Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 282055

Area Forecast Discussion
National Weather Service Sioux Falls SD
355 PM CDT Wed Jun 28 2017

.SHORT TERM...(This evening through Thursday)
Issued at 355 PM CDT Wed Jun 28 2017

Surface front located just southeast of the forecast area as of 20Z.
More stable flow should keep our forecast area dry through much of
tonight, with current gusty west-northwest winds diminishing quickly
as sunset approaches. Next mid-upper level wave begins to push into
the western Dakotas after 06z, which should spread mid-level clouds
into our area by late tonight. This should keep temperatures fairly
mild despite the light winds, with lows in the upper 50s-mid 60s.

The broad wave continues to slide east across the northern Plains
Thursday, while a secondary wave lifts northeast out of Colorado
toward western Iowa by 18Z. This large-scale forcing should aid in
the development of scattered showers/storms across the forecast area
through the day, and the question becomes how far north the warm
front returns toward the southern part of the CWA by late in the
day. Models still not showing great consistency in this location,
with the Canadian farthest north, while the ECMWF and NAM remain
farther south. With proximity of the boundary, at least with the
elevated warm front, and the wave moving into the area, will ramp
pops up into higher end of chance/scattered range prior to 00Z. Mid
level lapse rates seem marginal in our far south at KSUX/KSLB, but
shear does increase through the late afternoon, and would be locally
enhanced if the low level boundary reaches the area, so the threat
of isolated strong to severe storms seems reasonable. Temperatures
will generally be on the cool side of late June normals in the mid
70s to lower 80s, though far southern areas could warm further if
the warm front pushes far enough north.

.LONG TERM...(Thursday night through Wednesday)
Issued at 355 PM CDT Wed Jun 28 2017

Could see some thunderstorms around on Thursday evening as weakly
capped environment exists. 0-6 km Bulk shear approaches 50 knots
across the southern CWA with the focus in speed shear aloft.
Downdraft CAPE is 500-1000 J/kg, and with the main surface warm
front focused off to the south could see a few elevated storms
through the evening hours.

Some weak short waves continue to move across the eastern portions
of the forecast area on Friday, and have a lingering chance for
storms. Elevated cold front moves through the region late in the day
and temperatures will remain below normal through the weekend. With
850 hpa temps in the teens, high temperatures should remain in the
70s through lower 80s through much of the weekend.

A series of shortwaves are expected to move under the influence of
zonal flow Sunday night. Appears to be a fairly strong capping
inversion through much of the day, but cap weakens as disturbances
approach. Nice veering wind profile, and with warm front across the
area could see all modes of severe weather possible.

Scattered thunderstorm chances continue Monday if not even further
into the week as dirty flow continues.  Low level flow looks to
prevail out of the south, thus raising the instability potential.
For now, have a dry forecast for Tuesday into Wednesday, but would
not be surprised if pops get added to the forecast once timing
becomes more clear.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1215 PM CDT Wed Jun 28 2017

Isolated MVFR ceilings lingering in far southeast corner of the
forecast area, east of KSUX, to start the period, but this should
improve by 20Z, leaving VFR conditions to dominate across the area
through this TAF period. Occasional wind gusts to 20-25kt through
the afternoon should diminish quickly by sunset.

Chance of thunderstorms will return to the area on Thursday. At
this time, any morning storms are expected to remain southwest of
the TAF locations, primarily in south central South Dakota. Threat
of storms will then expand eastward through the afternoon, after
this TAF period.




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