July 2020: The Hottest Month in Baltimore History
Official weather records for Baltimore date back to 1871. Never, during these last 150 years, has the monthly Mean Temperature (the average between the daily Maximum and Minimum Temperatures) ever been higher than the 81.7° that occurred in July 2011 and the 81.5°, which was recorded in three other Julys – 2010, 1995, and 1949. July 2020 goes down in the record books with the new all-time highest Mean Temperature of 82.6° for any month, a departure of +5.6° from the 30-Year Normal (currently 1981-2010) of 77.0°, and nearly a full degree higher than the previous record. Additionally interesting is that four of these five all-time high Means have occurred at Baltimore-Washington International Thurgood Marshall Airport (BWI), and only once at the historically warmer downtown Baltimore location (Custom House in 1949 – official records were moved from this downtown location to the airport beginning in August 1950).
The monthly Average Maximum Temperature of 92.7° just missed exceeding the all-time maximum of 92.9° (from 2011) as the final day of the month only reached 81° under cloudy, rainy skies, bringing the month-to-date average through July 30th down from 93.1° but still ranking as #2 warmest month of all time.
The monthly Average Minimum Temperature of 72.5° was not the record-warmest reading but did make the top-10, ranking at #4 (tied with July 1931 and also with August 1939) and is the warmest July beginning in 1951 after records moved to BWI, the warmest being the 73.5° from 1949.
Other all-time temperature records set this month included the Number of Days in a single month with Maximum Temperatures ≥90° at 25 days (just passing July 2011’s 24 days) and Maximums ≥95° totaling 13 (tied with July 2012). Two days this month reached 100° (19th & 20th), below the all-time record of 5 days from July 2010. The “coolest” Maximum during July 2020 of 81° on the 31st was the only such value below 87° while the “coolest” Minimum was only 67° on the 15th, with not a single day below 70° the remainder of the month. A total of only 6 days fell to <70° this month, not an all-time record for Baltimore’s long-term record but is the new record for the BWI location, besting the 7 days from 1955. The downtown location at South & Water Streets recorded only 4 days <70° way back in 1872 for first place. However, the continuing streak of 16 consecutive days ≥70° (through July 31st) is the new all-time record for the BWI location, now ahead of the previous record of 14 days occurring during two periods ending on 7/26/2010 and 8/1/1959; the downtown extreme prior to records moving to the airport is still the 27 days ending on 7/21/1876.
With this being the hottest month ever recorded, oddly, not a single calendar-day record was set the entire month – not a daily High Maximum, High Minimum, nor High Mean Temperature. July 30th reached 97°, just one degree short of that day’s record of 98° (July 30th is still only one of three July days to have never reached 100°, the other two being the 12th (97°) and 13th (98°)). The High Mean Temperature was also just missed on the 30th with 86.0°, the record remaining 86.5° from back in 1933. Not a single day this month averaged below normal, indicating more that it wasn’t a month of extremely hot periods of weather but more just a persistent heat that brought this month into the record books.
The Top-10 months of record temperatures at Baltimore, including station locations through the historical archive (please click the links below):
With that being said, there is some doubt as to the full accuracy of the current Automated Surface Observing System (ASOS), the FAA’s weather instrumentation, at BWI. Especially over the last year or two, Maximum Temperatures at BWI’s suburban location appear to be running above what they should be and have even often superseded notorious urban hot spots in the DC/Baltimore area, such as Washington National Airport and The Maryland Science Center in downtown Baltimore’s Inner Harbor. Not only is the equipment possibly located too close to runway pavement but, more recently, satellite photos indicate new construction/black top occurring right next to the ASOS location, which could easily produce warmer-than-natural readings, especially on sunny, calm days or during certain wind direction. These conditions would likely be outside of National Weather Service observing standards. Here are links to recent articles on this subject:
The National Weather Service has revised data in the past when it was realized issues with certain data existed, such as when equipment has not met National Weather Service standards. It will be interesting to see if anything is revised with this month’s data to cause it not to be the all-time hottest month for Baltimore.