259 FXUS63 KTOP 211945 AFDTOP Area Forecast Discussion National Weather Service Topeka KS 245 PM CDT Wed Aug 21 2019 .SHORT TERM...(This evening through Thursday) Issued at 215 PM CDT Wed Aug 21 2019 Focus on t-storm development this evening and heavy rain/flooding risk. Messy surface pattern in place this afternoon with several outflow boundaries. Main morning outflow boundary has surged south toward the KS/OK border and has caused 955-850mb winds to become northerly. Another outflow boundary has pushed southeast of the Topeka area while it appears that the main synoptic boundary is trying re-establish itself near and north of I-70 toward SLN. Water vapor shows an MCV across NE moving southeast toward the area while a diffuse upper low appears to be located across southwest NE western KS. Over the next several hours it appears that forcing/lift may increase ahead of the NE MCV such that elevated convection may develop across central KS and this could become sfc based at some point this evening as instability increases. Other storms may develop ahead of the outflow boundary which would be along/southeast of I-35. MLCAPE may increase into the 1500-2000 j/kg range this evening with 30-40 kts of effective shear so there is a window of opportunity for a few severe storms this evening with a wind risk. It appears that any sfc based storms should shift southeast with time this evening while nocturnal low level forcing from a developing 30-35kt LLJ should help trigger more t-storms near and north of the 850-925mb thetae axis somewhere near I-70 after sunset. Storm motion is ESE at 15-20kts and given support from the right entrance region of the 250 mph jet we could see an axis of t-storms develop within an environment featuring MUCAPE in excess of 2000 j/kg with high water cloud depths and PWATS near 2 inches so intensity of rain could be very high and duration due to training may also become a problem for flash flooding wherever storms become oriented. Thus have issued a flash flood watch for this potential though still uncertain as to where exactly the heaviest rains will set up. .LONG TERM...(Thursday night through Wednesday) Issued at 215 PM CDT Wed Aug 21 2019 Looking ahead toward the end of the week into the weekend...the upper pattern is odd and features a highly amplified trough across the Great Lakes and northern Rockies with a ridge across the central plains. However as mentioned there appears to be a weak upper circulation that is forecast to drift across southern KS Thursday through Friday. This in combination with the proximity of the 850mb boundary will keep rain chcs in the forecast at least for the southern half of the area through Friday. The forecast beyond Friday is less confident with GFS now suggesting that a northern stream trough will emerge into the plains and bring more storm chcs to the region as early as Friday night/Saturday morning. Unfortunately it looks like we could find ourselves right back in northwest flow regime by Sunday with low level WAA beneath stronger mid level flow which could bring more bouts of organized storms into early next week. If there is any hope it is toward the end of next week when models suggest a stronger longwave trough may sweep through pushing a cold front south and ushering in much drier air and at least some relief from heavy rains. && .AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon) Issued at 1151 AM CDT Wed Aug 21 2019 VFR conditions will persist however thunderstorms will develop across the area after 21Z and persist at or around the TAF sites through much of the night. For now will carry MVFR conds however there could be periods of IFR conditions after 06Z tonight and will include once confidence in timing improves. && .TOP WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch from 7 PM CDT this evening through Thursday morning for KSZ021>024-026-034>040-054>056-058-059. && $$ SHORT TERM...Omitt LONG TERM...Omitt AVIATION...Omitt