Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 262326
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
626 PM CDT Wed Apr 26 2017

.SHORT TERM...(This evening through Thursday)
Issued at 326 PM CDT Wed Apr 26 2017

Main focus in the short term is cold temps tonight.

H5 low over the eastern Dakotas and the associated surface low over
Wisconsin at 18Z will continue to move east-northeast out of the
area through the overnight hours.  On the back side of the upper
low, drier air, as evidenced by satellite imagery, will gradually
make its way east.  As the surface low gets farther east, gusty wind
will subside within hours around sunset.

Temperatures tonight will be the coldest in the 7 day forecast
period as the base of the H5 trough rotates through the area dragging
-4 to -6C temps at H85 along with it. All areas are expected to go
 below freezing so people with vulnerable vegetation outdoors
 should make plans to mitigate the impacts of below freezing
 temperatures for several hours overnight. At this time, did not
 mention frost in the weather grids as clouds will hang on a bit
 too long and wind will remain around 10 mph in most places so
 conditions will not be ideal for widespread frost formation.

As dry air gradually works east and subsidence prevails, clouds will
begin to break up in the early morning hours.  Model time/height
sections indicate enough dry air that sunny skies can be expected on
Thursday as well as wind around 10 mph.  This in turn will allow
temps to warm into the lower 50s most areas, which will be 10 to 15
degrees more than today, but still below normal for this time of
year.

.LONG TERM...(Thursday night through Wednesday)
Issued at 326 PM CDT Wed Apr 26 2017

Thursday night and Friday morning will be another cool morning with
the potential for frost and freezing temperatures as high pressure
remains in place. Will lean towards the CONSMOS output which gives
upper 20s to lower 30s to most locations.

This will lead into a cool Friday as low pressure deepens across the
central Plains. This will likely bring increasing clouds to the
Missouri River into northwest IA with mostly sunny to partly cloudy
skies along and north of Interstate 90. Even with the sun
temperatures will be well below normal as a cool air mass remains
locked in place. Expect most locations to climb to between 50 and 55
degrees. Will continue the small chance for rainfall from the
Missouri River into southern parts of northwest IA as the 850mb to
700mb layer tries to saturate with some weak frontal forcing, but
with no instability and marginal confidence in saturation in this
layer the pops will be 30 percent or less.

By Friday night the weak wave that may support a little
precipitation will move east and any chances for precipitation
should again be small and along and south of a Sioux City to Storm
Lake line. Lows will again be in the 30s, with the coldest readings
near highway 14.

At this time Saturday looks dry for most locations with an increasing
threat towards the Nebraska state line by afternoon. This is in
response to deepening low pressure across the southern Rockies.
Highs should be in the 50s with a gradually increasing northeast
wind.

Saturday night through Monday morning still looking like the most
interesting time frame. The models are all in good agreement with a
deep mid level low pressure tracking from the central Plains towards
eastern IA during this time. This places areas along and southeast
of a Yankton to Brookings line with a good probability of of rain
and possibly snow. As is always the challenge this time of year the
rain snow will be determined by the lowest 1000 feet of the
atmosphere. What will need to be watched will be if any instability
aloft can get into the system The latest GFS hints that there will
be a bit of an enhanced mixed layer over parts of northwest IA late
Sunday afternoon and evening, confidence will need to increase to
start ramping up concerns about measurable snow. One thing that may
work in favor of snow is that the models in the mid range have
seemed to underdo the dry air ahead of these moisture surges so that
could support better dynamic cooling, especially if additional dry
air is in place.

Monday through Wednesday will see the pattern modify with
temperatures likely recovering back closer to normal. A trailing jet
streak could bring a shot of rainfall Monday afternoon and evening
but not expecting too much from this smaller system.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 625 PM CDT Wed Apr 26 2017

MVFR will likely be the dominant category tonight. There are
indications that conditions will go VFR through the day on
Thursday.

&&

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

$$

SHORT TERM...Sally
LONG TERM...08
AVIATION...MJ



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