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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

FXUS63 KTOP 230436

Area Forecast Discussion
National Weather Service Topeka KS
1136 PM CDT Sun Sep 22 2019

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Monday)
Issued at 252 PM CDT Sun Sep 22 2019

19Z water vapor imagery shows an upper low over the northern
plains. This has helped surface high pressure to build south
through western and central KS, pushing a cold front into east
central KS. This front is expected to push east of the forecast
area this afternoon taking the precip chances with it. The main
question is whether the fog that is expected tonight becomes dense
of a large area. Forecast soundings and models show the surface
ridge moving across the forecast area with skies clearing out this
evening. Event though models show some light southerly winds
developing over central KS, the expectation is for the boundary
layer to become decoupled with forecast soundings showing a fairly
deep layer of light winds and a strong nocturnal inversion. With
recent rains keeping good humidity in the boundary layer,
radiational fog is forecast to form. The magnitude of dry air
advection this evening and a general lack of lower visibilities
from the models provides enough uncertainty with dense fog to
preclude an advisory at this point. But the setup looks very
favorable for fog formation and have included some widespread
wording across eastern portions of the forecast area. 

The weather should clear by late morning Monday with sunny skies
and a southerly breeze. Temps monday area forecast to start the
day off in the lower 50s. But good insolation should warm temps
back to around 80 for most locations. 

.LONG TERM...(Monday night through Sunday)
Issued at 252 PM CDT Sun Sep 22 2019

Several chances for precip remain in the forecast through the end
of the work week. Return flow is expected to develop Late Monday
night and into Tuesday with a warm and humid airmass in place by
Tuesday afternoon. Models develop a fair amount of MUCAPE with
decent shear profiles. But synoptic forcing appears to be pretty
subtle as models show a broad cyclonic flow over the central
plains. There also is a lack of a surface boundary with southerly
winds expected to persist into southern NEB. Convective 
inhibition may diminish enough in the evening for a weak wave
within the pattern to spark some storms. If this occurs, there is
some potential for severe storms given 0-6km bulk shear around

For Wednesday a cold front is forecast to move south into southern
KS. Models want to bring the 850MB boundary into east central KS
or just south with moisture pooling along it. So have kept some
chance POPs across southern portions of the forecast Wednesday and
Wednesday night. 

A cutoff low over the southwestern U.S. is progged to lift out
across the central plains late Thursday night and Friday. This in
turn brings a surface wave through the forecast area and a chance
for showers and thunderstorms Friday and Friday night. However the
12Z models have now indicated that a cold front may move into the
central plains as this piece of energy lifts across the plains.
This has larger implications for the forecast Saturday and Sunday as
the models now linger a weak boundary over the area and are less
amplified with an upper ridge. Have not made many significant
changes to the forecast as this is the first run to show this. But
the uncertainty in the forecast for next weekend is above normal
and I would not be surprised if it changes.

Temperatures for the work week look to remain seasonal. The weak
boundary on Wednesday is expected to keep any warm up on the
modest side. So highs should range form the upper 70s to the mid
80s. Lows look to be mild as well with readings in the upper 50s
and 60s. 


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1134 PM CDT Sun Sep 22 2019

For the 06z TAFs, main focus is on the potential for areas of fog
to develop overnight into Monday morning (primarily near 
KTOP/KFOE), resulting in MVFR to IFR vis with periods of LIFR vis
possible. Otherwise, VFR conditions are expected.




LONG TERM...Wolters