Severe Thunderstorm Warning 270, NWS Kansas City, MO

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
623 AM CDT Sat Sep 23 2023

.Discussion...
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
  week.

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
potential.

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 12Z TAFS through 12Z Sunday Morning)
Issued at 619 AM CDT SAT SEP 23 2023

VFR conditions expected through this morning. A few scattered
showers cannot be ruled out near terminal space by 15-18Z, but the
greater concern is after 22Z when thunderstorms, some strong, will
develop near terminals. Gusty southerly winds are expected between
15-00Z. Frontal boundary will slow forward progress by late
evening, with stratus development along the boundary an increasing
possibility.

&&

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

Discussion...CDB
Aviation...Blair

Hazardous Weather Outlook
National Weather Service Kansas City/Pleasant Hill MO
513 AM CDT Sat Sep 23 2023

KSZ025-057-060-102>105-MOZ001>008-011>017-020>025-028>033-037>040-
043>046-053-054-241015-
Atchison KS-Miami-Linn KS-Doniphan-Leavenworth-Wyandotte-Johnson KS-
Atchison MO-Nodaway-Worth-Gentry-Harrison-Mercer-Putnam-Schuyler-
Holt-Andrew-De Kalb-Daviess-Grundy-Sullivan-Adair-Buchanan-Clinton-
Caldwell-Livingston-Linn MO-Macon-Platte-Clay-Ray-Carroll-Chariton-
Randolph-Jackson-Lafayette-Saline-Howard-Cass-Johnson MO-Pettis-
Cooper-Bates-Henry-
513 AM CDT Sat Sep 23 2023

This hazardous weather outlook is for northwest...north central and
west central Missouri...as well as extreme eastern Kansas.

.DAY ONE...Today and Tonight

 Strong to severe weather expected this evening into the night.

 More detailed information can be accessed at...
 https://www.weather.gov/eax/hwo

.DAYS TWO THROUGH SEVEN...Sunday through Friday

Additional rounds of showers expected for Sunday. Severe not expected
at this time.

 More detailed information can be accessed at...
 https://www.weather.gov/eax/hwo

Special Weather Statement
National Weather Service Kansas City/Pleasant Hill MO
946 AM CDT Sat Sep 23 2023

KSZ025-103-MOZ020-021-028-231515-
Atchison KS-Leavenworth KS-Platte MO-Buchanan MO-Clinton MO-
946 AM CDT Sat Sep 23 2023

...A strong thunderstorm will impact portions of north central
Leavenworth, southeastern Atchison, Buchanan, west central Clinton
and northern Platte Counties through 1015 AM CDT...

At 946 AM CDT, Doppler radar was tracking a strong thunderstorm near
Lewis And Clark Village, or 7 miles northwest of Weston, moving
northeast at 35 mph.

HAZARD...Winds in excess of 30 mph and nickel size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
St. Joseph, Atchison, Weston, Gower, Agency, Dearborn, Rushville,
Lewis And Clark Village, De Kalb, Iatan, Faucett, Bean Lake, Lewis
And Clark Vi and Lowemont.

This includes the following highways...
 Interstate 29 between mile markers 25 and 45.
 Interstate 229 between mile markers 0 and 2.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3934 9503 3949 9517 3978 9473 3956 9453
TIME...MOT...LOC 1446Z 235DEG 32KT 3946 9503

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...30 MPH

BT

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