The combination of heat and humidity produced peak heat index values, a measure of how hot the air feels, of around 108 degrees in Washington and 110 in Baltimore.
While the heat index values were the highest of 2018 so far, air temperatures remained well below record levels.
On Tuesday, a brutal combination of heat and humidity is once again expected, which has prompted a second straight heat advisory. Tuesday likely will be the fifth day of a heat wave that began last Friday, and is expected to continue through Friday of this week.
See below for hourly updates that we filed on Monday’s heat and humidity.
3:05 p.m.: Highest temperature and heat index of the year
The temperature held steady at 95 degrees between 2 and 3 p.m., but the humidity leaped back up. The 3 p.m. dew point bounced back to a suffocating 76 degrees. The combination of heat and humidity pushed the heat index to 108, the highest of the year so far.
As stifling as it has felt today, mainly due to high humidity, air temperatures are not close to records. Here are the records for July 2 around the area:
- Washington: 101 from 1898; high so far 95
- Dulles 98 from 1966; high so far 94
- Baltimore 103 from 1901; high so far 98
2:05 p.m.: An encore Tuesday?
The National Weather Service is predicting a repeat of today’s conditions on Tuesday. It has just issued a heat advisory from noon to 8 p.m. tomorrow for heat index values to reach 105 to 109 degrees. Air temperatures are expected to again reach the mid-to-upper 90s with dew points in at least the low 70s.
“Humidity will be similar to if not slightly higher than Monday,” the Weather Service said in its afternoon discussion, even though air temperatures may be a couple degrees cooler.
At 2 p.m. today, the air temperature in Washington hit 95, matching the hottest of the year so far. The humidity dropped a notch as the dew point fell from 76 to 72, producing a heat index of 103, down from 107 the previous hour.
1 p.m.: It now feels hotter than it has all summer
The 1 p.m. heat index in Washington soared to 107 degrees, thanks to an air temperature of 94 and dew point of 76. This is the summer’s highest heat index so far.
The air temperature still needs to rise another degree to match the summer’s hottest reading of 95 set June 19, but should have little trouble getting there over the next couple of hours.
12:25 p.m.: Excessive heat warning for Baltimore
As the combination of heat and humidity could push the heat index or feels-like temperature to 110, the National Weather Service has issued an excessive-heat warning in Baltimore, its most severe heat alert. “Dangerously high temperatures and humidity could quickly cause heat stress or heat stroke if precautions are not taken,” the warning says.
At noon, the heat index at the Inner Harbor in Baltimore was 108 degrees, thanks to an air temperature of 96 and dew point of 75.
Washington’s heat index could also come close to 110 this afternoon, but it remains under an advisory rather than a warning. At noon, the heat index held at 105 degrees, the same reading as at 11 a.m. The temperature went up to 92 degrees, but humidity eased modestly. The dew point dropped from 78 to 76, which is still extremely high.
Throughout the region, heat index values were over 100. Here’s a selection:
- Dulles: 102
- Manassas: 105
- Leesburg: 107
- Gaitherburg: 103
- Fort Belvoir: 106
- Quantico: 104
- College Park: 101
- Fredericksburg: 102
- Stafford: 107
- Baltimore-Washington International Marshall Airport: 103
11:05 a.m.: Heat advisory criteria met an hour before it even begins
The heat index, the temperature it feels like factoring in the humidity, has already reached 105 in Washington, which is the criteria for a heat advisory. Officially, the heat advisory doesn’t take effect until noon, but we’ve met the criteria an hour early.
The 11 a.m. air temperature was 90 in Washington, with a ridiculously high dew point of 78.
As long as the humidity stays this high and the temperature keeps rising, we could see heat index values near 110 this afternoon.
10:15 a.m.: The humidity is not just oppressive — it’s offensive
The air temperature at 10 a.m. in Washington of 86 degrees, by itself, sounds manageable. But the dew point, an indicator of humidity, is 77 degrees — which is extremely high. Here’s a chart to help you understand how rank this humidity level is:
Factoring in this obscene mugginess, it already feels like it’s 97 degrees outside.
The 77-degree dew point is the highest this summer so far in Washington.
And the 86-degree air temperature is the second highest in the nation at the moment, only behind the 87 degrees in New York City.