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

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FXUS63 KEAX 170858
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
358 AM CDT Sun Sep 17 2017

.Discussion...
Issued at 327 AM CDT SUN SEP 17 2017

Ongoing rain showers over the Kansas City Metro area likely in
response to a less than stout, but present low level jet nosing
into the area. This jet is characterized by H85 wind out of the
southwest around 20 to 30 kts. Deep isentropic ascent along this
warm air advection regime is likely the main source of ascent for
thunderstorm production. Very high PWAT values, ranging in the
1.5" to 2.0" range (roughly 150 to 200 percent normal) is
providing the necessary moisture for very efficient rain rates
with these storms. Already some gauges in the KC area have
recorded over 3 inches of rain, although these areas of 3-4+
inches of rain are isolated, with roughly 1-2 inch reports being
the normal across the metro, at least as of 330 am. Flash flood
guidance for the area, considering the very dry last couple of
weeks, is rather high, with 3-6 hour accumulation guidance of
around 3-4 inches. Areas that exceed those amounts in a 3-6 hour
range will see the best chance for isolated flash flooding.
Through the day on Sunday the low level boundary will gradually
slide southward, taking with it the best chances for rain as the
day progresses. Areas north of I-70 should see conditions improve
in the morning hours on Sunday, with areas roughly along and just
south of I-70 improving by Sunday evening. Areas much further
south than I-70 will have at least a 30-40 percent chance of rain
through the entire day.

By Sunday night/Monday morning chances for rain across the entire
area increase. The best chances for rain will likely focus around
the 12z to 18z time frame, when a shortwave trough moves through
the area. PWAT`s for this trough will once again be very high,
again on the order of 1.5 to 2.0 inches. These high PWAT values
are likely due to moisture being drawn northeastward from
Tropical Storm Norma. Water vapor imagery shows a pretty decent
connection from Norma to our area. These high PWAT values will
again make rain rates very efficient and the area could see an
additional 1-3 inches of rain, with perhaps some isolated higher
amounts Sunday night into Monday morning. Perhaps contrasting from
recent flooding events in and around Kansas City, is the lack of a
real bulls-eye focus of the low level jet right on the KC metro.
Also, the low level boundary should be to the north, which will
shunt the low level focus north of KC. The bulk of the precip will
likely be in response to the shortwave trough moving through at
that time. When the trough moves through there should be some
subsidence in its wake, which should lower chances for rain
through the rest of the day on Monday. There could be some strong
to severe storms on Monday, as that shortwave ejects through the
area. ML Cape values should be around 1000 J/kg and keep layer
shear around 20-30 kts. The combination of these parameters should
yield at least a marginal atmosphere for strong to severe
thunderstorms. The timing of the trough will dictate quite a bit.
At the moment, given the timing of its arrival before mid day,
instability will not be maximized, thus severe weather concerns
are a bit subdued with this Monday activity.

The active pattern should continue through the rest of the week,
although with some question marks. The southwest flow aloft will
remain over the area, but the better ascent may remain just west
of the forecast area. Mid/upper flow may become much more
meridional, as opposed to zonal for the middle to latter part of
the week, which may keep the area free of much in the way of
convection, but confidence in this time period is rather low at
this time.

&&

.Aviation...(For the 06Z TAFS through 06Z Sunday Night)
Issued at 1220 AM CDT SUN SEP 17 2017

Multiple rounds of thunderstorms are expected to impact the TAF
locations as a cold front pushes through the area from the NW.
There is currently an area of thunderstorms just south of KMCI
over KMKC and KIXD that is expected to move out by 8Z as the
surface cold front moves to the SE. Winds are expected to shift to
the NW at all stations by 08z as well on the backside of the cold
front. The second round of storms will start to move into the area
after 08z from the NW, but there is some uncertainty as to how
long these storms will last and their exact timing so a TEMPO for
TS was added to the terminals. The threat for these storms is
generally from 8-11Z with some chance of them lasting longer in
the southern portion of the area. MVFR ceilings will develop on
the backed of the cold front just after the second round of the
thunderstorms. A period of IFR ceilings is possible just after
sunset for the southern terminals through the early afternoon. All
ceilings will start to rise with KSTJ clearing out first in the
afternoon and the southern terminals finally clearing out around
sunset with VFR expected from that point through the end of the
period. There is a chance for storms to return in the afternoon on
Sunday but there is not much consensus for when and where that
will occur at this time so it was kept out of the forecast for
now.


&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
MO...NONE.
&&

$$

Discussion...Leighton
Aviation...Barham



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