Thursday, April 14, 2005

Play Ball!

Nationals vs. Arizona Diamondbacks, 7:05pm on April 14, RFK
Winds will be northeasterly from 10 to 15 mph, diminishing during the game. Temperatures will be about 65 when the gates open, but expect them to drop steadily after sunset at 7:44 from the game-time level of 58 down to the lower 50's by the 7th-inning stretch and into the 40's on the way home. Go Nats!


Today's weather map shows a weak low pressure area moving away from the North Carolina coast and high pressure dominating virtually the entire country east of the Rockies. The only precipitation showing on national radar in the eastern two-thirds of the U.S. is an area of lingering showers in the eastern Carolinas. Under brilliantly sunny skies, temperatures are rising from an official low of 42 through the 50's at mid-day toward highs in the mid 60's. Some of the outlying areas were down into the 30's last night with Frederick at 37, Dulles at 39, Culpeper at 33.

Under clear skies, temperatures should drop to near 40 tonight. Tomorrow should be slightly cooler with highs around 60.

Baseball and the atmosphere

Images (click to enlarge): Magnus force, from American Scientist

The May-June issue of American Scientist has an article on "Predicting a Baseball's Path". It explains how the spin of a baseball pitch interacts with the air through the "Magnus force" to affect the ball's motion. A ball moving through air has a turbulent wake behind it. The direction of spin affects the location of the "separation points" where the air flow becomes turbulent. In the case of topspin (movement of the top of the ball is in the direction of the pitch), the upper separation point is deflected upward, so the air in the wake has upward momentum. By the law of conservation of momentum, the ball must move downward. Conversely, a ball with backspin will move upward. By controlling the axis of rotation of the pitch, the pitcher can determine the direction of deflection of the ball.

Wednesday, April 13, 2005

Good afternoon, Charlottesville


Last night's rain showers were widely scattered and mainly confined to the south of the Washington metro area. The official rain bucket collected a minimal 0.01". As a weak low pressure area moves slowly off the Carolina coast, skies have cleared in the area. Temperatures were into the upper 50's by noon and lower 60's at 2pm. Here on the admittedly non-standard CapitalClimate Weather Patio, it's 65. In southern Virginia, where clouds and some light rain prevail, temperatures are only in the upper 40's.


Under mainly clear skies, temperatures should be in the low 40's tonight, with highs tomorrow near 60.

Nationals vs. Arizona Diamondbacks, 7:05pm on April 14, RFK
Outlook for the Nats' home opener: Light, mainly easterly breeze at game time; temperature 54, falling to about 50 by the 7th inning stretch. No rain!

Founding Father, Monticello Meteorologist

Today is the 262nd anniversary of the birth of Thomas Jefferson. The third President of the United States was a dedicated weather observer, recording the temperature at Monticello every day at dawn and at 4pm. He also recorded wind direction and speed and precipitation. The Washington and Jefferson Snowstorm of January 27-28, 1772, was so-named in recognition of the fact that it was recorded by both future presidents. Jefferson, who had just returned from his honeymoon, reported a snow depth of about 3 feet. According to David Ludlum's "Early American Winters", this was "the greatest snowstorm in the history of the middle and lower Potomac Valley." In 1776, Jefferson began to recruit volunteer weather observers around the state of Virginia. This was the forerunner of today's Cooperative Weather Program. The Thomas Jefferson award is the highest award for volunteer weather observation. No more than 5 of these awards are presented each year for "unusual and outstanding achievements." As President, Jefferson also created the Coast Survey (now the National Geodetic Survey), the country's first civilian scientific agency and the oldest component of what is now NOAA, the National Oceanic and Atmospheric Administration.

Current conditions in Charlottesville:
Clear skies, temperature 58.

Monday, April 11, 2005



The Washington metro area enjoyed a three-base hit today, as the picture-perfect spring weather continued for a third day. Despite a northeasterly wind behind a cold front which moved through from the north overnight, a sunny sky pushed temperatures to near 70 or a bit above by mid afternoon. The only cool spots in the region were those with cold-water influences: Ocean City was at 50, and Annapolis was 59 at 3pm. The regional radar is clear. In fact, the only precipitation in the eastern half of the country is in the Gulf States ahead of the low pressure area which brought nearly 2 feet of snow to eastern Colorado and closed 200 miles of I-70 over the weekend.


The cooler air which is now moving in over us will be reinforced by the strong "meridional flow" pattern which we are in. As the pattern continues through the week, we can expect cool and damp conditions, as described by Jason below. Expect lows tonight in the low to mid 40's and highs tomorrow in the mid to upper 50's with increasing cloudiness.

Blog log: Vote early and often!

The WeatherBug Storm Chase 2005 blog has narrowed down the field to 3 contestants to go storm chasing with them. Read about the 3 candidates, and then cast a vote for your favorite.

Broadcast news

The radio Weather Talk guys Justin Berk and Tony Pann have launched a web site in connection with their show. The first show was yesterday afternoon. If you listened, tell us your impressions of the show in the comments section (link below). I suspect that for at least some parts of the DC area, reception for the Baltimore station will be weak at best. In west-central Montgomery County, I could tune it in only on the upstairs clock radio at maximum volume.

Nationals vs. Arizona Diamondbacks, 7:05pm on April 14, RFK
See Jason's post below for a preview of the conditions for the Nats' home opener Thursday night, and watch this space for updates during the week. The blogger gods willing, we'll have a last-minute update Thursday afternoon, so you'll know what to wear and whether to bring your brolly. (Hopefully, umbrellas won't be banned if they're necessary.) One thing we can be confident of at least: With a 7:05 starting time, you won't need sunscreen.

Seasonal Outlook

Latest seasonal forecast: Click here.

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