It's just typical that fog kind of put a damper on the meteor watching, especially since so many nights in the Middle Atlantic area has been clear for the past couple of months. Not only has there been virtually no rain, but there hasn't been many cloudy or foggy periods. As I'm writing this, it's raining for only the second time this November. The only other rain this month occurred on November 3 when 1/100 of an inch of rain fell. Before that, the last measurable rain fell on October 16. So, in the past 35 days, including today's rain, less than about 1/10 of an inch of rain has fallen!

The record for the most consecutive number of days without any rain in Washington is 35, back in August and September of 1995. The driest calendar month in Washington occurred in October of 1963, when no rain at all was recorded. These conditions are pretty extreme, but it's not unusual for parts of the eastern US to experience short term dry spells (several weeks without any measurable precipitation). In fact, rain has been scarce in the Washington D. C. area during some portion of each of the last three years.

Forests are tinder dry in many places in the eastern US, and not surprisingly, wildfires have been a big problem in recent days in the Appalachian Mountains of Kentucky, Tennessee, Virginia, and West Virginia. With the temperatures being above normal this month and with the air containing so little water vapor, evapotranspiration rates are very high, and what little moisture that remained in the leaves has been sucked dry. Because of the extremely dry leaf litter on the forest floor, it only takes a spark for a conflagration to begin. Last week, in eastern Kentucky, the largest fires in at least a decade shut down schools and highways and sent a number of people to hospitals with breathing difficulty. Nearly 1000,000 acres of forests have burned in Kentucky this month and about 25,000 acres of Tennessee woodlands were up in smoke.

In parts of Florida, Alabama and Georgia, a severe drought has persisted for most of the summer and fall - farm ponds have shriveled and streamflow is in some cases just a trickle. Across much of the eastern US, the moisture in the soil has been almost completely spent. Fortunately there was sufficient rain during the growing season, except in the deep south, so that harvests have been, in general, rather bountiful. For farmers, it's a bonus to not have their harvest effected by soggy conditions, and although there's not much growing going on now, it's very important to have a reservoir of moisture available for crops in the early spring. If rain falls after the ground freezes, much of it runs off into streams and rivers and the soil doesn't directly benefit. After a long dry spell, it takes time for water to infiltrate down into the aquifers, but usually this process is expedited after the trees lose their leaves.

So what has happened to the rain this autumn? In the fall, when tropical storms and hurricanes don't come ashore, the eastern US can expect to experience dry conditions. That's what happened both this year and last. Not a single tropical system has hit the US mainland this fall. Even when tropical systems skirt our region, and we miss the strong winds, we usually pick up quite a bit of rainfall. But this fall, not a drop of the meager rains we've received has been attributed to a tropical storm or hurricane.

One reason why these storms have missed the eastern US and steered clear of our shores is because they were prevented from making landfall by dominant fair weather systems anchored over the US. The preferred position of the polar jet stream for the past couple of months has been in a more or less west-east orientation across the northern tier of states. Thus, on many days this fall, weather systems have moved across the US from the west and northwest to the east and southeast. Winds from this direction do not often bring much moisture with them and deter tropical systems that might otherwise want to move northwestward towards the US mainland.

Storms from the Pacific may drench the west coast with rain, but their moisture supply is well depleted by the time they make it to the east coast. While cold fronts moving across the Great Lakes will pick up some water vapor from the lakes, the eastern US rarely gets soaking rains from fronts moving in from the northwest. Most of the eastern US receives its precipitation from the Gulf of Mexico and from the Atlantic Ocean. Weather systems that might tap these water bodies have not yet developed this autumn - the positions of the polar and the subtropical jet streams have simply not favored their development. As a result, this has been one of three driest autumn periods in over 100 years in Rhode Island, Connecticut, New York, Pennsylvania, Delaware, Maryland, Virginia and North Carolina.

Although there really isn't a marked wet or dry season in the eastern US, precipitation can vary considerably from one month to another, from season to season and from year to year. At Baltimore Washington International (BWI) Airport, for example, the wettest month is August, averaging 3.92 inches, and the driest month is October, averaging 2.98 inches. The past couple of years we've experienced wet summers and dry autumns, whereas, in 1998 and 1999, the summers were dry and the autumn were wet. It's too early to attribute the shift in the weather patterns over the past few years to anything other than natural variability.

Hope you have a nice Thanksgiving!