Thursday, September 20, 2018

Fall Folklore

The beauty of fall can also bring indicators of how the surrounding environment is preparing for the winter ahead. There are two popular folklore that people tend to look for this time of the year. The first being the woolly bear (Isabella tiger moth caterpillars). Their striking appearance usually catches your eye by late summer, thus spreading fears of an overly warm or particularly snowy winter. The fascination is fun but usually doesn't prove scientific unless you happen to find "the one" that lines up with the actual outcome of winter. They vary from region to region and are part of the bristled species of caterpillars which can lead to mis-identification. The image above shows how you can be sure you are spotting a true woolly bear and not an impostor. 
To have some fun with the folklore of the little guy, here are a few tips: 
  1. Woolly bears have 13 segments made of black and orange and are known to represent the 13 weeks of winter.
  2. The front segment represents the start of winter, the middle segments represent the middle weeks of winter, and so forth.
  3. The position and length of the orange bands signify when and how long a warm period (weeks) will occur during the winter. 

Another popular folklore that think of when using nature to predict an upcoming winter is the persimmon seed. When a persimmon seed if cut in half, it reveals a kernel in the distinct shape of a spoon, knife, or fork. Each of those shapes are believed to represent a type of average winter condition we can expect ahead. Here is a guide to identifying the shapes and their meanings:

  1. Knife: Very cold and icy. Winds will "cut" right through you.
  2. Fork: Warm and dry. Powdery, light snow is possible.
  3. Spoon: Cold and snowy. Snow to "shovel" can be expected.

Pictured below is a set of persimmon seeds I cut open last fall that I collected from multiple fruits from a tree at Noble Park. Despite the outlook of a slightly milder winter per NOAA, the seeds I dissected gave the "spoon" and "knife" appearance in most cases. One seed produced a fork-like shape. 
I'd love to see what you are collecting in your part of the Local 6 area so we can compare notes and see if folklore can verify this upcoming winter!

Monday, September 3, 2018

El Nino Watch for Fall and Winter

The Climate Prediction Center has entered into El Nino Watch with a 60% chance of episode development during the Fall (Sep-Nov) and a 70% chance of episode development by Winter (Dec-Feb). Meteorologists monitor the status of El Nino and La Nina because it can have a direct impact on the large-scale weather pattern over the United States, especially during the Summer and Winter months.

The following two graphics show how temperatures and precipitation are typically impacted by an El Nino episode during the winter months.  Winters tend to be warmer than normal and precipitation stays fairly average. The two maps compare previous winter El Nino episodes to the long-term average from 1950-2007.

NOAA/NCDC - Click to enlarge
Forecasting into the season ahead can be more accurate when looking to similar weather patterns of the past. Meteorologists look at monthly data from Dec - Jan - Feb to determine a winter season average, or define that period of time as Meteorological Winter. An average winter in the Local 6 area shows an average temperature of 37 degrees, average precipitation total of 12.18" and average snowfall of 8.4".
The National Weather Service in Paducah has historical data that covers 6 of the past strongest El Nino episodes in the past 75 years (according to current forecast trends).
The similar El Nino episodes include the winters of 1957-19581965-1966, 1972-1973, 1982-1983, 1991-1992 and 1997-1998. In each episode, temperatures averaged close to or above normal. In these 6 cases, the stronger the El Nino episode, the warmer the winter averaged. 1997-1998 was a record strong episode and temperatures averaged about 4 degrees warmer for the season. For the entire central region, (IL, IN, OH, WV, KY, TN, MO) it still holds the record for 2nd warmest winter.

Credit: Paducah NWS

Moving on to precipitation. Most of the cases averaged close to normal for the season with the exception of winter 1982-1983. I believe this to be an exceptional case since on one single day, (Dec 3) a record 4.65" of rain was recorded. If we exclude that one single day, 1982-1983 would also calculate close to average. In the central region precipitation ranked 35th driest during the record El Nino episode of 1997-1998.
It is a completely different scenario for snow totals. As the El Nino events in this post gained strength, the average snowfall dropped significantly. Winter 1957-1958 was the only season that came close to the average with 7.9".
(NCDC - El Nino of 1997-1998)

Simply put....warmer El Nino winters tend to bring less snow to the Local 6 area but do not leave us short-changed in precipitation. If the predicted El Nino episode ahead materializes as predicted by NOAA, we could be looking at a warmer winter than last year and continue with our slightly wetter weather pattern.
As a personal forecaster's disclaimer.....remember it only takes ONE snow event to make a big impact. In most of the winter cases from the past, we had quite a few TRACE snow days, just not accumulating. Use this information as guidance and for planning.

What is El Nino or La Nina? 
The way scientists identify a developing episode of El Nino or La Nina is by monitoring the warming/cooling waters off the coast of South America. When the westerly winds over the Pacific weaken, it allows for the oceanic circulation to bring cooler waters to the surface near South America then spread westward into the central Pacific. This phenomenon is known as La Nina. In opposition, the strengthening of westerly winds can build very warm water further east toward the coast of South America. This phenomenon is known as El Nino. The El Nino and La Nina related patterns of tropical rainfall cause changes in the weather patterns around the globe.