April 2018 featured a bit above normal rainfall and below normal temperatures at the three major airports in the DC area. There were generally cool temperatures all month except for a brief 2 day mini-heat wave on the 13th and 14th when I had maximum temperatures in the 80s and lows in the 60s. The 84° high was the highest temperature of the month. Just a few days before I had my coldest max temperature readings in the 40s on the 8th and 9th, with a 42° max on the 9th the coldest max of the month. The coldest min temperature of the month (31°) occurred on the 8th. It was the only freezing minimum of the month, though many other days were close in the 33°-34° range. Another cold day with high winds was on the 17th, following our biggest storm of the month and the lowest barometric pressure (29.47”) on the 16th. The 2.22” total on the 16th was about 62% of the monthly amount (3.57”) and so far the wettest day of the year at my station. There were 10 days with measurable precipitation, probably about the normal amount. The modest highest barometric pressure reading of the month (30.51″) on the 21st was in a brief 4 day dry period at that time. The month was mostly partly cloudy (12 days) to cloudy (13 days) with only 5 clear days (same as March).

There were 398 heating degree days (HDD) and 17 cooling degree days (CDD) during the month. There were 7 foggy
days, unfortunately no days with snow (including trace amounts), 3 windy days and 2 days with thunder. The windy
day category is subjective with no personal real data values to back it, just based on my email daily weather posts
that are also posted on weathertogether.net. A 52 MPH gust was recorded on the 19th at a nearby Gaithersburg
station, according to the April PRESTO summary.

Daily max/min temperatures varied more widely than March throughout April. My maximum temperature frequencies
included 2 days over 80°, 3 days between 70° and 79°, 11 days between 60° and 69°, 11 days between 50° and
59°, and 3 days between 40° and 49°, On the minimum temperature frequency side of things, there were 12 days
between 30° and 39°, 12 days between 40° and 49°, 3 days between 50° and 59°, and 2 days at or above 60°.
The coldest daily max temperature was 42.4° on the 9th and the warmest daily min temp was 64.6° on the 14th.

The diurnal range daily monthly average was 18.5°. Our greatest daily range of temperature was 31.1° on the 12th°,
formed from a high of 75.3° and low of 44.2° as I was ramping into our brief 2 day mini-heat wave over the following
2 days. We had one more day with a range over 30° (30.6° on the 30th) and an additional 10 days with daily ranges
above 20°. Our lowest range of temperature was 6.3° (44.2°-37.9°) on the 17th. It was on the cloudy, blustery,
chilly day after our big rainstorm on the 16th. There were 5 other days with diurnal temperature ranges less than 10.0°. The distribution of both the low and high diurnal range days were spread fairly evenly throughout the month.

With yet another month to study the most recent instrument changes made in mid-August, data appears to be stable and an overall data quality improvement success. I am still constantly checking on my data quality frequently along with some of my Maryland weather cohorts. I did bring in my snowboard by the end of the month. I intended on bringing it in earlier in the month, but actual snow threats during the first part of the month delayed the snowboard removal. My rain gauge has been restored to fully operational mode, with both the inner and outer cylinders and the funnel in place. I also have continued as close to daily (as time allows) GLOBE Cloud observations, complete with submission of sky pictures at the time of the observation, usually timed with the passage of satellites and also solar noon right now with the time change 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.

APRIL 2018 – ROCKVILLE 2.8 WNW MARYLAND – SUMMARY STATISTICS

Average high temperature 61.5°
Average low temperature 43.0°
Mean temperature 52.3°

Precipitation 3.57″
Greatest daily amount (date) 2.22″ (16)
Greatest storm total (dates) 2.25” (15-16)
2018 year-to-date precipitation total 11.82″

Snow 0.0″
Seasonal snowfall total as of 4/30/2018 11.7″

High temperature for the month (date) 83.9° (13)
Low temperature for the month (date) 31.1° (8)

Highest barometric pressure (date) 30.51” (21)
Lowest barometric pressure (date) 29.47” (16)

Peak wind gust (date/direction): N/A

Heating degree days for the month: 398
Cooling degree days for the month: 17

Greatest diurnal range (date): 31.1° (12)
Least diurnal range (date) 6.3° (17)

Number of days:

Fog 7
Windy 3
Thunder 2
Cloudy 13
Partly Cloudy 12
Sunny/Clear 5
Max temp = 80° 2
Min temp = 32° 1
Precip = 0.01” 10

2018-04-Rockville-2.8-WNW