Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 181131
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
531 AM CST Sat Feb 18 2017

.SHORT TERM...(Today and Tonight)
Issued at 400 AM CST Sat Feb 18 2017

A perfect Saturday is expected over the region.  With light winds
through the day, temperatures again climb well into the 50s with a
few 60s in the Missouri River valley. A bit of cirrus will arrive by
mid-day. Upper clouds and a light southerly wind will prevent any
big drop in temperatures overnight. Lows will bottom out in the
lower to middle 30s.

.LONG TERM...(Sunday through Friday)
Issued at 400 AM CST Sat Feb 18 2017

The greater degree of meridional flow by Sunday is likely to have a
detrimental impact on sunshine, both from increased threat of mid-
to high-level clouds, and potentially a northward push in stratus
level clouds toward mid to late day. It will be very mild
regardless, with mainly 60s for temperatures, and dewpoints likely
to reach the mid 40s to around 50 on increasingly strong southerly
winds.

Deeper moisture profiles will continue to evolve Sunday night as
sharp trough begins to lift/shear northeast into the central high
Plains by morning.  Stout low-level jet will provide a conveyor of
moisture which will be in place as band of lift forcing wraps north
and northeast later night and into Monday morning. Weak elevated
instability suggests that embedded thunder will occur with the
overall area of showers.  With eastward shift in the best conveyor
belt through the morning, should see more of a drier/quiet time
later morning into midday on Monday as drying aloft pushes through
the area. Upper trough is fairly sharp, and will be pushing through
areas near/east of I-29 along with the frontal convergence during
the afternoon.  Signal is difficult to filter from the noise, but
there is potential for some destabilization to occur between exiting
clouds/precip in the morning and approach of the sharp lower- to mid-
level trough during the afternoon. Best chance for this to occur
would be across southwest MN.  Some of the 0-1km shear values could
get interesting, and will have to watch for perhaps even a small
severe weather threat provided the larger scale can be a bit more
supportive rather than a bit less than favorable with main PV
advection already outpacing the lower level boundary earlier in the
day.

At this point, appears that drying behind the frontal boundary along
with a rapid decrease in mixing/gradient by late evening will allow
temps to fall enough by midnight to decrease the potential to set an
all-time record high min temp for Monday.

Tuesday still has the look to be the warmest day of this
exceptionally mild stretch of weather.  Threat for cloudiness would
seem to be at a lower level, and lower levels will be working toward
more of a west to southwest wind direction. With 925 hPa temps from
+12 (SW MN) to +18 (SC SD) temps well into the 60s and even some
lower 70s toward south central SD and the Missouri River valley are
likely.  These latter areas are also more likely to find dewpoint
readings mixing into the lower 30s, a reversal from most of the
early part of this warm stretch which largely resulted in higher
than forecast dewpoints.

Still watching for the flow to settle into a more zonal
configuration on Wednesday, with a wave moving along the
International border. This feature will play a somewhat critical
role to initiating a cooler and drier air push into the region.
Wednesday in the meantime will remain mild as winds turn toward more
northerly with time and more significant cooling begins toward
evening. Should still see highs reach the mid 50s to lower 60s,
warmest through the Missouri River valley.

Next trough in the southern branch will begin to encroach on the
central plains by Thursday, with initiation of precipitation in the
warm advection wing later Wednesday night into Thursday. There is
likely going to be some uncertainties on precipitation timing and
type with potential wet bulb impacts and variation in strength of
cold push (stronger with current 00z ECMWF). Likely will see some
mix or change to snow for areas from south central to east central
SD sometime on Thursday, but a larger scale transition going through
Thursday night with approach of main upper wave and collapse of
thermal gradient toward developing system. On strictly a big picture
view, strength of dynamic frontogenetic forcing and the proximity of
dry slot would bring thundersnow into the game as well. Solutions
also indicate likely development of trowal. Overall, this system
does remain fairly progressive, at least until really wrapping up
heading east Friday. Potential for a very impactful system remains
fairly strong with consistency of troughing signal on the larger
scale, despite some minor latitudinal and timing differences. Trends
have been to settle baroclinicity southward a bit, placing potential
for significant snow accumulations within the forecast area. Best
advice at this point is to continue monitoring the system potential,
which is still 5 to 6 days out!

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 531 AM CST Sat Feb 18 2017

VFR conditions expected into Sunday.

&&

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

$$

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



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