Baltimore Sun

Heat and humidity return ... briefly

Just when you thought you were rid of this July heat and humidity, it returns for an short encore. Forecasters expect the mercury at BWI-Marshall Airport will reach 90 again this afternoon after a two-day respite in the upper 80s.  If they're right, it would be the 40th day this year with 90-plus heat.

We can expect highs in the low 90s and rising humidity as clockwise winds around a departing high-pressure system bring us more warm, wet air on southwest winds out of the Gulf. A component of that wind will sweep down off the Appalachians, heating up as it loses altitude and gets compressed. Heat index numbers will rise to the upper 90s, if the forecast is correct.

The solar heating and incoming moisture will raise the chances for showers and thunderstorms as Wednesday rolls into the evening. That's especially so near the Chesapeake, where a bay breeze is liklely to kick up, and collide with the warm, wet air out of the mountains.


On Thursday, the next cold front is expected to cross the region, with higher chances of generating afternoon thunderstorms, especially east of I-81, forecasters said. Some storms could approach severe proportions, and could drop significant amounts of rain. Until it gets here, we could see highs in the low 90s. If so, that makes 41 days.

Skies are likely to clear overnight, leading us to cooler, drier weather on Friday and Saturday, with highs in the mid-80s. Then the cycle begins again, with high pressure moving off the coast on Sunday, bringing us warmer, wetter air out of the south and west. But while temperatures and dew points will rise, forecasters expect things to remain fairly comfortable, compared with what we've seen in most of July.


Passage of yet another cold front late Sunday will usher in more dry and seasonable weather as the first week of August unfolds, with highs in the mid-80s. No 90s in sight for the moment.

Still looking for an ID on my butterfly. Anyone? I'm leaning toward the dark form, female, of the eastern tiger swallowtail.

(SUN PHOTO: Frank Roylance)