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

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FXUS63 KEAX 171121

National Weather Service Kansas City/Pleasant Hill MO
621 AM CDT Thu May 17 2018

Issued at 318 AM CDT THU MAY 17 2018

A closed upper level low, and associated pinwheeling shortwave
troughs, will be the main player for todays weather. With little
change in the pattern from yesterday a similar situation is expected
today, but with a slight shift to the SE.  Currently some isolated
showers and thunderstorms are forming along a minor shortwave trough
along the KS/MO border which will last until around sunrise with
pulse type storms. As the low shifts to the SE in the late morning,
heating and the added associated lift aloft will re-initiate
convection over central MO. A weak surface convergence boundary
will also provide a focus for these storms to develop. The storms
will have a similar evolution as yesterday with downdrafts and
outflows becoming the main driving mechanism for secondary
development. SBCAPE values will climb into the 1500 to 2000 J/kg
range over central MO creating the potential for isolated strong
winds with downdrafts with the cold pocket aloft adding to
possible small hail growth. These storms will be most likely
diurnally driven, but just as today they may continue into the
evening depending on how the cold pool and outflow boundaries
develop. High temperatures will reach into the lower 80s, with
some areas in central MO only reaching into the upper 70s due to
cloud coverage and cold pool developments.

The pattern will finally start to shift as this upper level low
moves out of Missouri on Friday allowing a short-lived upper
level ridge to move over the area. Behind this ridging a shortwave
trough will exit the southern Rockies developing a surface low
pressure over western Kansas and a southerly return flow over our
areas. This will allow temperatures to climb into the mid to upper
80s on Friday. This shortwave trough will slowly move to the NE
eventually leading to the formation of a warm frontal boundary
Friday night into Saturday morning over eastern KS and western MO.
Isentropic accent along this boundary aided by a LLJ will bring
precipitation chances back into the CWA Saturday morning. There is
still some uncertainty to the exact placement of the warm front
with the GFS placing this boundary north of the MO River, while
the ECMWF places it more along the river. This will have dramatic
influences on the weather Saturday morning into the afternoon,
and with this uncertainty PoPs remain relatively lower near the MO
River for this reason. Convection along this boundary will have
the potential for severe weather as SBCAPE values climb to near
2500 J/kg with 0-6km bulk shear values near 30-40kts. This system
will need to be monitored for any adjustment north or south of
that boundary as the event moves closer. The placement will have
a dramatic effect on where the main impacts may be. There is much
more model consensus for severe weather to form near the triple
point over SE Nebraska in the afternoon Saturday. Models are
starting to show signals for a possible MCS to push through
northern Missouri Saturday night into Sunday morning. The cold
front appears to move into the CWA and stall Sunday morning behind
the possible MCS. This will provide the focus for possible
afternoon TS over central Missouri. There looks to be enough
instability for strong to severe storms, but a lack of shear will
minimize this threat. Temperatures behind the cold front on Sunday
will drop back into the 70s, making it feel a little cooler than
it has.

Going into Monday the model uncertainty really starts to show up
with the GFS and ECMWF showing a wide spread in solutions for the
next round of active weather. The GFS solution is more aggressive
along the now stalled cold frontal boundary over central Missouri
with the ECMWF pushing the focus more south. Due to this
uncertainty all the PoPs from Monday through Wednesday remain low,
although very widespread. More details will need to be resolved
as this timeframe gets closer.


.Aviation...(For the 12Z TAFS through 12Z Friday Morning)
Issued at 617 AM CDT THU MAY 17 2018

The main concern for the period will be scattered thunderstorms
that will form over eastern KS and western MO from an upper level
disturbance moving through the area. There is some uncertainty to
where these storms will develop so VCTS has been added to the TAFs
for show this potential. If thunderstorms develop and look to
affect the terminals directly this will be added to the forecast
to convey this threat. This thunderstorm threat will decrease in
the afternoon with VFR conditions and a SE 5-10kt wind remaining
from the rest of the period.




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