Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 191733 AAC

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1233 PM CDT Wed Jul 19 2017

Issued at 1228 PM CDT Wed Jul 19 2017

See below for an aviation forecast discussion for the 18Z TAFs.

UPDATE Issued at 1119 AM CDT Wed Jul 19 2017

Severe Thunderstorm Watch 419, valid until 3PM CDT, came out
shortly before 1030AM CDT for the convection that moved down into
north central South Dakota and attached itself to the leading edge
of the best low level moisture advection/gradient and mid-level
thermal advection (700hpa temps between +10C and +12C) cloud-
bearing shear this morning has easily been in excess of 40knots. A
number of large hail/strong straight-line winds and torrential
rainfall has been accompanying this convection, which is now
moving into southeast South Dakota. The influence of this
morning`s MCS is that the boundary layer remains cool and stable
in the Enhanced Risk area, and questions surround where the next
round (afternoon/evening) of strong to severe thunderstorms will
initiate, if they develop at all. Latest Rapid Refresh model data
suggests a rather formidable mid-level capping inversion (700hpa
temps warming to +14C or better) moves over most of the cwa by 21Z
today. Will continue to monitor trends. Will likely be knocking
high temps down across portions of north central into northeast
South Dakota and west central MN.

UPDATE Issued at 711 AM CDT Wed Jul 19 2017

12z aviation discussion updated below.


.SHORT TERM...(Today through Friday Afternoon)
Issued at 409 AM CDT Wed Jul 19 2017

Pretty active short term period setting up with threats ranging from
extreme heat to severe storms. First off, upstream radars are
beginning to light up a bit as warm air advection and large scale
lift spreads into the Dakotas. Upper level jet max over the region
as well as weak impulse move eastward into the region. High
effective bulk shear may support a few elevated supercells with hail
over the next several hours across the western and central Dakotas,
although activity may be a bit isolated/limited.

Main story will be later today and through the afternoon/evening
hours as warm front lifts into the region. Strong instability
combined with good amounts of deep layer shear will support strong
to severe storm potential. Ascent will be aided by a strong upper
level jet positioned over the region. Low level moisture will also
be abundant with dewpoints peaking around 70 degrees across the
eastern CWA. Confidence on convective trends through the day could
be better though. CAM solutions seem to be latching on to the idea
that the activity currently moving out of MT and into the western
Dakotas will continue moving eastward through the day. There should
be upscale growth and/or additional development across southern ND
and northern SD through the afternoon. To what degree though - in
regards to areal coverage - is the main question. Will continue to
see additional development of strong to severe storms during the
late afternoon hours across the eastern CWA or into adjacent areas
of southeastern ND into western MN. Activity is expected to congeal
into a forward propagating MCS by late afternoon into this evening,
mainly affecting MN. Interesting to note that many of the CAM
solutions suggest this may be more of an afternoon event for our CWA
before activity moves eastward into MN this evening.

The other big story today is the heat, which will be out in full
force across central/south central South Dakota. After taking a look
at low level temps across the southwest CWA and favorable southwest
surface warming/mixing winds, decided to increase highs a few
degrees. Forecast highs are now around 105 to 110 degrees over the
southwest CWA - combine that with dewpoints in the 60s and heat
indices will be a concern for sure. Heat advisory from previous
shift was expanded another row of counties north after new apparent
T grids were completed. Currently have heat indices forecast around
110 degrees over the southwest CWA. Highs across the
northern/northeast CWA are very tricky today and will be largely
affected by the position of the warm front this afternoon. Any cold
pool outflow from convection across southern ND this afternoon could
also keep temps across northern SD cooler than forecast.

The weather pattern looks to stay active with another round of
strong to severe storms possible Thursday night and Friday.
Temperatures will stay very warm to hot as well with highs in the
80s and 90s.

.LONG TERM...(Friday Evening through Tuesday)
Issued at 409 AM CDT Wed Jul 19 2017

The long term models continue to show the period beginning with the
broad upper level high pressure area across the southern U.S. with a
decent short wave trough moving across southern Canada. This trough
will move southeast across the Great Lakes region through the
weekend while upper level heights build over the western U.S. The
models then show this ridge out west building into the central U.S.
into early in the week while upper level troughing digs into the
Pacific Northwest. The only decent chances of showers/storms will be
Friday night with waa in response to the southern Canadian trough.
Otherwise, it looks to be dry across the region into Monday with
chances coming back late Monday night and Tuesday. It is expected to
cool down after Saturday when it should be from zero to around 5
degrees above normal. Sunday and Monday are expected to be from zero
to around 5 degrees below normal. It is expected to warm back up
into Tuesday.


.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
Issued at 1228 PM CDT Wed Jul 19 2017

Thunderstorms will be moving out of the ATY terminal probably
within the next hour or two. There is the potential for additional
thunderstorm activity to impact the PIR and ATY terminals for a
few hours later this evening (at or after 23Z). Overall, expect
VFR weather to prevail over the next 24 hours, except in or around


SD...Heat Advisory until 8 PM CDT /7 PM MDT/ this evening for



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