644
FXUS63 KTOP 020859
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
359 AM CDT Tue Sep 2 2025

.KEY MESSAGES...

- A few rain showers may be possible this morning. Look for
  gradual clearing through this afternoon.

- Seasonably strong cold front arrives Wednesday afternoon.
  Thunderstorms will develop along the front and some of the
  storms may be severe with large hail and damaging wind gusts
  along and south of I-70.

- There may be another chance for showers and thunderstorms
  Sunday into Monday.

&&

.DISCUSSION...
Issued at 336 AM CDT Tue Sep 2 2025

Early this morning a broad upper level trough was located across the
eastern US. Northwest mid and upper level flow was noted across the
Plains on the west side of the upper trough across the eastern US. A
weak perturbations embedded within the northwest flow was
located southwest of EMP and weak ascent near the perturbation
was causing scattered showers across the central and northeast
counties of the CWA. An amplified upper trough was located
across north central Canada. A closed upper low was located off
the coast of WA/OR, cut off from the northern jet stream.

The 7Z surface observations showed northeast to east winds
across the CWA with the higher dewpoints in the lower 60s across
the central and southwest counties of the CWA. A near
stationary front was located across southeast NM, east-southeast
across south central TX into the northern Gulf of Mexico. Winds
are very weak north of the boundary, thus frontolysis may be
occurring.

Today through Tonight:

As the mid level perturbation over eastern KS continues to dig
south-southeast into norther OK, we should see the rain chances
decrease through the morning hours and skies to become partly cloudy
during the afternoon hours. Highs will reach the mid to upper 70s.
The amplified upper trough across central Canada will dig southeast
into the upper Midwest by 12Z WED. A cold front will push southward
across the northern Plains into northern NE and northern IA.
Tonight, expect dry condition with mostly clear to partly cloudy
skies.

Wednesday through Wednesday night:

The amplified upper low will dig east-southeast into the northern
Great Lakes and a strong northwest upper jet will dig southeast
across the Plains with H5 winds increasing to 40-45 KTS. Strong
low-level CAA will cause the front to push southward across the
northern counties of the CWA by around Noon. Now the question
will be is how fast will the front move southward through the
afternoon hours and when will deep moist convection develop
ahead of the front. The CAMs all have differing solutions on
when thunderstorms will develop along the front during the
afternoon hours. The 6Z HRRR is much farther north with a
slower speed of the front pushing south, with surface based
thunderstorms developing along or just north of the I-70 corridor
around 20Z. The other 00Z CAMs show the front moving south of
I-70 with surface based thunderstorms developing farther south.
The environment ahead of the front by mid to late afternoon
will have MLCAPES in the 1500-25000 J/KG range and effective
shear of 35 to 45 KTS, which will allow for potential supercell
thunderstorms development, particularly in the first hour or two
of storms developing. If a supercells develop, then there may
be large hail risk, with up to 2 inch in diameter hail possible
and the potential for a weak tornado or two. The low-level
vertical wind shear will be sufficient for some component of
stream-wise vorticity in the 0-3km level ingesting into storm
updrafts. The hodographs will be slightly curved with southwest
low-level winds veering with height to the northwest. However,
if the front is moving faster to the southeast these storms may
get undercut and any weak tornado potential will cease as the
low-level inflow into the mesocyclone will be cutoff. At this
time the greatest threat for severe thunderstorms will be in the
20Z-02Z along and south of I-70. The initial discrete storms may
be supercells with the primary hazards of large hail and
damaging wind gusts and an outside chance of a weak tornado. The
discrete supercells may congeal into a line of storms along the
advancing cold front by late afternoon, which would place
damaging wind gusts as the primmer hazard. Once the front pushes
southeast of the CWA during the late afternoon and early
evening hours, the severe thunderstorm threat should end. There
may be elevated showers and storms north of the front across
east central and northeast KS into the early evening hours but
these storms will not be severe.

Ahead of the front high temperatures should reach into the mid 80s.
North of the front along the NE border highs may only reach the
upper 70s.

Thursday through Friday night:

Most of Thursday will be dry behind the first front. A second
H5 trough will dig southeast on the west side of the upper low
over Ontario Canada and the northern Great Lakes. The richer
moisture will be south of the area but stronger ascent ahead of
the H5 trough digging southeast across the Plains combined with
anisotropic lift will cause showers and a few elevate
thunderstorms to develop late Thursday night into Friday. Highs
Friday will be much cooler with cloud cover and periods of
showers through the day. HIghs will only reach the mid 60s north
to around 70 degrees south. The H5 trough will shift east-
southeast across the Mid MS River Valley and the secondary cold
front pushes southward into OK and north TX. The rains showers
will push southeast of the CWA Friday evening.

Saturday through Tuesday:

The upper low across the northern Great Lakes will shift east across
eastern Canada and New England by next Monday. The northwesterly
flow will become zonal late Saturday into early next week. Minor
perturbations may move east across the Plains along with richer
moisture advection for small chances for showers and
thunderstorms through Tuesday. The ECMWF keeps the higher rain
chances west and south of the CWA. The GFS forecast a more
amplified perturbation moving across the Plains Sunday night
into Monday. If the GFS solution verifies, we may see a higher
chance for showers and thunderstorms Sunday night through
Monday. Tuesday may be drier behind a weak front. Highs through
the period will be in the lower to mid 70s.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1231 AM CDT Tue Sep 2 2025

The low IFR/MFVR stratus will remain in place across KMHK
through 16Z TUE. At this time forecast soundings show the low
stratus remaining west of KFOE and KTOP, with VFR stratus at
KFOE and KTOP. There may be a few rainshowers around the
terminals through the morning hours. By late morning the cloud
cover should scatter out.

&&

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

&&

$$

DISCUSSION...Gargan
AVIATION...Gargan