Friday, June 23, 2006

Drought Busters

Tonight and Tomorrow

Forecast Confidence: Medium-HighThere 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.

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. 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").

Thursday, June 22, 2006

Air You Can Wear

Tonight and Tomorrow

Tonight will be warm and humid, with lows only in the mid 70s downtown, near 70 in the 'burbs. The chance of thunderstorms through this evening is 20%. Tomorrow will again be warm and humid, but more cloudiness will keep highs around 87. The chance of thunderstorms, especially in the late afternoon and evening, is 60%.

For the extended outlook, see Josh's post below.

The remnants of some storms which had deluged parts of Ohio yesterday moved through the Washington DC metro area this morning, limiting early temperature rises. The breakout of sunshine, however, has pushed the muggometer setting to "Sticky". The most oppressive readings are in the southern fringes of the region, where Fredericksburg and Stafford have reported heat indices over 100. Both of these stations, along with Culpeper, reported temperatures of 99° at 4pm.

On this anniversary of the drenching from the remnants of Agnes in 1972 (see Today in Weather History to the right), we finally have a chance over the next 5 days to put a serious dent in the area's precipitation deficit, especially if a possible tropical tap develops. Scroll down to Josh's earlier post for details.

A Finger in the Dike

The experience of New Orleans with Katrina has created greater awareness of the threat of flooding from tropical storms. Yesterday's WaPo had an article, "An 800-Pound Gorilla Waits to Escape in S. Florida", which described the risk of flooding from a breach of the dike around Lake Okeechobee in southern Florida. The dike, originally built in reaction to a devastating flood from a hurricane in 1928 which killed over 2000 people, has deteriorated according to a recent engineering study. The Palm Beach Post published an earlier special report on the subject, including a number of web extras and links to related stories.

Tuesday, June 20, 2006

Praying for Rain

Tonight and Tomorrow

Lows tonight will be near 70 in the city, down to the low 60s in the cooler 'burbs with moderate humidity. Tomorrow will be sunny with highs near 89 and increasing humidity.

For the extended outlook, see Jason's post yesterday, and check back for Dan's post tomorrow.

Be careful what you wish for. With the Washington metro area needing rain to help close a widening precipitation deficit this year, some places got more than they wanted yesterday. Matt showed a radar picture of the total precipitation in his earlier post. Here is a wider regional view from the National Weather Service experimental precipitation analysis. The heaviest precipitation of 1.5" and above (yellow and gold areas) extended from just south of the District across central Prince George's County and eastward to the middle of the Chesapeake Bay and the Eastern Shore. Most of Montgomery County outside the Beltway, on the other hand, had 0.10" or less.

New Reign Begins

Here's someone who probably knows how to seriously pray for rain. Before this week, it's not likely you would have seen "Episcopal" and "oceanographer" in the same sentence. Katharine Jefferts Schori is not only the first woman elected to head the Episcopal church in the U.S.; she also has a doctorate in oceanography, making her the first earth scientist to hold that office. Her specialty is critters rather than currents, however. She studied oysters and squids and worked for a while for NOAA's National Marine Fisheries Service.

Monday, June 19, 2006

Some Showers and Storms in the Area

A line of showers and some thunderstorms moved through the Washington DC metro area from about 4-5pm. Some places had moderate to heavy downpours, while others received little or no rain. Official amounts ranged from 0.02" (Dulles) to 0.10" at National and 0.21" at BWI, where rain is continuing.

A smaller area of storms is now moving northeastward toward the western suburbs, and could reach the downtown area around 6pm. Scattered showers are still possible through the evening, but activity will likely diminish after this next batch. You can track the storms with the radar loop from WJLA-TV.

See Jason's post immediately below for the forecast through the rest of the week.

Seasonal Outlook

Latest seasonal forecast: Click here.

Latest 3-month temperature outlook from Climate Prediction Center/NWS/NOAA.