Capital Weather Live

Always a human at the helm: Updated around-the-clock by Capital Weather meteorologists.

Happening now: Slowly falling back into the 80s this evening. Muggy through the night with lows in the mid-70s to near 80.

What’s next? Another hot one tomorrow with a smoky haze possible. A bit less hot Friday but with more significant smoke possible. Seasonable temperatures this weekend with a chance for scattered showers and storms both days.

Forecast in detail

Tonight: Evening readings slowly fall back through the 90s under mostly clear skies. Continued muggy overnight with lows in the mid-70s to near 80. Confidence: High

Hourly Forecast | Pollen, Air & UV

Tomorrow (Thursday): Partly to mostly sunny with temperatures soaring once again. Highs reach the mid-90s to near 100 with heat indexes peaking around 100 to 105. Wildfire smoke could be present closer to the ground than today, helping to promote a Code Orange air quality alert for the region. Light winds variable in direction in the morning come from the west around 10 mph again in the afternoon. Just a slight chance of a late afternoon or evening thunderstorm. Confidence: Medium-High

[How to stay safe in the heat]

Tomorrow night: Slight chance of an evening thunderstorm. Otherwise it's another steamy evening with temperatures dropping back through the 90s into the upper 80s under partly cloudy skies. Remaining muggy overnight with lows in the mid- to upper 70s. Confidence: High

A look ahead

We should take the edge off the heat just a bit on Friday, as the dome of hot high pressure starts to retreat. Highs aim for the low to mid-90s with partly to mostly sunny skies. Humidity should come down a bit as well, but the smoke could be worse than Thursday. Could see a few showers or thunderstorms pop up Friday evening or overnight with lows around 70 to 75. Confidence: Medium

Pretty typical temperatures this weekend with highs in the mid-80 to low 90s. With lower pressure and humidity trending higher again, both days have a chance for scattered showers and storms at some point, especially during the afternoon into evening. Saturday night lows in the upper 60s to low 70s. Confidence: Low-Medium

Today’s daily digit — 0/10: Extreme heat. No likey. | 🤚 Your call?
The digit is a somewhat subjective rating of the day’s weather, on a 0-to-10 scale.

When we describe how humid it feels outside, you'll almost always see us talk about dew point instead of relative humidity.

Relative humidity gets a lot of the attention. But when it comes to describing how muggy the air actually feels, it's often misleading.

Dew point tells the story much better.

Think of dew point as a direct measure of how much moisture is in the air. More specifically, it's the temperature to which the air would have to cool before becoming saturated and producing dew.

This may sound technical, but the takeaway is simple: the higher the dew point, the muggier it feels.

Relative humidity, on the other hand, doesn't tell you how much water vapor is actually in the air. Instead, it tells you how close the air is to being saturated at its current temperature.

Cool, saturated air often contains less moisture than hot air that's not even close to saturated.

Consider two afternoons:

• Day A: 72 degrees with 80 percent relative humidity
• Day B: 92 degrees with 45 percent relative humidity

Most people would assume Day A is more humid because the relative humidity is nearly twice as high. In reality, there's more moisture in the air on Day B.

[How humid does it get in DC? A look at dew points through the year]

The key is that relative humidity measures how close the air is to saturation — not how much moisture is actually in the air. Since temperature plays such a big role, relative humidity can change dramatically even when the amount of moisture stays exactly the same.

Consider a crisp autumn morning with a relative humidity near 100 percent. Overnight cooling pushes the air close to saturation, driving up the relative humidity even though there's not much moisture in the air. It may be damp enough for dew or fog to form, but it certainly doesn't feel muggy.

Dew point cuts through that confusion because it measures the moisture itself.

It gives us a much better sense of whether you're stepping into comfortably dry air or the kind of soup that leaves your shirt sticking to your back after a five-minute walk.

Around the DC area, summer dew points routinely climb into the upper 60s and low 70s. During the most oppressive heat waves, they can rise into the mid-70s and occasionally approach 80. At those levels, the air feels heavy, perspiration evaporates less efficiently, and simply being outdoors becomes exhausting.

It's also why visitors from the West are often surprised by summers here. Places like Phoenix and Las Vegas may experience much higher air temperatures, but their dew points are frequently 30 or even 40 degrees lower. The heat can be extreme, but it's a different kind of heat because the air contains much less moisture.

