Heat advisory 1-8 p.m. on Sunday for heat indices up to 105

Two hour radar loop of rain and storm movement through the area. Refresh page to update.

4:45 p.m. update: A code orange air quality alert has been issued for Sunday across the D.C. and Baltimore region. Air quality may become unhealthy for sensitive groups. Those at most risk include children, the elderly, and those with heart or lung conditions.

4:35 p.m. update: It’s ended up fairly sunny this afternoon as temperatures head mainly for the mid-80s to near 90. Instability has crept up as the morning showers moved off and sunshine returned. Despite that, no areas of storminess are nearby at present. It seems anything that might pop up would tend to be isolated at this point, but we’ll stick with a risk of showers or storms the next few hours.

3:15 p.m. update: The NWS has issued a heat advisory for the area that will run from 1 p.m. to 8 p.m. Sunday. Heat index values are expected to reach the 100-105 level Sunday afternoon.

10:50 a.m. update: Showers are moving off to the east. We should see this first batch of rain end everywhere rather soon. Some breaks in the clouds may show up as this activity winds down, but clouds remain quite numerous to the west and there is even some more light shower activity off to the southwest to watch.

How the morning has progressed certainly complicates the afternoon forecast. It seems unlikely we’ll reach originally expected highs, and perhaps it’ll end up about 4-8 degrees lower than anticipated. Maybe more in spots if clouds hold tough. That in turn lowers the instability potential for storms, which should make the odds of intense or widespread activity lower, but doesn’t mean we won’t see any rain. Either way, it’s super humid out there.

9:50 a.m. update: Showers — some rumbles — are quickly progressing through the area, with the heaviest activity on the front end and light to moderate stuff behind. The batch is weakening overall as well. It should be out of here before too long.

A few have asked where the rain came from. Well, it basically popped up just to our west, possibly on an old boundary from previous activity. We did have a risk of some morning showers in PM Update yesterday, which I regrettably removed given weather models and radar last night. A 10-hour loop from Weather Underground highlights the progression well:

And more from NWS at 4 a.m.:

A MOIST AIRMASS IN PLACE ACROSS THE MID-ATLANTIC THIS MORNING WITH TEMPS AND DEWPTS IN THE 70S. WEAK ISENTROPIC LIFT WILL CONTINUE ACROSS THE REGION THIS MORNING. SHOWERS AND THUNDERSTORMS ACROSS N WV WILL LIKELY ENTER THE HIGHLANDS THIS MORNING. HI RES GUIDANCE KEEPS THE ACTVITY ACROSS THE HIGHLANDS WITH LITTLE EASTWARD PROGRESSION THIS MORNING. MOST OF THE REGION SHOULD STAY DRY THIS MORNING.

9 a.m. Update: Some early showers with some embedded thunder moving through over next couple hours, then onto the heat…

Original Post

TODAY’S DAILY DIGIT
A somewhat subjective rating of the day’s weather, on a scale of 0 to 10.

4/10: We should expect hot and humid in July, but that doesn’t mean we need to like it. PM storm risk, too.

EXPRESS FORECAST

Today: Partly sunny. PM storms possible. Highs: 90-96.
Tonight: Evening showers or storms, clearing. Lows: 72-78.
Tomorrow: Mostly sunny. Highs: 93-99.

FORECAST IN DETAIL

If you’ve been missing the high heat of typical D.C. summer recently, this weekend is for you. For everyone else, this probably won’t be the best weekend in recent history. On the bright side, it shouldn’t be all that rainy. It will be rather humid though, and that sun is going to beat down for most of the time. Take it easy, and hydrate!

Today (Saturday): We should see a good deal of sunshine for much of the day. Add in dew points near and above 70, plus increasingly hot temperatures, and it’ll certainly be feeling like “peak summer.” Highs reaching the near 90 to mid-90s range feel more like near or above 100 thanks to the humidity. Isolated to scattered showers and storms become more likely during the afternoon and into the evening. It seems the best odds are in the 4 p.m. range onward out west and then advancing into the immediate area in the hours after that. Some of these storms could be strong to maybe even severe given high moisture levels. However, heavy rain and lightning would be the main threats with any activity. Confidence: Medium-High

Tonight: Any showers or storms move east and wind down during the evening. After that, we’re left with a humid mid-summer night. Temperatures only make the 70s under partly cloudy skies. Downtown could be close to 80. Winds are light from the south. Ahh, July! Confidence: Medium-High

For related traffic news, check out Dr. Gridlock. Keep reading for the forecast through the weekend…

Tomorrow (Sunday): High pressure moves overhead for the day. That means fewer clouds and more heat. This certainly looks like a contender for the hottest day of the year (at least so far) as highs head for the mid-and-upper 90s most spots. With humidity hanging out in near-oppressive levels, heat indices past 100 seem likely for much of the area at times. In the city it could pass 105. Confidence: Medium-High

Tomorrow night: It’s a pleasant if toasty evening with some increase in clouds. A storm complex out to the west may try to approach the area overnight. A risk of showers presents itself near or after midnight. For now, no real “big storm” risk locally given the timing. Lows are in the 70s again, with downtown threatening an 80-degree low if it doesn’t rain. Confidence: Medium-High

A LOOK AHEAD

We’ve got partly to mostly sunny skies on tap as we start the work week Monday. Given the air mass in place, that means more heat and high humidity. It could be pretty close to Sunday’s level on both as well. I’ll go with mid-90s as it seems there may be a bit more cloudiness than Sunday, and this humid air mass can prove hard to heat to full potential. An isolated storm or two can’t be ruled out late day. Confidence: Medium

A front tries to drip through the area on Tuesday, but there’s some question as to how far it gets. It should be enough to bring some more cloudiness in and keep temperatures down another notch compared to prior days. Near 90 to low 90s seems like the best bet. Skies should be partly cloudy and humidity remains pretty high. A shower or storm is possible, mainly late. Confidence: Medium