FXUS63 KABR 082328 AAA

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
628 PM CDT Wed Jul 8 2020

Issued at 624 PM CDT Wed Jul 8 2020

The forecast is on track this evening. No major changes are
planned. Showers and thunderstorm chances remain through the next
few hours even though development is currently occurring to the
south and east. Still watching areas along the trough boundary
from Roberts county southwest to the bootheel of Lyman.


.SHORT TERM...(This Evening through Thursday Night)
Issued at 345 PM CDT Wed Jul 8 2020

Forecast challenges surround timing/placement of potential
convection along the far southern edge of the CWA over into the I-29
corridor and west central MN by early this evening, persisting into
the early overnight hours.

Currently, a surface frontal boundary is positioned over the CWA
from near Britton area down to around Miller to near the Chamberlain
area. This boundary is slowly sagging south and east in the region.
Skies are generally partly to mostly sunny and winds out ahead of
the boundary are from the south, while winds behind the boundary are
out of the northwest. Temperatures out ahead of the front are in the
upper 80s to lower 90s, with readings in the upper 70s to lower 80s
behind the front. MLCAPE values are well above 3500J/kg throughout
and east of the Prairie Coteau, while effective deep layer bulk
shear values range from near 35 knots out over Marshall/Roberts
Counties down to near 25-30 knots across Lyman/Buffalo/Hand
counties. 0-3km CAPE and 0-1km shear/SRH values are also worth
noting this afternoon across northeast South Dakota and west central
MN, at least, for the next 3 or 4 hours. LCL's are also their lowest
across northeast South Dakota this afternoon.

If any thunderstorms develop along this low level source of
forcing/focus within this environment by early to mid-evening, they
are expected to have the potential to become severe storms, capable
of 1 to 2 inch diameter hail and wind gusts of 60 to 70 mph. Storms
would have a general northeast movement along or close to the
frontal boundary, and could affect the far southern/southeastern
forecast zones, depending on where the boundary is located. Given
the low level set up, an isolated tornado risk cannot be ruled out
over far northeast South Dakota over into west central MN. This
activity is expected to wane by 1-2 AM CDT on Thursday, give or take
an hour.

Then, for the rest of tonight through Thursday night, drier air
accompanying surface high pressure will be building into the region.
Should be looking at dry/stable weather conditions over the CWA
during this time. Temperatures should be running close to or perhaps
a few degrees above normal through the period.

.LONG TERM...(Friday through Wednesday)
Issued at 345 PM CDT Wed Jul 8 2020

The long term begins with a broad and persistent upper-high across
the southwestern US and westerly flow aloft across the Northern
Plains. A pronounced shortwave will thus shift from Montana to the
Dakotas through the day Friday, and by peak heating, will promote
convective development across the CWA. Confidence is increasing for
the possibility of severe weather. Southerly winds at the surface
will increase through the morning and into afternoon as high
pressure shifts into MN and low pressure moves in from the west, and
moisture will increase in response with mid 60s dewpoints possible
by the mid to late afternoon. The most eyebrow-raising aspect of
this forecast is the potential 40-60 knots of deep layer shear,
meaning supercell thunderstorms are possible. At this time, the SPC
highlights Central South Dakota as having the best chance at seeing
this activity. However, thunderstorm chances are fairly high across
the whole CWA through Friday night as a cold front shifts east.

The upper-level ridge amplifies some for the weekend, deflecting
additional waves of energy to the east. Thus the area should be dry.
However a large upper-low drops southeast from southwestern Canada
shortly after/by early next week, and a wetter pattern will follow.
Details on timing and location are too difficult to discern at this
time. Regarding temperatures through this period, no great swings,
either cool or hot, are anticipated. The warmest day will most
likely be Monday, as warm air aloft builds in with the deepening
upper-level trough, with high temperatures of perhaps ~90 degrees
around the Missouri River and mid to upper 80s elsewhere.


.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 624 PM CDT Wed Jul 8 2020


VFR conditions will prevail through the next 24 hours. KATY may
see some thunderstorms this evening that could briefly drop cigs
and vsby.




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