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

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FXUS63 KEAX 231747
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
1247 PM CDT TUE AUG 23 2016

.Discussion...
Issued at 417 AM CDT TUE AUG 23 2016

A cool and clear morning to start out Tuesday could become stormy as
the day progresses. Weak southerly flow at the surface will
transport warm and moist air into the area throughout the day. Warm
air advection ahead of a developing surface trough could bring some
scattered showers and thunderstorms to the area through the day.
Well off to the west, namely across western/central Kansas, a weak
shortwave trough has kicked off a round of showers. This area of
showers will glide northeast across eastern Nebraska and Iowa
through the late morning and early afternoon hours. As it moves east
it should encounter increasingly unstable environment as the
morning/afternoon heating occurs. An uptick in convection with this
activity is expected as it moves through the more unstable
atmosphere. This activity could also conceivably lay down an outflow
boundary, which could come into play in southern Iowa or northern
Iowa later in the afternoon and evening. Expect this morning/early
afternoon round to stay predominantly north of the forecast area,
but the southern extent of this activity could graze far northwest
or north central Missouri. Perhaps hindering mid day high
temperatures will be building clouds along weak isentropic ascent
associated with the warm air advection ahead of the surface trough;
plus any cloud debris from other convection could hinder surface
temperatures later today, and in turn will make the convective
scenario and any attendant severe concern rather conditional.

Should the boundary layer be able to destabilize sufficiently in the
afternoon/evening another round of deep convection will be possible.
Models at this time prog nearly 2500 to 3500 J/kg of MLCAPE, which
should be sufficient for robust convection. Hindering the ability
for storms to become organized is a lack of deep layer shear, which
will only be in the 25 to 35 kt range since mid level winds appear
to be rather weak. However, with the warm front lifting north and an
increasing low level jet through the afternoon and evening low level
shear will be rather impressive, displaying perhaps 100 to 200 m2/s2
of 0-1 SRH, with increasing values of 0-1 SRH through the evening
and after dark as the low level jet continues to increase.  The end
result could be storms which lack any incredible definition, but
enough low level spin that in conjunction with the strong
instability will bring a non-zero concern for tornadic activity
later today. Increasing tornado concern will be present should an
aforementioned outflow boundary come into play. Considering the
uncertainty with cloud cover and temperatures (instability) and the
presence/locations of any boundaries (low level shear) trends will
need to be monitored through the day. Also, considering the location
of the cold front well north/west of the forecast area it`s unlikely
that the front itself will be the impetus for any deep convection.
It will likely need to form with the presence of the mid level wave
or with the warm front/outflow boundary.

By the late evening into the overnight period one or several linear
segments should be present in the area, and they will likely be in
an environment conducive to embedded tornado activity, so the
occurrence of one or more QLCS-type mesovortex tornadoes is also
possible later tonight.

Wednesday will see the remnants of Tuesday`s convective event push
off to the east while the cold front slowly drifts into the forecast
area for Wednesday. As the warm air advection process continues
through Tuesday night and into Wednesday cloud cover is likely to be
present on Wednesday. As the cold front sags into northern Missouri,
models have it stalling somewhere near the HWY 36 corridor, which
will be the focus for showers and thunderstorms through the day on
Wednesday. This activity could bring some flooding concerns to areas
mainly north of the Missouri River Wednesday and Wednesday night.
Mid level out of the W/SW becomes parallel to the stalled surface
boundary, which will cause a training of storms over that low level
boundary. PWAT values likely approaching 2+ inches will be
responsible for efficient rain production. Should several hours of
ongoing moderate to heavy rain occur across northern Missouri
flooding of local rivers and streams, especially those susceptible
to even modest amounts of rain will likely occur. At this time flash
flooding does not look likely considering high flash flood guidance
due to recent dry stretches, but flash flooding cannot be ruled out,
especially in areas traditionally susceptible to flash flooding.

The active pattern will likely continue through the end of the week
and into the weekend. Through Friday the surface boundary should sag
southward into southern Missouri, which will help bring some rain to
areas south of the Missouri River, then by the weekend the boundary
lifts back to the north in response to a deepening surface low out
west. Southwest flow aloft over the warm sector should keep rain
chances alive through the end of the week and into next weekend, and
perhaps beyond into early next week.

&&

.Aviation...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 1240 PM CDT TUE AUG 23 2016

Challenging forecast for this TAF period given that the area could
see two rounds of storms tonight, in addition to impacts caused by
lowered ceilings and gusty winds outside of storm activity. Some
storms may have the potential to become strong to severe with gusty
winds as the primary hazard, although cannot rule out a tornadic
threat. The first round is mentioned in this TAF issuance with the
TEMPO group at all four terminals but the second round will need to
be evaluated and potentially added for the next TAF issuance.
Currently, the second round appears to occur around midnight through
about 4am, give or take an hour on either end. As mentioned, lowered
ceilings persisting throughout much of the TAF period at the
terminals, plus breezy conditions this afternoon will be impactful to
aviation interests.

&&

.EAX Watches/Warnings/Advisories...
KS...None.
MO...None.
&&

$$

Discussion...Leighton
Aviation...lg



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