Area Forecast Discussion
Issued by NWS Sioux Falls, SD

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS63 KFSD 171759

Area Forecast Discussion
National Weather Service Sioux Falls SD
1259 PM CDT Mon Jul 17 2017

.SHORT TERM...(Today and Tonight)
Issued at 409 AM CDT Mon Jul 17 2017

Breezy south-southwesterly flow is expected across the region today
ahead of an approaching cold front that will stall across central
portions of the state.  With the southerly flow, will once again see
above normal temperatures across the region.  Cut back dew points
mainly along and west of the James, where dry air will mix down from
aloft. Further to the east, this will be more difficult.  Approach
heat advisory criteria, but given current forecast is slightly
below, left headline out for now.

Other concern is strong short wave moving east across Nebraska
today. Could see some storms develop in response to this both late
this afternoon and into tonight. Have a slight risk for severe
weather, but am thinking severe weather will be limited by the
lack of shear through the column and lack of instability/low level
moisture. 0-6 km bulk shear values are near 20 knots, making it
difficult for any potential storm to organize. Can`t rule out that
a storm would be able to produce hail, but with freezing levels
near 15K feet, it may be difficult for any hail to reach the
surface. Nice inverted V profile on the uncapped atmosphere across
the north and into central South Dakota may lead to a wind gust
to near 60 mph.

.LONG TERM...(Tuesday through Sunday)
Issued at 409 AM CDT Mon Jul 17 2017

An unsettled pattern returns to the area Tuesday through the middle
portion of the week, as upper ridge flattens and strong westerlies
set up across North Dakota/northern Minnesota. Tuesday will begin
with isolated to scattered, mainly elevated showers/storms moving
across the area. This activity could leave behind various weak
surface boundaries, but will also have the primary cool front
sagging southward across the region through the day as a mid-level
wave slides east across South Dakota. Surface destabilization may be
dependent on ability to recover from morning activity. However, any
areas near/south of the main boundary are expected to warm enough,
especially given steepening lapse rates aloft, to produce ample
instability by mid-late afternoon. This combined with increasing
deep layer shear with approaching jet should be supportive of strong
to isolated severe storms along and ahead of the front in the late
afternoon/evening. This threat should wane during the overnight as
the front pushes southeast of the area, the wave exits to the east,
and overall storm activity decreases. In addition to the isolated
severe threat, localized heavy rain also a possibility, as models
project precipitable water values approaching 1.75 to 2 inches, with
warm cloud depths exceeding 4km ahead of the front. Temperatures on
Tuesday will be dependent on precipitation/cloud coverage, but will
generally lean toward cooler highs in the lower 80s across southwest
Minnesota, to lower-mid 90s through the Missouri River Valley. With
humidity levels remaining high, may need to consider a heat advisory
in our southern areas, where we`ve seen multiple days with heat
indices in the mid-upper 90s.

Boundary projected to lift back to the north on Wednesday, as a
couple of waves slide east across the Dakotas in the afternoon and
overnight. Some question regarding how far north the boundary will
progress, and exact timing/trajectory of the forcing aloft. However,
seeing multiple solutions pointing to potential MCS affecting some
part of our forecast area Wednesday night. Shear/instability remain
supportive of isolated severe wind/marginal hail threat, with
locally heavy rain still possible as well. After a relatively quiet
Thursday, cannot rule out a repeat performance Thursday night,
though confidence in pattern details at that range is quite low.
Midweek temperatures again will be strongly dependent on convection
and resultant boundary locations, but generally looks to remain warm
in our far south and west, with more seasonable readings across the

Transition to somewhat calmer pattern Friday through the upcoming
weekend, as the strong upper jet shifts eastward and slight ridging
retreats westward into the Rockies. Could still see spotty storm
potential through the weekend, but in generally looks like a drier
period with seasonable temperatures.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1250 PM CDT Mon Jul 17 2017

The main impacts are brief strong gusty winds, and increasing
thunderstorm chances through the TAF period. Isolated storms
possible across KHON this evening with the passage of a cold
front. KFSD and KSUX could also see periods of TSRA, but
confidence in timing and coverage is not high. Therefore, did not
mention it in the TAFs. Overall, VFR conditions will prevail at
all sites.




AVIATION...05 is the U.S. government's official web portal to all federal, state and local government web resources and services.