000
FXUS63 KTOP 181725
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1225 PM CDT Fri Aug 18 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 355 AM CDT Fri Aug 18 2017

Two fairly weak MCSs were moving towards the area this morning. One
is in eastern NE moving southeastward, but weakening in the process.
The resulting outflow is pushing out ahead of the convection and new
development is trying to take place well behind the boundary. Only a
few models are developing additional convection over the advancing
outflow as it approaches far northern KS. Another complex is moving
eastward through central KS. The resulting outflow has pushed into
north central KS and isolated to scattered convection has developed.
Most of these showers and storms should stay generally along and
south of I-70. The latest trends are showing this convection not
really gaining much intensity as the low level jet weakens later
this morning. There may only be a few lingering showers remaining
once it reaches far eastern KS later this morning.

Later today a cold front will move southward through NE and reach
the area around mid day. The environment in this area should be
capped, but surface heating across east central KS should weaken the
cap by the time the front arrives in the afternoon. The main
shortwave energy driving this front will track over IA so the
forcing might not be particularly strong. Therefore the models might
be struggling with convective initiation and storm coverage. Through
out today increasing southerly flow will try to wash out the front
draped across OK, which could allow 70 dew points to advect back
into east central KS. This moisture may also dictate whether the cap
can weaken enough for storms to form. Due to the northern shortwave
the deep layer shear will be around 40 kt out of the northwest,
which will increase the directional component. Given the potential
for sufficient instability and this effective shear a few storms may
be strong to severe. Large hail and damaging wind gusts will be the
primary threats. The large scale models as well as the WRF and HRRR
ensembles show wide varying solutions so confidence in location and
coverage is low at this point. In fact the current convective
complex over the panhandles could move into central OK and disrupt
the moisture return in the lower levels. If storms are able to form
along the cold front they will move through east central KS during
the evening and likely exit around midnight. Brief heavy rainfall is
also possible with the stronger cells.

.LONG TERM...(Saturday through Thursday)
Issued at 355 AM CDT Fri Aug 18 2017

Upper flow becomes more zonal this weekend. Lee troughing in western
Nebraska will bring some convergence and could allow for storms to
form there and enter the local area Saturday night and could linger
into Sunday. By this time there could be weak upper waves passing
through from convective remnants over the central and southern
Rockies. Modest southerly surface winds and southwesterly winds just
above should provide a warmer weekend with highs in the upper 80s to
mid 90s.

Monday continues to be a difficult forecast period. Am becoming more
concerned with mid and high clouds being more persistent in deep
southwest flow, sourcing areas where at least diurnal convection
will be prevalent this weekend. Models are also reasonably
consistent with a weak upper wave making its way northeast into
western Kansas late in the weekend, with its speed becoming more
uncertain into Monday. With good moisture present, at least small
precipitation chances exist, with somewhat better chances in the
afternoon in daytime heating. Greater thunderstorm chances come
in late Monday night into Tuesday evening as a stronger upper wave
pushes southeast through the Midwest and drags a cold front
through the region. Timing differences increase with this system,
but these periods bear watching for severe weather potential.

Wednesday afternoon into Thursday should bring dry and mild
conditions with surface ridge in place.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1221 PM CDT Fri Aug 18 2017

For the 18z TAFs, VFR conditions are expected through the period.
There is the potential for some isolated thunderstorms to develop
along a passing boundary, however short-range models continue to
diminish the potential for any scattered activity to develop near
the TAF sites. KTOP/KFOE have the best potential, but still have
only kept a mention of VCTS. Winds will become light and variable
behind the boundary overnight into Saturday morning. There is the
slight chance for some reduced visibilities Saturday morning,
however there is too much uncertainty to mention in the TAFs at
this time.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Sanders
LONG TERM...65
AVIATION...Hennecke