Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 122331

Area Forecast Discussion
National Weather Service Sioux Falls SD
631 PM CDT Tue Sep 12 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 232 PM CDT Tue Sep 12 2017

Quiet weather continues this afternoon as we remain stuck under weak
flow aloft. This has resulted in clear skies and temperatures in the
80s at most locations. By this evening, a weak piece of energy
sneaks off of the wave currently evident on WV imagery over WY, and
slides along the NE/SD border. This could be enough to utilize some
very subtle elevated instability originating from the 850-700 mb
level. Current thinking is that dry air in the low and mid levels
will limit this activity to just sprinkles however.

Wednesday looks to be another warm but quiet day across the region
as we remain between systems. High temperatures look to be a touch
higher than this afternoon with 850mb temps in the low to mid 20s C,
resulting in widespread mid 80s to mid 90s. Otherwise, looks for
plenty of sunshine and southerly winds to continue.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 232 PM CDT Tue Sep 12 2017

Strong southerly surface pressure gradient in place on Wednesday
night, especially east of the James River, as low pressure deepens a
bit over central SD. This should keep temperatures very mild through
the night and will lean much closer to the CONSRaw output for
morning lows which usually handles the windier nights much better.
Will have to watch the Buffalo Ridge area as well with winds
possibly turning a bit south southwest and a fairly shallow
inversion in place. This pattern is occasionally supportive of
stronger winds on the ridge so will go a little higher, but not too
high as the wind direction is not quite normal to the Buffalo Ridge.
Will have to keep an eye on thunderstorm chances towards central SD
late Wednesday night as a weak wave moves through SD. For now
chances will remain on the low end.

Thursday looks to be warm, breezy and a little humid as a weak
boundary drifts into central SD. A very small chance for early
morning showers and thunderstorms as the weak wave moves through. By
afternoon a boundary in central SD behind this wave does not appear
as though it will produce any convection during the day as model
soundings are strongly capped and mid and upper level heights are
rising behind the exiting wave.

Friday late afternoon into Friday night will see a threat for
thunderstorms. A surface front will be in place across central SD
into northeast SD with the warm sector in place across most of the
area. Most of the warm sector looks pretty capped into the evening
but locations a little closer to the boundary may see enough heating
to break the cap. The area near the boundary is also more in line
with the forcing from the upper level wave. Shower and storm motion
will likely be easterly so the threat will shift east Friday night.
While severe weather should not be a major issue an isolated strong
to severe storm will be possible west of Interstate 29 with about
1500 J/kg CAPE and surface to 3 km shear about 30 knots.

Saturday a tougher call with some disagreement on timing of the cold
front. Will lean towards the slightly slower solutions as the upper
level jet is progged to lift northeast which should allow the warm
sector to heat out a bit before the cold air settles in. Increased
lows a bit everywhere on Friday night with potential for clouds and
southerly winds and increase highs a bit in northwest IA and
southwest MN along and ahead of the front.

Sunday into Tuesday will see cooler air settle in. Looks like the
cool down will not be real significant and it should be fairly short
lived as a trough of low pressure aloft deepens across the Rockies
and an upper level ridge builds into the area.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 630 PM CDT Tue Sep 12 2017

VFR is expected through the TAF period.




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