Short-Term Weather Lore Holds a Kernel of Truth

Before the Internet, The Weather Channel, and NOAA radios, our ancestors relied on nature to tell its tale of upcoming weather. Moss growing on the south side of trees and squirrels hiding their nuts deep underground were thought to foretell a severe winter ahead.

Some natural prognostications like these are grounded in truth, given our current knowledge of meteorology, but others are purely fiction, according to State Climatologist Jim Angel of the Illinois State Water Survey at the University of Illinois at Urbana-Champaign.

Short-term weather forecasts based on nature observations are more likely to be accurate than long-term seasonal predictions.  In fact, there may be some merit to the notion that bad weather is coming when cattle lie down in the pasture and birds fly low.

“Many animals have a better sense of hearing and smell than we do, so when humidity, air pressure and wind direction change right before a storm, as well as the distant rumble of thunder, some animals may become restless,” Angel said.  “They can pick up on weather changes hours before we can.”

Predictions based on the appearance of the sky are thought to be particularly valuable, since certain clouds are associated with certain weather conditions, according to Angel.  Clouds described as mare’s tails and mackerel scales are very high-level cirrus and cirrocumulus clouds that can precede an approaching warm front, with rain not far behind.

Likewise, a halo around the moon is actually the refraction of moonlight through the ice crystals that make up high-level cirrus clouds, indicating an approaching low-pressure system bringing rain or snow.

Long-term forecasts, such as winter weather predictions, are much more uncertain.

“Centuries ago, it was important to determine how severe the winter would be so that adequate wood and supplies would be stored for the duration,” Angel said.  “The early settlers’ lives may have depended on their predictions, so they were grasping at anything to forecast the coming weather.  However, the size of the brown band on woolly worms, the groundhog seeing its shadow, or spoon-shaped persimmon seeds are just happenstance.”

Even with today’s modern technology, the theoretical limit of daily weather forecasts is about two weeks. Within the 6- to 14-day range, forecast errors can be large enough to limit their usefulness.

That is why forecasters typically only discuss general patterns of weather behavior beyond five days, usually in terms of probability or odds. For example, the 8- to 14-day forecast may show the eastern U.S. with an increased chance of below-normal temperatures.

The same is true for seasonal forecasts that are driven by both long-term trends and specific weather patterns such as El Niño.

For the upcoming winter, forecasters look at historical records to decipher a pattern.  The Midwest is under the La Niña effect, which is characterized by unusually cold waters in the eastern tropical Pacific Ocean.

The National Weather Service’s winter forecast for Illinois is an increased chance for above normal temperatures in the southern two-thirds of Illinois, and equal chances of above, below, and normal temperatures in the northern third of Illinois. All of Illinois has an increased chance of above normal precipitation.

What does the woolly worm predict?

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Source: Jim Angel, Ph.D. (217) 333-0729, Fax: (217) 244-0220, jimangel@illinois.edu

Editor: Lisa Sheppard (217) 244-7270, sheppard@illinois.edu

The Illinois State Water Survey at the University of Illinois at Urbana-Champaign, a division of the Institute of Natural Resource Sustainability, is the primary agency in Illinois concerned with water and atmospheric resources.

Record Low Pressure on Great Lakes Storm

According to the National Weather Service

New record set today for the lowest pressure in a non-tropical storm in the mainland U.S. The massive storm system barreling across the central U.S. had a minimum central pressure of 28.24″ or 956 mb (equivalent to the minimum pressure of a Category 3 hurricane). This breaks the old record of 28.28″ (958 mb), set on Jan. 26, 1978, during the Blizzard of 1978 (aka the Cleveland Superbomb). This is also lower than the March 1993 Superstorm (aka “The Storm of the Century”), or the “Witch of November” storm that sank the Edmund Fitzgerald in 1975, or even the Columbus Day Storm of Oct. 1962.

Strong Storm to Hit Great Lakes

The National Weather Service has predicted a strong low pressure system, or cyclone, to hit the Great Lakes on Tuesday and Wednesday. The central pressure could be as low as 959 millibars (mb) (28.35 in), and associated with strong winds and significant wave heights on the Great Lakes.

 

October 26 forecast
Forecasted surface weather map for Tuesday, October 26, 2010 (NOAA NWS).

 

The Great Lakes are no stranger to storms like this. The most notorious have hit in November and have included high winds, heavy snow, and treacherous waves.

  • The Great Lakes Storm of 1913 – occurred on November 6-11, 1913 and sank 19 ships and killed 250 people. The lowest pressure was 968 mb (28.35 in) with winds up to 90 mph and 35 foot waves;
  • The Armistice Day Storm of 1940 – occurred on November 10-12, 1940, and sank 5 ships and killed 154 people (many were duck hunters caught unprepared by the drastic change in weather). The lowest pressure was 967 mb (28.55 in) with 80 mph winds.
  • Edmund Fitzgerald Storm of 1975 – occurred on November 10-11, 1975, led to sinking of the Edmund Fitzgerald with the loss of 29 men. The lowest pressure was 976 mb with winds in the 60-70 mph range with waves heights possibly up to 25 feet.

