Severe Thunderstorm Warning 259, NWS Topeka, KS

Area Forecast Discussion
National Weather Service Topeka KS
637 PM CDT Thu Sep 21 2023

...Update to aviation forecast discussion...

.DISCUSSION...
Issued at 251 PM CDT Thu Sep 21 2023

Key Points:

- Showers and thunderstorms tonight. A few could be strong to severe.

- Better chance for severe storms Saturday. Details are still
uncertain, but coming into better focus.

Today's pattern across the CONUS is dominated by several upper lows,
with two weak ones over the Midwest and Southeast, and a large/deep
upper low over the West Coast. This latter system is the focus for
our forecast over the next few days. Broad southwest flow aloft is
stretching east from the upper low, including a fairly strong
subtropical jet bringing mid-level moisture from the eastern Pacific
to the southern Plains. Within the southwest flow aloft, one initial
shortwave trough is moving onto the Central Plains. The leading edge
of ascent from this shortwave is approaching north-central Kansas,
promoting the development of northeast-moving elevated showers and
thunderstorms. Farther west, the initial stages of surface based
development are apparent across NW Kansas and SW Nebraska. Assuming
these do develop in the next few hours, they should continue to push
east later this evening into north-central Kansas. Scattered
convection should eventually move into northeast and east-central
Kansas after midnight, lingering into Friday morning. Across the
entire area, instability and shear will be just enough that some
hail and gusty winds could accompany the stronger cells,
particularly if the storms become better organized across western
Kansas.

After this convection clears the area tomorrow morning, much of
Friday afternoon and evening look to be dry. The best mid-level
height falls will remain located across Nebraska, with rising
heights over the dryline to our west limiting the odds of storm
development. By early Saturday morning, increasing WAA in advance of
the main upper low could result in an area of elevated storms. This
will be one of two keys with regard to Saturday PM's severe weather
potential. If too much convection develops Saturday morning and
lingers into mid-day, this could limit afternoon instability ahead
of the cold front. Assuming morning convection is limited though,
there should be plenty of instability across the area. Near 70
dewpoints and steep mid-level lapse rates would lead to 2000-3000
J/kg of ML CAPE. The degree of shear is the other key feature to
watch, and will be dependent on the placement of the upper low to
the north and the subtropical jet to the south. Some guidance has a
gap between these two features with weaker winds aloft, leading to
effective shear only 30 to 35 kts. While this would still be enough
for a wind/hail severe risk given the aforementioned instability, it
would reduce the overall ceiling of the severe risk. On the other
hand, if the subtropical jet is more in phase with the upper low,
shear would be much stronger across our area, on the order of 45 to
50 kts. This would increase the ceiling for this event, and would
likely lengthen the window for any supercells capable of all severe
hazards. While these details still need resolved, guidance is
consistent on an afternoon/evening frontal passage. This could still
shift by a few hours, but confidence is increasing that storms would
develop roughly mid afternoon along the Flint Hills, moving east
into northeast and east-central Kansas during the late afternoon and
evening. Again though, the role of morning convection and the
exact jet structure are still uncertain, so stay tuned.

Beyond Saturday, the upper low will lift northeast and slow down
over the Upper Midwest. This would keep weak northwest flow aloft
over the region. Temperatures look to stay near average, with just a
few low chances for rain as the upper low wobbles northeast of here.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 631 PM CDT Thu Sep 21 2023

Trends suggest that mainly showers and possibly an isolated
thunderstorm should remain in the vicinity or over the terminals
for only short periods of time until a better chance for storms
moves in from the west later, generally after 06Z. Have tried to
time out the best window for storms to impact the terminals in the
TEMPO group. However, confidence is only low to medium.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

DISCUSSION...Reese
AVIATION...Drake

Hazardous Weather Outlook
National Weather Service Topeka KS
255 PM CDT Thu Sep 21 2023

KSZ008>012-020>024-026-034>040-054>056-058-059-222000-
Republic-Washington-Marshall-Nemaha-Brown-Cloud-Clay-Riley-
Pottawatomie-Jackson-Jefferson-Ottawa-Dickinson-Geary-Morris-
Wabaunsee-Shawnee-Douglas-Lyon-Osage-Franklin-Coffey-Anderson-
255 PM CDT Thu Sep 21 2023

This Hazardous Weather Outlook is for central Kansas, east central
Kansas, north central Kansas and northeast Kansas.

.DAY ONE...This afternoon and tonight.

Scattered thunderstorms are likely this evening into Friday morning,
initially across north central Kansas this evening before spreading
east after midnight. Widespread severe weather is not expected, but
some storms could produce small hail and gusty winds.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Thunderstorms are again likely Saturday, particularly across
northeast and east-central Kansas. Some of these storms could be
severe, so stay tuned for future details.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

&&

More detailed information can be found at:
www.weather.gov/media/top/DssPacket.pdf

Special Weather Statement
National Weather Service Topeka KS
741 PM CDT Thu Sep 21 2023

KSZ054-058-220115-
Coffey-Lyon-
741 PM CDT Thu Sep 21 2023

...A strong thunderstorm will impact portions of northwestern Coffey
and east central Lyon Counties through 815 PM CDT...

At 741 PM CDT, Doppler radar was tracking a strong thunderstorm over
Neosho Rapids, moving east at 15 mph.

HAZARD...Wind gusts up to 50 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...
Lebo and Neosho Rapids.

This includes Interstate 35 between mile markers 140 and 150.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3844 9602 3844 9595 3843 9595 3843 9582
      3833 9581 3832 9602
TIME...MOT...LOC 0041Z 263DEG 13KT 3838 9598

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...50 MPH

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