Area Forecast Discussion
Issued by NWS Aberdeen, SD

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819
FXUS63 KABR 181742
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
1242 PM CDT Mon Sep 18 2017

.UPDATE...
Issued at 1231 PM CDT Mon Sep 18 2017

No major changes with the short term. Main focus will be on the
development of storms Tuesday afternoon. We continue to get
positive reenforcement with latest guidance and CAM solutions on
the development of storms just to the west of the strongest part
of the capping inversion as the front moves between the
James/Missouri valleys during the later afternoon hours.

Aviation discussion has been updated below...

&&

.SHORT TERM...(Today through Wednesday Afternoon)
Issued at 411 AM CDT Mon Sep 18 2017

Weak upper level shortwave is moving across the Dakotas early this
morning with about a 30 knot low-level jet in place. Isolated
showers and even a thundershower have developed over the past couple
hours. There is some minimal elevated instability to work with, so
have included a thunder mention in the grids. Expect this activity
to be out of the area later this morning, making way for dry
conditions today and warming temperatures into the 70s and low 80s.

For tonight, focus will be on the influx of low-level moisture
surging northward across eastern SD and west central MN. Models are
starting to latch onto a stratus deck moving northward through the
area, it`s just a matter of how far west the stratus deck reaches.
But, there seems to be pretty good agreement now in the stratus
clouds moving in so have increased sky grids. Also took a look at
fog potential - which several of the hi-res models are trying to
indicate. Liked how the CONSShort and ECAM visibility output try to
bring some fog into the higher terrain, especially the Coteau and
Leola hills region. Can see this happening perhaps as we get moist
upslope flow into the higher terrain where there will already be low
CIGs (more confidence in this for the Coteau). Day shift will have
to try to fine tune where the best potential is for stratus and fog,
and just how far west.

Then, focus shifts to Tuesday with the approach of the cold front.
Threat for strong to severe storms still looks pretty good Tuesday
afternoon and evening for the eastern CWA. A plume of moderate
instability will develop over eastern SD Tuesday afternoon with
plenty of 0-6km bulk shear on the order of 50 to 60 knots. Even the
0-1km shear is showing about 30 knots across eastern counties by 00Z
Wednesday. Atmosphere will be capped much of the day, but with the
approach of the cold front`s surface convergence and also the mid-
level wave, the cap should be overcome. Damaging winds appear to be
the biggest threat as storms will likely congeal into lines or
bowing segments after initial discrete development. Given the low-
level shear, a tornado or two cannot be ruled out either. Inserted
T+ into the grids given the decent threat and also our upgrade to
Enhanced Risk.

.LONG TERM...(Wednesday Evening through Sunday)
Issued at 411 AM CDT Mon Sep 18 2017

Sfc high pressure and southwest flow aloft will leave the region dry
and seasonably warm on Wednesday and Thursday. A low will move into
South Dakota Thursday night. Most of the precip associated with the
low will focus on the warm front to the northeast in MN/ND, but
could see some showers and thunderstorms across far northeast SD and
west central MN with this system, as well.

On Friday, more energy begins to eject out of the deep longwave
trough over the western CONUS. Showers and thunderstorms will become
more widespread Friday through Sunday. The enhanced moisture will
also suppress temperatures, as will the passage of the sfc low.
Expect temps to only top out in the 50s and 60s at the sfc as H85
temps fall to 2C by Monday when the upper trough digs into the
Plains.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
Issued at 1231 PM CDT Mon Sep 18 2017

KATY seems to have the greatest impact over the next 24 hours with
some MVFR ceilings in the area already. This will break up with
daytime heating but redevelop overnight, lowering to ground level
potentially with IFR Visby/CIGS. KABY seems less likely to be
impacted, but the potential exists for MVFR cigs. For KPIR/KMBG -
we could see a low level jet overnight which will result in wind
shear. Otherwise we anticipate VFR conditions. Thunderstorms will
develop outside of this TAF period but we anticipate KABR and KATY
terminals to be effected by storms Tuesday PM.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&

$$

UPDATE...Connelly
SHORT TERM...TMT
LONG TERM...Wise
AVIATION...Connelly



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