Month: October 2016

Connecticut Drought 2015-2016

/ Marshall Atwater / Leave a comment

The average precipitation in Connecticut is about 44 inches per year.  In 2016, about 26 inches of precipitation has been recorded at Bradley Airport.  We are currently 40 per cent under the normal amounts from March through last week.   Even normal precipitation for the year will be less than 34 inches for the year.

A review of data from Bradley Airport shows only 8 years since 1950 that had less than 38 inches.  The years are shown in the table.

Year Total Precipitation (inches) 
1965
 29.45
1980 31.69
1957 32.22
2001 33.03
1964 34.55
1981 35.15
1985 36.88
1963 36.92

 

The year 2015 was also below normal and only had 39.21 inches, making the current drought in the longest since the drought 50 years ago.  One of the worst of the recent droughts and which was one of the longest droughts in Connecticut occurred from 1963 to 1966 with 3 of the years being  among the top 8 dry years.  The dryness affected both agricultural production and created water supply problems.

2016 Winter Forecast

/ Marshall Atwater / 1 Comment

As we approach the end of 2016, it is now time for a winter forecast.  2016 is noted for its dryness and will be 12-15 inches of precipitation below normal.  It has also been generally warmer than normal.  The normal snowfall at Bradly Airport is 45 inches.

Several organizations recently issued winter forecasts.  One can look at the Old Farmer’s Almanac that says “Winter is back” and predicts colder  than normal temperatures with above normal snowfall for southern New England.  The Weather Bureau forecasted the winter to be near normal in temperature and precipitation.  AccuWeather predicted “Frequent storms across the northeastern U.S. this winter may lead to an above-normal season for snowfall.   The Northeast is going to see more than just a few, maybe several, systems in the course of the season…. Overall, it’s predicted that the region will total a below-normal number of subzero days, though the temperature will average 3-5 degrees Fahrenheit lower than last year.”  The Weather Channel is forecasting colder than average in New England and probably more snow than average snowfall.  Meteorologist Judah Cohen, of the private forecast firm Atmospheric and Environmental Research in Massachusetts, relies on Siberian snow cover in the month of October to discern how key weather patterns will likely evolve downstream, above North America and Europe, during the winter. Cohen thinks this winter is going to be a predominantly cold and snowy one from the northern Plains to the Upper Midwest on southeast to the Mid-Atlantic and Northeast. http://mashable.com/2016/10/21/winter-outlook-snow-cold/#M7QH.LqMskqL)

I examined the data at Bradley Airport to find similar years and used those years to make a forecast for the forthcoming winter.  Most similar years had between 35 and 42 inches of snow.  In general, the warmer years had smaller snowfall amounts.  Based on this, I predict that 36 inches of snow will fall this winter and that the temperature will be near normal.  I estimate about 5 inches will fall in December.

Northwestern Connecticut Visit

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It was a day in late October during the peak of the autumn colors when we decided to take a trip to northwestern Connecticut, where we have not been in 20 years.  As we left Tolland, the sun was shining through the trees highlighting the yellow color.  The trees in the lowlands were nearly bare, having been bright red a few days earlier.  Traveling on Rt 84 through the Connecticut River valley, many of the trees still were green.  On Rt 4 in Farmington, trees in bight yellow and red became prominent.  In  Unionville. The Farmington River and the trees presented a scenic view.   Torrington have had some development in the eastern portions with new shopping and eating areas.

Traveling north on Rt 8 had colorful hills on each side of the highway.  Traveling through Main Street in Winsted, one could see the stores on one side of the street as the side near the Mad River, which is now nearly dry.  The buildings on the river side were never rebuilt after the 1955 flood had destroyed the street.

We then traveled through scenic woods to the Barkhamstead Reservoir where Rt 318 travels over the dam.  There are hills on both sides of the valley that were in various reds and yellows near the peak of the season.  This was probably our first visit to the dam in 40 years.  We then traveled through Granby and Ellington to Tolland.

Vertical Absorption of Ground Emitted IR by Carbon Dioxide

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Infrared radiation emitted by the earth needs to balance the incoming solar energy to keep the climate in equilibrium.  Radiation is emitted by the surface.  However, before it reaches space, it is absorbed within the atmosphere by carbon dioxide and water vapor.  The amounts of energy absorbed depends on the concentration of CO2 and water vapor, often called greenhouse gases.  The absorption results in a temperature increase with IR energy emitted in both upward and downward directions or converted into other forms of energy.  The radiation calculations are well defined and many models have been developed for the calculations.  Here we will use an early model developed by the author that were used in early meteorological mesoscale models (Atwater, 1971).  More recent models may use line by line calculations.

The ground is the input source of IR to the atmosphere.   There is very little that is written on the vertical absorption regarding the surface flux which is dependent on the path length of the absorber.  The emission of IR and conversion to other energy forms at the various levels will not be examined here.

The results for the surface transmission (1-absorption) are shown in the following graph for total CO2 and water vapor transmittance (CO2=280ppm) and for carbon dioxide transmittance at 280ppm and 560ppm for the lowest 300 m..  It is assumed that the carbon dioxide absorbs 18.5% if the total spectrum.

ir-absorption

 

The results show that about half of the surface IR radiation is absorbed within 150m (about 20 mb) of the ground, both for the total spectrum and the CO2 portion of the spectrum.  With the increase CO2 concentration, half of the energy in the CO2 spectrum is absorbed within 50m of the surface and 2/3 are absorbed by 300 m .  More than 99% of the CO2 spectrum is absorbed by 7000m.

The amount of radiation absorbed in each of the lowest layers is shown in the following table.

Layer Thickness  mb Layer Thickness  m Top of Layer m Radiation Differential W/m2
1 8 8 3.2
2 18 26 .5
3 26 52 .2
4 34 87 .07
4 35 121 .04
4 35 156 .01
5 44 200 -.01

Most of the increase in absorbed radiation is in the first 8 meters of the ground with much of the remaining radiation in the next layer.  About 90% of the increased absorption due to a doubling of the carbon dioxide occurs within 26 m (about 3 mb) of the ground.  Above about 175 meters, the absorption of the ground flux is reduced due to reduction of infrared flux reaching the levels.

In most climate models the lowest layer is often 10mb thick with the increased absorption assumed to occur in a much deeper layer.  In an earlier paper, Raisanen (1996) did a study of the vertical resolution needed to minimized errors in climate models for radiation calculations and found a number of systematic errors near the surface when the layers were thickened.  He attributed this to sharp differences in temperature in the region rather than the rapid absorption near the surface of both water vapor and carbon dioxide.  Models with layers too thick may not properly account for conversion of radiant energy to convective energy.  The impact on climate models should be further investigated.

Atwater, M.A., 197l:  The Radiation Budget for Polluted Layers of the Urban Environment.  J. Appl. Meteor., 10, 205-14.

Raisanen, P, 1996: The effect of vertical, resolution on clear sky radiation calculations: tests with two schemes.  Tellus, 48A,403-423.