So what has La Nina meant for our spring, historically?
La Nina is starting to fade, the Climate Prediction Center says. But then, it usually does as we move from winter toward summer. The big news with regard to La Nina — the intermittently recurring cooling of equatorial Pacific sea surface temperatures, displayed as the large patch of blue in the bottom graphic (sea surface anomalies) in this chart – is that forecast guidance indicates it will disappear entirely by June. That’s not shocking, either, but there have been a couple of instances in whichLa Nina has extended or recycled into an encore season — as it did in 1954-55/55-56 and in 1998-99/99-2000.
Meteorological spring consists of March, April and May, and we’re now about halfway through March that is, so far, running very close to normal in temperature and quite a bit above normal (half an inch) in rainfall. But I took a look at what spring held following 10 previous winters in which La Nina was either rated moderate or strong — this one appears to have peaked at 1.4 degrees Celsius below normal over 3 consecutive 3-month cycles, at the upper end of “moderate” literally a click below “strong.” I used rounded-t0-whole-number figures for quick calculation, but that should be good enough to give a thumbnail sketch on what is historically expected in our region (using Roanoke Regional Airport data) during what we call a La Nina spring.
* La Nina springs averaged at least 2 degrees above normal 3 out of 10 times and near normal or 1 degree above normal 5 out of 10 times. That left only two seasons – in 1971 and in 1989 — when temperatures averaged significantly below normal, about 2 degrees, over the 3-month spring period.
* La Nina springs were near normal or below normal in rainfall 9 out of 10 times. Only 1971 was otherwise, and it was only about an inch above normal (see next bullet point). Of the nine, five were 2 inches or more below normal.
* While La Nina springs leaned to the dry side, 6 out of 10 of them had at least one month that was an inch or more above normal. So rainy spells, like we’ve had in early March, are not unusual. The wettest was May 1971 that had 7 1/2 inches of rain, putting it about 4 inches above normal — barely offsetting two preceding dry months. So you could make the case that none of the 10 springs following a moderate or strong La Nina were wet seasons.
* Half of the La Nina springs — those in 1955, 1965, 1974, 1976 and 2000 – had at least one month that was at least 4 degrees above normal. Two of them — in 1955 and 2000 – had at least two months 4 degrees or more above normal. Not coincidentaly, those were the warmest among the strong/moderate La Nina springs, each averaging about 3 degrees above normal.
* Sharply cold months were few and far between in the 10 seasons studied. March 1965 was the coldest, about 5 degrees below normal (later offset by a May that was 5 degrees above normal), while March 1971 and March 1999 each were about 3 degrees below normal.
* Of the 30 months in the 10 moderate/strong La Nina springs, 16 were at least a degree above normal, 4 very near normal and 10 at least a degree below normal.
* Of the 30 months, 7 were at least 1 inch above normal in rainfall, 4 were very near normal, and 19 were at least an inch below normal.
* Perhaps most surprising — there has been at least some measurable snow in APRIL in 4 of the 10 seasons, which is definitely statistically above the curve. The most was 7.3 inches that fell on April 6-7, 1971 (’71 keeps showing up as the weirdo La Nina spring), apparently a very wet snow as the temperature did not get below 33 at Roanoke. (Blacksburg got 11 inches and Lynchburg 4 in the same event). This is Roanoke’s biggest April snowfall on record.
So, the overall conclusion is pretty much what we always say — a moderate to strong La Nina leans our region toward warmer than normal and drier than normal weather, with some short-term variability.
March 16, 2011 - 7:21 PM
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Great, great research, Mr. Rain Man!!! Just fabulous. I am telling way too many people how pleasantly shocked and grateful I am that we had this very wet spell. Speaking of wet, I visited Franklin County this afternoon with my sister “riding shotgun” so that I could show her Smith Mntn. Lake. And I noticed a difference between eastern Franklin County (from about Wirtz all the way to Westlake Village and down Scruggs Road) and the Roanoke area. Not nearly as much green grass in Franklin County, which I assume is because they have not received as much rainfall as Roanoke.
Today was one of those rare days when the actual high and low (at RRA) almost exactly matched the normal high and low. Actual high: 58. Normal: 58. Actual low: 39. Normal: 37. Actual mean: 48. Normal mean: 47.
Looks like winter will return BIG TIME one week from today. The March 24-31 period looks very cold……could we see some white???
Who’s saying winter comes back big time as early as March 24?
Models show a decent cold front pushing through about that time, and there is some pattern tendency toward a few more below-normal days by the end of the month. Not sure I’m seeing a big time return to winter.
