Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 180330

Area Forecast Discussion
National Weather Service Sioux Falls SD
1030 PM CDT Fri Mar 17 2017

.SHORT TERM...(This evening through Saturday)
Issued at 312 PM CDT Fri Mar 17 2017

Area of stratus will struggle to shift east this evening into the
overnight hours as flow decreases overnight. While the stratus is no
more than 1000 feet thick, will keep low slightly warmer in the

Models suggest that 925 RH dries out relatively quickly on Saturday
leading to nice warm up across the area. The strong solar heating
should work at melting any lingering snowpack across the area.  Air
is relatively dry aloft, so have kept dew points low during heating
hours tomorrow.  If winds were stronger, it would be a red flag type
of day, but winds should remain under criteria.

.LONG TERM...(Saturday night through Friday)
Issued at 312 PM CDT Fri Mar 17 2017

Saturday night, low pressure will nudge into the western plains with
high pressure situated over the MS Valley. Therefore the pressure
gradient will increase combined with a 30 to 40 knot low level jet
near 925mb. In effect, this will create a warm front which will move
eastward across the forecast area. With the increasing southerly
winds, blended in some warmer bias corrected ECMWF and GEM Global
lows for Saturday night in with the super blend readings. Our south
central SD counties may not dip much below 50 degrees, compared with
lower 30s in our far eastern zones where snow cover or recently
melted snow cover will hold temperatures down relatively speaking.
Finally due to the low level jet, did increase wind speeds on the
Buffalo Ridge by 3 to 5 knots late Saturday night and early Sunday.

Sunday will follow with troughing developing along strong westerlies
in south central Canada, south of an upper low in central Canada. In
response, a cold front/wind shift will begin moving through our
western zones in the afternoon, but the cold air advection is
forecast to begin a fair amount behind the actual wind shift.
Therefore Sunday still looks like an unseasonably warm day with
highs in the 60s and 70s. 60s will be prevalent over recently melted
snow covered locations, with 70s elsewhere. In fact, manually raised
highs a few degrees in our southwest zones from Mitchell to Gregory
county as diabatic warming should take hold just ahead of the wind
shift. Therefore have upper 70s going for south central SD, but if
everything comes together right, would not rule out 80 to 85 in that
area. There is one fly in the ointment at least for our eastern
zones. Both the NAM and GFS paint stratus based near 900mb moving
northward, generally along and east of Yankton to Brookings late
Saturday night and Sunday morning. There is a lot of stratus right
now down in the southern plains, so this is a plausible scenario
given the strength of the low level jet Saturday night. However,
both models also show the stratus moving eastward basically out of
our forecast area during the Sunday afternoon hours, so it should
not really hinder highs.

After Sunday, temperatures will revert back closer to seasonal
normals, perhaps just a bit above normal. Late Tuesday night and
Wednesday are a challenge in terms of pops. The GEM Global still
shows some light precip across the area, whereas the GFS anchors
another very large anticyclone throughout south central Canada early
and mid week next week, ushering low level dry air into this area.
Therefore it is dry. So only chance pops are warranted at this time
for light rain or snow depending on surface temperature. But either
way the precip should be no big deal. Of bigger importance is late
in the week when the various models still show a large disturbance
moving through the region. The 12z ECMWF was not available, but the
GFS continues to have most of the forecast area on the cold side of
this system. But the 850mb temperatures are positive, suggesting a
cold rain. There is some weak elevated instability noted in
northwest IA and immediate adjacent locations Thursday night,
generally at and above 800mb, along the warm front aloft. At this
time it is a bit too weak to include TSRA in the forecast for those
locations, but will monitor for future forecasts. More of a
challenge is temperatures late this week, and our diurnal
temperature curve between Thursday night and Friday may be too


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1014 PM CDT Fri Mar 17 2017

VFR conditions expected through the period. Only concern is the
possibility of fog at HON during the 09z - 12z timeframe.
Confidence in fog was low enough to preclude mention in the TAF.




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