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Pop Goes the Heat Wave

Dan Stillman @ 11:35 PM

Weather Channel radarThe short-lived heat wave ended with a bang last night. After yesterday's high temperatures of 97 (National), 95 (Dulles), 99 (BWI) and 100 (La Guardia) caused problems across the Washington area and cancelled flights in and out of New York, severe evening thunderstorms blew through much of the I-95 Corridor (locally, most storm activity was focused from DC toward points north and east).

Today, we return you to your regularly scheduled typical summer conditions, but with one wildcard -- a tropical storm off the Carolina coast.

Pictured: Severe storms last evening from DC to New York marked an end to the short but intense heat wave, courtesy the Weather Channel.


Forecast Confidence: HighA return to more typical heat ... Scattered PM storms. Slightly cooler air arrives courtesy of the weak cold front that sparked storms in some areas yesterday evening. We'll see partly sunny skies with highs in the upper 80s to near 90, and still rather humid. With the front still in the area, scattered showers and thunderstorms are possible (40% chance) during the afternoon and evening, but probably not of the severe variety. Tonight, showers and thunderstorms may linger as temps head for lows in the low-to-mid 70s.


Forecast Confidence: Medium-HighWarm and humid. Although a few clouds associated with Tropical Storm Beryl (discussed later in this post) may make their way overhead, we should see more than enough sunshine to lift high temps to around 90. An isolated shower or thunderstorm can't be ruled out, but the chances are slight. Overnight, partly cloudy with lows in the low 70s.


Forecast Confidence: Medium-HighHeating up again ... PM storms? Southerly flow ahead of the next cold front pushes temps and humidity back up a notch, with highs climbing into the low 90s. The approaching front may very well touch off late-day showers and thunderstorms. Overnight, clouds and a few showers may linger, lows in the low-to-mid 70s.

The Weekend

Forecast Confidence: Low-MediumAn uncertain forecast. Friday's front may stall out across the Mid-Atlantic, and low pressure could develop along the front. The result could be shower and thunderstorm activity, especially late Saturday into early Sunday. However, the details are still quite sketchy. For now, we'll call both Saturday and Sunday partly sunny and somewhat humid, with highs in the mid-to-upper 80s and a 30% chance of showers and thunderstorms.

Tropical Wake-Up Call

Tropical Storm BerylThe tropical season, which lately had been quiet, came to life rather suddenly yesterday as Tropical Storm Beryl formed off the Carolina coast, about 160 miles southeast of Cape Hatteras, N.C. The eastern coast of North Carolina is under a Tropical Storm Watch. Tropical storm force winds may clip the Mid-Atlantic coast as the storm tracks north and eventually northeast.

Will Beryl affect the DC area? If the current forecast track holds, which I think it will, then impacts here will be minimal. Maybe a few strong breezes or a shower tomorrow for our outlying areas to the south and east.

Pictured: Visible satellite image of Tropical Storm Beryl, courtesy NOAA.

Going With the Outflow

Click for animationThanks to photographer Ian Livingston who pointed out this nifty radar animation posted yesterday on Eastern US Weather Forums. The feature to look for is the outflow boundary -- the arcing string of dark green pixels -- moving from east to west across the District.

Outflow boundaries are lines of clouds, which sometimes produce precipitation, created by winds flowing out and away from thunderstorms. When the relatively cool outflow winds run into warmer air away from the storm, the warmer air is forced to rise and a new line of convection may form. In this case, the outflow boundary was produced by a storm that popped up around 4:30pm yesterday in Prince George's County before quickly dissipating.

Pictured: An outflow boundary (circled in white) was visible on radar yesterday, courtesy Weather Underground.

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