815
FXUS63 KTOP 192349
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
649 PM CDT Thu Sep 19 2024

.KEY MESSAGES...

- Warm afternoon followed by scattered thunderstorms this evening
across far eastern KS, a few severe possible.

- Widespread rainfall over the weekend. Potential for 1-3 inch
totals in spots, especially along/north of I-70.

- Cooler conditions arrive behind Sunday cold front passage.

&&

.DISCUSSION...
Issued at 227 PM CDT Thu Sep 19 2024

The main near-term concern is thunderstorm potential along and ahead
of a cold front that is just beginning to move into north-central
Kansas. The main upper low driving this cold front is all the way up
in southern Canada, so our area is far removed from the best upper
support and height falls. Our 18z sounding supports this, with a
strong subsidence inversion around 550 mb and plenty of dry air
aloft. These will act together to limit convective development this
evening. On the other hand, the low-levels are more favorable for
storms to form. Southerly winds have kept dewpoints near 70 degrees
across far eastern Kansas, and deep mixing in the boundary layer is
helping to erode the low-level cap that exists. As the front moves
east this evening, still think low-level convergence and lack of CIN
will be enough to develop a few thunderstorms across far eastern
Kansas 5-8 PM, despite the unfavorable mid-level ingredients.
Assuming a few storms do form, 35 kts of shear and 2000-3000 J/kg of
MLCAPE will be enough for damaging winds and large hail. Can`t
completely rule out a brief tornado if winds stay more southeasterly
in the wake of early-day convection, but the overall threat is very
low. The bulk of the threat will end by 10-11 PM as the front
continues pushing east and the boundary layer cools.

Friday will be a quieter day as the front stalls to our south and
heights rise across the region. Still looks to be a warm day with
highs in the 90s assuming clouds become mostly clear north of the
warm front. Friday night and into Sunday, attention turns to an
upper low over the Southwest that will lift northeast towards the
Plains. As this occurs, isentropic ascent over top the old frontal
boundary (which will slowly lift north as a warm front) will lead to
repeated rounds of showers and storms. The main question is how far
north the warm front lifts as the system approaches and surface low
pressure deepens over the High Plains. Heavier rain, potentially
several inches in spots, will occur to the north of the front`s
eventual position, while lighter rainfall totals will occur to the
south. Much warmer temperatures are also expected south of the front
vs to its north, particularly Sunday as the surface low moves across
the area. Currently leaning towards a slightly farther south track
of the warm front and surface low, with the heaviest rain along and
north of Interstate 70. However there is certainly room for changes
either north or south.

Beyond Sunday, cooler and drier conditions are expected as the low
pulls off to the east and upper troughing amplifies over the Ohio
Valley. Lingering cloud cover may keep temperatures in the 60s
Monday, while even the 75th percentile of high temperatures stay in
the 70s through mid-week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 647 PM CDT Thu Sep 19 2024

The storm chances this evening will be east of the terminals.
Expect scattered high clouds and southwest to west winds will
become light and variable through the night, then winds will
become easterly at 8 to 10 KTS by early Friday afternoon.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Reese
AVIATION...Gargan