023
FXUS63 KTOP 200738
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
238 AM CDT Wed Aug 20 2025

.KEY MESSAGES...

- There is about a 10% chance for a pop-up shower this afternoon.
  Severe weather is unlikely

- Warm temps are expected to remain in place through Friday with
  highs around 90. The humidity should be a little lower though.

- A taste of fall is in store for the region early next week with
  temps potentially 10 to 15 degrees below normal. Increased spread
  in the models means the forecast values may change with later
  forecasts.

&&

.DISCUSSION...
Issued at 238 AM CDT Wed Aug 20 2025

An upper ridge remained centered over the Four Corners per the 07Z
water vapor imagery. This set up weak northerly mid and upper level
flow over the forecast area with no obvious wave upstream. Surface
obs also showed weak ridging nosing into north central KS.

For today there is a non-zero chance for a pop up shower. Models
show some instability remaining with CAPE values around 1500 J/kg
this afternoon. But mid level lapse rates are progged to only be
around 5.5 C/km. Meanwhile the surface ridge is forecast to
gradually expand over the forecast area limiting foci for
convergence. If there was a remnant outflow boundary or thermal
gradient, a shower could develop with there being little inhibition
to surface based convection. CAMs suggest very isolated coverage if
anything were to pop up. So chances look to remain less than 20
percent for any given location and have left the forecast dry for
now. Skies have cleared out this morning with light or calm winds in
the boundary layer. This would seem to set up ideal radiational
cooling conditions. But temps have been slow to respond with them
just now getting into the lower 70s. Still think patchy ground fog
will develop in low lying areas through sunrise. This should not be
long lived as forecast sounding being to mix out the boundary layer
shortly after sunrise. There is not a lot of cold air advection with
this surface ridge with it generally bringing air in from the east.
With decent insolation, highs are forecast to warm around 90 this
afternoon. The good news is dewpoints are expected to mix out into
the upper 60s making the heat index only a few degrees warmer than
the actual temps.

Not a lot of change in the forecast for Thursday through Saturday.
An upper ridge axis is progged to swing north to south over the
forecast area through Friday with weak ridging at the surface.
Unless some convectively induced wave develops, there doesn`t appear
to be much forcing for precip until Friday evening when a cold front
moves into the area from the north and northwest. Model progs of QPF
are still rather hit or miss as the front enters the forecast area
and as a result the NBM POPs don`t increase until late in the night
Friday. This may be a function of the frontal timing or quality of
moisture ahead of the boundary. So will see how things change once
some of the shorter term guidance gets included in the blend.

The big news in the weather is going to be a taste of fall by early
next week. Operational models and ensembles continue to show a
Canadian high pressure system diving south through the plains with
the promise of much cooler temperature, potentially 10 to 15 degrees
below normal for late August. However folks should take this with a
grain of salt as ensembles and the NBM show increasing spreads in
the forecast data. This is suggestive of lower predictability with
this pattern and in fact the 12Z ensemble cluster analysis from
yesterday still shows as many as 40 to 50 percent of the members with
a warmer forecast. A break down of the individual ensembles shows
the GFS, with its very strong warm bias, close to the 90th percentile
in temps. The Canadian is down around the 25th percentile while the
ECMWF fits closer to the 50th percentile. Since the NBM weighs the
ECMWF more heavily, it may be a good first guess with temps. In
general confidence in the pattern change and a cool down is good, but
the numbers for highs and lows are probably going to fluctuate over
the coming days. This will probably be the case for POPs as well as
the NBM continues to be a little more bullish with POPs early next
week than the 00Z GFS/ECMWF would support. Like with the temps, the
forecast will come down to how strong the surface ridging is and
where the warm air advection pattern with the return flow sets up.
Given the lower predictability have not made changes to the NBM
initialization.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1217 AM CDT Wed Aug 20 2025

Will be watching for ground fog development as the clouds continue
to clear out this morning. Forecast soundings show the boundary layer
mixing by 14Z so FG shouldn`t last long if it develops. A CU field
is expected to develop by early afternoon with bases at 5 to 6 KFT.
There may be enough instability for an isolated SHRA to develop as
well. But coverage is expected to be less than 20 percent so will not
include in the forecast. Overall VFR conditions should prevail once
any fog lifts with a light east to northeast wind at the surface.

&&

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

&&

$$

DISCUSSION...Wolters
AVIATION...Wolters