FXUS63 KEAX 231738

National Weather Service Kansas City/Pleasant Hill MO
1238 PM CDT Sat Sep 23 2023

Issued at 311 AM CDT SAT SEP 23 2023

Key Messages:

- Strong to severe storms are likely this afternoon and this
  evening. Large hail and damaging winds are the most likely
  hazards. A few tornadoes are possible as well.

- Drier weather with above normal temperatures are expected next

Water vapor imagery with 500mb heights overlaid shows a robust
shortwave trough moving into southeastern WY and western SD and NE.
This system will be the main player for storms this afternoon and
this evening. Further east, a strong low-level jet has developed
over the eastern Plains in response to the strengthening upper-level
flow associated with the WY shortwave trough and upper-level ridging
over Mexico. VWP plots to our west and southwest show this low-
level jet to be in the 40-50 kt range at 500m AGL. An area of
convergence is noted over eastern KS and this is leading to some
AC development as of 07Z. Models are all in decent agreement with
strong isentropic ascent developing in this area of convergence
and then lifting that to the northeast. This isentropic ascent,
which shows up well at 310K may lead to isolated to possibly
scattered showers and storms in the predawn hours over eastern KS
and western MO. Have maintained the low PoPs from the previous
forecast, with some small adjustments, to account for this

This afternoon, the main area of thunderstorms will affect the area.
Upper-level flow will steadily increase as the upper shortwave trough
moves east. While we`ll see broadly diffluent upper-level flow over
the area, the strongest diffluence will be across IA as the
shortwave is moving into central and eastern NE and SD. Surface and
low-level flow will be more backed to our north, closer to the
surface low. This will keep the best chances for tornadoes to our
north. Further south the combination of strong moisture transport
bringing upper 60 and lower 70 degree dewpoints into eastern KS
and western MO, along with steeper lapse rates aloft, will lead to
a very unstable airmass for late September. SREF MLCAPE
probability of exceeding 3000 J/kg is 10-20% across our
southwestern zones. But greater than 90% for 2000 J/kg. This
strongly suggest we`ll see MLCAPE values in the 2000-2500 J/kg
range with a small potential for even greater values. This
instability, coupled with deep-layer shear in the 30-40 kt range,
oriented westerly across the north-south oriented boundary, favor
supercells initially before storms congeal into an MCS. That MCS then
dives to the south to southeast away from the area and into the
instability axis. Instability in our area weakens with time in the
evening and eastward extent. Thus, it looks like the most likely
areas for severe storms will be eastern KS and western MO, where
all hazards are possible, with diminishing severe weather
potential as the storms move eastward into the evening hours.
These storms will also be very efficient rainfall producers thanks
to very anomalous precipitable water values 2-3 standard
deviations above normal. Precipitable water values greater than
1.75" have a return interval of once every 2 to 5 years for this
time of year. Given this, as well as the recent heavy rainfall,
flash flooding will also be a concern with this system.

Low-level moisture will be slow to move out of our eastern zones as
the upper-low closes off over the northern Plains and Upper Midwest.
This will keep the potential for additional showers and storms going
into Sunday. For next week, upper-level ridging builds into the
middle of the country. This will lead to drier weather conditions
with temperatures in the low to mid 80s for afternoon highs, with is
about 5 to potentially 10 degrees above normal for the time of year.


.Aviation...(For the 18Z TAFS through 18Z Sunday Afternoon)
Issued at 1235 PM CDT SAT SEP 23 2023

Thunderstorms from this morning have exited east of the terminals,
although additional redevelopment remains possible over the next
few hours. The main event for thunderstorms looks to be in the 21z
to 01z time period at STJ and the 22z to 02z time period for the
KC metro terminals, with the greatest threat for strong to severe
storms in the 22z to 00z time frame. Storms should largely exit
by around 2z to 3z tonight, although it is possible some showers
may linger longer. Winds this afternoon should remain out of the
south and breezy, turning SW and decreasing behind the storms





NWS EAX Office Area Forecast Discussion