Monday, March 16, 2015

The Results Show: Reviewing our 2014-2015 Winter Outlook

Now that it is mid-March with highs in the mid 70s, we can probably safely safe winter 2014-'15 is over for the Mid-South. That doesn't mean we won't see temps drop below freezing for a couple of hours some morning or frost on the ground. In fact, on average the last freeze date is still about a week away (March 22 at Memphis International Airport, later in outlying areas), but we don't see it getting that cold this week!

Methodology behind this year's outlook

So, in the name of full transparency (and perhaps curiosity more than anything), I thought it would be educational to re-visit the winter outlook I prepared early last November. As I said then, "if I got paid for accurate long-range outlooks, my family would be hungry!" As a reminder, my outlook was based on a few key pieces of data:
  • 10 analog years with weak El Nino conditions (1952, 1953, 1954, 1959, 1970, 1977, 1978, 1988, 2005, 2007)
  • Recent research by NWS-Memphis on El Nino impacts in the Mid-South
  • Research and 2014-'15 winter outlooks composed by WeatherBell, WeatherTrends360, and NOAA
Going into this winter, there was a better than 50/50 chance we'd see weak El Nino conditions before the season was over. As it turns out, NOAA declared just this month that El Nino had officially arrived. So while it didn't start until March, it actually takes a few months of above average Pacific sea surface temps to make it official. We were basically dealing with weak El Nino conditions in the Pacific for at least part of the winter.

The MWN Winter Outlook

Here's the outlook I made November 10, 2014 for the upcoming winter:
  1. Temps slightly below to below average (possibly as cold as 2013-'14)
  2. Precipitation near average
  3. Snowfall near to above average (average is about 4")
  4. Periods of large temperature swings and possible severe weather
For the sake of this discussion, since we had some of the earliest measurable snowfall on record last November and the biggest snow/ice events into the first week of March, I'm calling "MWN Winter" the period from Nov 10-Mar 10. I'll also look at the period meteorologists define as winter, which is Dec 1-Feb 28.

The Results... drum roll please

Let's look at each point in succession:
  1. "Temps slightly below to below average" - CORRECT - The most recent 30-year average temperature for Nov 10-Mar 10 is 45.6°.  This year's average was 42.0°, which is more than 3.5° below normal, but not quite as cold as last year (41.3°), which will be remembered for a January that was colder than any since the mid 1980s. This year, February was #7 coldest on record. In 141 years of record-keeping, this period ranked #26 coldest, or in the top 20%. For meteorological winter, this year's average was 41.1°, which was 2.7° below the most recent 30-year average of 43.8°. 
  2. "Precipitation near average" - INCORRECT - Total precipitation for the Nov 10-Mar 10 period was 13.22", which was 6.28" below the latest 30-year average. In fact, parts of the metro were classified as being in "severe drought" during this winter. For meteorological winter, precipitation totaled 8.25", or 5.63" below normal.
  3. "Snowfall near to above average" - CORRECT - Snowfall (which includes sleet, but not freezing rain) averages 3.8" a year in Memphis based on the 30-year climatological record used by the NWS. For the entire winter (our Nov 10-Mar 10 window), total snowfall was 6.1". Since some of that was outside the traditional "meteorological winter" period, the total is higher for MWN winter than meteorological winter (2.3", or 1.1" below average). We firmly believe that the 3.1" in March in 0.2" in November (which was some of the earliest on record) should count though!
  4. "Periods of large temperature swings and possible severe weather" - PARTIALLY CORRECT  - Starting with the second point, there were no severe convective storms this winter, which was what we were alluding to in this outlook. However the series of ice and snow storms that affected the Mid-South from mid-February to early March arguably had a wider impact on the entire metro than a round or two of severe thunderstorms would have. I believe these were "severe" for winter, but will only take half-credit for them! As to the point of large temperature swings, I think I nailed this one. Looking strictly at daily average temperatures (which averages the high and low for a day) between Nov 10-Mar 10, there were a total of 30 instances in which the daily average temperature varied by more than 10°F on consecutive days (many of them were much more than 10°). This is not a swing of 10° between one day's high (or low) and the next day's high (or low), it is the average daily temp moving by that much, which is harder to accomplish. All in all, despite the general cold weather pattern, we saw frequent large temperature swings over the course of the winter, from warm to cold, or from cold to colder!
In sum, 3 of the 4 points made in this year's winter outlook were correct, which surprised even me when I went back and re-visited the winter numbers. I can't guarantee that kind of accuracy on winter outlooks going forward, but this year I seemed to be on the right track!

What were your overall impressions of this past winter? Comment below or drop us a Facebook comment or tweet! We'd love to hear from you!

Erik Proseus
MWN Meteorologist

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1 comment:

jwood38019 said...

BOOYAH!!!!! Love Mr. Fallon!