Wednesday, March 23, 2005
Raining on Mickey
Dan Stillman @ 12:30 AM
The D.C. area will wake up this morning to a good ol' fashioned soaker. It's been a while since we've had a wash out of a morning like this, so expect a difficult rush hour thanks to those who have "forgotten" how to drive in the rain.
Today: Rain should remain fairly steady at least through early afternoon, then becoming more showery in nature later in the afternoon and evening. Windy throughout the day with temperatures in the mid-40s.
Tonight: We'll keep a chance of scattered showers until around midnight. Otherwise, cloudy and misty with lows in the mid-to-upper 30s.
Tomorrow: Still cloudy, but with a couple breaks of sunshine possible during the mid-day and afternoon hours. The dry weather and highs in the lower 50s might be just nice enough for a trip over to the Woodrow Wilson Plaza at the Ronald Reagan Building to check out the 75 Mickey Mouse statues on display.Tomorrow night: Clouds increase again ahead of the next storm system, but it should remain dry for Purim revelers. Lows in the upper 30s to near 40.
Friday: A decent chance of some more rain, but doesn't look like a wash out. Highs in the mid-to-upper 50s.
The Weekend: Saturday has the potential to be pretty darn nice -- partly sunny with a high near 60, maybe even into the lower 60s. As for Easter Sunday ... you guessed it: looks like more rain.
Hail to Early SpringThe first day of spring took the area by storm on Sunday as pea- and nickel-sized hail came down in parts of Northern Virginia. In some ways, it's actually easier to get hail now than it is later in the spring and summer. That's because cold air aloft, leftover from the winter, extends closer to the surface during early spring.
Hail forms in thunderstorms as water droplets are carried upward by strong vertical winds into below-freezing air. There are several factors that affect hail formation, but freezing level is one of the most important. When the freezing level is relatively close to the ground, as is typical this time of year, water droplets have a shorter distance to climb before they reach the cold air. A shallow freezing level also means less time for a hailstone to melt as it falls to the ground.
The graphic above shows the temperature (right black line) and dewpoint (left black line) versus height on Sunday. Just to get your bearings, the vertical graph lines represent temperature in degrees Celsius, as labeled along the x-axis, while the horizontal graph lines represent altitude, as labeled along the y-axis (ignore any diagonal lines). The red arrow marks where the temperature drops below freezing (0 C), which occurs at an altitude of approximately 1500 meters, or about 5,000 feet. For comparison, typical summertime freezing levels are substantially higher -- around 10,000 feet.
So how do we get hail during the summer with such high freezing levels?
Warmer summertime temperatures serve as the equalizer. They can trigger more instability in the atmosphere than cooler, springtime temps, causing air within thunderstorms to rise higher.
Photograph courtesy of the Ronald Reagan Building and International Trade Center; Graphic courtesy of the University of Wyoming
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