Area Forecast Discussion
Issued by NWS Aberdeen, SD
FXUS63 KABR 231729 AAB
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1229 PM CDT TUE AUG 23 2016
Issued at 1040 AM CDT TUE AUG 23 2016
As of 15Z, a surface low pressure and associated cold front is
located over north central South Dakota. This front should slowly
cross the region today and will eventually become the focal point
for late afternoon convection. A few CAMS are suggesting storms
could be a little later than currently forecast. May need to lower
pops until closer to 0Z.
.SHORT TERM...(Today through Thursday Afternoon)
Issued at 344 AM CDT TUE AUG 23 2016
Downslope wind event is ongoing over the Coteau with Peever having
seen gusts from 45 to 55 mph for the past several hours. Already
issued an SPS late last night to highlight the localized strong and
gusty winds which look to last up through 12Z or so based on the
latest RAP 925mb winds.
Otherwise, for today we will be watching a cold front progress
eastward across the CWA. Will see two results on opposite ends of
the CWA today, with dry air and fire weather concerns west and
strong thunderstorm potential over the east. First, for fire weather
concerns, there will be quite a bit of dry air moving in across
central SD today behind the frontal passage. Currently noting some
20s and 30s dewpoints across eastern MT early this morning behind
the front. Gusty northwest winds will also develop through the day
in the wake of the front. Current forecast RH values fall to around
20 percent or below west of the Missouri, along with some wind gusts
in excess of 25mph. Have therefore issued a Red Flag warning for
fire zones 267 and 268.
Turning to thunderstorm potential, models all showing the frontal
boundary over the eastern CWA between 21Z and 00Z. Moderate
instability develops over the eastern counties, although bulk shear
values could be better. Depending on just how high dewpoints get,
there could be some capping issues to contend with initially. It
still appears better chances may be from 00Z to 02Z across the
eastern CWA. Still a potential for a few strong to perhaps severe
storms with hail and gusty winds being the main threats. This
activity will push into MN later this evening.
Wednesday and Thursday look quiet with cooler conditions in the wake
of the departing cold front. Winds will remain breezy on Wednesday
as the pressure gradient remains tight in advance of the approaching
high pressure system. Increased wind speeds a bit from guidance.
Surface high pressure eventually begins making it into the area
later in the day Thursday, with winds becoming lighter.
.LONG TERM...(Thursday Evening through Monday)
Issued at 344 AM CDT TUE AUG 23 2016
The right entrance region of a 80kt jet will support the
development of a weak upper wave embedded within a broad upper trof
to start things off. Warm advection in the low/mid levels will
generate around 200j/kg CAPE within a nearly moist adiabatic
environment between 6 and 15kft, which may be the northward extent
of a plume of moisture from the southwest monsoon, although the
connection is tenuous. Either way we should see a broad area of
stratiform precipitation with a few convective elements move across
the forecast area Friday.
A second, more dynamic upper wave with jet level support progresses
across the area Saturday, with a Q vector bullseye across the
northern tier of the CWA into North Dakota. While the surface
pressure pattern will be weak, a surface trof is evident within
guidance. This feature takes on more of a dryline form as thermal
advection in the low levels is minimal.
Dry air with stronger thermal advection takes over on Sunday/Monday
as a trof develops in central Canada. Temperatures at 850mb end up
around a standard deviation above climo, so expect another round of
temps in the upper 80s/low 90s to close out the extended.
.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 1228 PM CDT TUE AUG 23 2016
VFR conditions are expected through the taf valid period except
during any thunderstorms late this afternoon and evening at KATY
SD...Red Flag Warning until 8 PM CDT /7 PM MDT/ this evening for SDZ267-