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

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FXUS63 KEAX 161730
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
1230 PM CDT Sat Sep 16 2017

.Discussion...
Issued at 245 AM CDT SAT SEP 16 2017

Southerly winds continue today in response to the surface low to
the west across the High Plains. Warm air advection within this
southerly low level flow has caused a few areas of showers and
thunderstorms to develop across northeast Kansas and far eastern
Nebraska. These areas of showers appear to be closely tied to the
location of the low level jet, which is currently racing over
central Kansas and nosing into southeastern Nebraska. Isentropic
surfaces indicate that the cloud bases associated with these
showers are around 600 mb, and forecast soundings concur, by
indicating cloud bases around 10 to 15 kft. These showers could
form through the day mainly in the form of light rain or
sprinkles in the same areas they are currently forming in, as the
low level jet persists through at least the morning hours, into
the afternoon hours. The best chance for showers and thunderstorms
will be around sunset and in the hours directly after sunset.

Good moisture will be in place over the area, with temperatures
reaching the middle to upper 80s. This should yield an unstable
environment, producing around 1500 to 2000 J/kg of ML CAPE. This
will set the stage for an advancing cold front to push into the
area, kicking off a round of strong to severe thunderstorms later
this afternoon/evening. Storms will initially form in far NE
Kansas and SE Nebraska along the front perhaps as early as 22z,
but more than likely an hour or two thereafter. Initial storm mode
will be quasi-discrete, with a chance at some mid level rotation
given the 20 to 30 kt deep layer shear. Hazards associate with the
initial storm formation would be strong winds and perhaps some
large hail up to golf ball in size. Storms should quickly evolve
into a a linear system likely in the 03z to 05z time frame,
forming a cold pool, and pushing through western and central
Missouri, including the KC Metro area. By the time these storms
get to Kansas City it will likely be around midnight and boundary
layer conditions will be cooler and decoupled so while there could
be some isolated to scattered strong wind gusts, the bulk of the
severe weather should be concluded by the time the complex reaches
KC. This complex will push south and east, while weakening
through the night, into southern and central Missouri, perhaps
bringing some much needed rain to a large portion of the area.
Rain rates should be fairly efficient, at least for this time of
year, since PW values will approach 1.5" to 1.75" across the area.
For comparison, normal PW is around 1.00" to 1.10" for mid
September, yielding PW values 150% to 175% normal.

For Sunday, the boundary causing the Saturday night thunderstorms
will stall south of I-70, which will bring continual chances for
rain along and in the vicinity of that boundary through the day on
Sunday. Low level jet will strengthen on Sunday night/Monday
morning and will use that boundary to produce periods of moderate
to heavy rain Monday morning. Quasi-zonal mid to upper level flow
from the W/SW will run over that boundary and perhaps cause a
training situation Sunday night and Monday morning, with several
rounds of thunderstorms running over the same areas along the
boundary. The moisture supplying both the Saturday evening and
Sunday night systems appears to have its source region from
Hurricane Norma in the E PAC. Moisture from the tropical system
will wrap around the broad ridge over the southeast US/Caribbean,
producing a stream of anomalously high PW`s into the area. If the
training situation is prolonged there could be some potential
there for a flooding situation Sunday night.

The pattern will remain active through the rest of next week as
southwest flow in the mid to upper levels persists. Surface
troughing to the west will keep a steady flow of warm/moist air
pushing into the area with generally southerly surface winds. An
unstable environment should be in place, given the warm and moist
surface conditions and with the SW flow aloft there should be
ample shear for organized strong to severe storms at time next
week in the vicinity of eastern Kansas and western Missouri.
Detail at this point are a bit elusive, but given the general
trend of the location of the best mid/upper flow the better
chances for severe storms will likely be across far eastern Kansas
and western Missouri through the week next week. Not every day
looks like it will bring severe weather, but given the SW flow
pattern, rounds of severe weather will be dependent on cloud
cover from convective debris, timing of shortwaves, placement of
the broad upper trough, placement of low level boundaries, etc...
But given the general pattern there does appear to be at least a
couple chances at some severe storms in the area this upcoming
week.

&&

.Aviation...(For the 18Z TAFS through 18Z Sunday Afternoon)
Issued at 1230 PM CDT SAT SEP 16 2017

Complex aviation forecast setting up for the next 18 to 24 hours.
Warm and humid airmass ahead of an advancing cold front is helping
to produce scattered showers and storms across northeastern KS and
northwestern MO. As the front moves southeast later this afternoon
and this evening, showers and storms should become a more
widespread. Have added a tempo group to try and capture the most
likely timing for storms into the terminals. In the wake of the
storms, showers or an area of rain is possible and as cooler air
moves in behind the front, ceilings will likely become low MVFR
and possibly IFR.

&&

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

$$

Discussion...Leighton
Aviation...CDB



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