>Bermuda High heat pump to roast East Coast today

Like I expected, the thunderstorms yesterday that blew up on Chicago’s western horizon supressed what was going to become the hottest day of 2009 and since 2006 as outflow cut the heating process. This front responsible has pushed through and high todays will remain in the 80s rather than the 91 degrees set at O’Hare yesterday. I looked at the chart just before I went to bed and I didn’t think the thermometer would get above 91. Meanwhile I also pointed out that highs in Minneapolis would get no better than mid-80s, they got 84, so a pretty good guess.

DYNAMICS BEHIND TYPICAL SUMMER HEAT AND TODAY’S HEAT

Ok, as for today, the entire mass of hot, humid air has pressed east overnight from the Plains to east of the Appalachain chain and across the coastal plain and sets it’s sights on bringing the Eastern Seaboard it’s hottest day of meteorological summer. The core of high pressure is still centered over Georgia but other factors will play a role in bringing a hotter day than yesterday to the I-95. A warm front that was drapped across New Jersey yesterday seperated a warm, sunny, not so humid day from Philly to Boston but the front kept the southwest heat pump from entering the Northeast, today, the front has progressed northward, therefore opening the door to southwest winds which will pick up as the sun starts working on building the surface heat. As this heat builds at the surface, activating the clockwise winds circling the high pressure core, this will pump the heat that is centered over the Deep South right up the I-95 corridor making for likely the most uncomfortable day of the entire summer as humidities are right up at Caribbean and Gulf Coast levels all the way to Connecticut and Mass. I am talking about 70 degree dew points and an air mass that will warm into the low 90s today from Virginia to Massachussetts.

How hot it will be depends on a few factors

1) Strength of the high pressure

2)Location of the core and oreintation to the I-95 and coastal plain.

3) wind flow direction and strength, if you get a combination of very stronger upper-level high pressure, a clockwise flow that blows over and down the Appalachains from a west to southwest direction that enhances the already very hot air this is when you get 100 from DC to New York, usually DC is the easiest to make 100 and happens more regularly than Philly on north. The Virginia Mtns are closer to the DC metro area and therefore Washington gets more downslope enhancement than any other I-95 metropolitan area. Philly, Trenton, New York and up to Boston requires strong high pressure and even a front not far the the west which creates stronger winds that converge between the high and the frontal boundary straight into NYC to force the thermometer to 100 or better. Similar to Philadelphia. The Delaware at Philadelphia and Hudson, East and Harbor surrounding Manhattan, may play a cooling role but then again DC has Chesapeake Bay beside it, but the mountains closer to it’s west may allow less cooling.

Another major factor is when high pressure is strong and enough to produce upper 90s across the I-95, as the land heats, this activates the sea breeze. Sometime seabreeze can have a major moderating effect to the eastern suburbs of these cities.

What too expect today… The west to southwest flow will come off a high that is likely not powerful enough to first of all support heating of the air itself to the mid-upper 90s as well as force strong enough west, southwest winds to downslope and push all the way to the coast. West, southwest winds hower is transporting enough heat but will not enhance the warming, it is simply the case to why so hot today. DC may be the only place that’s influenced by downsloping off the Virginia Mtns as a west wind will blow across eastern Virginia, across the metro DC area and over the Chesapeake to the Delmarva. A stunning day for the beach. DC is also nearer the core of high pressure, therefore another reason behind warmer temps.

Two other areas that can boast higher temps is Newark and LaGuardia as they both have a highly urban environment. Newark is also “west” of the city and slightly more inland, meaning hotter air temps are often found here. LaGuardia’s runways likely pump the thermometer higher there and all that daytime heating is retained and released to warm the nightime air to unusually high levels like we saw in August 2006 when the nighttime low only fell to an astonishing 87 degrees. Purely because of concrete retaining 102 degree after heat long into the night. It was said to be 91 degrees still at 1am. Many areas of DC, Balt, Philly, NYC and Bos all see hotter nights than surrounding country and therefore new nighttime lows are more common than new daytime highs because of urban expansion. 80 degree nights aren’t unusual when days warm to the upper 90s. High humidity also plays a factor in keeping nights warmer.

I even question heat cooking polutants that thrive on those hot, sweltering days. Mass traffic running up and down the I-95 build up a thick brown layer of pollution, restricting visability, creating breathing problems and even poor views on top of tourist attractions. I remember driving past NYC and Philly and hardly being able to see the skyline just a few miles away because of the vast build up of ground level ozone due to large volumn of traffic and not forgetting vast amount of planes flying in and out of the major airports. Home to 55 million, this is one of the busiest and most congested regions on the planet.

Central Park, central to Manhattan island. Why not so hot? Plain and simple. The lush vegetation brings cooling to Central Park, plants and greenry shed moisture and keep the air cooler as well as the plants and trees lack of ability to absorb heat, unlike concrete.

Sometimes a high will not bring up as much humidity as others and that can be mainly down to it’s position to the Northeast, wind flow might not come from the southwest, therefore not tapping the Gulf or Atlantic, therefore if strong enough, the cities and coastal plain may be able to heat more so because of lesser amounts of water vapor, which often restricts the sun’s heating of the surface as some of it’s energy is diverted into evaporating those water molecules rather than heating up the ground.

So, long and short, despite it being a hot, humid and likely soupy afternoon with plenty of ground level ozone, it’s not going to be near as hot as past years. DC will take a run at the century mark this afternoon, and Baltimore coming a close second with 97, Philly will make 93, Newark 93, LaGuardia 91 and Boston 89. As for Central Park, it will be a very close call as to whether they will actually hit 90 for the first time this summer or will is wait for another time? I call for a high of 90 there but wouldn’t be surprised to see an 88 or 89 there.

Thunderstorm Activation

Several factors can play into thunderstorm development so long as the atmosphere isn’t “capped” and heated aloft, several factors can play into producing storms.

1) a little disturbance floating within the general flow of the mid-upper levels can be the energy source that can activate thunderstorms when the sun warms the surface and stirs the thermals, forming cumulus which build vertically into towering cumulonimbus towers.

2) The atmosphere even during blistering hot days can form clouds, despite a “capped” atmosphere with puffy fair weather cumulus dotting the sky and surface temperatures into the mid and upper 90s, some isolated pop-up thunderstorms can blow up, when surrounding areas are high and dry.

3) A nearby frontal system is a major activator to strong thunderstorms as this energy source and air mass divider slides straight into a sweltering hot, humid air mass, often these types of storms are fast movers and therefore produce tremendous rainfall, dangerous and violent lightning displays and damaging straightline winds, often cutting power and bringing down trees etc.

4) Sea breeze thunderstorms, when hot air builds and starts to rise, inland. Cooler ocean air moves inland creating not only a cooling along the coast, but haeted land and cool ocean air can meet and is forced to rise and form thunderstorms.

Pop-up, isolated thunderstorms are most common when Bermuda high pressure dominates the East Coast and brings sweltering heat, thermals are activated as the land heats, but by capping the atmosphere, which is when strong ridging takes place, thunderstorms will not form inland but sometimes where cool waters lie, this can be enough to form storms.

Thanks for reading. Stay tuned for more updates later.

-Mark