Same alarm, same bedtime, and from November it feels twice as hard. The reason is that your alarm is a fixed clock and your body is running on a variable one.
Your clock runs on light, and there is less of it
The suprachiasmatic nucleus — the master circadian clock — is entrained primarily by light hitting specialised receptors in the retina. Those receptors are most sensitive to bright, short-wavelength light, and they are the reason morning light shifts your clock forward.
In winter you wake in darkness. There is no morning light signal, so the clock drifts later. Your body is still in biological night when your alarm says it is morning, and the mismatch is exactly what it feels like.
Melatonin is still elevated. Melatonin secretion is suppressed by light and continues in its absence. Waking in the dark means waking while it is still circulating, which is the chemical version of grogginess.
The cortisol awakening response is mistimed. That scheduled surge is entrained to your light-anchored clock, so if the clock has drifted the surge arrives late.
Core temperature is still low. It bottoms out roughly two hours before natural waking and rises from there. A drifted clock means the rise has not started.
Light through a window does not count for much
The scale here surprises people.
Bright outdoor daylight runs to 10,000 lux and above, and even a heavily overcast winter day is typically 1,000 to 5,000. Ordinary indoor lighting is 100 to 300 lux. Windows cut outdoor light substantially, and being a few metres inside a room cuts it further.
So "I get plenty of light, my desk is by the window" is usually not true in the terms your circadian system uses. (Why outdoor light beats every indoor substitute.)
Some of it is genuinely seasonal
Seasonal affective disorder affects a minority meaningfully — low mood, low energy, oversleeping and carbohydrate craving on a reliable autumn-to-spring pattern. A larger group get the subclinical version, sometimes called the winter blues.
If your winter tiredness comes with persistent low mood, loss of interest, or a real change in function, that is worth a doctor's appointment rather than a lighting adjustment. Light therapy has genuine evidence for SAD, and it is a treatment rather than a lifestyle tip.
What actually helps
Get outside as early as you can, every day. Even in darkness at your wake time, getting out at first light — mid-morning if that is what winter gives you — is the strongest available signal. Twenty minutes, no sunglasses. This is the intervention that matters most. (How much and for how long.)
Use a lightbox if the sun rises after you do. A 10,000 lux box for 20 to 30 minutes shortly after waking is the standard protocol and it is well evidenced. This is the one situation where an indoor substitute is genuinely worth it.
A dawn simulator alarm. Light gradually rising for 30 minutes before your alarm. Evidence is more modest than for a lightbox but it targets exactly this problem — waking while melatonin is still high.
Hold your wake time constant. Consistency matters more when the light signal is weak, because routine is carrying more of the entrainment load. (Why the wake time is the anchor.)
Keep evenings dark. Under-discussed and important. If your only bright light comes from screens at 10pm, you are actively pushing the clock later at the time of year it is already drifting. (The dimming protocol.)
Do not sleep in longer just because it is dark. Extending sleep shifts the clock further and makes the following morning worse.
The thing that quietly compounds it
Winter degrades sleep quality independently, and most people blame the season rather than the cause.
Indoor heating drops bedroom humidity to roughly 15–25% — drier than the Sahara. That thickens nasal mucus, inflames the lining, and pushes people into mouth breathing, which fragments sleep through micro-arousals you never remember. (Why your nose gets worse every winter.)
So part of "winter mornings are hard" is a mistimed clock, and part of it is that you are sleeping worse than you were in June. A hygrometer and a humidifier at 40–50% address the second half, and they cost very little. (Titan's write-up of the underlying research.) (What nasal breathing changes across a night.)
The bottom line
Waking in darkness means waking while melatonin is still circulating, with the cortisol surge mistimed and core temperature still low. Your alarm is fixed; your clock has drifted.
Get outside at first light every day, use a lightbox if the sun rises after you do, keep the wake time constant, and keep evenings genuinely dark. Then humidify the bedroom, because winter is degrading the night as well as the morning.