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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

                            
000
FXUS63 KTOP 202340
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
640 PM CDT Tue Aug 20 2019

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Wednesday)
Issued at 345 PM CDT Tue Aug 20 2019

The threat for showers and storms gradually increases tonight and
into Wednesday, with the best chance coming Wednesday afternoon.

The effects of the early morning MCS that rolled through Iowa and
Missouri are still being noted over the forecast area, with a 
stout 15 to 20 kft mid-level cloud deck holding firm over parts of
the area. Nevertheless, even with the clouds, heat indices across
the area rose into the 105 to 115 degree range with dewpoints
approaching 80 degrees in many locations.

The differential heating zone induced by these clouds, and 
possibly the outflow boundary from the complex itself, has 
facilitated the development of a surface convergence zone that as 
of 3pm had sunk southward to along a line from Salina to Garnett. 
The overall baroclinicity along this boundary was very low, with 
little in the way of a theta-e gradient along this wind shift. A 
stout H850 cap will keep the threat of surface-based convection 
near zero. Isolated showers have peculated within this regime of 
higher mid-level moisture, but with only a small portion of the 
EML above this layer, there has been little in the way of elevated
instability for these parcels to realize and these convective 
elements have been very short-lived. Kept some slight chance PoPs 
going for the next few hours closer to the mid-level moisture 
plume along I-70, but the cloud shield is gradually waning and 
little impacts are expected.

Attention then turns towards tonight and the development of a LLJ
across central and eastern Kansas. Confidence in the LLJ sparking
convection is low, with the best moisture located well above the 
LLJ and the warm nose possibly keeping convection at bay. An MCS 
is progged to move across southern Nebraska overnight closer to 
the synoptic H850 front, but even some of the CAMs are keeping 
this threat north of the forecast area until near sunrise 
Wednesday. How this convection unfolds will dictate convective 
evolution during the day on Wednesday. Latest consensus is that 
the near-surface warm front sags towards the I-70 corridor at peak
heating, which will serve as the focus for renewed shower and 
thunderstorm development. Questions arise if the morning activity 
does not wane as forecast, then the boundary may sink further 
south than forecast. The environment will support heavy rain- 
producing cells with PWATS around 2 inches and deep warm cloud 
depths. The overall severe threat will depend largely on the 
degree of warming on the south side of the front, and agree with 
the SPC Marginal Outlook in place for tomorrow given the lower 
confidence of convective evolution.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 345 PM CDT Tue Aug 20 2019

Periodic chances of rain pepper the long term forecast with lower
than average confidence in the timing and location of any 
rainfall.

Widespread convection will be ongoing across much of the area 
Wednesday night into Thursday morning attendant with the event 
discussed in the short-term section. The warm frontal boundary 
looks to reside south of the forecast area for the latter portion 
of the week, limiting the convective threats and keeping 
temperatures on the cooler side. A gradual warming pattern ensues 
for the weekend and early next week as southerly flow becomes 
reestablished. Several perturbations work through the W/NW flow 
during this time, but the lack of inter and intra-model 
consistency makes pinning down the impacts of these waves very 
difficult.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 632 PM CDT Tue Aug 20 2019

Thunderstorm chances will begin to increase overnight with the 
best chances occurring tomorrow afternoon into tomorrow night. 
Thus, have included mention of VCSH at terminals after 09Z and 
VCTS at KMHK after 20Z with increasing confidence in localized 
chances. LLWS will be marginal tonight with 30 to 35 kt 
southwesterly winds around 2000 ft AGL. CIGS are expected to 
decrease to near MVFR category by late in the TAF period as
thunderstorms become more likely.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 9 PM CDT this evening for KSZ008>012-020>024-
026-034>040-054>056-058-059.

&&

$$

SHORT TERM...Skow
LONG TERM...Skow
AVIATION...Teefey