After a very dry start to July 2018 with only 0.03″ of rain through the 14th at the airport in Baltimore (Baltimore/Washington International Airport (BWI)), and just 0.41″ covering the 33-day period June 12 – July 14, 2018, historic amounts of rain began to fall in mid-July as a seemingly endless flow of moisture from the south occurred. Within the 10-day period July 16th-25th, 15.38″ fell at BWI, far exceeding any previous July total dating back to 1871 in the historic precipitation archive (the previous monthly record was 11.03″ way back in 1889 when official observations were taken downtown at the corner of Holliday and E. Baltimore Streets, near City Hall). Here are some of the lofty amounts that were observed:

Calendar-Day Amounts (and daily records):

• 3.35″ (17th) – previous daily record: 1.81″ (1897)
• 4.79″ (21st) – previous daily record: 2.76″ (1887)
• 4.07″ (24th) – previous daily record: 1.73″ (1961)

The combination of just these 3 days exceeded the previous monthly record for July! This is also the first time that 3 daily amounts ≥3.00″ have ever occurred in any single month.

24-Hour Amounts:

• 4.79″ (21st, in the 16-hour period 8:00 A.M. – Midnight)
• 4.07″ (24th – see 8/2/2018 and 9/15/2018 UPDATES below)
• 4.04″ (16th-17th), covering the 24-hour period 4:00 PM – 3:00 PM).

These times are based on Eastern Standard Time (the NWS standard throughout the year).

*The hours for the 4.07” amount from the 23rd-24th cannot currently be determined with the website that I have access to. If I do find the info., I’ll update this blog (For subsequent info., see “UPDATES,” below, for 8/2/2018 and 9/15/2018).

2-Day Amounts:

• 5.49″ (23rd-24th)
• 5.29″ (21st-22nd)
• 4.46″ (24th-25th)
• 4.21″ (16th-17th)

Please note that these July 2018 amounts are preliminary until verified by the National Centers for Environmental Information (NCEI).  

UPDATES:

8/1/2018

With another 0.97” reported on 7/27/2018, 0.27” on 7/30, and 0.06” on 7/31, the monthly total at BWI ended up at 16.73”, the second-highest total for any month dating back to 1871 (1.62” below the all-time record of 18.35”, set during the 2-hurricane month of Aug. 1955 (“Connie” and “Diane”). Also remarkably, at the end of July, Baltimore’s precipitation total stood at a preliminary 41.42″, which already exceeds the average annual amount.

8/2/2018

I had noticed a discrepancy between the daily totals and the sums of the hourly totals (both being NWS websites) for both the 23rd and 24th days of the month. After e-mailing NWS-Sterling about it, I received the following reply: “There was a malfunction with the gauge (which shows up in the hourly reports) those 2 days. So, the observer took manual measurements . . . .”  The reported ASOS totals vs. the manual totals: 23rd – 0.77″ vs 1.42″; 24th – 3.50″ vs. 4.07″.

9/15/2018

A revised Local Climatological Data publication (unedited) was finally issued, changing various hourly amounts for both the 23rd and 24th of July. For the 24th, the hourly amounts for the 4.07″ indicate the maximum 24-hour amount fell exactly within the calendar day (only a trace fell the last hour of the day on the 23rd, 0.00″ fell the first hour of the 25th). The daily amounts for the 23rd of the month were also revised but not fully as the new total is 0.81″ for the day (previously was 0.77″), still well under the actual total of 1.42″ reported.

 

Click the link below for hourly reports for several of the heavy rain events:

BWI_Heavy-Rain-Events_July-2018_Update-2018-08-02

 

To view the all-time record amounts for Baltimore covering calendar-day, 24-hour, 2-day, and monthly periods, click the following links:

Baltimore_Top-Ten-Wettest-Driest-Individual-Months-Years.pdf

Baltimore_Top-Ten-Wettest-Calendar_24-HOUR_2-Day-Totals.pdf