Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 270857
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
357 AM CDT Thu Apr 27 2017

.SHORT TERM...(Today and Tonight)
Issued at 357 AM CDT Thu Apr 27 2017

Despite clouds and wind, temperatures on the overnight have been
mainly a few degrees either side of freezing, with most areas at 08z
now subfreezing outside the lower Missouri River valley.  Clouds
have again started to back westward toward south central SD as lobe
wraps around upper low in northwest MN, and the primary challenge in
the shortest term will be breaking up cloudiness.

Would not be shocked to find a couple of flurries through the early
morning hours mainly across southwest MN where temps in cloud-
bearing levels touch a more likely ice-generation range. Otherwise,
will see quite a few clouds remain through at least mid- to late-
morning across the area, but increasing subsidence should begin to
work on clouds, probably in uneven fashion, by midday and lead to
some decent sunshine during the afternoon for most. Highs should
reach the 40s to lower 50s, warmer than Wednesday, and will probably
feel even better given tendency for winds to gradually ease by this
afternoon.

For most of the area, influence of exiting upper low will be hard to
shake, with perhaps only the immediate Missouri River valley feeling
effects of strong jet emerging late night into the Central Plains.
Sharp mid level ridge axis will maintain a dry trajectory over much
of the area, with the low-level northeast gradient maintaining a
strong dry layer below 700 hPa while some higher clouds spread in
late, which will be hard for precip to breach even by late night.
Have kept a minimal PoP southwest of the Missouri River across south
central SD and extreme northeast NE very late tonight

Temps tonight will again be a concern for those with vegetation of
concern, with readings likely dropping into the mid to upper 20s
near/north of I-90, and subfreezing for most locations north/east of
the Missouri River.  With less wind, frost will be a more likely
scenario for the coming night, and have introduced into weather
grids for the night. Ongoing temps preclude any need for highlight
on frost/freeze.

.LONG TERM...(Friday through Wednesday)
Issued at 357 AM CDT Thu Apr 27 2017

The primary concern in the medium and extended portions of the
forecast is the storm system focused on Sunday and Monday. Latest
guidance continues to support high precipitation chances beginning
Saturday night and continuing into Monday, and support an increased
risk of accumulating snow.

Latest model guidance maintains a fairly consistent on the influence
of this storm on the region, however there are some fairly
significant details or differences that are yet to be worked out.
GFS/EC have both exhibited trends of slowing this system down as it
enters the Plains on Sunday, with a bit of a southern jump with the
00Z run. This in return pushes the highest precipitation chances
into Sunday night.  Secondly, the 00Z ECMWF deepens the wave a bit
faster than it`s previous run, introducing a stronger warm advection
fetch Sunday night, narrowing the corridor of strongest dynamical
cooling, and pulling a dry slot into NW Iowa.  No strong preference
on models tonight, and a blended solution only produces minor
differences.

What this all boils down to is an increasing rain risk Saturday
night as initial warm advection and upper divergence spreads into
the region.  There may be some initial slowing in precipitation due
to a northerly dry air intrusion, but what this will do is allow
temperatures to begin to fall or stall through Sunday morning.
Through good collaboration tonight, have regionally lowered
temperatures back towards the upper 30s and lower 40s on Sunday.
Temperatures will remain more problematic the further north and west
you travel on Sunday, due to the larger influence of precipitation.
50s could be possible in Huron if rain stays southeast.

The biggest forecast concerns fall on Sunday night into Monday as
the main upper trough pivots through the area.  With a slowdown in
solutions, the heaviest precipitation will focus itself Sunday
evening, with an elongated and impressive trowal remaining focused
over MN on Monday. Precipitation type remains highly dependent on
the lowest 1000 ft of the atmosphere Sunday night, but confidence
growing that rain will change over to snow across the CWA given
nocturnal cooling of the boundary layer and axis of intense
dynamical cooling aloft. Unfortunately, for those in Minnesota, snow
may linger well into Monday as cold air is pulled southward out of
southern Canada. Have collaborated a fairly large drop in
temperatures on Monday east of I-29, with blends taken from the
CONSRAW and WPC guidance.

Still far too early to talk about specific snow amounts, given the
synoptic and mesoscale uncertainties in this system, but it may be
time to start talking a bit more about the dreaded late Spring
"snow" word.

Slow recovery will take place next week with the continuing
northwest flow.  At this point temperatures may try to reach back
towards normal levels, with no meaningful precipitation anticipated.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1039 PM CDT Wed Apr 26 2017

MVFR to lower end VFR will be the dominant categories through
Thursday morning. Then by late morning Thursday and Thursday
afternoon, most of this stratus should begin to clear out
providing more widespread VFR conditions.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...Chapman
LONG TERM...Dux
AVIATION...MJ



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