Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 191133

Area Forecast Discussion
National Weather Service Sioux Falls SD
633 AM CDT Sun Mar 19 2017

.SHORT TERM...(Today and Tonight)
Issued at 339 AM CDT Sun Mar 19 2017

Unseasonably warm temperatures will be the main story of today, with
strong southerly flow ahead of an approaching cold front. Low level
jet continues to tap into warm air advection, with breezy
southeasterly winds at the surface turning more southerly through
mid morning. Cold front arrives in south central SD late
morning/midday and races eastward through the forecast area this
afternoon and early evening. Moisture will be lacking, therefore
expect the frontal passage to be dry. With ample sunshine, a well
mixed environment, diminished snowpack, and extremely warm near
surface temperatures, highs should reach the 60s or lower 70s for
most areas. West of the James River into the Missouri Valley, we may
even see some mid and upper 70s breached.

Winds turn northerly behind the front this evening and tonight,
however not a great deal of cold air filters into the region
overnight, but we will see some mid and high clouds filter
southward, most notably across areas north of I-90. Lows tonight
will be in the 30s.

.LONG TERM...(Monday through Saturday)
Issued at 339 AM CDT Sun Mar 19 2017

After the dry Spring-like weekend, a more active pattern will
dominate across the northern Plains as we actually move into Spring
through the upcoming work week. A northerly flow of cooler air will
prevail on Monday, though despite some increase in clouds, we should
remain on the warm side of normal for the first day of Spring, with
highs from the upper 40s in southwest MN/east central SD, to the mid
to upper 50s through the lower Missouri River Valley. A mid-upper
level wave will slide east along the South Dakota/Nebraska border
Monday night, with a decent mid level front developing into south
central South Dakota by late Monday evening, and further into far
northeast Nebraska by daybreak Tuesday. The wave and associated mid
level boundary sink farther south by early Tuesday afternoon, which
should bring an end to any precipitation chance except perhaps the
Sioux City-Storm Lake area after 18Z. Temperatures surface and aloft
support initially light rain, mixing with/or changing to snow for a
time later Monday night/early Tuesday, as saturation cools the lower
level temperatures. At this time, do not expect much in the way of
accumulating snow, perhaps up to an inch in higher elevations of
Gregory County, but otherwise generally a dusting to half inch. NAM
is a bit more robust with its snowfall potential, but this solution
is an outlier and have followed greater consensus of GFS/GEM/ECMWF.
As mentioned by the previous shift, will also maintain a fairly
sharp northeast edge to precip chances, generally south of Huron to
Sioux Falls to Spencer Iowa, as northeast flow around Canadian high
pressure keeps low levels dry across the northeast half of the
forecast area.

Should see a dry but cool period Tuesday afternoon/night as a weak
mid-upper level ridge works across the region. Wednesday could be a
raw day, with cool temperatures in the 30s to lower 40s and a brisk
southerly breeze. A wave sliding up the back side of the the upper
ridge into the Dakotas late Tuesday night and Wednesday could spread
another round of light precipitation across the area. Models have
been maintaining their respective preferences with regard to the
strength of this wave, and the resulting amount of coverage of
precipitation on Wednesday, with GEM/ECMWF stronger and a little
wetter, while GFS remains weaker and somewhat drier. Timing remains
similar, but with lingering uncertainty, will stick with pops in the
high chance range, as confidence to bump to likely not quite there
yet. Here again we see a potential for some light early morning snow
accumulations, mainly west of the James River. But slowly warming
temperatures through the day should result in a cold rain as the
precipitation lifts northeast in the afternoon.

Main show remains focused on the end of the week, with a stronger
trough tracking into the High Plains Thursday, then progressing east
toward the Mississippi Valley on Friday. Differences abound between
the models with this system, again maintaining their respective
preferences from previous runs, with the GFS farther north/faster,
ECMWF farthest south/slower, and GEM between these two. All look
to be fairly wet for this forecast area Thursday through Friday
morning, though, with precip chances lingering into Friday night for
parts of the area if the slower/farther south ECMWF pans out. To
this point, despite differences in latitudinal track/timing of the
system, temperatures look to remain warm enough for primarily rain,
with brief shots of snow possibly mixing in at the onset early
Thursday, or as precipitation departs Friday/Friday night. GFS/GEM
also continue to show potential for some isolated thunder as the
wave lifts into the area Thursday night, resulting in precipitation
amounts possibly topping an inch in some areas.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 630 AM CDT Sun Mar 19 2017

VFR conditions are expected through the TAF period. Low level
winds shear of 40 to 50 kt at 2000 ft AGL will continue to be a
concern through 15z.




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