Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 171725

Area Forecast Discussion
National Weather Service Sioux Falls SD
1225 PM CDT Fri Mar 17 2017

.SHORT TERM...(Today and Tonight)
Issued at 358 AM CDT Fri Mar 17 2017

Frontal boundary draped across southwest Minnesota and northwest
Iowa will quickly exit to the east within the next hour. Weak
instability tracking through south central SD into the Missouri
Valley has triggered a few spotty light rain showers, however, given
the extreme dry layer below 700 MB, expect very little if any
precipitation to reach the surface. This activity will likely
continue to diminish through daybreak.

With surface low pressure moving through the Upper Midwest, and high
pressure expanding over the northern Plains, the pressure gradient
will remain fairly compact today. Winds will increase from the
northwest through midday, becoming gusty throughout the region this
afternoon. Strongest winds will be near and north of I-90 where
gusts to 40 mph will be possible, while sustained winds will average
15 to 30 mph. With the gusty winds and lack of snow cover in south
central SD/Lower Brule area, fire danger will be a concern. The dry
conditions and Humidity dropping as low as 30 percent this afternoon
will lead to high or very high fire danger in this area this
afternoon. Will hold off any fire weather headlines with highs only
in the 50s and marginal humidity, but we will need to keep an eye on
this area this afternoon given the gusty winds.

Skies will be mostly sunny for most locations today, however some
low/mid level stratus will filter southward into east central SD and
southwest Minnesota this morning through this evening behind the
departing low. Temperatures will remain seasonably mild today,
although a little cooler across the Missouri Valley compared to
yesterday. Hedged towards the BCCONSRAW for highs, which is a smidge
warmer in the Missouri Valley, but still conservative where snowpack
remains. Highs will be in the 40s and 50s.

Winds gradually decrease this evening and tonight, as the surface
high expands across the region and return flow begins arriving in
south central SD late tonight. Temperatures will cool into the 20s.

.LONG TERM...(Saturday through Thursday)
Issued at 358 AM CDT Fri Mar 17 2017

Main focus through the weekend will be on temperatures, as snow
continues to gradually melt and well-above normal temperatures push
into the area with upper ridge moving east across the Plains. Still
anticipate temperatures to remain just a few degrees above normal
Saturday with relatively light winds as surface ridge moves across
the forecast area. Exception will be west of the James River, where
increasing southerly flow and lack of snow will help warm readings
into the 50s-lower 60s.

Sunday should be the warmest day of the weekend, and of the forecast
period. Models indicating 850mb temperatures well into the double
digits, with favorable south-southwest low level flow to aid mixing
ahead of a cool front which drops into the area late Sunday/Sunday
night. Broad model consensus has been trending a bit warmer from run
to run, and was already ranging from lower-mid 60s over current snow
covered areas, to mid 70s through the Missouri River Valley. Given
the forecast temperatures aloft and favorable mixing profile, have
nudged even a little warmer in areas near/south of I-90 in South
Dakota, and into the western portions of northwest Iowa, where snow
cover is currently non-existent or less than a couple of inches (in
other words, most likely to melt by Sunday).

As mentioned, cold front moves through Sunday night, but moisture is
limited and upper support weak, so little if any precipitation is
expected with the passage. Temperatures through next week currently
look to be fairly close to seasonal normals for highs, with readings
in the 40s to mid 50s. Lows will likewise be close to normal early
in the week. However, mid to late week becomes more active, with an
eventual increase in low level moisture holding up overnight lows as
a low level jet develops across the Plains Wednesday night and draws
some higher dew points northward.

For Wednesday, weak mid-upper level wave moves across the Northern
Plains. GFS shows low level moisture still lacking at this time, and
thus produces little if any precipitation with this wave. Canadian
and ECMWF a little more robust with precipitation chances, and thus
will stick with mid-high chance pops across the area later Tuesday
night into Wednesday. Temperatures aloft still below zero at this
time, so potential for some light snow accumulations if the precip
does pan out.

Upper level pattern later in the week is far from in agreement, with
the GFS developing a strong upper low over the central High Plains
by late Thursday, while the Canadian/ECMWF show a more open trough
tracking into the Northern Plains. Either of these scenarios brings
a threat of precipitation to our area again by Thursday/Thursday
night, though timing/location are varied among the solutions. The
greatest consensus for precipitation chances comes by the latter
half of Thursday, and possibly more so beyond this forecast period
Thursday night, as the upper troughs and associated surface front
move through the area. Increased moisture and marginal instability
indicate greater potential for showers than stratiform rain, with
some weak elevated instability possibly bringing a little thunder to
southern parts of the area. With lower confidence in timing and
location as mentioned above, though, will hold off introducing
thunder at this time.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1215 PM CDT Fri Mar 17 2017

Area of stratus across central and eastern South Dakota will
gradually shift to the east this evening into the overnight. Could
see some MVFR conditions in the stratus.

Gusty northwest winds will settle down this evening.




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