927 
FXUS63 KFSD 032122
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
322 PM CST Thu Jan 3 2019

.SHORT TERM...(This evening through Friday)
Issued at 322 PM CST Thu Jan 3 2019

Temperatures continue to overachieve anticipated highs, especially 
in those portions of northwest Iowa where snow cover is limited to 
non-existent. Will continue to follow this trend for highs Friday, 
nudging values toward the highest of available guidance generally 
near and east of Iowa Highway 60 corridor. Remainder of the region 
still has plenty of snowpack to melt away, so will stay below this 
highest potential, but still in the upper half of guidance given the 
continuation of modest westerly flow which is generally favorable 
for mixing.

Before we reach tomorrow, though, should see another rather mild 
night with lows in the 20s for most areas. Expect to see enough of a 
lingering westerly breeze and/or thin high cirrus to keep widespread 
fog at bay. Cannot rule out some patchy fog, potentially in slight 
upslope areas east of the James River Valley as indicated by mainly 
NAM-derived models. However, confidence in occurrence tonight is 
rather low so have not included in the forecast at this time.


.LONG TERM...(Friday night through Thursday)
Issued at 322 PM CST Thu Jan 3 2019

Another day of snowmelt adding to boundary layer moisture, combined 
with even lighter winds in slackening gradient, could lead to a 
greater chance of fog development Friday night into Saturday. Again, 
valleys/weak upslope areas are most susceptible, and will include 
the mention of patchy fog for this period for now. Any potential fog 
could have an impact on highs Saturday, and with the overall weaker 
flow, did not deviate much from blended highs. Exception is in our 
downslope areas in southwest Minnesota, and nudged highs a little 
higher in those areas. 

Models continue to show a broad trough swinging through the northern 
Plains Sunday/Sunday night, and the main question at this point is 
how much moisture will be available. Early Sunday evening, forecast 
soundings indicate a deep dry layer between a saturated ice-bearing 
layer above 10kft, and a potential stratus layer below 4kft. This 
layer does see some increase in moisture as the wave swings through, 
so could see some light precip reach the ground Sunday night. If 
precip does occur, will have to watch for precip type issues. Dry 
layer starts off quite warm, but saturation will erode this warm 
nose to some extent. Fortunately, also looks likely that surface 
temperatures ahead of the boundary will remain above freezing thanks 
to a modest inflow of boundary layer moisture in southerly flow 
ahead of the wave, so may be looking more at a straight rain-to-snow 
scenario than a risk of icing. Of course, with NAM model tendency to 
heavily suppress surface temperatures over snow cover, this is the 
one contrary solution to the above idea of warmer surface temps, so 
will still bear watching over the coming days.

Upper ridging and associated low level warming build back into the 
region in the wake of this wave, leading to a continuation of the 
dry and mild forecast through the end of this forecast period.


&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1114 AM CST Thu Jan 3 2019

VFR conditions persist into the evening hours. Patchy fog may be
possible after midnight, but confidence too low to indicate at
this point. 


&&

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

$$

SHORT TERM...JH
LONG TERM...JH
AVIATION...Dux