top border

Please note, not all links may be active. This site is a snapshot of an earlier time.

Cooling Down Toward an Uncertain Weekend

Dan Stillman @ 12:30 AM

Snow Lover's Crystal Ball

Next Chance of Snow: Saturday PM (30% chance); Monday (25% Chance)
Potential Impact: Saturday PM; Monday

Commentary: A lot of uncertainty with both of these events. Precipitation looks like a pretty good bet from the first one, but it could be more rain than snow. The second event is a coastal storm and has the potential to be more of a blockbuster, but depending on the exact track it could be an all-or-nothing situation for the Washington area. More details are provided in the forecast below.

Forecast in Detail

Today: Partly cloudy early, then clearing skies in the afternoon. Breezy with a high in the mid 50s. Tonight: Clear with diminishing winds. Lows in the mid 30s in town, upper 20s in the 'burbs. Tomorrow: Partly cloudy with a high near 50. Tomorrow night: A cold front will kick up winds from the northwest. Look for a low around 30. Friday: Cold and windy with partly sunny skies and a high only in the low 40s.

It's shaping up to be an eventful first weekend of December. Clouds will thicken during the day on Saturday as temps reach a high in the low-to-mid 40s and an area of precipitation approaches from the southwest. A first guess at timing would be for precipitation to break out Saturday night, possibly starting as snow before changing to rain.

As one storm departs on Sunday, it sets the stage for a possibly more significant wintry threat on Monday. Like the first, this next storm will also be approaching from the south -- the source location for many of Washington's biggest snowstorms. The current track favors snow over rain, but it is still quite uncertain at this early stage, and even a complete miss is possible.

The Uncertain Art of Hedging

An interesting story from the Seattle Times talks about an experimental University of Washington forecasting system soon to be made public over the Internet. The system will provide probabilistic predictions of certain weather conditions -- like the percent chance that temperatures will drop below freezing on a given night -- rather than the more traditional deterministic forecasts that express a meteorologist's best guess. has embraced the trend toward probabilistic forecasting and describing the amount of uncertainty associated with a particular forecast. In advance of winter storms, we sometimes post probability graphs or pie charts showing the percent chance of various outcomes. And just recently we've incorporated a confidence level indicator into all of our forecasts (see earlier in this post for example). To be fair, many of the local TV mets have also done a good job over the past few years at qualifying how confident they are in their forecasts.

We're interested to know what our visitors think about the idea of expressing forecast confidence and uncertainty. How much hedging is too much hedging? And when are words better than numbers. For example, when talking about the chance of rain or snow, do you prefer descriptors like "slight," "decent," "pretty good" and "likely," or do numerical expressions such as "chance of snow 40 percent" or "1-in-3 chance of seeing a shower or thunderstorm" speak more to you?

The Tropical Season That Just Won't Die

Tropical Storm Epsilon, the 26th named storm in the Atlantic this season, is expected to slowly strengthen but fall short of reaching hurricane status. As of last night, Epsilon was moving west toward Bermuda, but is expected to turn north and then northeast, away from any land masses. The 26 named storms in 2005 shatters the previous record of 21 in 1933.

Global warming alarmists will tell you the large number of storms is evidence that humans are negatively influencing the Earth's weather and climate. Global warming skeptics will point out that our recordkeeping only goes back to the mid-1800s, and that some storms may have gone unnoticed before the first weather satellite was launched in 1960.

No matter which side you're on, there's no arguing this has been a helluva of a year for the tropics. Today -- the last day of November -- is the traditional end of the tropical season. But considering the season we've had, I don't think anyone would be surprised to see it continue into December. Since 1944, December has seen a total of four tropical storms and two hurricanes, none of which made landfall in the United States.

Comments are closed for this archived entry | Link | email post Email this post