July 2021 had above average temperatures with just a bit drier than normal precipitation amounts that were widely spread throughout the month with three very modest three day dry spells. The equally modest wettest measurable rain period of the month occurred in a 3 day stretch between the 1st and the 3rd (0.78”).

My maximum temperature average (87.2°) was 0.8° above normal but my minimum temperature average (69.5°) was 3.6° above normal, resulting in the mean temperature average of 78.3° turning out to be 2.2° above normal. My total precipitation of 3.36″ was 0.49” below the
normal July value for my station of 3.85”. There were 11 days with measurable precipitation and 2 days with trace amounts, fairly evenly distributed during the entire month.

There were three relatively “cool” days in July with max temperatures below 80° but barely (78.5° on the 3rd, 78.3° on the 18th and 78.9° on the 31st – only the 3rd was wet (0.04”) and the other 2 days were dry). There technically was 1 day with a min in the 50s (59.8°) but that statistically gets listed as a 60° reading. There were 11 days with max temps of 90° or more, topped off by the 94.1° max on the 6th. There was a significant 7 day period between the 11th
and 17th with max temperatures of 90° or more.

The monthly maximum daily precipitation amount of 1.28″ was reached on the 17th marking the end of that 7 day hot spell. This event was the month’s most notable one in many regards. The thunderstorm that hit the hardest around 1600-1630 on that day knocked out power briefly (lightning/thunder almost instantaneous directly overhead that when it hit I almost jumped right out of my seat!!!) but much more significantly knocked out the elevator service to my
apartment building, and was not restored till the next Monday. It also fried my Cable TV connection I have that was not restored till the following Thursday by a Comcast technician. The peak wind gust recorded across the street on that day at 1607 was 56 MPH, easily the highest gust of the month, and the second highest of the year, only surpassed by a 59 MPH PWG back on April 30.

The extreme barometric pressure readings of the month were rather muted and occurred 3 weeks of each other. The lowest value of 29.76” on the 2nd occurred during that brief 3 day brief wet period mentioned earlier while the highest value of 30.21” occurred on the 23rd
in the middle of a brief 3 day relatively pleasant, dry weather period.

The highest dew point temperature reached during the month was 78° recorded on 2 separate days (7th and 13th). There were 25 days with dew point values of 70° or greater. The lowest dew point value of 52° occurred on the 22nd during that highest pressure of the month period previously mentioned. There were a total of 8 days during the month with dew points in the 50s, including 6 of the last 10 days of the month.

July had 5 cloudy, 25 partly cloudy, and only 1 really clear/sunny day, about what to expect for a dry summer month. We had a few days (20,21) with haze/smoke from the Western Wildfires and two days affected by the weak remnants of Tropical System ELSA on the 8th and 9th (only 0.67” rain and a 32 MPH PWG from the N on the 9th). There were 414 heating degree days and 0 cooling degree days during the month. There were 3 foggy days but only 4 windy days (30+ MPH but only 1 of 40+ MPH but it was a doozy as previously detailed on the 17th). Most days during the month had PWG values in the moderate teens (12) and twenties (15) range.

My maximum temperature frequencies included 11 days over 90°, 17 days at or over 80°, and 3 days between 70° and 79°. On the minimum temperature frequency side of things, there was 1 day < 60°, 12 days between 60.0° and 69°, and 18 days of 70° or more. The coolest daily
max temperature day was 78.3° on the 18th while the warmest daily min temp day of 74.9° was reached on the 12th and 13th.

The diurnal range daily monthly average was 17.7° (-2.8°). Our greatest daily range of temperature was 23.5° on the 6th (94.1°- 70.6°). We had a total of 7 days with daily ranges above 20°. Our lowest range of temperature was 9.2° (78.3°- 69.1°) on the 18th , the day after our big thunderstorm day of the month. It was the only July day with a daily range under 10°.

July 2021 was generally dry with one notable hot period but still no real extremes save for the thunderstorm on the 17th. Groundwater reserves are currently in fairly good shape from a wet August so far. Extreme heat has stayed away for the most part, keeping lawns and gardens fairly green. The tropics have flared up a bit recently, but have been pretty quiet as far as our immediate area. We shall see what, if any activity will develop.

JULY 2021 – ROCKVILLE 2.8 WNW MARYLAND – SUMMARY STATISTICS

Average high temperature 87.2° (+0.8°)
Average low temperature 69.5° (+3.6°)
Mean temperature 78.3° (+2.2°)
High temperature for the month (date) 94.1° (6)
Low temperature for the month (date) 59.8° (3)

Precipitation 3.36″ (-0.49“)
Greatest daily amount (date) 1.28″ (17)
Greatest storm total (dates) 1.28” (17)
2021 year-to-date precipitation total 19.02″ (-5.40”)

Highest barometric pressure (date) 30.21” (23)
Lowest barometric pressure (date) 29.76” (2)

Peak wind gust (date/direction): 56 (17/W)
(USG data across the street)

Heating degree days for the month: 0
Cooling degree days for the month: 414

Greatest diurnal range (date): 23.5° (6)
Least diurnal range (date) 9.2° (18)

Number of days:

Fog 3
Windy 4
Glaze/Sleet/Snow 0
Thunder 5
Cloudy 5
Partly Cloudy 25
Sunny/Clear 1
Max temp = 90° 11
Min temp =< 65° 4
Precip = 0.01” 11

Detailed EXCEL spreadsheet data file for July 2021: 

Rockville 2.8 WNW July 2021 Data