UK weather maps show exact date of December 'heatwave' - 10 hottest counties

What the latest maps say about December warmth

Forecast maps produced by WXCharts and other data providers have started to show a notable rise in temperatures as we move into the early days of December. In practical terms, that means more sun, longer feeling-of-spring air on some afternoons, and a break from the cold that has gripped many parts of the country. When models project temperatures approaching 17°C on a December day, you’re looking at a reading that sits well above the typical averages for the month in many regions.

It’s essential to interpret these signals correctly. While 17°C is unusually warm for December in the UK, it isn’t a heatwave by official standards. Still, it’s a striking departure from the ordinary and can influence how you plan your week—whether you’re choosing to exercise outdoors, run errands, or schedule home maintenance.

How forecasts are built: WXCharts, MetDesk, and the big picture

Forecasts don’t come from a single crystal ball. They’re the result of a blend of data from multiple sources, calibrated by meteorologists to produce the most reliable predictions possible. Two names you’ll hear a lot are WXCharts and MetDesk. Here’s how they come together to form a forecast you can use:

• Data inputs: Weather maps pull in temperature, pressure, humidity, wind patterns, and cloud cover from numerous observational networks and satellites.
• Model ensembles: Rather than relying on one model, forecasters run several simulations with slightly different initial conditions. This helps gauge the range of possible outcomes and identifies where confidence is high or low.
• Local nuance: The UK’s landscape—coastlines, hills, and urban heat islands—can tilt temperatures by several degrees from one area to another. That’s why a region near the sea may differ from a nearby valley or hillside.
• Calibration and interpretation: Forecasters compare model outputs with real-time observations and adjust for biases, giving you a usable daily forecast.

Technically, you’ll often hear about a “ridge of high pressure” steering milder air from the south or west, or a “trough” dipping in, bringing cooler conditions. When maps align to suggest a brief warm spell in December, it often means a temporary shift in wind patterns and atmospheric pressure that nudges temperatures upward for a few days. But weather maps aren’t an oracle—they’re best interpreted as guidance, not guarantees.

Is 17°C in December a heatwave? Understanding UK thresholds

Despite the warmth, it’s important to separate curiosity from alarm. A temperature reading of 17°C on a December afternoon is striking, but heatwaves in the UK have a formal definition that usually involves sustained high temperatures over multiple days and a regional threshold that’s tailored to what’s normal for that area. In practice, a 17°C day in December is not a heatwave by official criteria, but it does highlight how December can surprise us with unusually mild spells.

To give you a sense of scale, the warmest December day on record in the UK was much hotter than 17°C. On December 28, 2019, parts of the Scottish Highlands reached 18.7°C. That notch above 18°C remains exceptional for late December, underscoring how rare sustained warmth is in the depths of winter rather than a daily blip.

So why does a map show a 17°C December day, and should you take it seriously? It’s a prompt to plan for a few comfortable days—dress lightly, enjoy extended daylight, and still keep your heating habits sensible. It also signals that winter 2024–25 might be more mercurial than a strict, predictable pattern would suggest.

Why does December sometimes feel warmer than usual?

There’s a neat analogy here: winter is a tug-of-war between warm air shoved from the south and bitter air sweeping in from the north. When the battle tilts in favor of the warm side, you’ll notice milder days and brighter skies. Several factors influence that tilt, including:

• Jet stream meanders: The path of the jet stream can shift, allowing warmer air to spill southwards into the UK landscape for short stints.
• Blocking high pressure: A stubborn high-pressure system can trap mild air in place for several days, giving you a pleasant streak in December.
• Oceanic patterns: Sea-surface temperatures and larger climate oscillations can subtly tilt the odds toward mild spells in wintertime.
• Urban heat island effects: In towns and cities, people feel the warmth a little more due to dense infrastructure and human activity.

Looking back: memorable December warmth and how it compares

It’s helpful to place this potential warmth in historical context. December has hosted extraordinarily warm days in the past, and those moments aren’t the everyday norm. The record December day in the UK—November? No, December 28, 2019—still stands out as a rare event where temperatures climbed to nearly 19°C across certain regions. Those moments become reference points for meteorologists when explaining the atmosphere’s quirks to the public.

By comparing what could be a 17°C December day with those rare peak events, you get a sense of scale: today’s warmth is more of a “bright moment in an otherwise chilly month” rather than a full-blown summer reverie. For homeowners, that means a short window of comfortable weather rather than a long-term shift in climate norms.

What this means for households and energy use

Milder days don’t just feel nicer—they can influence how you heat your home, how you budget for energy, and when you decide to schedule maintenance. Here are practical angles to consider:

• Heating demand dips briefly: If your home isn’t well insulated, you’ll still feel the chill as soon as the sun vanishes, but on milder days, you may rely less on heating. This can save you money, but use the moment to your advantage by running small comfort heating without overdoing it.
• Ventilation and air quality: Warmer days often bring more air movement. Open windows for short periods to air out spaces, which can improve indoor air quality and reduce the need to overheat rooms.
• Maintenance timing: A milder stretch is a great window to schedule routine maintenance, such as boiler servicing or a radiator check, without interrupting your daily comfort. Maintenance performed now can help ensure your system runs efficiently when it’s cold again.
• Insulation still matters: Mild spells aren’t an excuse to skip insulation upgrades. If you’ve noticed drafts or cold spots, a practical upgrade now can pay off in future drafts and bills.

