453
FXUS63 KTOP 301941
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
241 PM CDT Tue Apr 30 2024

.KEY MESSAGES...

- Thunderstorms developing this afternoon along a cold front will
quickly becoming strong to severe with large hail, damaging winds
and a few tornadoes possible.

- An active weather pattern continues Wednesday into Thursday and
again this weekend with persistent chances for thunderstorms.

&&

.DISCUSSION...
Issued at 240 PM CDT Tue Apr 30 2024

Another afternoon and evening of severe weather is shaping up once
again across the central Plains as a mid-level wave approaches from
the west and has begun to eject into Nebraska as noted on water
vapor imagery. Surface analysis across Kansas shows a deep surface
trough and low over central Kansas with a cold front and dry line
extending south into southwestern Kansas. Strong warm sector WAA has
pushed 60 degree dewpoints as far north was eastern Nebraska with
mid-60 degree dewpoints beginning to make their way into east-
central Kansas. With ample afternoon warming, temperatures across
the area have reached the low to mid 80s and will be expected to
warm a few degrees further over the next several hours.

Over the next few hours, residual BL capping that is noted in the
TOP 18z sounding will slowly erode as the cold front approaches from
the west. MLCAPE values ranging from 2500-3500 J/kg, 0-6 km shear of
35-50 knots (higher values in northeastern Kansas and lower values
in central Kansas), 7.5-8 C/km mid-level lapse rates and increasing
low-level wind shear will be present ahead of the boundary late this
afternoon and evening, setting the stage for severe storms in
eastern Kansas. CAMs over the past 6 hours have been fairly
consistent in developing convection between the 21-23z timeframe
along the boundary draping from Seneca to Council Grove. Convection
should quickly intensify from there, zipping down the frontal
boundary into southeastern Kansas. Given the environment, very large
hail (up to 2+ inches), damaging winds (>70 mph) and a few tornadoes
will be possible with the strongest and most organized supercells.
Shear vector orientation in relation to the surface boundary should
keep convection isolated for several hours before the boundary
begins to move more southeast this evening promoting the congealing
of storms. Another thing that will need to be watched is how the LLJ
will impact ongoing convection into the evening hours. An increase
in 0-1 km and 0-3 km shear should point to an increase in tornadic
activity just after sunset. If convection can stay isolated enough
until then, a tornado or two cannot be ruled out. With storms moving
rather quickly across the area tonight, not expecting a widespread
flooding concern. That said, as the front begins to move more
south/southeastward south of I-35, a localized flooding concern
could take shape, especially in areas that saw several inches of
rain the past week. FFG across this area is currently sitting around
1-2 inches, and with HREF QPF probabilities ranging from 0.75-1.5
inches, we could see localized flooding south of I-35. Issued a
Flood Watch for Anderson and Coffey counties as that seems to be the
area with the highest chances for hydro concerns.

By early Wednesday morning, the surface and 850mb boundaries will
stall across southern Kansas and northern Oklahoma, keeping the
better QPF axis to our south. Throughout the day Wednesday, another
mid-level wave will deepen another lee cyclone in southwestern
Kansas and push the stalled boundary north as a warm front. Rain and
storm chances along the frontal boundary will continue for much of
the day Wednesday and might help to mitigate Wednesday evening`s
severe weather chances. Given MUCAPE around 1000 J/kg and decent
wind shear, some elevated warm advection storms Wednesday could
become strong to marginally severe with hail being the main hazard.
By Wednesday afternoon, the surface low moving out of southwestern
Kansas could begin to develop convection along the dry line in far
south-central/central Kansas. This convection will race off to the
northeast and could impact portions of north-central Kansas
Wednesday evening and overnight into Thursday. There still remains a
fair amount of uncertainty with how well these storms will be able
to maintain their strength as they approach north-central Kansas
with Wednesday morning convection possibly stunting severe
parameters across the area. Any storms that can sustain themselves
will pose risks for large hail, damaging winds and an isolated
tornado. Confidence still is medium/high with all of the area having
a threat of heavy rainfall Wednesday afternoon into Thursday as
strong moisture convergence along the frontal boundary becomes
draped across the area. A Flood watch may be needed for this
timeframe.

Precipitation chances will begin to decrease into Friday
morning as the upper trough axis shifts to the east and surface
ridging builds into the area. A few more waves moving across the
Plains will keep mention of thunderstorms in the extended forecast
into early next week, so not many hints of many breaks in the active
weather appears likely.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1231 PM CDT Tue Apr 30 2024

Several aviation hazards over the TAF, first with winds this
afternoon and later with thunderstorm concerns. Winds will
remain gusty this afternoon out of the south, gusting upwards of
30 mph. A frontal boundary moving in from central Nebraska will
develop convection around the terminals between 22-00z this
evening, with better confidence in convection at KTOP and KFOE.
Storms will likely develop near KMHK and quickly move east.
Following the cold frontal passage, winds will shift to the
northwest, becoming calmer into Wednesday morning. Some rain and
thunderstorm chances will increase late Wednesday morning and
into the afternoon as a warm front pushes north.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 8 PM CDT this evening through Wednesday
morning for KSZ058-KSZ059.

&&

$$

DISCUSSION...Griesemer
AVIATION...Griesemer