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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

                            
000
FXUS63 KTOP 202342
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
642 PM CDT Sat Jul 20 2019

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Sunday night)
Issued at 239 PM CDT Sat Jul 20 2019

Embedded perturbations are passing through west to east flow aloft 
this afternoon via water vapor imagery. Gravity waves emanating 
southward from the decaying MCS across Iowa are showing little signs 
of causing additional storm development this afternoon. Resulting 
clouds from the waves on visible satellite are showing little 
upscale growth. Meanwhile, a weak 700 mb perturbation over northern 
Kansas/south central Nebraska has resulted in a few scattered 
showers and thunderstorms developing in the last few hours. There is 
an outside chance these showers could reach as far east as north 
central Kansas after 5 PM, but overall weak effective shear values 
are less than 20 kts and would not expect severe convection. Main 
concern would be winds up to 50 mph. 

For tonight, the inverted sfc trough axis shifts eastward, veering 
winds to the north over north central Kansas. The incoming minor 
perturbation coming off the high plains looks to track into 
northwest Kansas and Nebraska later this evening with most model 
guidance generating much of the qpf along the h85 front, north of 
the CWA. After midnight, introduced slight chances as its possible 
for these storms to impact northern Kansas through Sunday morning. 
With the exception of output from the GFS, much of the area should 
stay dry overnight as overnight lows are generally in the middle to 
upper 70s.

On Sunday, short term models continue to trend slower with the 
front, staying mostly north of Interstate 70 through late afternoon. 
The hot and humid airmass is therefore allowed to return across east 
central Kansas with highs back into the middle 90s. Heat indices are 
likely to reach the 103 to 106 degree range so have decided to 
continue the Excessive Heat Warning for these areas through 7 PM 
Sunday. 

In terms of precip, forecast soundings have the capping inversion 
holding in place, precluding any thunderstorm development until late 
afternoon and evening. Enhanced forcing arrives by that time with an 
upper trough dropping southeast towards the midwest by 7 PM Monday. 
Confidence increases by this time for more widespread convection 
developing along and behind the front as it progresses southward 
throughout the evening. Despite the ample instability in place, 
effective bulk shear values are marginal in the 20 to 30 kt range. 
Could potentially see isolated severe storms with damaging wind 
gusts and small hail. What is a more widespread concern is the heavy 
rainfall potential as PWAT values increase to 150% of normal in the 
2.25 to 2.35 inch range. Warm cloud depths are also fairly high to 
over 10,000 feet. Model guidance qpf has been fairly consistent 
between runs of widespread values up to 1.5 inches over far eastern 
Kansas through Monday morning. Locally higher amounts are likely, 
but have not issued any headlines given the uncertainty in training 
convection and higher FFG values.

.LONG TERM...(Monday through Saturday) 
Issued at 239 PM CDT Sat Jul 20 2019

Precip exits the area before sunrise Monday with a much cooler, 
pleasant airmass returning to the region. Highs in the lower 80s 
with overnight lows in the 50s are forecast through Wednesday as 
weak, northwest flow holds over the central CONUS. The upper ridge 
to our west begins to break down and spread eastward by Thursday, 
increasing temps back into the lower 90s on Friday and Saturday. 

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 639 PM CDT Sat Jul 20 2019

A weak cold front/outflow boundary will move southward across the
terminals during mid morning hours shifting winds to the east and
northeast. Scattered afternoon thunderstorms will develop across
the terminals after 20Z SUN and continue into Sunday evening.
There may be brief MVFR conditons if thunderstorms Sunday
afternoon move across the terminals.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 8 PM CDT this evening for 
KSZ008>012-020>024-034>038.

Excessive Heat Warning until 7 PM CDT Sunday for KSZ026-039-040-
054>056-058-059.

&&

$$

SHORT TERM...Prieto
LONG TERM...Prieto
AVIATION...Gargan