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fxus63 ktop 181037 

Area forecast discussion
National Weather Service Topeka Kansas
537 am CDT Wed Sep 18 2019

..update to aviation forecast discussion...

Short term...(today and tonight)
issued at 313 am CDT Wed Sep 18 2019

Very sticky to uncomfortable dewpoints remain in place for the
foreseeable future -- especially in the near term -- with
temperatures around 90 yielding heat index values in the mid to
upper 90s.

Overall, the upper flow pattern remains devoid of an significant
trough bringing cooler and drier air into the region probably until
next week when a more significant modified Canadian high pressure
cell can build into the region. Until then, the broken record of
hot and humid conditions holds. The near term forecast for today
and Thursday doesn't really change much or offer much in the way
of precipitation chances. Currently, the high amplitude ridge that
has been over the area is flattening and shifting east of the
area. Tropical depression Imelda is slowly trying to lift north
through southeastern portions of Texas. Meanwhile, a compact upper
shortwave is continuing to lift into the Dakotas with the best
forcing remaining well north of the area. The main Pacific trough
is still trying to make its way onshore over the Pacific
northwest. This will leave a southwest flow regime over the
central rockies into portions of the Central Plains. Lee troughing
remains in place along the Front Range of The Rockies into
portions Nebraska. Thus the best convergence and isentropic ascent
along with the low level jet tonight also remains northwest of the area.
Elevated storms remain well north of the area and are currently
struggling to back build into extreme northeastern Nebraska as the
upper trough axis is lifting trough the region taking on a more
negative tilt.

With the orientation of the previously mentioned shortwave and the
lack of a significant convergence associated with the low level jet over the
area, most short term model guidance has continued to back off of
developing precipitation into the area. There may only be some
isolated showers or a storm develop into the early morning hours.
This similar pattern remains into Wednesday night and Thursday
morning. However, have kept slight chance pops mainly north of I-70
due to a a bit better low level jet convergence. But, moisture again remains
at a premium aloft, so not too optimistic in any widespread shower
or storm development even into Wednesday night and early Thursday
time frame. Highs again Thursday remain into the 90s with high near
surface dewpoints with little relief from daytime mixing giving way
to upper 90 heat index values again.

Long term...(thursday through tuesday)
issued at 313 am CDT Wed Sep 18 2019

Into the weekend, a frontal system may begin to finally move into
the area as the previously mentioned Pacific trough impacts the area
and lead waves emanating from this trough lift into the plains.

Still low predictability in the overall evolution of the larger
scale western trough into the Saturday and Sunday time frame, but it
does look like a wet pattern will be in place for much of the
upcoming weekend. This could be further enhanced by the northward
advection of higher Theta-E air associated with tropical depression
Imelda. As more southwest flow component remains and upper flow
increases over the region along the eastern flank of the deeper
trough spanning through much of the western conus, can't rule out
some episodes of severe weather and heavy rainfall. The European model (ecmwf)
suggests stronger upper flow than the GFS and to some extent the
Canadian solution. This could lead to shear profiles more
supportive of more organized severe weather. Will have to wait a
bit longer to tell for sure. The other main hazard would be
related to the heavy rainfall potential. With no antecedent
rainfall, concerns overall may be mitigated. But, with precipitable water amounts
easily pushing the 90th percentiles for time of year, concerns
would likely be elevated and dependent on additional moisture
associated with previously mentioned tropical influences. Also,
frontal positioning is going to be critical. Right now the frontal
zone is anything but clear as to where it may linger. The GFS
focuses mostly over east central areas into Missouri. The European model (ecmwf)
has the focus further north essentially along the Kansas/NE border.
Again, this positioning will be critical.

Have kept precipitation chances into the early portion of next week
as the boundary struggles to push very far south of the region with
return bring back isentropic ascent back over the boundary into the
region. Eventually, into the latter portions of the week, it
appears most deterministic guidance is trying to suggest that a
stronger and drier Canadian airmass pushes into the Central Plains.
As a result the area could potentially see dewpoints dip into the
40s! Relief with this dry air has not been felt for a long time and
would certainly be newsworthy.


Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 526 am CDT Wed Sep 18 2019

VFR continues at ktop/kfoe/kmhk with southerly winds increasing to
around 10 kts during the mid to late afternoon. Isolated thunderstorms and rain
develops north and west of terminals this aftn, remaining far
enough from terminals to not mention in tafs.


Top watches/warnings/advisories...

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