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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
501 PM CST Thursday Dec 18 2014

Short term...(this evening through friday)
issued at 348 PM CST Thursday Dec 18 2014

Stratus currently covering the entire region...and think the clouds
stay locked in through the night and into tomorrow. Clearing line in
central South Dakota will probably approach our far western areas
such as Gregory and Brule counties. So could see some clearing there
later tonight...and some sun in those locations tomorrow. This is
the area that could see some fog development later tonight if they
are able to added in fog mention. The rest of the area
will stay locked in the low clouds through tomorrow...with nothing
able to scour out the low level moisture. Given the cloud
cover...raised lows do not think temperatures will be
able to fall more than a few degrees from current readings.

One question is whether we are able to get any flurries out of the
stratus tonight. Models suggest moisture layer deepens enough for
this to be a possibility...but moisture depth and saturation both
seem borderline. Expect cloud top temperatures to be right around
-7c to -10c...right on the edge of ice production. Thus can not rule
out a little light freezing drizzle as well. Moisture depth looks to
decrease from west to east through the think the light
precipitation threat should wane by morning. Will need to keep an eye on
things...but at this time think that even if we do get freezing will not be heavy enough to cause much of an issue.
Otherwise cloudy but slightly warmer conditions tomorrow. Clouds
will prevent US from warming too much...but still thinking we get
into the low to middle 30s.

Long term...(friday night through thursday)
issued at 348 PM CST Thursday Dec 18 2014

Moist low level flow will continue to bring low stratus to the bulk
of the forecast area Friday night through Saturday night. Some
decease in cloud coverage will be possible on Saturday...
particularly in the west where temperatures will quickly warm into
the middle and upper 30s and may soar even higher if substantial
clearing does occur. Without much lift in the cloud
layer...measurable precipitation is not expected. Cannot rule out
some patchy drizzle/freezing drizzle potential...but with cloud tops
too warm for ice Crystal growth...flurries are not expected. Model
soundings suggest that the cloud depth is a bit too marginal for
widespread drizzle or freezing drizzle...with the exception of parts
of northwest Iowa on Saturday night. Surface temperatures will be in
the upper 20s at this will leave mention of patchy
freezing drizzle.

Potent storm system begins taking shape over the northern plains
Sunday afternoon as a trough emerges from the Canadian rockies and
digs into North Dakota. Still looking at some fairly significant
model differences regarding the track and confidence in
temperature trends and precipitation timing is somewhat low. It does
look like an initial wave swings into the area Sunday night...with
the Gem and NAM around 6 to 12 hours faster than the European model (ecmwf) and GFS.
With this wave some broad lift noses into the area and should allow
some light precipitation to form mainly across the eastern half.
Surface temperatures cool while the mild air aloft erodes. Expect a
wintry mix of precipitation...with snow...sleet and freezing rain
possible. With the better forcing likely to our east...any
precipitation will be very light and preliminarily it looks like
snow and ice amounts would be very minimal.

Secondary wave follows quickly on Monday...slows and deepens over
the middle and northern Mississippi Valley into Monday night. The Gem
is the outlier with a weaker open wave and was therefore discarded.
The latest GFS and European model (ecmwf) are quite a bit further east with the low
center compared to previous runs. It slowly wobbles off to the east
through Tuesday night with light precipitation impacting our area on
the back side of the low. With a more eastern track...the best
potential for precipitation for US will be across our eastern half
Monday into Tuesday. Cooler air advecting into the area behind the
low will allow the rain and snow mix on Monday to switch entirely to
snow Monday night. Winds will also pick up from the northwest Monday
night and Tuesday and become quite breezy. Highs on Monday will be
mild in the 30s...and cool slightly into the upper 20s to middle 30s on

Stratus clouds stick around the region Wednesday with another
possible weak wave diving along the upper level northwest flow.
Slight chance of light snow will accompany this wave across our
northeastern half. Cooler temperatures filter back into the region
middle week dropping readings back below normal.


Aviation...(for the 00z tafs through 00z Friday evening)
issued at 459 PM CST Thursday Dec 18 2014

Clouds look to prevail through the overnight hours...likely MVFR
to IFR at times. The back edge of the stratus will approach khon
after midnight...with short term guidance suggesting that fog will
develop on the back edge of the stratus. Will include a period of
LIFR fog for Hon that should lift into an additional stratus layer
into Friday.


Fsd watches/warnings/advisories...
South Dakota...none.


Short term...chenard
long term...

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