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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
534 PM CST Wednesday Mar 4 2015

Short term...(this evening through thursday)
issued at 352 PM CST Wednesday Mar 4 2015

The last bitterly cold night for the forecast period is expected
tonight before the warming trend finally arrives. Arctic high
pressure slides southeast across the northern plains
tonight...moving overhead in the early morning hours before shifting
into the middle Mississippi Valley Thursday afternoon. Breezy northwest
winds late this afternoon will drop below 10 miles per hour this evening before
turning light and variable overnight with the arrival of the high
pressure center. With clearing skies expected after
sunset...temperatures will drop below zero for most locations. Lows
will range from around zero in south central South Dakota to the middle teens
below zero in east central South Dakota and southwest Minnesota. Wind chills
drop to around 20 to 25 below where the coldest ambient readings
will be found...but given that winds will be well under 10
miles per hour...will hold off on issuing any wind chill headlines.

Return flow on Thursday brings increasing southerly winds through
the day. Warm air advection begins in earnest in across areas west
of the James River where plenty of sunshine and little to no
snowpack will allow temperatures to mix into the middle 30s to near 40.
To the east...recent snowcover and weaker warm air advection will
limit warming but will still be an improvement from today. Highs
will mainly be in the 20s.

Long term...(thursday night through wednesday)
issued at 352 PM CST Wednesday Mar 4 2015

Strong southwest winds are expected to develop Thursday night with
winds increasing into the 35-40 knot range at 925 hpa in the evening
hours along the Buffalo Ridge. With elevated areas remaining
somewhat mixed...have raised forecast lows...especially along the
Buffalo Ridge.

Friday looks to be the first of several warmer days as 925 hpa temperatures
warm into the single digits above zero. With lingering snow pack
across the north and east...was fairly conservative in warming north
of I-90 and east of I-29.

Friday night models show a shortwave dropping down in northwest
flow. Tough call in terms of where to place any potential probability of precipitation...as
moisture is extremely limited and wave placement is somewhat
inconsistent. For now...focused probability of precipitation across northeast corner of the
forecast area closest to where the middle level wave tracks in both the
European model (ecmwf) and NAM. The GFS is further to the south and west....tracking
closer to a khon-kfsd-kslb line. Precipitation type is also quite
tricky...but given timing think any precipitation that falls will
mainly be snow.

Another moisture starved wave drops down in northwest flow on
Sunday. Models indicate cold air advection behind both waves on
Saturday and Sunday...though the strength of the cold air remains in
question. Have a 5 degree c spread in the 925 hpa temperatures on
Sunday...and have therefore stuck fairly close to super blend
guidance over the weekend.

Mild conditions expected Monday through Wednesday of next week.
With 925 hpa temperatures climbing to + 10 c or more...have sided towards
the warmer side of guidance with limited snow pack expected by then.
Stuck closer to guidance on Wednesday as flow near the surface
starts to take on a southeasterly flavor. With the easterly
component...the mixing potential decreases some along with the
increased potential for stratus.

&&

Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 534 PM CST Wednesday Mar 4 2015

Any lingering MVFR ceilings east of a khon to kfsd to kslb line
will dissipate soon after 00z...leaving VFR conditions through the
forecast period. With deep Arctic airmass in place...and weak flow
to weak warm advection at lower levels toward daybreak at kfsd and
ksux...will have to monitor for development of some shallow ice
fog...perhaps due to man made influences...by late night and early
morning.

&&

Fsd watches/warnings/advisories...
South Dakota...none.
Minnesota...none.
Iowa...none.
NE...none.
&&

$$

Short term...
long term...
aviation...Chapman

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