With the Obamas in Martha’s Vineyard and the passing of Senator Kennedy, there hasn’t been a shortage of national news coverage of Massachusetts this past week. Nonetheless, tropical storm Denny is jockeying for attention as it makes its way towards Boston. Although there’s significant uncertainty in the storm’s track (and hence how much rain will fall here on campus), there is confidence in the prediction of the storms intensity. Because of the surrounding dry air, the upper-level convergence, and a southern shift of the jet stream, Denny will likely not become a hurricane.
A Little Bit of Everything
It’s becoming that time of year when terms like “pop up thunderstorms” or “hit-or-miss showers” are often found in the forecast. When one minute it is sunny, the next it can be pouring rain. As we transition to the summer season, if there is sufficient convection, moisture, and lift, this can trigger thunderstorms. Today’s chance of thunderstorms may make you wonder how there can be thunderstorms when it’s not that hot. This is because the convection from today’s scattered thunderstorms is “upside down.” Typically, convection is trigged from the strong heating at the surface. Instead, the instability here is from the cold air aloft. This too can drive buoyancy differences and help initiate thunderstorms.
Forecasting: Just Half the Battle
A TV meteorologist can make a perfect prediction, but yet, on days like yesterday, the public can be outraged by what they perceive as a “busted forecast.”
A Load of Pressure
Did you feel like there’s been extra pressure on you? Maybe it was due to all of your professors conspiring to schedule their exams all on the same week? While that could be true, it could from the air column above you exerting extra pressure instead. There has been a slow-moving high pressure system that has dominated the eastern half of the US. Over the last seven days, the sea-level pressure in Boston has averaged about 1025 millibars — roughly one to two standard deviations above normal. That system has moved well off the coast, but another one has already moved in to take its place. For those graduate students, MIT athletes and others stuck at MIT during spring break, the good news is that this system too will also be a slow-mover, so another rain-free stretch of weather is expected over the next seven days.
A Cold Winter — Now What?
Sure the calendar doesn’t say winter is over until March 20th. But meteorologists are impatient; they don’t wait until that date to close the chapter on winter. Instead, they consider December, January, and February (DJF) the winter months. (Meteorologists are also so impatient that the hundreds of weather stations across the U.S. have been programmed to report the hourly meteorological conditions seven minutes before the top of the hour.) With February coming to an end tomorrow, was the DJF temperature in Boston below average? You don’t need me to tell you that the answer is yes, but not as much as you might think. Surprisingly, December and February were slightly above-normal, while January was a whopping four and a half degrees Fahrenheit colder than normal. Thus, as a whole, DJF will turn out to be one degree Fahrenheit below normal.
Predictions of the Future and Never Materialized Scenarios
What would have happened if you went to Caltech instead of MIT? What would life be like if that hobby or activity you’ve spent years pursuing was never introduced to you? Just like in real life, the track of weather systems has a full spectrum of various, but plausible, scenarios, and we generally focus on what actually transpired. But every so often, we ask ourselves, what would have happened? What would have happened if I had asked that guy or girl out on a date? In the version of today’s weather the question is: what would have happened if the jet stream shifted less? For about 5 days last week, all weather models had a major storm debilitating the northeast today. Forecasts of three feet of snow and wind gusts in excess of 80 mph were plentiful.
Steady Blue (Clear View) and Democrats Too?
Can today’s weather affect the US election? According to an article in the June 2007 edition of the <i>Journal of Politics</i>, it can. In any election, rain and wind can impact voter turnout. Although there is likely a low correlation, there appears to be a signal in this study: rain benefits Republicans. Because democrats are more likely to live in urban areas, rain will impact Democratic “peripheral” voters more. The city folks are likely to have longer time outdoors, such as walking to polling stations, waiting for public transportation and in longer lines at urban polling places. As a result, these peripheral voters are presumably less inclined (or even less able) to go vote, and hence fewer democrats show up when it is raining. According to the study, for each inch of rain (above normal), the Republican presidential candidate received an extra 2.5 percent of the vote. So in a close election, rain can impact the election results.
Fronts, Friends, and Forecasting
There are all kinds of fronts in the weather world. The traditional ones are the cold and warm fronts. But there are also the occluded, stationary, polar, and arctic fronts. My favorite one is the so-called back-door cold front (yes, the words back and front are used to describe the same phenomena). What they all have in common is their depiction in separating two regimes. Its like an intervening friend who tells you not to go out with this person because he or she is simply trouble. In this case, the friend is the front, the one trying to separate the two parties.
Sunny September to Continue
When people ask “When’s the best time to visit Boston?” I smile and think to myself, “could they have asked an easier question?” September is certainly the best time. Climatologically, this is the month with the most number of sunny days. Combine that with the comfortable temperatures, this is the month where anybody would be able to enjoy the outdoors (OK, maybe not those pesky skiers). Excluding the effects of the two tropical storms, this September is no different. In fact, if you blindly believe the numerical weather prediction models, there will not be any rain for the next two weeks!
