Cold Weekend, Cold Winter?

COLD WEEKEND!

The weekend we just enjoyed was a cold one.

On Saturday (OCT 28) the high temperature was 41° tying the record Cold High Temperature set in 1910.

On Sunday (OCT 29) it was even colder. The high was only 39° but the record Cold High Temperature for that date is 34° set in 1925.

The last time we had a high temperature as cold as 39° was March 15, 2017 when the high was 33°.

Of course you have to have chilly air to have a high of 39° but chilly air can warm 20° with bright sunshine.

Thick Weekend Cloud Cover

The key to the weekend chill is thick cloud cover working with the chilly air. The cloud cover above us Saturday was 18,000 to 20,000 feet thick (or a bit more).  Enough sunshine gets through to brighten the night sky but not enough to warm the ground which warms the air.

Thick cloud cover  kept the air cold over the weekend.

The clouds were not as thick on Sunday, but thick enough that the weak, late October sunshine could not mix them out.

"Mixing out" means surface heating by the sun causes thermals of warm air to rise. If air rises it has to sink nearby to replace the rising air. This exchange mixes the moist air in the clouds with drier air and the cloud layer can thin or completely evaporate.

In summer clouds mix out much more easily because of the strong sunshine than in the other seasons.

COLD WINTER?

Now to answer the question from Steve Horstmeyer's What's It Mean Meme #2.

One weekend of cold weather is not evidence that an entire season will be cold.

Now if we see the pattern that caused the chilly weekend persist and cold days are becoming common it could signal a trend.

For now we have to watch the  La Niña that is strengthening in the Equatorial Pacific.

More on that and other winter trends as they develop.

-Steve Horstmeyer