Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 161120

Area Forecast Discussion
National Weather Service Sioux Falls SD
520 AM CST Sat Dec 16 2017

.SHORT TERM...(Today and Tonight)
Issued at 346 AM CST Sat Dec 16 2017

Fairly thick high and mid-clouds are expected today, but should be
another mild day with 925 hpa temps continuing to remain above 0C.
Weak northerly flow will allow slightly cooler air to filter into
the region from the north, so expect thermal gradient from north to
south throughout the day.

Models have backed off on precipitation chances for tonight, and
have dried out the forecast. With that said, some models hint at the
potential for stratus.  Low lying stratus appears to be thickest
across the central portion of the state.  There is still a remote
chance at some drizzle if the stratus is able to induce
collision/coalescence. Confidence at this point is not strong enough
to include in the forecast given the lack of dynamics.

.LONG TERM...(Sunday through Friday)
Issued at 346 AM CST Sat Dec 16 2017

Mild temperatures continue into the first half of next week.  Models
still suggest a mid level trough moving from the Pacific NW into the
plains on Thursday.  With fairly good agreement of a system amongst
the various solutions, raised pops across northwest Iowa by blending
Superblend and CONSALL.  With that said, still quite a bit of
differences in duration and precipitation amounts. GFS is fairly
light and transient, while the ECMWF suggests a longer duration
system, but both models take the crux of mid level energy and focus
it well to the south. It is interesting to note that ECMWF continues
to trend further south with each model run iteration.  Upper level
dynamics certainly increase Thursday night into Friday, just a
question of how this will match with what is occurring closer to the
surface. It appears however, that once the cold air pours into the
area on Wednesday night into Thursday, the region will be much
cooler heading into the weekend and even the following week.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 516 AM CST Sat Dec 16 2017

Confidence is fairly high that the TAF sites will be VFR for much
of the day. However late today and tonight, there is a risk of
MVFR ceilings developing, but the degree of development and where
the ceilings will impact the most remains rather uncertain. The
low level flow will become northerly tonight, which could usher
down MVFR which resides to the north in ND and the northern half
of MN. However many ensembles in the numerical models dry up the
stratus before it impacts the TAF sites. That said, they agree
that southwest MN could indeed have MVFR conditions tonight where
TAF sites do not exist in the Sioux Falls forecast area. Toward
the end of the TAF period near 12Z Sunday, KSUX could also receive
MVFR stratus, but from a system moving through the southern jet
stream in the central plains.




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