Tuesday, November 27, 2012

Winter weather postponed ... but for how long?

You might remember a week or so ago that I wrote about the computer models predicting an outbreak of very cold weather around the beginning of December.

Forget about it.

The king of weather for the eastern United States is a low pressure system off the Pacific Coast. It's called a positive East Pacific Oscillation (EPO) -- one of the many ingredients that goes into creating our weather. Here's what it means.

The positive EPO tends to send Pacific air masses into the central and eastern part of the country. For the most part, the atmospheric flow is zonal -- sort of like a flat west-to-east line.  There are some wrinkles, of course, but you get the basic idea. When that happens, our weather tends to be mild.

The pattern hasn't been exactly west-to-east in recent weeks, because a northwest flow has delivered some chilly air into the Carolinas. But the positive EPO has prevented the really cold air in Alaska from descending southward. High temperatures are below zero this week in Fairbanks.

Several factors are needed for wintry weather to develop in the Carolinas. They include a negative North Atlantic Oscillation (NAO) and possibly a strong high pressure system near Greenland.  That tends to send the really cold air into the eastern part of the United States. Add a stormy pattern, and you get snow, sleet and freezing rain.

We actually have a negative NAO now, but the positive EPO is overwhelming it -- blocking the cold air from coming south.

In addition to the positive EPO, we're also in a decidedly non-stormy pattern. Rainfall this month is more than 2 inches below average.

So how long will all this ask?

As usual, the computer models disagree.  But based on the many forecasts I've read in the last day or two, there seems a consensus that we'll stay mild through at least the first half of December.

In other words, the start of winter has been postponed.

Then again, December is typically not a big month for snow and ice in the Carolinas. That happened in 2010, but it's unusual. Most years, January and February are the real wintry months.

We need a change in the non-stormy situation.  Rainfall is badly needed, but there aren't many signs of that changing within the next 10 days either.

In the immediate future, this mild pattern means we'll be flirting with 70 degrees early next week.

CHILLY NOVEMBER: We're approaching the end of what has been a chilly month in Charlotte. The average temperature for November is 3.2 degrees below average, which makes this among the 15 coldest Novembers since records started being kept in Charlotte in the 1870s.

Sunday morning's low of 21 degrees marks the earliest it has been that cold in four years. Charlotte had a record-breaking low of 13 degrees on Nov. 22, 2008, and it dropped to 18 degrees a few days earlier. That month was 5.7 degrees below the average.

Temperatures the next few days will be around average, and it's doubtful that we'll see any more 20s in the remaining days of the month.


Anonymous said...


Anonymous said...

I had no problem understanding. There's probably a sandbox nearby if you want to stick your head in it and not learn anything new.

Anonymous said...

Why exactly is rainfall "badly needed"? I understand we're over 2 inches short for Nov, but why is that a bad thing?

Anonymous said...

So basically the whole article comes down to the last sentence, "temperatures the next few days will be around average", but we can't really predict much more than that (because we did a couple weeks ago and were wrong).

Hmm... Thanks??

Anonymous said...

@anonymous 11:29:

Let's see, why is no rain a bad thing? Do you like to drink water? Do you like to bathe? Do you think that water comes from some never ending source?

And to all the other responses, you do realize that weather is not an exact science, don't you? Humans really have only been studying weather for less than 80 years. There is a lot to learn.

Thanks for the article Steve. I have been curious about the NAO and what effects Sandy had on that. I guess that if it did, it wasn't enough to open the gates from the north.

Anonymous said...

Let's see, why is no rain a bad thing? Do you like to drink water? Do you like to bathe? Do you think that water comes from some never ending source?

Uhhhhh, we're TWO INCHES behind for THIS MONTH. That's it. It's really not that dire, is it? Is rain really "badly needed" in Charlotte right now?

I understand rain is needed -- or this would be a desert! But rain isn't "badly needed" every time we fall a tiny bit behind a meteorological average for a short timeframe.


Anonymous said...

I have this feeling that despite all the forecasts for a cold and snowy winter in the Northeast US (except the National Weather Service), we will see a warm and snowless winter. Perhaps a few storms that produce a little snow for the I95 cities if it manages to get cold enough.

Anonymous said...

I really hope it snows this winter. I would love to get a little use out of the sleds we bought last year.

Anonymous said...

Mecklenburg County is 523 sq mi (2.19e+12 sq in)

times 2 inches down(for the month, nevermind the year)

= 4.38e+12 cubic inches

converted to gallons

= 18,961,038,961 gallons.

Give or take. Just saying... 2 inches doesn't seem like much, but it is.

John said...

Anonymous 12:26 PM...

I suggest you keep your day job, whatever that is. Monthly rainfall measurements are cumulative. It's not just about 2 inches... the local area is currently in a "Moderate DROUGHT status". Check out http://www.ncdrought.org/

I have family who are fire fighters and they are worried about fires with all these dry leaves on the ground. Yeah, it's a big deal.

Anonymous said...

"Just two inches isn't a big deal"? Your wives have been trying to not hurt your feelings.

Anonymous said...

Did no one understand the comment, "2 inches doesn't seem like much, but it is". Explaination, the person is saying that despite the small amount it still is a "BIG DEAL". Therefore, why spout unwarranted gibberish?

Anonymous said...

Well to me it's a professional and understanding answer it makes sense...I Live in E.Pa and our winter last year was anything but..