Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 131633

Area Forecast Discussion
National Weather Service Sioux Falls SD
1133 AM CDT Tue Mar 13 2018

.SHORT TERM...(Today and Tonight)
Issued at 310 AM CDT Tue Mar 13 2018

Cirrus continues to thin and drop southward early this morning,
making it possible for fog to develop over northern portions of
South Dakota. While not anticipating any widespread issues
locally, could see this fog build southward towards Huron,
Mitchell, and Chamberlain by daybreak.

Today: Plenty of sunshine today, but winds are expected to be on the
light side due to high pressure moving through the Tri-State area.
Could see similar temperatures to those of Monday, but temperatures
aloft have cooled slightly from Monday, and mixing won`t be nearly
as efficient.  Still temperatures will hover near to slightly below
normal in most areas.

Tonight: Expecting a light southwesterly surface fetch through the
night ahead of an approaching cold front dropping south from North
Dakota and northern Minnesota. This should keep overnight lows on
the warmer side of guidance, slightly above normal.

.LONG TERM...(Wednesday through Monday)
Issued at 310 AM CDT Tue Mar 13 2018

As we move into the medium and extended portions of the forecast,
the good news is that there is a bit more certainty in the forecast
for the end of the week, but still a few questions to be answered.

Wednesday: Temperatures will be the biggest concern
for Wednesday. As we`ve mentioned before, a cold front will settle
into the MO river valley by mid-day Wednesday. Despite the light
winds along and behind the front, mixing should be sufficient to
push temperatures into the 40s nearly everywhere, with highs closer
to 60 on the Missouri River.

Thursday: Light easterly flow at the surface will prevail for
Thursday as the axis of a sharp 500 mb ridge sits overhead. Low
level temperatures do cool slightly Thursday, so I`d anticipate 30s
in northern portions of the CWA and mid 40s near the MO River.  A
few models are hinting at a bit of stratus draining down into
central SD by Thursday morning.

Friday-Saturday:  Looking ahead to our next chance for precipitation
on Friday and Saturday, we`ve seen a considerable trend in the
medium range guidance over the past 24 hours.  That being, we`ve
seen the GFS and GEM all trend significantly towards the ECMWF
solutions that have been very consistent during the past three runs.
In general the GFS has consistently trended deeper with the upper
wave moving through the Great Lakes Thursday night, and has trended
much higher with the ridging over Manitoba and Saskatchewan, both
steering features for the upper wave that will race eastward out
of the newly established West Coast trough. The favored track of
this wave takes it across the Central Plains Friday into Saturday.
The EC remains the furthest south solution, with the GFS slightly
further north.

What we should see is an elongated band of precipitation rotating
northward into the MO River valley late Friday.  Some questions
regarding precipitation type. Feel the blends may be overstating the
rain potential given the dynamic cooling and precipitation intensity
within the corridor of precipitation moving northward. Timing is
also critical. Should this wave pivot through more in the evening
and overnight, then it`s possible we see a few inches of snow in
the MO River valley by Saturday morning. Also of note is the high
pressure sitting across the western Great Lakes, and likely
capable of producing a very sharp edge to precipitation as it
advances northeast.  Speaking of high temperatures on Saturday,
light winds and cooler low level temperatures may leave us
struggling to reach to far beyond the lower 40s. Given the trends
in the models, have weighted the forecast into the weekend more
heavily towards the ECMWF.

Sunday-Monday: Another chunk of the West Coast trough ejects
eastward as we start the new work week. Still considerable
uncertainty regarding this feature, but confidence in guidance has
increased enough to allow likely PoPs to be mentioned in the
grids. Obviously the precipitation types and amounts will depend
highly on the track, timing, and dynamic cooling of the system as
it moves through. Downstream blocking will be very key to this
forecast again. That said, it certainly does look like a system
that could bring accumulating snow to the area however along with
cooler temperatures.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1132 AM CDT Tue Mar 13 2018

VFR through the period. Some patchy fog possible late tonight but
chances a little too low to include in forecast.




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