textproduct: Topeka

KEY MESSAGES

- Thunderstorms increase in coverage from north to south this afternoon and evening. There remains a marginal risk for severe storms mainly for damaging winds.

- Rain becomes widespread overnight with repeated rounds of heavy rainfall potentially leading to flooding. Flood Watch remains in effect for most areas north of I-70.

- Rain ends by mid-day Wednesday with warmer and drier conditions through the end of the work week. Another rain chance comes for the weekend with cooler temperatures early next week.

DISCUSSION

Issued at 427 AM CDT Tue Sep 15 2026

We remain in southwest flow aloft for now with an upper trough moving out of Manitoba and into Ontario early this morning while the ridge remains dominant over the southeast US. Sfc low pressure is centered over western KS with its associated cold front extending from northwest KS up through south central and southeast Nebraska. As the front slowly works its way into the area today, thunderstorm chances increase into north central and northeast KS this morning, although coverage looks to be limited initially. Convergence along the front should strengthen by mid to late afternoon, helping to provide some better lift for scattered storms, a few of which could be strong to severe into the early evening. The front looks to make it to around a line from Abilene to Manhattan to Oskaloosa by peak heating. Moisture pooling along the boundary should aid in developing CAPE to 3000-4000 J/kg south of the front with more modest shear around 25-30 kts. Given these parameters with inverted- V profiles, think damaging wind is the primary hazard with any stronger updraft that could get going and then collapse. As for temperatures, north central and far northeast KS likely only see highs in the 70s today, even falling into the 60s this afternoon with clouds and rain moving in sooner. Those areas along and south of the aforementioned line will have more time to heat up and should see highs in the 80s to low 90s before storms eventually develop.

Heading into tonight, the system evolves into a heavy rain and flooding threat. The sfc front should stall somewhere around southeast KS with isentropic lift over the boundary into our area, and the LLJ helping to feed moisture and sustain storms into our area as well. Model guidance has been consistent in placing the moisture axis right over the CWA with Pwat between 2-2.3", which is well over max values for mid-September. The 00z CAM guidance seems to highlight the area of the going Flood Watch well, with several of the HREF members showing swaths of 3-5" in far northeast KS, even higher in more extreme cases. The RRFS has been less bullish on that idea and the 06z runs of the HRRR and NAM Nest have backed off on those higher magnitude amounts as well, but the 06z has trended a bit further south with the 2-3" amounts. In any case, think an inch or two is a solid bet for most places given the setup, while 3" with locally higher amounts would be possible in locations that see multiple rounds. Opted to leave the location of the Flood Watch as is, but if more CAM guidance suggests heavier rain could end up further south, an expansion may be needed.

Rain should come to an end by mid-day Wednesday as the LLJ weakens through the morning and upper level perturbations get pushed north of the area. The upper ridge in the southeast US looks to retrograde through the end of the week, which would push the trajectory of any embedded waves aloft north of the area and give us a chance to dry out. This also favors WAA through the end of the week, leading to afternoon temperatures returning to the 80s and lower 90s.

A shortwave moving from the Intermountain West across the northern Rockies brings our next chance for rain this weekend with a more meaningful change in air mass behind the system. Ensemble differences in timing and strength of the system keep likely PoPs in some part of the forecast area Friday night through early Sunday morning, but given the differences there should be plenty of dry time within that time frame. There is better agreement on cooler temperatures early next week with highs in the 70s.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 559 AM CDT Tue Sep 15 2026

VFR early with deteriorating conditions this afternoon and beyond. An approaching cold front looks to slow down enough to keep morning showers and weak storms north and west of terminals. Winds look light and variable while the sfc trough passes before the front fully shifts winds to the north. From there, thunderstorm chances increase late this afternoon and may be more scattered at first before rain and storms become more widespread later this evening and continue through the overnight hours. Cigs drop to MVFR and eventually IFR, and heavy downpours could result in IFR vsby at times as well. Conditions don't look to notably improve until just beyond this TAF period.

TOP WATCHES/WARNINGS/ADVISORIES

Flood Watch from 1 PM CDT this afternoon through Wednesday afternoon for KSZ009-KSZ010-KSZ011-KSZ012-KSZ021-KSZ022-KSZ023- KSZ024-KSZ026.