595 
FXUS63 KFSD 022323
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
523 PM CST Fri Mar 2 2018

.SHORT TERM...(This evening through Saturday)
Issued at 403 PM CST Fri Mar 2 2018

A much milder night in store in a stout southeasterly surface flow, 
this thanks to surface high pressure to our east and a surface 
trough over the Western High Plains keeping a gradient across our 
area. Skies will be mostly clear with lows in the upper 20s to mid 
30s.

With continuing warm air advection across the region, temperatures 
will be even warmer on Saturday, but with increasing low level 
moisture models are suggesting stratus developing over much of the 
area during the day. While this may temper highs just a bit, still 
looking at readings in the 40s from I-90 northward, to the 50s to 
the south. Did add some drizzle to portions of our east later in the 
day with the warm air advection above the low level moisture, and 
both the GFS and NAM are outputting some very light QPF in the 
afternoon. 

.LONG TERM...(Saturday night through Friday)
Issued at 403 PM CST Fri Mar 2 2018

The main message for the longer term period is the major storm 
expected to effect the region later on Sunday through Tuesday. The 
devil is in the details however, with models still exhibiting 
differences with regard to track and timing of the system.

Prior to that, an upper level trough over the western CONUS begins 
to shift eastward on Sunday. With continuing warming thermal 
profiles, the warming trend will continue with highs climbing into 
the mid 40s to mid 50s. There will continue to be a drizzle threat 
during the day, with soundings indicating moisture being confined to 
800 mb and below. 

On Sunday night the upper level low encroaches on western SD as a 
surface low tracks across Nebraska. With deepening moisture across 
our area, could have a period of bona fide rain on Sunday night, and 
cannot rule out isolated thunder over portions of our west with 
models indicating weak instability with ML CAPE values of 100 to 200 
J/KG over portions of the area overnight. 

The forecast becomes fuzzier after that - dependent on the evolution 
of the previously mentioned surface low, and how quickly colder air 
wraps in behind the system. At this point, models continue to range 
in the low centered anywhere from southern ND (ECMWF) to far 
southeastern SD (GFS) by Monday afternoon. Even so, almost all 
models pointing toward much of our area being dry slotted on Monday 
afternoon -lessening precipitation amounts for much the central and 
eastern parts of our CWA. Using a consensus of models because of 
differences, thermal profiles look to cool on Monday, with the 
better chance of receiving snow during the day lying over south 
central SD and the western James River Valley. Again, because of 
model differences, what occurs to the east is less certain. What is 
more certain, is that strong winds will develop across the area in a 
tightening gradient, and any areas that do receive snow could have 
an issue with blowing snow. Temperatures will slowly drop later in 
the day as the low becomes situated to our east, with all areas 
changing to snow by Monday evening, though amounts at that point 
look to be generally light. Soundings would indicate very little 
chance of freezing rain with thermal profiles cooling quickly. 
Models are showing light snow lingering into early on Tuesday.

In summary, while it is too early to forecast snowfall totals, the 
better chance of at least moderate, to possibly heavy snow will 
exist from the James River Valley and westward, with lesser amounts 
to the east.

With the departure of the storm, the remainder of the week looks to 
be dry with temperatures at or just below normal for this time of 
year.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 518 PM CST Fri Mar 2 2018

VFR conditions into the overnight period. We will be dealing with
minor LLWS into Saturday.

Stratus will build northward Saturday morning and overspread the
forecast area through the day. IFR conditions will be likely later
on Saturday and we may also see periods of fog or drizzle by the
afternoon. 

 &&

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

$$

SHORT TERM...JM
LONG TERM...JM
AVIATION...Dux