Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 201721

Area Forecast Discussion
National Weather Service Sioux Falls SD
1221 PM CDT FRI MAY 20 2016

.SHORT TERM...(Today and Tonight)
Issued at 348 AM CDT Fri May 20 2016

Upper level trough spinning through the Central Plains early this
morning triggering a few light showers/sprinkles well to our south
with expansive mid level clouds spreading northward through eastern
Nebraska and Iowa. This trough projected to track eastward toward
the mid-Mississippi Valley today, while another trough begins to
drop south into the Red River Valley. With combined weak lift from
these two features, think we will see fairly extensive cloud cover
develop by midday. High-res models continue to indicate isolated to
scattered radar coverage developing as well. However, with forecast
soundings indicating only a very shallow unstable layer, and with
relatively dry near surface layer persisting, do not expect more
than spotty sprinkles with minimal threat of measurable rainfall.
Thus will keep pops less than measurable through the afternoon, but
have expanded coverage of sprinkles to much of the area along and
east of the James River Valley. With the more extensive cloud cover
and cooler low level air working into the area around the Central
Plains trough, have cooled temperatures today a bit from previous
forecast, but still looking at highs a couple of degrees either side
of 70.

Any afternoon sprinkles expected to diminish with sunset, but with
northern wave continuing to drop southward across the forecast area
overnight, and weak warm advection/low level convergence west of the
James River later tonight, will hang on to narrow band of slight
chance pops for parts of the Missouri and lower James River Valley
areas after 06z tonight. Should be another mild night with lows in
the lower to mid 50s.

.LONG TERM...(Saturday through Thursday)
Issued at 348 AM CDT Fri May 20 2016

Southerly flow is expected to increase throughout the weekend
ahead of a trough approaching from the west. With the increasing
southerly winds, will see dew points rise but capping inversion
looks to be strong enough to mainly keep convection tied to the
trough moving through sunday night. Appears there could be a fair
amount of stratus around the region on Sunday morning. Models
erode the stratus through the morning hours, but am a little
worried this maybe overdone. With relatively small differences in
the MEN ensemble, kept blend temperatures but will have to watch
this closely.

Temperatures on Sunday will obviously have a strong impact on
instability and severe potential for Sunday night.  SPC has kept the
slight risk for the western half of the forecast area, but am
concerned with 00z models slowing down timing of the trough.  If
storms are elevated, the effective shear is fairly minimal with
mainly speed shear throughout the depth of the troposphere.  NAM
suggests the storms would be closer to surface based, and with the
increased speed and directional shear, a few storms in central South
Dakota could produce strong damaging winds of hail.  After the
initial wave lifts through  additional rounds of showers and
thunderstorms are possible throughout the week.  with discrepancies
in the details in the extended, stuck close to guidance blend for
the time being.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1219 PM CDT Fri May 20 2016

A few light showers or sprinkles may impact the terminals this
afternoon, however VFR conditions are expected into Saturday
morning. Winds are expected to remain south southeast into
Saturday morning.


.FSD Watches/Warnings/Advisories...


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