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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

FXUS63 KTOP 260010

Area Forecast Discussion
National Weather Service Topeka KS
710 PM CDT Sun Aug 25 2019

Issued at 331 PM CDT Sun Aug 25 2019

20Z water vapor and profiler data shows an upper trough along the
KS/MO state line moving off to the east. Meanwhile another speed 
max/shortwave was propagating southeast over the northern Rockies.
At the surface, a weak meso scale low was noted south of the KC 
metro while high pressure over the Ozarks weakened. The larger 
scale pattern had low pressure in the lee of the Rockies and high 
pressure over the Great Lakes. This has allowed low level moisture
to remain over the region with dewpoints in the mid and upper 60s
across the forecast area. 


...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Monday)
Issued at 331 PM CDT Sun Aug 25 2019

For tonight, the thinking is for generally quiet weather to 
persist as the upper trough and vertical motion associated with it
continue to move east. Forecast soundings show low level RH to 
remain fairly high with the stratus expected to hang around. Some 
of the model solutions are developing some very light QPF towards 
12Z. Think this is driven mainly from some weak isentropic upglide
within the stratus deck. So there may be some light mist or 
drizzle across northeast KS towards daybreak. Since this is not 
expected to lead to measurable precip, have POPs less than 20 
percent. But have added a mention of patchy fog across northeast 
KS where the upglide is progged to be focused. Have lows remaining
fairly mild overnight thinking the stratus deck will limit 
radiational cooling. 

A cold front is still on track to move through the area on Monday. 
Forecast soundings from the NAM and GFS show a strong elevated mixed 
layer advecting over the boundary layer by Monday morning 
effectively capping the boundary layer. So the front is progged to 
move through much of the forecast area dry. However by the late 
afternoon, forecast soundings finally weaken the cap enough for 
convection to develop along the front. This may occur across our 
eastern counties around 4 pm. Deep layer shear of 40 to 50 KT and 
most unstable CAPE values over 4000 J/kg would support an organized 
severe risk along and east of the front. The risk for tornadoes 
looks to be pretty conditional on how the low level winds shape up
ahead of the front. For the most part, models have surface winds 
veering to the southwest as the cap is likely to break. So the 
main concerns with the storms may end up being damaging hail and 
winds. Will have to pay attention to low level winds profiles 
tomorrow afternoon though. Trended highs up a little across east 
central KS where models have good warm air advection ahead of the 
front. Think some of this warmer air could mix down to give highs 
in the mid and upper 80s. Across northern KS, clouds and eventual 
cold air advection may limit highs closer to around 80. 

.LONG TERM...(Monday night through Sunday)
Issued at 331 PM CDT Sun Aug 25 2019

There is some signal from the models for light precip Tuesday 
afternoon and Tuesday evening as the surface ridge and dry low 
level air moves in. However forecast soundings show some weak warm
air advection in mid levels as a shortwave moves through the mid 
MO river valley. There is a brief window where some saturation 
occurs with some very modest elevated instability tries to 
develop. Have kept a 10 percent POP because of this rather than
the lower chances from the National Blend of Models (NBM). But 
the mid level lapse rates don't look terribly good for elevated 
storms. Although I can't rule out a shallow shower or two in the 
afternoon and evening either. 

The next chance for precip looks to come in Thursday night through 
Saturday. Models show another frontal system moving into the central 
plains with some return flow developing in advance of this system. 
Synoptically, forcing for precip is not that impressive, but 
models do advertise a low amplitude wave moving through the region
by Saturday. So have some chance POPs in the forecast for this. 
Outside of these periods, surface ridging and relatively dry air 
is expected to limit precip chances to 10 percent or less. 

Temps are likely to be below normal for Tuesday and Wednesday with 
highs around 80 and lows falling into the 50s. The return flow 
mentioned earlier looks to advect warmer air back into the region by 
Thursday. So have trended highs warmer, back to seasonal norms, with 
highs in the mid and upper 80s. The frontal system late in the week 
is forecast to cool temps off again for the weekend. 


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 655 PM CDT Sun Aug 25 2019

VFR to MVFR ceilings are expected to deteriorate again overnight
to IFR or lower, especially northeast of a line from CNK to TOP. 
Areas of fog may also result in MVFR to IFR restrictions. Showers 
and thunderstorms may affect these same areas in the morning 
hours, with a cold front swinging through during the day and 
shifting winds to the northwest at 15 to 25 kts and igniting 
showers and storms southeast of a line from TOP to EMP after 20Z.




SHORT TERM...Wolters
LONG TERM...Wolters