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

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FXUS63 KEAX 201128

National Weather Service Kansas City/Pleasant Hill MO
628 AM CDT Fri Oct 20 2017

Issued at 332 AM CDT FRI OCT 20 2017

Friday morning`s surface pattern is characterized by a tight
pressure gradient between a deepening surface trough over the
High Plains and a building surface ridge over the Mid South
region. This southerly flow will pick up through the day, bringing
winds up to around 15 to 25 mph. Over the next couple days this
constant southerly flow will cause warm/moist air to push into the
region ahead of a rather potent mid/upper level wave, which will
eject through the area Saturday and Saturday night. Despite some
upstream troughing and a passing shortwave or two over the next 24
hours, expect the dry air to hold off any real chance for rain
until at least Saturday morning, but more likely Saturday evening.

By Saturday evening enough warm air advection will be ongoing to
have some passing stratus during the morning hours. There could be
a few pockets of light rain through the morning hours, but for the
most part the entirety of the atmospheric profile looks a little
lacking for deep saturation and precipitation formation. The best
chance for rain with this system will come later in the evening
when the main system ejects out and the attendant cold front
pushes through the area. Timing for this round of thunderstorms
will likely begin across far NW Missouri and NE Kansas in the 5 to
7 pm range, with arrival into the KC metro in the 7 pm to 9 pm
range. Enough moisture will build into the area ahead of this
front to build around 1000 to 1500 J/kg of MLCAPE. 40 to 50 kts of
deep layer shear will combine with the moderate instability to
bring a threat for strong to severe storms Saturday evening. The
bulk of the activity at this point looks to be tied to the front
as strong low and mid level ascent coincide. This would yield more
of a linear mode of convection, lending itself to more of a wind
threat than hail. Good low level shear on the order of 150 to 250
m2/s2 of 0-1 SRH will yield a marginal concern for an embedded
mesovortex or two as the line pushes east. Any hail concerns would
be relegated to any pre-line convection that may yield an isolated
supercell, but at this point hi-res models do not paint a
favorable picture for high or even medium confidence in pre
frontal supercellular development. PWAT values will range from
1.25" to 1.6" inches as the line moves through, which is rather
high for mid/late October, thus rain rates will be relatively
high. Despite the progressive nature of the frontal boundary and
the linear convection, there is still a potential for much of the
area to see at least 1 inch of rain, with perhaps many areas
seeing upwards of 2 to 3 inches. While this does not look like a
major flash flooding event (mainly due to the progressive nature
of the system) it is possible that there could be some nuisance
flooding in normal flood zones and a few local streams. Expect
this activity to push into C MO by late Saturday night, likely
reaching Columbia around midnight, with rain coming to an end
everywhere by sunrise on Sunday morning.

Strong surface ridging takes hold of the pattern as the rain moves
out of the area late in the weekend. While temperatures will be a
bit cooler on Sunday, the real cool temperatures come in by mid to
late week as a mid level trough and reinforcing surface ridging
bring cooler air from Canada. Morning temperatures through the
middle to late part of the week could go as low as the middle 30s
across northern Missouri. This could yield some frost in that
area, but models at this point don`t show a surface ridge parking
directly over those areas, thus surface winds could stay up around
5 to 10 mph, which would make frost difficult to form. Should
winds drop to below 5 mph on those mornings will need to watch out
for frost, again mainly north of I-70 each morning Wed and Fri


.Aviation...(For the 12Z TAFS through 12Z Saturday Morning)
Issued at 625 AM CDT FRI OCT 20 2017

Southerly winds will pick up through the day and continue through
the overnight hours. LLWS will be a concern through the overnight
hours as FL015 winds will approach 50 kts out of the southwest between
03z and 12z. Preventing a line in the TAF is the surface winds
remaining up around 15 to 25 kts. Low stratus could move in around
09z, but confidence in flight restrictions is low at this point.




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