Drought Busters

Tonight and Tomorrow

There is a Flash Flood Watch in effect for the entire DC region which has now been extended from 8pm tonight through Sunday morning. Conditions will be mostly cloudy and humid with an 80% chance of showers or thunderstorms tonight (mostly after 7pm) through tomorrow. Lows overnight will be in the low 70s, and tomorrow's highs will be in the low 80s.

For the outlook through Sunday, including weekend event forecasts, see Camden's post below.

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Last night's late thunderstorms put on a spectacular light show in much of the Washington DC area, but heavy rain was again, like Monday, mainly limited to southern portions of the region. National picked up 0.71" of rain, and Dulles had 1.51", most of which fell in one hour. This was more than enough to set a new record for June 23 at Dulles. Most of the Maryland suburbs north of the Beltway, however, had very light amounts.

This afternoon's activity has been concentrated around the lower Potomac, Northern Neck of Virginia, and the Eastern Shore. Salisbury MD has had over 2.6" of rain, and Wallops Island VA was walloped with just under 3" in one hour. The heaviest storms are now slowly working their way into the Virginia Tidewater area.

As a cold front approaches and stalls out over the Mid Atlantic region, showers and thunderstorms are likely through tomorrow. As noted above, there is a Flash Flood Watch in effect for the entire area through Sunday morning. Rainfall amounts are expected to average 2 to 4 inches, with locally higher amounts. For an example of what 5"+ of rain can do in the wrong place, check out the photo of the parking deck at the Crabtree Valley Mall in Raleigh during a recent flash flood. Note the 7-foot clearance barrier.

CapitalWeather.com photo by Sarah Scolnik

Climate Corner

The National Center for Atmospheric Research (NCAR) yesterday announced the results of a study by NCAR scientists Kevin Trenberth and Dennis Shea on trends in Atlantic sea surface temperatures (SSTs), which have been associated with increased tropical storm activity. The researchers found that global warming explained 0.8° of the rise in tropical Atlantic SSTs, but the so-called Atlantic multidecadal oscillation (AMO) accounted for only 0.2°. This raises serious doubts about theories proposed by Colorado State's William Gray, among others, that the recent increase in hurricane activity is due strictly to the AMO.

The NCAR results are consistent with an article, "Atlantic Hurricane Trends Linked to Climate Change", (subscription required) in the June 13 issue of the American Geophysical Union publication EOS. The article, by Michael Mann of Penn State and Kerry Emanuel of MIT, describes a statistical (regression) analysis of tropical Atlantic SSTs. The authors conclude:

In short, there is no evidence that a natural climate oscillation such as the AMO contributes to long-term tropical North Atlantic SST variations.

In fact, they find that the apparent effect of the AMO may actually be the result of a partial masking of the global warming trend by aerosol cooling effects ("solar dimming").