Relative humidity still has its uses. It's important in forecasting fog, clouds, and whether the air is nearing saturation. But if your question is simply, "How humid is it going to feel?" there's a better number.

So when we're talking about how humid it's going to feel, you'll hear us focus on dew point far more often than relative humidity. We think it's the most accurate —and most useful — way to describe what you'll actually experience when you step outside.

After multiple failed attempts in the past decade, is this the time daylight saving time becomes permanent year-round?

The House passed the Sunshine Protection Act on Tuesday, which would make daylight saving time permanent – no more "spring forward" or "fall back" – except for states that opt out before the bill is enacted. Passage by the Senate is not a sure thing, but if the bill is adopted by that chamber, President Trump has signaled he will sign it.

Polls have shown that while most Americans don't like changing the clocks twice a year, they are largely split on whether it should be daylight saving time or standard time that becomes permanent.

Permanent daylight saving time would mean an extra hour of sunlight for running errands or exercising after work during the colder months of the year. But it would also mean darker mornings. In DC, sunrise would occur after 8 a.m. from around Thanksgiving Day until Valentine’s Day.

Wildfires burning in parts of Minnesota and western Ontario, Canada, are sending thick plumes of smoke toward the eastern United States.

Dense smoke has already spread into parts of the Great Lakes and Northeast, reducing air quality and turning the sky eerie shades of orange and red. Here in the DC area, lower concentrations of smoke arrived Tuesday but remained high enough in the atmosphere that they didn't affect air quality.

That could change. While the thickest smoke is expected to stretch from northern Wisconsin to Massachusetts on Wednesday, it should sink south into Pennsylvania Wednesday night into Thursday. Around that time, smoke concentrations may increase modestly in the DC area, especially across northern Maryland.

The period of greatest concern locally will be late Thursday night into Friday, when winds from the northwest may direct the plume directly through the Mid-Atlantic.

Here is what we might expect:

• Reduced air quality: The smoke may become thick enough to increase fine-particle pollution near the ground, although it's too soon to know by how much.
• Smoky odor: The air may smell like a campfire.
• Reduced visibility: Hazy skies could limit how far you can see.
• Slightly cooler temperatures: Thick smoke can block some sunlight, trimming afternoon highs by a couple of degrees.
• More vivid sunrises and sunsets: Smoke particles scatter sunlight, often producing especially vibrant oranges and reds.

The last major incursion of Canadian wildfire smoke into the DC area occurred in June 2023. During that episode, the region experienced its worst smoke pollution on record, with two days of widespread unhealthy air and surreal, Mars-like skies.

It's too early to know whether this event will approach that level, but we'll be watching closely and provide updates as the forecast becomes clearer.

Even the thin veil of smoke overhead Tuesday evening helped produce an especially colorful sunset. See some photos below:

With highs forecast to flirt with the century mark Wednesday and Thursday, DC's total of 100-degree days this year could climb even higher up the record books.

DC currently has four days at or above 100 degrees, tied for the eighth-most in any year since modern records began in 1872. A fifth 100-degree day would move this year into a tie for sixth, while six would tie for fourth.

If DC reaches 100 on Wednesday, it would also tie the record for the most 100-degree days through July 15—the midpoint of meteorological summer—with five, set in 2012.

This year is also on pace to join a select group in another way. Twelve years have recorded three separate 100-degree heat waves, with cooler periods in between. This summer appears poised to become the 13th.

Also consider:

• Eleven days at or above 95 degrees already matches the full-season average.
• With 25 days at or above 90, this week's heat should push the total past 30 by late week. The seasonal average is about 40, and 90-degree days often continue well into September.
• Summer's average temperature of 79.5 degrees through Monday is tied for the fifth warmest on record to this point.

It's shaping up to be one of the hottest summers in recent memory. And with forecasts increasingly pointing to a strong El Niño this winter, it's worth noting that the following summer is often the one that brings the most relentless heat.

A heat advisory is in effect for the DC area Wednesday from 11 a.m. to 8 p.m.

The National Weather Service expects heat index values – how hot it will feel from the combination of heat and humidity – to reach 105 in the heat advisory area.

"Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors," the Weather Service said.

[Cooling centers: DC | Maryland | Virginia]

Extreme heat kills more people in the United States than any other weather hazard, according to Weather Service data. Here are important safety tips to get through this week's heat wave...

See more heat safety infographics here.