Breaking the Dry Spell?

The two essential ingredients for showers and thunderstorms are moisture and vertical motion. With dewpoints at the ground from 68° to 72°, there is plenty of moisture around. The vertical motion for yesterday's storms was provided mainly by heating: a threepeat in the form of a third consecutive day of 90°+ temperatures.

Today is a somewhat different story, since a persistent high overcast has limited temperatures, at least by mid afternoon, to the low 80s. (This overcast, which has nevertheless allowed a fair amount of strong June sun to penetrate, led to forecasts for today ranging from 76 on a certain cable channel to 80 from the local NWS. For a check on how PM Update did, scroll on down to here).

Vertical motion is being helped today by a nearly stationary front draped across Pennsylvania. Therefore, more widespread storm activity is possible late this afternoon and through tonight. The NWS has issued a flash flood watch for Washington DC and the immediate area. By mid afternoon, radar was showing storms widely scattered from near Hagerstown to southwest of Richmond. These were generally moving northeast.

Tonight and Tomorrow

Showers and thunderstorms are likely late this afternoon through tonight. Some locally heavy downpours could produce flash flooding. Lows will be in the mid to upper 60s. Some showers may linger through early afternoon tomorrow, especially in the eastern portion of the region, with gradual clearing later in the day and highs in the mid 70s.

Yesterday's Rain

The map from the NWS of total precipitation centered roughly on DC shows that yesterday's rainfall was quite disappointing in much of the metro area. Except for a very small portion of far western MoCo where amounts were as high as possibly 2.5", most of the area saw 0.1" or less, and large portions of the District and adjacent Virginia were completely dry. Official DC reports were a trace at National and a whopping 0.02" at Dulles. BWI, which benefited from stronger storms in the Baltimore area, had 0.24". Amounts were also higher over the Bay and large portions of the Maryland Eastern Shore.

Climate Corner

The climate change documentary, "An Inconvenient Truth", which opens today in several area theaters, is reviewed in today's WaPo Style.

Muggy; Thunderstorms Possible

A ridge of high pressure is weakening over the Mid Atlantic area, but the setting is still at "steamy" on the muggo-meter in the Washington metro area. Dulles had reached 90° by 2pm, but National was still no higher than 89° at 4pm. Dewpoints around the region were mostly in the upper 60s, with some at 70° or above.

In a pattern similar to yesterday's, showers and thunderstorms, some of them heavy, have broken out in the mountains to the west. In spite of very weak steering currents aloft, these do have some eastward motion. At post time, they had begun crossing I-81 in Virginia. The heaviest storms were mainly west of Winchester.

Some of these storms may make it as far as at least the western suburbs by this evening. Isolated storms could also break out at any time. At 4:16, the National Weather Service issued a Special Marine Warning for a small, but strong, thunderstorm moving slowly eastward over Baltimore harbor.

Tonight and Tomorrow

Tonight will be warm and humid with a 40% chance of thunderstorms through this evening, especially to the west of the District. Some storms may be severe, and locally heavy downpours are possible. Lows will be from the upper 60s to low 70s. Tomorrow will be mostly cloudy with showers or thunderstorms likely and highs in the low 80s.

DC AC

Move directly to summer. Do not pass "Go." Do not collect $200. It's air-conditioning season in the Nation's Capital region today as temperatures have soared into the 90s by early afternoon. Unlike the beautifully dry conditions over the holiday weekend, humidity is also high.

Several locations in the region with dewpoints in the 70s were reporting heat indices over 100 as early as 2pm. By 4pm, Dulles had reached 95° and National and BWI had hit 94°. The robo-observer at Frederick checked in with 97°. The highly non-standard exposure here at Afternoon Blog Central in Montgomery County briefly touched triple digits.

Temperature chart at 4pm today from Unisys

A more easterly flow should knock temperatures back into the upper 80s tomorrow, but humidity will remain sticky. For tonight, keep the AC cranked high as you enjoy the waning hours of cheap electrons before the Pepco rates ratchet up 39% in Montgomery and Prince Georges Counties at midnight tomorrow night; BGE rates will go up 72%.

Tonight and Tomorrow

Tonight's lows should be near 70 in the city to the mid and upper 60s in the 'burbs. Tomorrow will be partly cloudy and continued humid, but with highs only in the upper 80s.

Political Science: Irony is Not Dead

Joel Achenbach's cover article "The Tempest" in Sunday's WaPo Mag is a lengthy (7500 word) exploration of the skeptic mindset in the realm of climate change. It focuses mainly on Colorado State hurricane researcher, general curmudgeon, and DC native William Gray. Achenbach, whose expertise seems to be more in the area of political science than physical science, gives a fascinating view of the power of faith. In spite of the mounting evidence, Gray is seemingly unable to see the cruel irony in vehemently rejecting climate models as a hoax because models can't predict the details of the weather next month, while at the same time his own reputation rests on the statistical modeling of the number and intensity of hurricanes in a season, even though his models can't predict the details of any individual storm.

A transcript of this morning's interactive discussion with the author is available online.