Gaithersburg 2 WNW Maryland – August 2015 Climate statistics and summary by Kevin Shaw, NJWO member and observer in charge

by Kevin Shaw, Observer in charge

Average high temperature 84.6° (- 0.3°)
Average low temperature 64.8° (+ 0.7°)
Mean temperature 74.7° (+ 0.2°)
Precipitation 1.27″ (- 2.40″)
Greatest daily amount (date) 0.59″ (20)
Year to date precipitation 28.47″ (- 1.48″)
High temperature for the month (date) 94° (17)
Low temperature for the month (date) 57° (27)
Highest barometric pressure (date) 30.22″ (28)
Lowest barometric pressure (date) 29.74″ (11)
Peak wind gust (date/direction): 23 (4/WSW)
Heating degree days for the month: 0
Cooling degree days for the month: 301
Greatest diurnal range (date): 27.9° (16)
Least diurnal range (date) 7.2° (10)

Fog days: 5
Thunder days: 3
Sunny/clear days: 16 Partly Cloudy days: 8 Cloudy days: 7

Days with measurable precipitation (=>.01″) = 6
Days with maximum temperatures of 90 or more = 4
Days with minimum temperatures of 70 or more = 6

by Kevin Shaw, observer in charge

August 2015 was not a particularly noteworthy month in most respects. The only really notable aspect of the month was its below normal rainfall total. 1.27 inches of rain fell during the entire month on only 6 days with measurable amounts. This total amount turns out to be my fourth driest August ever in my 36 year period of record. My all-time driest August was in 1989 when only a meager 0.61″ of rain fell. There were 3 days with thunder. The wettest day of the month was a very unimpressive 0.59″ that fell on the 20th. No daily records of precipitation were set during the month. The 6 measurable days was below the normal amount of about 9 days. Regarding temperatures, there was the usual pattern of below normal maximum average temps being offset by slightly greater above normal average minimum temps. No record high or low temperatures were set. The only temperature record for the month was the high minimum record set on the 19th, the warmest min temp of the month, when 75 was reached. Monthly Temperature extremes of 94 (17) and 57 (27) were not really close to setting daily records.

An interesting two-month precipitation study of the two main summer months of July and August for my 36 year period of record shows that July/August 2015 (3.37″ – 1.27″ in August, 2.10″ in July) came in the third driest of all time for that 2 month period. The driest two month July/August period was in 1997 when a combined total of only 2.94″ fell (0.63″ in July, 2.31″ in August). The second driest was in 2006 when only 3.05″ fell (0.88″ in August, 2.17″ in July). The fourth driest was in 1998 when 3.50″ fell (1.62″ in August, 1.88″ in July).

The average maximum temperature for the month was 84.6° (-0.3°), the average minimum temperature was 64.8° (+0.7°). The resultant mean average temperature for the month was 74.7° (+ 0.2°). Nothing really notably statistically as to record extremes on any of those temperature statistics. As in June and July we had a modest 4 days with max temps at or above 90°, considerably below the long term normal of 9.0. There were an about normal amount of days with minimum temperatures of 70° or more with 6. Unfortunately I don’t have a long-term average amount for that statistic.

The month’s total precipitation amount of 1.27″ was 2.40″ below the normal July amount of 3.67″. The 6 days of measurable precipitation during the month was below the long term average of 9 days. The year to date (YTD) precipitation total of 28.47″ now puts us 1.48″ below the normal YTD average amount for this time of year of 29.95″.

The monthly barometric pressure extremes were a very modest 30.22″ on the 28th in the middle of one of our two dry periods during the month with the 29.74″ lowest pressure value being recorded on the 11th, during one of our few cloudy, lightly wet periods during the month. Average barometric pressure for the month was 29.99″, within .001″ if you averaged the two extreme values (30.22″ and 29.74″). So far with six months study under my belt, this relationship has shown up as the same in March, 0.06″ difference in April, and 0.02″ in May and June, 0.005″ in July, and 0.01″ in August. These values look very promising for developing some sort of relationship there. Further study needed at least through the rest of the year.

The distribution of 16 sunny, 8 partly cloudy and 7 cloudy days coincided with the significantly below normal monthly precipitation 1.27″ amount.

There were 0 heating degree days and 301 cooling degree days. There were 5 days with fog observed. The peak wind gust during July was a modest 23 MPH out of the WSW during a brief but intense shower very early on the morning of the 4th.

My maximum temperature frequencies included 4 days at or above 90°, 22 days between 80° and 89°, and 5 days between 70°and 79°, On the minimum temperature frequency side of things, there were 5 days below 60°, 20 days between 60°-69° and 6 days with minimums of 70° or greater.

The diurnal range average was a bit below normal (19.8° vs the normal 20.8°). The max daily range of 27.9° occurred on the 16th when we were soaring into the 90s during our biggest heat wave of the month, The lowest daily temperature range of 7.2° occurred on the 10th during our coolest max temp day of the month with lots of clouds and light rain. We had a total of only the one day during the month with a diurnal range less than 10° while there were a considerable 15 days with ranges of 20° or more, distributed fairly evenly throughout the month.

Except for the extreme dryness of the entire month, August 2015 was not particularly chock full of headlines. Temperatures were lacking in extremes, no real exciting weather occurred with much the same daily statistics for days on end. September is starting out hot and dry, hopefullythat trend will be reversed very soon. Details in a few weeks, Enjoy the coming fall weather, hopefully sooner rather than later!

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