. A few hours of IFR visibility are likely as snow moves
through. In the wake, weak flow is likely to result in some at
least MVFR visibility and IFR ceiling conditions through the
morning for KSUX, with just the IFR ceilings for KFSD and MVFR
ceilings around KHON.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...Dux
LONG TERM...Dux
AVIATION...Chapman