For the fourth weekend in a row, the clouds and their accompanying rains paid another visit to Northwestern Middlesex County as well as the rest of the Central Jersey area. The inclement weather actually began in earnest on Friday with a wet, windy, and dreary day. According to the data measured by the rain bucket with the GWC WX Station here in South Plainfield, there was just under an inch of rain for the day on Friday (actually 0.96 inches). Saturday and Sunday also saw some measurable precipitation with 0.06 on the first day of the weekend, and 0.05 on the second.

So far this month (May 2008), there has been some form of measurable rain on 8 of the first 18 days. Now, while this didn’t match the rainfall in the first two weeks of April 2008 (rainfall on 9 of the first 12 days), it has still been a rather wet month by May standards. With Friday’s rain, there have been two of the top four rainiest days this year during the month of May 2008. The second highest rainfall occurred on May 9th. Moreover, there has already been 2.75 inches of rainfall during the month. Compare that to what occurred for the entire month of April (2.93 inches), and you can see that there haven’t been May flowers, but rather, May showers. For the year, there has been a total of 15.21 inches of rainfall.

Moving on to the temperature data for the day and the month thus far, the high on Sunday reached 63 degrees, and that occurred at 11:10 AM while the low for the day was 51, and that took place at 6:30 AM. The mean temperature for Sunday was 57.4 degrees while the mean has only been below 51.4 degrees twice this month. The maximum high for this past week was actually reached on Wednesday, May 14th when the mercury climbed to 76 degrees while the lowest also occurred on that day at 43 degrees, and the resulting diurnal range of temperature was 33 degrees, the largest for the week. So far this month, the average mean temperature has been 57.4 with the mean max being 67.2 while the mean min dropped to 47.6. Consequently, the average diurnal range of temperature for the month of May 2008 has been 19.2.

Another interesting stat that hasn’t been discussed much so far in the past two months or so of local weather discussions has been the number of Heating Degree Days. This was always a weather statistic that perplexed me during my studies of Meteorology at Rutgers a few years back. According to the latest edition of the C. Donald Ahrens book, Meteorology Today: An Introduction to Weather, Climate, and the Environment, the number of Heating Degree Days is a indicator of how cold the weather is. This is always a very critical statistic when it comes to measuring energy consumption, and with things being the way they’ve been in recent years with the gradual rise in the price of oil, and its ripple effect on gas prices as well as prices of other consumer goods, especially in just the past couple months. Ahrens states that, “Heating degree-day is a form of the degree-day used as an index for fuel consumption. On the contrary, a Cooling degree-day is, “a form of degree-day used in estimating the amount of energy necessary to reduce the effective temperature of warm air. A cooling degree-day is a day on which the average temperature is one degree above a desired base temperature.”

Going beyond the definitions, these numbers are calculated by different means. First, the heating degree-day is tabulated by taking the mean temperature for the day, and subtracting that from 65 degrees, the base temperature used in the formula. So, for example, the heating degree days for today would be 7.6 (65-57.4). When you are able to determine the heating degree days for the year, you can figure out a rough estimate of heating requirements for a particular location. Meanwhile, the cooling degree day is determined by taking 65 degrees, and subtracting that from the mean. So, today there would be 57.4-65, which is -7.6, which would indicate that this would be a heating degree day since the value was negative. Having knowledge of this kind of information can also be useful in determining the size and type of equipment to install in a house for proper air conditioning.

So, for the month of May, there has been 140.2 heating degree days and 3.0 cooling degree days. For the year, there has been 3051.5 heating degree days and 4.6 cooling degree days. However, the trend for heating degree days is going down while its rising for cooling degree days. Another indication that the physics of the earth and sun are changing, the days are getting longer, the perpendicular angle of the sun is getting closer to the Northern Hemisphere, and the colder air that had dominated the weather in much of the United States for a good portion of the year to date is retreating back toward extreme Northern Canada, Alaska, and the North Pole. According to the latest forecast discussion from the Mount Holly office of the National Weather Service, “A series of fronts and low pressure areas will rotate around a mid level low that will move very slowly from southeastern Canada to the Canadian maritimes through the week. High pressure will very slowly build toward the area toward the end of the work week.”

Translation, there is going to be some sort of chance of precipitation from the rest of today through Wednesday with the highest likelihood of rain projected for the late afternoon on Sunday. A Coastal Flood Statement was issued for the region, and it indicated that there is a chance for spotty and minor coastal flooding in light of the presence of the full moon on Monday. This threat is expected to exist for the next several days. Meanwhile, a Special Weather Statement was also issued for the region, and it stated that a line of strong to severe thunderstorms is approaching the Central Jersey area.

As of 4:20 PM, the line of thunderstorms extended from Upper Bucks County to Upper Montgomery County and trailing into the Lower Susquehanna River Valley in Pennsylvania. This line of storms contain heavy rain, potential dangerous lightning, hail, and winds in excess of 45 miles per hour. These storms will be moving east and continue affecting Bucks, Montgomery, and Chester until 5:30 PM while they will begin to impact Central Jersey including Hunterdon, Mercer, Somerset, and Middlesex County within the hour.