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.

Showers Dampen Holiday Getaway

Very light showers moving through the Washington DC metro area this morning have raised humidities to summer levels. The persistent clouds, on the other hand, have suppressed temperatures somewhat, although by mid afternoon Dulles was 80° and Manassas was 82°. The clouds may also have the effect of suppressing the development of showers in the less-sunny areas.

Radar at mid afternoon showed an area of scattered showers extending from near Hagerstown southward to just northwest of Charlottesville with the heaviest activity in the southern portion of that area. These were all moving eastward, and showers or thunderstorms should become more numerous in the metro area late this afternoon and this evening. In the next hour or two, I-95 south of the Beltway is the most likely target.

Tonight and Tomorrow

Showers and possibly some strong thunderstorms are likely through this evening. Lows overnight will be in the low to mid 60s. Tomorrow will be partly cloudy with highs around 81 and somewhat lower humidity. For the rest of the holiday weekend, scroll down to Camden's post below.

DC: Dank and Cloudy (But Improving)

Yes, Virginia (and DC and Maryland, too), there was a sunrise this morning, but a pesky overcast kept temperatures suppressed until sunshine began to break out this afternoon. At Dulles, the temperature jumped from 66° to 71° to 75° from 1pm to 3pm. Humidity at the surface is also much more noticeable today, with dewpoints as much as 20° higher than yesterday.

Precipitation on radar at mid afternoon was mainly confined to a narrow band from southeast of Harrisburg across the head of the Chesapeake Bay to offshore of Ocean City. By late afternoon, there was a very small, but intense, cell in the vicinity of Williamsburg. All 3 major local airports reported merely a trace of rainfall, continuing the dry trend of this spring which has been broken only with a small excess of April showers.

As Josh explained earlier, what might have been a simple story of warmth building eastward from the center of the country into the Mid Atlantic area will be complicated by an upper-level low-pressure trough moving eastward just to the north of us.

Photo of today's sunrise by CapitalWeather.com photographer Kevin Ambrose

Tonight and Tomorrow

There is still a slight chance of a shower somewhere in the region through this evening. Otherwise, conditions will be dry and mild, but with increasing humidity and lows only down to the mid 60s. Tomorrow will be more summer-like with a mixture of sun and clouds and a 60% chance of showers or thunderstorms by evening; highs should be in the low 80s.

For the all-important holiday weekend forecast, scroll down to Josh's post below.

Tropical Topics

The official start of hurricane season is now a week away, and the National Center for Atmospheric Research (NCAR) has published a backgrounder page on their web site with lots of information on tropical cyclones. There are many links to further information for all levels of interest, from education for kids to the latest research results.

DC: Delightfully Comfortable

After some high clouds this morning, the Washington DC metro area is enjoying a beautiful late spring afternoon with sunny skies, northerly breezes, temperatures in the low 70s, and low humidity (dewpoints mainly in the mid 30s). As the high pressure currently dominating the Mid Atlantic region gradually slides eastward, temperatures will continue to warm and there is a chance for some much-needed showers tomorrow afternoon or evening.

Photo of yesterday's brilliant sunset by CapitalWeather.com photographer Kevin Ambrose

Tonight and Tomorrow

For tonight, increasing clouds will be accompanied by lows in the upper 50s in town to the low 50s in the colder 'burbs. Despite variably cloudy skies, tomorrow's highs should be near 80 with a 50% chance of showers by evening.

For the outlook Friday through the weekend, scroll on down to Dan's earlier post.

Political Science

The movie "An Inconvenient Truth" opens today in New York and Los Angeles and around the country through June. This documentary on climate change is based heavily on a presentation developed by former Vice President Al Gore to spread the word about this important topic.

Given the high visibility of the main actor and the polarized state of current politics, reports indicate that the slime machine has already geared up to trash the messenger. Fox "News" weighed in with a counter-documentary this past Sunday which featured only the very small minority of scientific skeptics. However, reporting from the Cannes Film Festival in today's NY Times, movie reviewer A.O. Scott says,

Appearances to the contrary, Mr. Guggenheim's movie is not really about Al Gore. It consists mainly of a multimedia presentation on climate change that Mr. Gore has given many times over the last few years, interspersed with interviews and Mr. Gore's voice-over reflections on his life in and out of politics. His presence is, in some ways, a distraction, since it guarantees that "An Inconvenient Truth" will become fodder for the cynical, ideologically facile sniping that often passes for political discourse these days. But really, the idea that worrying about the effect of carbon-dioxide emissions on the world's climate makes you some kind of liberal kook is as tired as the image of Mr. Gore as a stiff, humorless speaker, someone to make fun of rather than take seriously.

The movie gets good marks for its scientific accuracy from the RealClimate blog. Wonkette Ana Marie Cox has a review of the D.C. premiere in the online version of Time Magazine.

In DC, the film will be shown beginning June 2 at the E Street and Georgetown theaters. It will also be playing in the metro area at the Bethesda Row, Gaithersburg Rio 18, Shirlington, and Cinema Arts Fairfax. The AP reports, via USA Today, that the White House movie theater is not scheduling any showings.

The book tied in to the movie won't be released until June 13, but it has already risen to number 129 (up from 240 yesterday) on the Amazon.com bestseller list.

DC: Dry, Cool

We're back. After a week at the beach, PM Update returns to a dry, cool DC.

It's a rare day less than a week before Memorial Day in Washington DC when you need a long-sleeve shirt (sweatshirt in the shade) and SPF45 sunscreen to mow the lawn. It would take heavy clouds and an east wind to set a record low high temperature, but this morning's official low of 46° was only 1° above the record minimum for the date. (The record low of 45° for the 23rd happens to be the highest record minimum for the month.)

Even near the peak for the day, temperatures this afternoon are struggling to reach the upper 60s with a few locations on the southern fringe of the region making it to 70. The NatCast temperatures have been adjusted a bit downward accordingly.

The real story of coolness so far this May is in the cooling degree numbers. Using a benchmark level of 65° average temperature as the reference point for requiring air conditioning, only 4 days this month have met the criterion, and they were all within the first week.

Meanwhile, although temperatures will moderate in the next couple of days, the dryness of this spring continues; through today, the monthly precipitation is about 25% below average. The nearest rain on this afternoon's weather map is in central Florida.

CapitalWeather.com chart from NWS data, photo © Kevin Ambrose

Tonight and Tomorrow

Clear skies and light winds tonight should allow temperatures to drop again to the 40s in most locations: near 50 in the city to low 40s in the colder 'burbs. Tomorrow earns a well-deserved CapitalWeather.com Nice Day seal of approval: a few scattered clouds and high temperatures making it back into the low 70s with low humidity.

For the remainder of the week and the holiday weekend outlook, scroll down to Jason's post from yesterday. And if you haven't already, make sure to check out our Summer Outlook in Matt's post immediately below.