The science behind sea breeze fronts

We have all been there before: A warm summer day is rudely interrupted by a sudden wind shift accompanied by cooler temperatures. Sometimes, clouds move in and sky conditions turn overcast. Other times, strong thunderstorms suddenly develop. No matter what the situation, a sea breeze causes a disruption in an otherwise pleasant and warm summer day. Originating from our local ocean waters, these temperature and wind shift boundaries are the center of many difficult forecasts.

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Jet Streaks and Upward Vertical Motion

Good afternoon, everyone! We are starting a new series of videos called “Weather Education”, where we give educational videos regarding some of the commonly used meteorological terms we use to make forecasts. We detail what these terminologies mean, and how they are applied in weather forecasting. Anything from how to read a forecast sounding, how to forecast banding of precipitation, how does a low pressure form and deepen, temperature advection, frontogenesis, the differences between an extratropical and tropical cyclone, forecasting severe weather, and much more will be covered!

Today’s debut video will focus on one of the more classic topics in synoptic meteorology: jet streaks and upward vertical motion. Often times in looking for areas where lift will be enhanced for precipitation, low pressure formation, and even thunderstorms, we look to see where localized wind maximums in the jet stream — or jet streaks — are located. And from there, we look to see where a certain region is relative to these jet streaks. The above video details why jet streaks are so important, why certain regions of the jet streak favor rising or sinking air, and how these jet streaks were crucial in the formation of the Blizzard of 2016 and Hurricane Sandy.

We hope you find this video informative! We are really excited to debut this video series, and hope to continue these videos pretty often. Any feedback is greatly appreciated, as well as suggestions on other topics you guys would like covered!

Forecast Soundings and Radiational Cooling

850mb temperatures are only around average or slightly below average. There is a large Southeast ridge with positive 500mb height anomalies. The previously large North Pacific block that generated our cold and snow last week has been replaced by negative height anomalies, cutting off the US from any cold airmass. So why is it so cold tonight? What it essentially comes down to is surface high pressure and radiational cooling.

On the heels of the piece of the Tropospheric Polar Vortex that got sent towards the US from the aforementioned North Pacific block was a very large surface high pressure system with Arctic origins. While the Polar Vortex quickly retreated back into the Arctic and the US was being replaced by a much warmer airmass aloft, this surface high pressure system was massive enough and had enough initially very cold source regions to deposit incredibly cold air into the US. The coldest temperatures were to our west in the Central Plains, where places in Texas dropped from the low 80s to the upper 30s within one hour! This cold air got modified somewhat as it headed east, but it still packed quite a cold punch on Monday, as temperatures in NYC did not get out of the 20s during the afternoon.

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The sea breeze and its cooling effect along the coast

Today was another one of those classic days where inland areas soared into the upper 70s, and coastal areas had trouble exceeding 60 degrees, with plenty of wind.

The explanation for this is the sea breeze. Whenever we have a warm, springtime airmass, the temperatures over the land warm up quickly. However, the sea is still relatively cold this time of year, especially considering how cold of a winter we had. The ocean has a high specific heat capacity, which means that it can absorb the same amount of heat as the land does, but will not warm up nearly as much as the land. Thus, during the day, the land will often be much warmer than the ocean.

The sea breeze circulation (top) and land breeze circulation (bottom). (Free Online Pilot Ground School).

The sea breeze circulation (top) and land breeze circulation (bottom). (Free Online Pilot Ground School).

Once the land heats up, thermodynamics dictate that the warm air must rise, since it is less dense. However, the relatively cold ocean does not have this same heat, as it is more dense, so the air does not rise. The rising air over the land creates a slightly lower surface pressure, since the air is escaping the surface, rather than exerting a force on it. The lack of rising air over the sea thus creates a slightly higher surface pressure, relative to the land. The atmosphere always wants to balance itself out, so to compensate for the air over the land escaping the surface, air from higher pressure has to flow towards it. This air happens to be coming from the colder ocean, which helps to create colder temperatures and windier conditions along the coast.

The circulation gets reinforced because when the air over the land rises, it creates an area of higher pressure at the upper levels of the atmosphere, since lots of air is rushing towards the upper levels. However, over the sea, there is no air rising into the upper levels, so the pressure is relatively lower there. The air with higher pressure aloft on the land thus flows towards the area with lower pressure above the sea. Now that this air is above the sea — where air at the surface is already heading towards the land — the air has to sink to replace the air that is leaving the sea. This sinking air towards the sea surface reinforces the high pressure, which reinforces the source of air that is blowing towards the land, which reinforces the sea breeze.

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Temperature and wind observations taken from Monday (4/14/14) afternoon at 4:48pm. Notice temperatures approaching 80 in New Jersey with relatively light winds, yet much cooler and windier conditions on Long Island. Also notice how in some areas, the southerly winds are stronger on Long Island compared to areas further west (Weather Underground).

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