thunderstorms

[weatherman123]

how do you forecast thunderstorms?

[Sheppie]

Well I'd say that it happens when air masses create weather as they are moved by winds around the globe. Fronts develop at the boundary where two air masses with different temperatures—and, usually, different humidities—come into contact with each other. The term front was suggested by the Bjerkneses because the collision of two air masses reminded them of a battlefront during a military operation. Thunderstorms result from the rapid upward movement of warm, moist air. They can occur inside warm, moist air masses and at fronts. As the warm, moist air moves upward, it cools, condenses, and forms cumulonimbus clouds that can reach heights of over 20 km (12.45 miles). As the rising air reaches its dew point, water droplets and ice form and begin falling the long distance through the clouds towards the Earth's surface. As the droplets fall, they collide with other droplets and become larger. The falling droplets create a downdraft of cold air and moisture that spreads out at the Earth's surface, causing the strong winds commonly associated with thunderstorms, and occasionally fog.

 

But here you read more:

http://www.scienceclarified.com/A-Al/Air-Masses-and-Fronts.html#ixzz3B177gKRS

http://www.theweatherprediction.com/clouds/

http://en.wikipedia.org/wiki/Thunderstorm

[tormenta]

You can also check out this video that explains how thunderstorms are formed

 

http://www.youtube.com/watch?v=O8kgfkjmdKA

[Metsfan]

how do you forecast thunderstorms?

Three basic steps I follow. 

 

1) Instability I.E. CAPE

 

2) Lift I.E. cold front/warm fronts

 

3) Moisture I.E. high Theta e, high dewpoints (60s and 70s)

[TalcottWx]

Sun heats ground. Surface temperatures rise noticeably higher than temps aloft. Hot air naturally rises. When a low pressure is around or a front of some kind there is enough lift to cause instability. Source of weather is naturally the extremes of warm and cool air meeting.

Things to look for : dewpoints and moisture, shear (too much shear can hurt storms fyi), lcl (low cloud base = easier tornado touchdown), mid and upper level wind fields (higher the better), boundaries that may form such as seabreeze or outflow. Marine airmasses inhibit convection. Also keep an eye out for 500mb temps as cooler air advection always helps storms. Warming in the mid levels obviously bad on the other side of the spectrum. Caps or inversions are good to look for. Inversions allow daytime heating to maximize until reaching a certain temperature that enables air to lift behind the height of the inversion. It can also be bad because the inversion may often never break. Lapse rates are also significant. Basically higher ml lapse rates mean steeper rise of air and greater, enhanced instability.

Generally for the new england area we mostly experience problems with marine taint inhibiting convection or struggles to clear clouds out in time for maximum day time heating. Often wind directions that create the most shear for portions of new england bring in marine airmasses.

Many times day time heating is maximized and there is no source of lift. Sometimes an airmass may feature plenty of shear and the threat never gets off the ground as an area stays fogged in so instability is never realized.

There is also elevated convection to help add to your confusion. Usually results from an influx of moisture or temperature change aloft. Requires no surface heating and can produce tornados and severe weather despite. Can be related to caa aloft from an ull or storm and its cold pool. Cold pool events often mean many hail reports due to the lower freezing level in the clouds.

some intense tropical lows can have sharp intense lines of convection like the one that produced the revere tornado this past summer. High shear low surface based instability but unstable atmosphere despite. Also tropical airmass meant very low lcl's/lifted condensation levels/cloud bases.

Don't forget about storm motion and speed. Often the flooding threat is overlooked. Due to the front or storms speed cells may move particularly fast or even slow. Slow moving cells with high dewpoints means a significant flooding threat. Check out wind direction in all levels too. If the winds do not indicate a high level of shear, unidirectional winds can result in equally as damaging straight line wind events.

Lots of cape and instability and moisture = lightning recipe. High shear environments = tornado threats. High humidity/dewpoints = flooding threats.

If you have ever visited Florida you understand tropical airmass thunderstorms. Storms fire on seabreeze boundaries in a thick, heavily moisturized, hot atmosphere. A ton of lightning and rain, but usually no tornados or severe weather for the most part compared to maybe the plains states. Most florida storms are often resulting from seabreeze boundaries with pretty slow winds aloft. Slow movers that lack any real shear. They pulse up and down and drop bucket loads of rain.

The plains combine the two ingredients of shear and moisture into particularly dangerous situations/tornado outbreaks. Tropical moisture rolls up from the Gulf due to a deepening low pressure system. Colder air is pulled down from the northern plains. In a tornado outbreak there is often a cap or inversion aloft that doesn't break until after daytime heating is maximized. The low provides cooling temps aloft, shear, intense lift, moisture, and steep lapse rates.

[TalcottWx]

Don't forget about timing. For the northeast, a few hours can mean a huge difference in terms of the front's progression and reaching the threat's potential.

also look up some information on eml's or elevated mixed layers. Generally often associated with steep lapse rates aloft due to a cap or inversion aloft. Breaks late in day through intense surface heating or lift and results in maximum intensification of thunderstorms.