Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 202044

Area Forecast Discussion
National Weather Service Aberdeen SD
344 PM CDT Sat May 20 2017

.SHORT TERM...(This Evening through Sunday Afternoon)
Issued at 344 PM CDT Sat May 20 2017

Forecast challenges include evolution of ongoing precipitation event
inside the deformation zone and TROWAL airstreams, as well as frost
potential across the far (west river) western forecast zones late

Currently, the very northwestern corner of the forecast area is
seeing sunshine, while the rest of the forecast area is under cloudy
skies with areas of light rain ongoing. Temperatures where it`s
cloudy and rainy have been holding generally in the 40s today, while
portions of central and north central South Dakota where sunshine
has occurred some today have been able to warm into the 50s to
around 60 degrees.

Basically, look for good chances for precipitation (mainly rain in
the 12Z model soundings) to continue overnight tonight across the
forecast area in the deformation zone where warm conveyer belt
processes (and eventually TROWAL airstream) will continue to feed
low/mid level moisture in ascending fashion back around to the
northwest and west of the upper low circulation over this cwa. The
loan caveat with this scenario is the very noticeable dry slot
currently moving northward across far eastern SoDak and western MN.
It`s possible to see precipitation filling back in across the
northern/western edge of the dry slot, keeping the good chances for
measurable precipitation going overnight across the I-29 corridor.
But, seeing the current radar/satellite trends, a new/different
solution appears to be materializing whereby, the dry slot would
continue to push northward all the way up into far eastern NoDak and
central MN, effectively shutting off rainfall, and replacing it with
"periods of light to moderate drizzle" overnight across the I-29
corridor and points east. The potential for this will have to be
monitored closely. There could still be some areas tonight (mainly
over the Leola Hills and the Sisseton Hills) that see some flakes of
snow mix in with the rain mainly after 06Z tonight. Overall, there
remains the potential for a trace to upwards of a quarter inch of
precipitation by event`s end Sunday morning between the Missouri
River and the James River. East of the James River over into western
MN, there could be an additional quarter inch to half inch of
precipitation through Sunday morning.

The other scenario worth noting is the potential to see clearing
late tonight across the far western forecast zones as the
deformation clouds begin to gradually pull away towards the east.
Winds will be light and low level dry air still in place over that
area could lead to some coverage of frost for a few hours prior to
sunrise Sunday. Will need to monitor skycover/satellite conditions
closely over the next 6 to 12 hours.

Guidance did not really show much in the way of change to the
forecast lows (generally mid/upper 30s to around 4o) tonight or the
forecast highs on Sunday (50s east and 60s west).

.LONG TERM...(Sunday Evening through Saturday)
Issued at 344 PM CDT Sat May 20 2017

The period begins with a weak upper level shortwave crossing the
region within northwest flow. This system will have some instability
to work with on Monday afternoon with thunderstorms possible. Upper
level ridging and a surface high pressure will settle over the
region Monday night with mostly dry conditions expected through
Thursday. The ridge will breakdown by Thursday night as a broad
upper level trough develops over the Pac NW. The upper level trough
will slowly track eastward for the rest of the work week and into
the holiday weekend. While this trough is still a week out, the
phase of the MJO favors below normal temperatures with above normal
pcpn for Memorial Day weekend. While below normal temps are
possible, they will be nothing like today`s readings.


.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
Issued at 1235 PM CDT Sat May 20 2017

Widespread rain showers broken out into a couple of large blobs
over the region (one over northeast South Dakota right now, and
another over far southeast South Dakota and northwest Iowa) will
continue to spread over portions of central and northeast South
Dakota through the rest of today and during the overnight hours.

KABR and KATY can expect the prevailing conditions to include
light rainfall through at least 06Z tonight before precipitation
begins to taper off/dissipate. And, these two terminals should be
in and out of MVFR/IFR cigs and/or visbies over the next 12 hours
before wholesale improving conditions begin to return.

KPIR will be on the western fringe of precipitation chances
through this afternoon into early this evening before
precipitation chances go away there. It`s possible KPIR could be
flirting with some MVFR cigs for a few hours mainly between late
this afternoon and late this evening. Otherwise, VFR conditions
should prevail there through the TAF valid period.

KMBG will likely remain dry and VFR throughout the TAF valid




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