This summer's unexpected heatwave across the UK and Europe has caught retailers flat-footed. Go into any London Oxford Street store this week and you’ll find the last remains of the mid-summer sale, while “new in” rails are covered in chocolate brown trouser suits ready for Autumn. The trouble is, it’s still 28 degrees and sunny with another heatwave expected this week. Shoppers aren’t looking for jumpers, yet the shelves are stocked for a forecast made half a year earlier, meaning many retailers have missed the immediate shift in consumer demand. It’s hard to not feel the disconnect. Somewhere back in January, a planning team sat in a meeting room and decided, with the best information they had at the time, that by early August the nation would be ready to shop for knitwear. It’s a process that retailers have used for decades, and the problem isn’t that they planned-ahead or got it wrong, it’s that the infrastructure behind the decision has no mechanism for course correcting once new information arrives. That's not a forecasting failure. It's a technology and process failure, and it's one that's becoming impossible to ignore.Six-month planning cycles are no longer viableThe heatwave is just one example of why rigid six-month planning cycles in retail are no longer commercially viable. Designed in an era that was steady and predictable, they assume stable supply chains, formulaic seasons, and shoppers who wait patiently for the "right" moment to buy. That world simply doesn’t exist today. Global supply chains have become fragile and prone to disruption at any point in the chain, while erratic weather patterns can change trading conditions overnight, and consumer demand is shaped as much by a TikTok trend that lands on a Tuesday, as it is by a season on a calendar. This has left retailers trying to run a business that demands agility on an operating system designed for a much slower rhythm.The result is the disconnect we're seeing on the shop floor right now. Having worked in retail for more than 20 years, I know first-hand that most planning systems are still built around static reports, disconnected spreadsheets and manual range-building processes that take weeks (sometimes months) to turn around. This creates a structural lag between changes in demand and when the business is able to respond. It is this lag that is quickly becoming the single biggest driver of markdowns, stockouts and wasted inventory that costs the global retail sector more than $1.7 trillion per year, according to analysts IHL Group. Rethinking planningIt’s clear to me that for retailers looking to achieve growth, they must rethink how planning, buying and merchandising get done. This starts with moving away from rigid, twice-a-year buying cycles built on legacy systems to data infrastructure that supports micro-season planning. This is shorter, more frequent windows where decisions about what to buy, when to reorder and how to promote in-store are made continuously and based on current data, not locked in months in advance based on a forecast made months earlier. Practically, this means implementing a few core capabilities, the first being real-time data visibility that allows teams to see live sell-through, stock position and intake at SKU level, rather than via a report that lands the following Monday describing what already happened.The second is more connected forecasting, where demand models can analyze external factors such as a heatwave, local events or social media trends as a trading signal rather than an anomaly discovered on the shop floor. This leads to the third capability, which is faster execution once a shift in demand is identified. The system needs to support quick decision making and action, whether that's an automated reorder, a reallocation of stock between stores and channels, or a change to in-store and online merchandising.Maintaining a live modelNone of this replaces long-range strategy. Retailers still need a financial plan, a range architecture and a clear vision. What changes is how that happens in practice. Planning becomes less about producing a fixed document twice a year and more about maintaining a live model of the business that can be interrogated and acted on continuously. That's a fundamentally different technology requirement than most legacy planning and merchandising systems were built to support, and it's why so many retailers are still reacting to demand shifts weeks after they've already cost them sales.For retail leaders, the practical takeaway is to start auditing where your planning and merchandising decisions get made, and how long it takes for a real-world signal, such as a heatwave, a stockout, a viral product, to translate into a change on the shop floor or the website. If that gap is measured in weeks rather than days, the constraint isn't your team's judgement, it's the infrastructure they're working with. This heatwave is just one visible example of a much broader technological and operational shift that retailers need to make. The businesses that treat it as a prompt to modernize, rather than a one-off weather event, are the ones that will be more commercially resilient the next time conditions change without warning.We've featured the best ERP software.This article was produced as part of TechRadar Pro Perspectives, our channel to feature the best and brightest minds in the technology industry today.The views expressed here are those of the author and are not necessarily those of TechRadarPro or Future plc. If you are interested in contributing find out more here: https://www.techradar.com/pro/perspectives-how-to-submit