There won’t be any snow.
Margusity has jinxed us again…
http://www.accuweather.com/blogs/meteomadness/story/47126/snow-in-the-eastern-us-thats-the-question.asp
We’re barely on the southern fringe of the area Henry M has highlighted anyway.
For it to snow HERE late next week, the cold front is going to have to be a lot stronger than it looks on either the GFS or Euro models today. Not impossible, but I’m not expecting anything more than a 50ish highs/30ish lows kinda front, with moisture pulling out way too early for any wintry weather mayhem.
Just as a reminder to anyone in the NRV/Burgs area, there is a Skywarn training class tonight at 630 at the Inn at Virginia Tech. It’s the Avdance class, so you have to have already been through the Basic training previously. I’m looking forward to it! In 2 years though, I’ve not had many severe weather reports to call in though. It’s mainly been snow, one instance of heavy rain, and once for some wind damage.
Kevin – I got my info from Raysweather.com (outstanding forecaster for NW NC MTNS) – I have follwed him for years. He is almost (but not quite) as reliable as you are. Today in his forecast he says qoute: “The beginning of the cold smackdown is scheduled one week from today. That will be a very rude awakening.” Maybe we do not get alot of snow (except high ground), but winter is hardly over yet.
Kevin-In my travels today I was talking to a long time lake resident who said that she thinks this is the windiest winter since she’s lived here (from the mid 70s). I’ve thought it was windy…but maybe not that windy (I haven’t been in my current home long enough to have a good enough history to go on).
What kind of measurement would show this? Are there records kept that would shed light on this?
Today was beautiful– I love seeing the trees in bloom. (Although, if anyone happens to have one extra snow day laying around, I’d be glad to accept it…)
Mike: I’ve heard Ray is very accurate for his region. I guess it’s all relative what a “cold smackdown” will be. Definitely a cold front in a week, but I’m not yet seeing a dramatic push of Arctic air with that, at least YET. Keep in mind he has elevation effects down there and upslope snow with any northwest wind, so could be a much bigger deal for western NC mountains (and WVa/far SWVa western slopes) than the Roanoke/New River valleys.
The 12Z Euro is much stronger with the push of Arctic late next week, but it appears to be well behind the cold front/wet storm system. But then quick recovery appears likely with a new low forming in the central U.S. ciruclating milder air back into the region.
I’d say Friday/Saturday next week might be the “cold smackdown.”
Betsy: The thing I keep hearing from long-time residents is that all of the winters now are much windier than those in the past. Haven’t really been able to quantify that. There are average wind readings for Roanoke Regional, but data on that hard to find past about the last dozen years.
Perhaps the NRV may see some snow flurries before the end of the month, and some of the highest elevations will actually get accumulations, but I will believe snow here in the Roanoke valley only when I see it. And the 6-10 and 8-14 day CPC forecasts do not agree with a major cooldown. From Roanoke northeastward there is a 33% chance (pale blue on the CPC map) of colder than normal weather for the March 25-31 period, but from Roanoke westward (which includes the NRV, the Mountain Empire, WV, and northwest NC), the CPC map is white, meaning equal chances of warmer or cooler than normal weather. I am sure that within that window there is an excellent chance of a day or two or 3 being well below normal (in fact, about a week ago I predicted that there will be such a cold spell before the end of March, when I also predicted that RRA will get at least 4 days of 70+ temps). But snow here? We’ll see, but I seriously doubt it. As for many parts of New England and upstate New York and perhaps even central and NE Pennsylvania, if I had to bet, I would say that they WILL get an accumulating snowfall or 3 before the end of March. Don’t forget that in order to have snow reach the ground it has to get through a surface layer, and around here that layer is getting toasted right now and for many of the days to come.
Because it is “Saint Patty’s Day,” did you do anything special to celebrate the day, Kevin-me-boy? I don’t know if you are Irish-American, but the name Kevin is about as Irish as Murphy’s pig, as my dear ol’ mom used to say. Anyway, the weather was terrific today. I wish I could have celebrated by being on the links. It was so cool this morning that I could see my breath.
I’m wearing green slacks, Doug. Does that count?
My first name is Irish but my family history on both sides is English and Native American.
Bad news for you unfortunate folks who suffer from springtime allergies. Pollen levels for Friday-Sun. will be 10-9-8, all in the high range. Trees involved: Maple, Ash, and Juniper. Per Jay Webb of WDBJ7 (I am watching him on My 19).