Smart steps to take during a milder spell

Even when days feel pleasant, winter isn’t “done” with us. Here are bite-sized steps you can take to keep your home comfortable and efficient while the temperatures cooperate:

• Schedule a boiler service: Regular servicing improves efficiency and reduces the risk of unexpected breakdowns when a cold snap returns. A quick service now can save bigger headaches later.
• Bleed radiators: Start at one radiator per room, especially if you notice cold spots near the bottom. Removing trapped air helps radiators warm more evenly and quickly.
• Check filters and vents: Clean or replace filters on boilers and ensure vents aren’t blocked by furniture or curtains.
• Seal gaps and drafts: Use draft stoppers or weatherstripping to cut heat loss, so your warm days aren’t wasted on reheating endlessly.
• Set back schedules wisely: If you’ll be away for the day, consider lowering the thermostat a notch to conserve energy without sacrificing comfort when you return.

Professional help: when to call in the experts

Between weather maps and changing forecasts, the real safety net for a comfortable home is a well-tuned heating system. If you’re unsure about your boiler’s efficiency, or you notice unusual noises, uneven heating, or fluctuations in pressure, it’s time to seek professional advice. A trusted local heating engineer can give you tailored guidance on keeping your system reliable through a volatile winter.

Two resources you might find useful as you plan ahead are:

• For dependable boiler servicing and heating installations, consider Harrow Heating. They understand the needs of UK homes and can help you stay warm efficiently, even when the weather wobbles.
• If your system is ready for a thorough clean to improve flow and heat distribution, a Powerflush can restore radiator performance and cut energy waste.

Radiator efficiency and the role of Powerflush

Over time, sludge and rust can accumulate in your central heating system, creating barriers to effective warm air distribution. That’s where a Powerflush can make a noticeable difference. Think of it as a spring clean for your entire heating circuit, not just a single radiator. A professional flush removes debris, improves flow, and helps radiators heat up evenly again. If you’ve noticed cold spots that persist after bleeding radiators, a Powerflush could be the next smart step to restore efficiency and comfort.

A practical plan for winter readiness

Weather unpredictability isn’t going away, but you can stay a step ahead with a simple, actionable plan. Here’s a practical checklist to keep in mind:

1. Review your heating schedule and set realistic comfort targets for the upcoming weeks.
2. Schedule a boiler service before the coldest part of winter hits, especially if you’ve noticed any quirks in performance.
3. Inspect insulation around doors and windows. Use temporary draft stoppers if you’re not ready to replace seals.
4. Bleed radiators now and then again after running the system for a few days to ensure air pockets don’t creep back in.
5. Consider a Powerflush if your radiators are slow to heat or show inconsistent performance.

Conclusion

In a country where the weather can swing from mild to brisk in a matter of days, December warmth shown on maps offers a moment to pause, enjoy a little extra sunshine, and plan for the months ahead. While a 17°C December day isn’t a heatwave by official standards, it serves as a useful reminder that climate variability is part of the modern winter. For homeowners, the best takeaway is practical preparation: service your heating system, optimize radiator performance, and keep plans flexible so you’re ready for whatever weather the season throws at you. If you’re seeking trusted local support, tools like Harrow Heating and Powerflush can help you stay warm efficiently, no matter what the forecast holds.

Frequently asked questions

1. Will December ever be truly hot in the UK again?

While warm spells are possible, a true, sustained hot spell in December is rare. Climate variability means you may see brief milder days, but long-lasting heat is unlikely in winter. It’s best to prepare for a mix of days—some mild, some cold—rather than expecting a summer-like December.

2. How is a heatwave defined in the UK?

UK heatwave definitions vary by region, but they generally rely on sustained high temperatures over several days that exceed local norms. The official criteria are region-specific and consider both temperature and duration, rather than a single hot day.

3. Should I adjust heating plans during a mild spell?

Yes. Mild spells are a good opportunity to perform routine maintenance, bleed radiators, and check insulation. They also give you a chance to test your boiler so you’re ready if colder days return.

4. When is the best time to schedule a boiler service?

Early autumn or late spring are common windows, but if you’ve noticed irregular heating, strange noises, or decreased efficiency, a service sooner is wise. A mild spell can make the service more comfortable and convenient.

5. How can I improve my heating efficiency without a major overhaul?

Simple steps include bleeding radiators, replacing dirty filters, sealing drafts, and ensuring thermostat programming reflects your actual daily routine. For a deeper boost, consider a Powerflush to restore radiator performance, or consult Harrow Heating for a professional assessment.