Thunderstorm Today, But Sunny Stretch to Continue
Welcome Class of 2012! From moving into to your dorm to outdoor events, the weather (so far) has shown its sunny side. The weather machine (the dome ball atop the Green Building) has provided five straight virtually cloud-free days. However, this afternoon will mark a short disruption to this pattern (a reboot), in the form of a cold front.
After 14 straight days of mostly sunny skies, dry conditions, and warm weather (remember that?), the streak came to an abrupt end yesterday. It was the longest such streak since mid-March 2006. While yesterday’s steady light rain was just a nuisance, today’s moderately heavy rain likely will dampen spirits (and the bottom of pants for that matter). The rain will last through the lunch hours, and by early evening, the last water droplets will likely come to an end.
There have been eight straight weekends in Boston with at least one drop of precipitation. This weekend will certainly be no exception. Although it is sunny during the daytime hours today, rain will be moving in later tonight. Not only will this possibly impact your Friday night plans, but due to the size of the precipitating region, this storm will also rain-in on your Saturday night activities as well.
Sunny Today But Wet Pattern to Continue
After yesterday’s rain storm, Boston is now over three inches above the normal liquid precipitation (3.3”) for all of February. Last year, there were only 2.2” for the whole month and only four cloudy days. This year, there have already been seven cloudy days. So what’s causing this unpleasant stretch of weather?
Whether you are an Obama or Clinton fan (or even a McCain supporter), there should be at least one thing everybody can agree on today: weather-wise, it’s a super Tuesday. Today features sunny skies, seasonably warm temperatures, and a light wind. If there were to be a vote for the best weather condition, I would argue today’s weather (OK, maybe a wee-bit warmer) would appease the largest number of people on campus. Slightly hotter would likely make anyone participating in an outdoor activity too sweaty and uncomfortable. If slightly cooler, some pedestrians may find the air has some bite.
Red Flagged and Chapped Lips
No, this is not about a dry-lipped freshman in danger of failing a class. Instead, it is in reference to yesterday’s dangerous fire weather conditions. Red flag warnings are issued by the National Weather Service (the so-called “real” meteorologists) when a majority of the following conditions occur: dry air, strong winds, and approximately 10 or more days without precipitation. We certainly had that yesterday. The first two can be attributed to yesterday’s strong vertical mixing. This “homogenizing” process “dragged” the air from 1 mile above towards the surface. Since the air above is almost always windier and drier, this caused the desert-like dryness (with relative humidity readings near 10 percent) and wind gusts of 35 mph.
Super High Fuels Record Warmth
Most were not here, or perhaps, some had forgotten. But last Thursday, while most of campus was relatively deserted, a -15°F wind chill reading was recorded at Logan
Persistence Presents Problems
There are at least five different strategies in forecasting. One could look at trends, e.g. today is warmer than yesterday, so tomorrow will be warmer than today. Another method would use climatology. For instance, tomorrow’s high would look at the maximum temperatures that occurred on that particular day of the year and take the average of that data set. Thirdly, a more sophisticated way is called the analog method. For example, one would recognize the current pattern with a similar one that happened in the past and expect the same result. The fourth method is using numerical weather prediction. Finally, the fifth strategy is called persistence. One would forecast the weather to behave as it is currently. For example, using this strategy, one would expect it to rain tomorrow, since it rained today.
Sunny Skies and Fall Foliage
Will today’s sunny skies help produce intense colors for the autumn leaves? Or is it the cold temperatures and the soil moisture that matter? While there is still some debate in the scientific community on the exact details, it seems to be a combination of the three. Cool temperatures (but not below freezing) and lots of sunlight in the preceding weeks help to kill the chlorophyll and setup the formation of anthocyanins, which create the sharp red and purplish colors our eyes are accustomed to seeing. Obviously, plenty of soil moisture will keep the tree “healthy” and help it hold onto its leaves. So with our somewhat rainy summer, sunny Septembers (climatologically the sunniest month of the year for Boston) and a rapid transition to cooler temperatures, the color intensity of our autumn leaves is one of the best in the world.
Comfort Is in the Air
While freshmen and first-year graduate students are likely being comforted by Orientation leaders and various MIT administrators, mother nature is providing comfort in her own way. Not only was it hot on Saturday, where Boston tied the all-time record high temperature of 96°F, it was also humid. Generally, dew point readings above 60°F is considered humid and over 70°F is oppressive. We topped off at 74°F Saturday afternoon, a reading normally observed near the Gulf of Mexico. Is it always this humid in Boston? According to the National Climatic Data Center, the average dew point reading in Boston is 62°F for August and a much drier 55°F for September.
No Warm-up in Sight
Even though Wednesday's Valentine's Day Storm is long gone, the low-pressure is leaving behind windy conditions. The system continued to strengthen over Nova Scotia yesterday causing the pressure gradient to increase and consequently the blustery conditions that will stay with us for another 24 hours. For any curious readers, the 2.5 inches of snowfall in Boston brings the total to 4.3 inches this season. (According to one TV meteorologist, the record lowest snowfall total for the entire season is 9 inches.)