Two books on the 1913 storm are Freshwater Fury (Barcus 1960) and White Hurricane (Brown 2004). The Wikipedia article is here. The weather conditions are described here. If you do a search on “Great Lakes 1913 Storm” you will find many web links.

For the Armistice Day Storm of 1940, I am not aware of any specific books. I have seen some magazine articles on it over the years. The Wikipedia article is found here. Minnesota Public Radio gives a detailed account of the human toll here. This storm was different from the 1913 storm because many of the deaths occurred on land.

The Edmund Fitzgerald Storm of 1975 is probably the most widely known outside of the Great Lakes region. The loss of life was limited to the sinking of the Edmund Fitzgerald. Quite a few books and web sites are devoted to this storm. Here is a journal article that details the weather conditions of that storm.

Winter Outlook for Illinois – Wetter and Warmer

NOAA’s Climate Prediction Center released their official winter outlook today. The major influence in this winter’s weather will be the moderate to strong La Niña event occurring in the Pacific Ocean.

Precipitation

The winter outlook calls for an increased chance of above-normal precipitation across Illinois. They also state that the Ohio River Valley (including Illinois) is … “likely to see increased storminess and flooding.” Other studies have shown an increase in snowfall in the Great Lakes region during past La Niña events, especially in the January-March period.

Temperature

The southern two-thirds of the state has an increased chance of above-normal temperature. Meanwhile the northern third of Illinois has “equal chances” of above-, below-, or normal temperatures.  This basically means that their forecast tools are providing no guidance on winter temperatures in northern Illinois, including the Chicago area.

 

Winter outlook for precipitation (NOAA)
NOAA Winter Outlook for Precipitation.

 

 

winter outlook for temperature (NOAA)
NOAA Winter Outlook for Temperature

 

October Is Warm and Dry

So far, October in Illinois has been both warmer and drier than normal. As of October 19, the statewide average temperature was 59.8 degrees, 1 degree warmer than normal. The statewide average rainfall was only 0.22 inches, 12 percent of normal. See table below.

If this were July, the dryness would be a major source of concern. However, the impacts are much less in fall. In fact, the warm, dry weather aided in the maturing and harvesting of corn and soybeans. At the moment, the impacts are mostly focused on:

  • winter wheat – farmers are waiting on rains for germination;
  • landscaping – trees and shrubs may need more water before winter arrives;
  • fall color – I’ve noticed that the fall colors on trees and shrubs this year are muted with lots of shades of brown and yellow.

The NWS forecast shows a weather system moving through Illinois over the weekend. The potential rainfall amounts from this system range from 0.25 inches along the Wabash River in south-eastern Illinois to 1.25 inches in north-central Illinois. Another system is expected to move into the region on Tuesday/Wednesday. So the current dry weather may be short-lived.

                                Illinois
                        10/01/2010 to 10/19/2010

Climate          <------Temperature----->   <---------Precipitation--------->
Division         Actual   Normal      Dev   Actual   Normal     Dev   Percent
-----------------------------------------------------------------------------
Northwest          55.2     53.4      1.9     0.09     1.82    -1.73        5
Northeast          55.8     53.7      2.0     0.27     1.82    -1.56       15
West               57.6     56.3      1.4     0.10     1.90    -1.80        5
Central            56.7     55.7      1.0     0.22     1.86    -1.64       12
East               56.0     55.4      0.6     0.38     1.86    -1.48       20
West-southwest     58.0     57.5      0.5     0.13     1.72    -1.60        7
East-southeast     58.4     57.8      0.6     0.28     1.92    -1.65       14
Southwest          58.9     58.9      0.0     0.23     1.85    -1.63       12
Southeast          59.8     59.2      0.6     0.35     1.84    -1.49       19

State              57.3     56.3      1.0     0.22     1.84    -1.62       12

Dev means Deviation From Normal, Percent means Percent of Normal

October Temperature Swings in Chicago

Like most sites in Illinois, Chicago has experienced large temperature swings in October. The month started with below-normal temperatures on October 2-5. The departures were as large as 8 degrees below normal on October 3 and 4.

This cold period was followed by a period of much above normal temperatures on October 6-12. The departures were as large as 16 degrees above normal on October 9 and 10. In fact, the high of 86 degrees reported at O’Hare on October 9 tied the record set in 1962.

Slightly above-normal temperatures prevailed on October 13-18. The early cold period and later warm periods resulted in an average of 58.7 degrees for the first 18 days in Chicago, 3.9 degrees above normal.

 

chicago daily data october 2010
Day by day temperature departures from normal for Chicago Illinois in October 2010.

 

Dry Conditions Persist in Illinois

Parts of southern and eastern Illinois have struggled with dry conditions since July/August. Those conditions have expanded in recent weeks across more of Illinois.  The latest U.S. Drought Monitor has slightly more than half the state in at least the “abnormally dry” category and 11 percent in “moderate drought”. Most of the impacts so far have been in agriculture and horticulture and not water supplies.

There is a strong La Niña occurring in the Pacific. Based on past events, Illinois is typically warmer and drier than normal during fall (September-November). By winter (December-February), the wetter than normal conditions typically appear in Illinois.