Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 221737 AAC

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1237 PM CDT Fri Sep 22 2017

Issued at 1232 PM CDT Fri Sep 22 2017

See updated aviation discussion below.

UPDATE Issued at 1021 AM CDT Fri Sep 22 2017

Only adjustments to the forecast this morning were to sky cover
and to add in the mention of some fog along the Sisseton Hills and
just to the west of the frontal boundary currently draped from
southwest to northeast over the CWA. No changes made to winds or
temperatures at this time.


.SHORT TERM...(Today through Sunday Afternoon)
Issued at 413 AM CDT Fri Sep 22 2017

Plenty of warm air will continue to surge northward, and that will
be no different for the daytime hours today. The result will be warm
nose of air above the sfc too, which will likely help keep
thunderstorms from developing (capped) until later this afternoon or
more likely this evening. However, if anything does get going late
this afternoon, expect winds to be the main threat with an inverted-
v look to the sounding with plenty of mid-level dry air, 30-40kt 0-
3km shear, and DCAPE values east of Brown to Spink Counties of over
1200j/kg (which continues into the evening hours). Hail will also be
a concern with 700-500mb lapse rates are at or above 7C/km. Brief
rotation will also be possible prior to 00Z over the northeastern
corner of the forecast area as 0-6km shear values are generally less
than 35kts, and 0-3km SRH are greater than 150m2/s2. Multicellular
storms are most likely, which is being indicated by the latest CAM
solutions. Overall, agree with the SPC downgrade from a slight risk
to marginal for our area. Will downplay the severe weather threat
in the HWO and mention isolated severe potential.

With the frontal boundary dividing the forecast area, temperatures
will vary significantly today northwest to southeast. Temperatures
will top out in the 60s northwest of Mobridge, to the 80s and low
90s across eastern SD and western MN. Breezy afternoon winds will
also be possible, mainly along and east of the James River Valley.

Much cooler and damp weather will settle in Saturday through at
least Sunday as the elongated area of low pressure meanders across
the region. By the end of the day Sunday, total rainfall could total
over a half inch over western Corson County to 1.5 inches over Lyman
to Brown County, to 2 to 2.5 inches east. Of course there is some
uncertainty as to where the highest amounts will fall. At this
point, the more steady rain looks to slide into the area Saturday
afternoon, and slide mainly to our eastern zones by Sunday

.LONG TERM...(Sunday Evening through Thursday)
Issued at 413 AM CDT Fri Sep 22 2017

The models were consistent and continue to agree well early on in
the long term with lifting a large upper level low pressure area out
of the southwest U.S. and into and across the Northern Plains Sunday
night through Tuesday. There was some disagreement from Tuesday
night through Thursday between the models. Therefore, good chances
of rainfall are still in store for the Sunday night through Monday
night period across our CWA. The GFS and Canadian hint at some upper
level short wave troughing affecting the region Wednesday night and
Thursday while the EC keeps us under northwest flow aloft. Thus, at
this time will continue with the consensus with it being mainly dry
across the region for Tuesday through Thursday. Much below normal
temperatures on Monday and Tuesday in the lower 50s to around 60
will warm to closer to normal into the 60s for Wednesday and


.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 1232 PM CDT Fri Sep 22 2017

A frontal boundary draped from southwest to northeast over the CWA
will keep an abundance of cloud cover over much of the area. This
evening, IFR/MVFR cigs will overspread the area, along with
chances for showers and thunderstorms. The thunderstorm chances
will diminish by morning, with just rain chances continuing on
Saturday morning.




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