Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO

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FXUS63 KEAX 181733

National Weather Service Kansas City/Pleasant Hill MO
1233 PM CDT Tue Apr 18 2017

Issued at 239 AM CDT TUE APR 18 2017

There are a couple periods of concern through the forecast. There is
potential for storms this afternoon/evening in northern MO. Severe
storms are possible Wednesday afternoon/evening and perhaps into the
overnight hours. And lastly, the growing potential for a widespread
heavy rain event Friday night through Saturday.

First, the potential for storms this afternoon/evening. Models
continue to show relatively weak instability and shear. So as a
shortwave trough passes well to the north of the area, the
associated cold front will move into northern MO and northeastern
KS. Given the weak upper level support that pushes well north of the
area anyway, and the weak anticipated convection, the front should
not make it much further south than northern MO. Have trimmed PoPs
back to account for this and confine them to mainly the far northern
tier of counties during the evening hours.

With a little more clarity as to how lingering convection and debris
may impact Wednesday, it`s looking more likely that strong to
potentially severe storms will affect the forecast area. Instability
should be stronger, with 1500 to perhaps 2000 J/kg of CAPE. Also, a
more dynamic upper system will approach the area with strong mid and
upper level winds. This will lead to stronger 0-6 km shear values in
the 40 to 50 kt range.  Despite surface winds being veered to the
south-southwest, there is a fair amount of turning through 500 mb.
It seems likely that, given the instability/shear combination, that
rotating thunderstorms can be expected. While the veered surface
winds would decrease the potential for tornadoes, mid-level rotation
could lead to large hail with the strongest cells. As the cold front
pushes through the area, a broken line of storms looks possible into
the overnight hours. Shear will still be relatively strong overnight
so the threat of severe storms may persist into the overnight as
well across eastern KS and western MO.

Cooler weather in the wake of the front is expected for Thursday and
Friday. But by Friday evening a strong upper system will move into
the Plains. Since the front never pushed very far south of the area,
moisture will pool along it. Then as the upper system pushes east
into the area, a strong surface low will develop and track through
Missouri. The strong lift associated with the upper trough and ample
moisture that was pooled just to our south, will allow for
widespread and potentially heavy rainfall to spread across the
forecast area. It`s possible that several inches of rain will occur
as the upper low is moving through from Friday night through
Saturday night. The GFS and Canadian models are the most aggressive
with this and show similar timing and low tracks. The ECMWF is
further south with the low and not as strong and as a result
dispenses less QPF. Even with its more southerly track of the heavy
rainfall, it still is producing precipitation in the forecast area.
Given this, feel confident going with categorical PoPs Friday night
into Saturday. The main question is where the axis of heavy rain
actually does develop. Feel it`s likely that this will be south of
the Missouri river and into southern MO.


.Aviation...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 1233 PM CDT TUE APR 18 2017

Patch of IFR ceilings over western MO and extreme eastern KS has
stopped spreading northward and is unlikely to make it north of
the Missouri River, and is in fact already beginning to lift into
MVFR. This trend will continue through the afternoon before
clearing out altogether by late afternoon.




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