JULY 2018 MONTHLY SUMMARY ROCKVILLE 2.8 WNW MARYLAND
By Kevin Shaw, Observer in Charge
July 2018 was a tale of two distinct, different patterns. The first 16 days of the month was hot and dry
(all 8 days of 90° maxs or higher, only 0.15″ of rain) while the last 15 days of the month were cooler and
very wet (over 98% of the month’s total rainfall, 3 days with maxs in the 70s, none in the nineties). The
highlight was the 4.02″ of rain that fell on the 21st, the wettest day of the month, year, and of my brief
station’s history. That kicked off a 5 day streak of heavy rains totaling 6.43″ that led to some area-wide
flooding and very soggy trips to the rain gauge. The big hot spell during the first half of the month was
highlighted by the heat wave streak the first 5 days of the month topped off by the 95.8° high on the
second, hottest reading of the month. The minimums were high most of the month, with 11 days of 70
or greater lows. The rainy period towards the end of the month also had some, with low diurnal ranges,
topped off with the 5.8° range on the 24th (78.6° – 72.8°).. 12 days of measurable rain was pretty close
to the normal amount for July. It was an incredibly diverse month with Mother Nature turning her “faucet”
off then on.
Once again, significant pressure differences during the month were muted, though not as much as June.
The lack of tropical activity didn’t put a crimp on our rainfall, but didn’t give us a very low pressure value
during the month. July’s pressure extremes included the extreme highest pressure for the month (30.39”
on the 8th) and the extreme lowest (29.66” on the 22nd). The month had 8 cloudy days, 15 partly cloudy
days, and 8 clear/sunny days.
There were 0 heating degree days and 382 cooling degree days during the month. There were only 5 foggy
days, but 7 days with thunder and 4 windy days (all in thunderstorms during our wet second half of the month).
The windy day category is subjective with no personal real data values to back it, just based on my descriptive
email daily weather posts that are also posted on weathertogether.net.
Daily max/min temperatures varied about the same as June. My maximum temperature frequencies included
8 days of 90° or greater, 18 days between 80° and 89°, and 5 days between 70° and 79°. On the minimum
temperature frequency side of things, there were 2 days between 50° and 59.9°, 18 days between 60° and
69.9°, and 11 days at or above 70°. The coolest daily max temperature was 73.6° on the very wet 21st
and the warmest daily min temp was 76.6° in the middle of the month’s longest heat wave on the 3rd.
The diurnal range daily monthly average was 17.1°. Our greatest daily range of temperature was 28.3° on the
9th, formed from a high of 87.3° and the monthly low of 59.0° as I was ramping up from a cool period to one
of our 90° max temps on the 10th. We had a total of 9 days with daily ranges above 20°. Our lowest range
of temperature was 5.8° (78.6°-72.8°) on the cloudy, wet 24th. There were only 2 other days with diurnal
temperature ranges less than 10.0°, on cloudy, but not particularly rainy days.
Recent changes to the station include a new base to the VP2 weather station, as the old one shifted too easily
and became slanted which can throw off the rainfall catch. Helping out is also a screen added to cover over
the small hole at the bottom of the gauge cone that will keep out pollen and leaf and twig litter, particularly pine
needles from the close by pine tree. Unfortunately a new development is adding un-natural amounts of water
accumulation to my tipping bucket totals, as the apartment complex automatic sprinkler system kicks off on
most days between 0300-0330 (usually adding between 0.03” and 0.06” to the day’s total). The cocorahs
gauge, located off property in a different location, does not get this artificial input to its official record. I am still
constantly checking on my data quality frequently (which caused me to discover the sprinkler system problem),
along with discussion and data comparison with several of my Maryland weather cohorts. I continue to
occasionally (as time allows) submit GLOBE Cloud observations, complete with submission of sky pictures at
the time of the observation, usually timed with the passage of satellites and/or solar noon (about 70 minutes
past actual EDT noon).
Please ask me any questions you want at any time about my station setup and/or my data through any means
available to you.
JULY 2018 – ROCKVILLE 2.8 WNW MARYLAND – SUMMARY STATISTICS
Average high temperature 85.9°
Average low temperature 68.8°
Mean temperature 77.3°
Greatest daily amount (date) 4.02″ (21)
Greatest storm total (dates) 6.43” (21-25)
2018 year-to-date precipitation total 30.41″
High temperature for the month (date) 95.8° (2)
Low temperature for the month (date) 59.0° (9)
Highest barometric pressure (date) 30.39” (8)
Lowest barometric pressure (date) 29.66” (22)
Peak wind gust (date/direction): N/A
Heating degree days for the month: 0
Cooling degree days for the month: 382
Greatest diurnal range (date): 28.3° (9)
Least diurnal range (date) 5.8° (24)
Number of days:
Partly Cloudy 15
Max temp ≥ 90° 8
Min temp < 60° 2
Precip ≥ 0.01” 12