I live in New Hampshire, USA. How come it continues to get colder here after the Winter solstice?

Submitted by WayneHudsonIII t3_zz4obm in askscience

Some context:

Where I live in NH, the average historical daily temp continues to drop after the Winter Solstice (December 21 this year) and doesn't level off and start getting warmer until about mid-January. Why is that?

Additionally, the average temperature climbs slower from Winter into Spring than it drops from Fall into Winter. What's going on there?

Based on my naïve understanding, I'd expect the temperature to be relatively symmetrical around the Solstice (Solstice - 1 roughly = to Solstice + 1, etc), but that's clearly not the case.

Can someone help explain this to a weather newbie?

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keithatcpt t1_j2cdfjr wrote

With anything that’s warmed by a heat source, there is a “thermal lag time” where the temperature of what’s being warmed doesn’t start increasing right away. The bigger the system, the longer the lag time, and the earth is a pretty big system. Also, the energy provided by the sun generally is the same a week after the winter solstice as it is a week before, when the northern hemisphere is still cooling off on average. That’s why the coldest month tends to be January. When things start warming up in late February into March, the weather patterns tend to be windy and stormy as more energy is heating the northern hemisphere, causing evaporation from the oceans which runs into the cold air over the continents.

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jrob323 t1_j2d2yst wrote

Replying to keithatcpt (#1,213,001)

Yeah there's a 90 degree phase shift as things continue to cool off, like the ocean. But that's also why id didn't start getting immediately cooler after June 21. If you remember, it actually keeps getting hotter and hotter for awhile. The ocean stores it up and starts dumping the heat back into the system in the fall.

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h3rbi74 t1_j2d72ic wrote

OP, a similar type of lag and cycling happens with big bodies of water— if you ever live near a lake or large pond, you will find that when summer first starts getting hot, the water is still REALLY COLD, and only starts to get truly perfect swimming temp when it’s already fall and the air is starting to be cooler.

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WayneHudsonIII OP t1_j2dfrf1 wrote

Replying to keithatcpt (#1,213,001)

Interesting. Thanks for your response!

So is the thermal lag time just the amount of time it takes to heat things up? So after the solstice, the energy from the sun is increasing but the temperature trails behind? Then at the Summer Solstice even though the energy from the sun starts to decrease, things still get hotter because that lag is catching up?

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darrellbear t1_j2e9nij wrote

Replying to keithatcpt (#1,223,772)

We have it easy in the northern hemisphere--Earth is closest to the Sun on January 3, farthest from the Sun in July. The southern hemisphere gets the worst of it in both months (hotter summers and colder winters), though it's mediated somewhat by more ocean in the southern part of the planet.

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