Stormys Weather
Insight into DC Winter Weather Forecasts
Q.  "I'm familiar with wind chill and heat index figures, but how about moisture and/or daylight vs nightime impacts on temperatures? It certainly feels a lot colder if it's dark and the air is wet. Is there an index or forumla of some sort that addresses these other factors?"

A.  There are several additional indexes you don't normally get to see through the media.   The best index to cover your question is the THWS index, which takes into account the Temperature, Humidity (moisture), Wind (cooling/chilling), and Solar Radiation (Sunshine/Warming).   I have included that index on the real time weather page, located just under the current wind direction guage.  In addition, there is a "comfort" calculation, which is displayed...which works in a general sense, but "comfort" is usually in the eye of the beholder.   Thanks for the question!   Stormy

Q.  "How do I use the RSS feature on the front page?"

A.  Rather than "push" e-mails out to a list of members, we decided to use a "pull" approach where the information, via this web site, could be more easily viewed, along with more graphics and the addition of a blogging/interaction capability when and if a winter weather system came into our area.   So...we'll use the RSS (Really Simple Syndication) feed instead.   Most browsers and e-mail software systems today let you "subscribe" to an RSS feed.   Depending on how the feed is set up, it will generate a message on your system letting you know something has changed or been released.    For the time being, Stormy will use only one RSS feed for the site:

Your browser/e-mail will ask for this address when setting up a feed.   Should conditions/forecast change we will add a new "headline" to the feed, which will give you a heads up something on this website has changed, and may be worth looking at.  We won't actually send the new info...merely a notice of change...a way to have you "pull" the information rather than taking the bandwidth to "push" it out to the list of subsribers.    Give us feed back on this approach.   I can pull this with firefox, but unable to get it through Windows Live Mail at this point.  Stormy

Q,  "What is a Heating Degree Day or Year?"

A.  Degree-Days  --- stolen from the web

Freezing winter weather or a long, sweltering summer--either one can increase your utility bills. But how much of the rise in the cost is a result of the weather? You can find out by using a unit of measure called the"degree-day."

A degree-day compares the outdoor temperature to a standard of 65 degrees Fahrenheit (F); the more extreme the temperature, the higher the degree-day number. Thus, degree-day measurements can be used to describe the effect of outdoor temperature on the amount of energy needed for space heating or cooling.

Hot days, which may require the use of energy for cooling, are measured in cooling degree-days. On a day with a mean temperature of 80 degrees F, for example, 15 cooling degree-days would be recorded (80 - 65 base = 15 CDD).

Cold days are measured in heating degree-days. For a day with a mean temperature of 40 degrees F, 25 heating degree-days would be recorded (65 base - 40 = 25 HDD). Two such cold days would result in a total of 50 heating degree-days for the 2-day period.

By studying degree-day patterns in your area, you can evaluate the increases or decreases in your heating or air-conditioning bills from year to year.

For the Stormy real time page...the algorithm is a little more complex.   Rather than wait until the end of the day to determine the mean temperature, the program Stormy uses is integrating values over minutes instead  of's a little more accurate.  A degree-month, or degree-year, as shown is merely the summation of those values over that time period.  A heating degree year is for the heating season...July 1 to June 30 the following year.  It's a way to determine how hot or cold a season was compared to an average value.   Stormy uses 65 degrees for both computations (hot/cold)

Q, "What are those airport charts?"

As you have probably heard Stormy speak about "translating" weather information into relevant operational information, this is the beginning of a Stormy winter experiment to predict airport performance based on the weather information.   The white line (usually near the top) represents a forecast in time of how the airport will perform as the weather changes.    Winds, precipitation, type of precipitation, and the "heaviness" of the snow are all modeled in this experiment.   We'll add a few more airports in the northeast over November and December and then monitor how well it works.   From a color point of view you would expect 1 hour delays in the purple band, 1-3 hour delays in the yellow band, and increasing probabilities of cancellations as one moves into the red band.   The bottom greenish band gets into airport closure predictions.   Obviously, we expect our forecast to remain near the top of the chart, but we want to examine the predictability out to 100 hours in order to "prepare" the system.  We'll try to update these twice a day....but every hour is possible.