Historic Heat Wave

     After many, many days of 90 degree temperatures in a row, many records were broken that have not been reached since the years of the Great Dust Bowl back in '34, and '36 (some of the hottest years on record at Fort Wayne). In fact, some all time record high temperatures have been breached several times throughout the heat wave.

     Before I describe all of the records that were broken, I want to give you some background information on why this heat wave formed, and what factors likely exaggerated the effects of an especially historic and legendary heat wave. As most of you probably remember, last winter was a very warm and wet (wet as in a lot of rain) winter. In fact, it came out to be one of our warmest on record, with every month of the winter season, December, January, and February recording temperature surpluses over 6 degrees above normal. While no record highs were set until the meteorological winter season had officially ended, we had quite a few days where temperatures were 20 degrees above normal, especially in February. Usually, during a normal winter season, the area receives a good winter freeze for several weeks, holding the moisture from the late Fall rains and early winter snows. During a warm winter though, evaporation rates are way up because the ground isn't frozen for long enough to hold moisture in. This is why coming into March, our top soils were already quite dry, regardless of the heavy winter rains. Usually, when the strengthening solar radiation hits the normally wet soils of our area, some of heat energy goes to evaporating soil moisture (which ultimately is a cooling process), while the rest goes to raising the temperature of the ground, which conducts into the lower atmosphere, causing a rise in surface temperature. When the ground is relatively dry, less heat energy goes to evaporating water, and more heat energy goes into heating the ground, which effectively raises the temperature of the lower atmosphere much higher and more quickly than a normally wet ground would. This also has an effect of reducing the relative humidity of the atmosphere, which ultimately hinders thunderstorm development. By the time the March “heat wave” hit the area, temperatures were much warmer than they otherwise would be, pushing daily temperatures above normal. Higher temperatures correspond to higher evaporation rates, which deprive the soil of its moisture. At the same time, the synoptic scale wind patterns, driven by the ocean currents and other large scale factors, favored ridging over the area, which means that high pressure is above the area. Higher pressure (pressure rises or more politically correct “height” rises) usually correspond to subsidence in the lower atmosphere (downward motion), and downward motion results in warming by compression, causing a rise in low and mid level temperatures and clear, sunny skies. This further hindered rainfall development during most of April and May. By May, we had two official heat waves (which normally does not occur), with temperatures in the first heat wave reaching the lower 90's, and temperatures during the second heat wave breaking all-time records for two days straight. This is when drought conditions developed across Northeast Indiana, while Northwest Ohio experienced abnormally dry (D0) conditions. With the same synoptic scale patterns that had started during the late winter, the high pressure area or upper level ridge continued to move back into the region after cooler periods of weather. Even in the cooler periods of weather, dryness continued intensifying the drought. By mid-June, a classic heat wave set up across the United States, with records broken in quite a few places. Here, temperatures were in the middle to upper 90's for 4 or 5 days in a row, until the heat broke on June 21 with a violent thunderstorm in some spots. At Fort Wayne International Airport, precipitation for that day was a mere 0.19 inches, while just north and west of Antwerp, Doppler Radar estimated that almost 2 inches of rain fell, right along the state line (my rain gauge recording 0.25 inches of rain from that storm in Antwerp). With continued dry conditions, the next heat wave set up in about a week's time, with the following week reaching well into the 100's, highs officially at Fort Wayne International Airport tied the all-time record high at 106, while Defiance Memorial Airport hit a record of 107 on the same day. During the next several days into July, upper level ridging built back into the area after the incredibly violent storm moved through. The heat wave culimnated by the middle of the week of the Fourth of July, with temperatures 101 and above for each and every day until Sunday. This was an unprecedented event, having four consecutive days above 100 degrees. This has never happened in the history of Fort Wayne with the next closest run of 100 degree temperatures occurring back in July of 1988, with only three consecutive days. With continued heat throughout the rest of the month, I expect that this July will become the hottest July on record, breaking last year's record. (This post will be updated as more information comes in.)

Most of the past heat waves of this year were rather dry with humidity levels not having much influence on the heat index. In the heat wave we had in the last week though, relatively wet soils from the violent thunderstorms and the maturing corn canopy contributed to excessive humidity, with dew points in the low to mid 70's occurring during the hottest part of the heat wave. This contributed to the heat indices that were over 110 at times. Also, favorable flow from the Gulf of Mexico, plus a series of upper level disturbances enhanced moist flow into the region. In theory, this should have produced multiple rounds of thunderstorms to help mitigate (which it did at times) the heat, but so far it has failed to do this because of a lack of strong lifting mechanisms, and strong capping (warm mid level temperatures) has thus far prevented widespread thunderstorm activity.

This heat wave's effects have also been exaggerated by the fact that the powerful derecho that slammed into the region, caused millions of power outages from Indiana to Washington, D.C. As of this writing (Friday, July 6, 2012), nearly 1.5 million are still without power in the areas affected by this storm in Ohio, West Virginia, and Virginia. Many people are without air conditioning during one of the worst heat waves in many years.

For what I think will happen in the long run, given no significant rainfall in the near future, drought conditions will continue, contributing to above normal temperatures, and exacerbating heat waves that plague the area. This will likely continue into August and even September before the changing climatic variables and ENSO phases within the Pacific affect the long-range patterns.