Tropical Storm Bill

Tropical storm development
Tropical storm development shows how important atmosphere-ocean interactions are in climate and weather. Tropical storms introduce and transport enormous amounts of heat and moisture into the atmosphere.

The video below shows the formation of Tropical Storm Bill in June 15 through June 17, 2015  as it makes it way westward across the the Gulf of Mexico in the easterly trade winds (remember: easterly trade winds flow FROM the East carrying weather systems westward).  Note that this is not a hurricane. A hurricane would be rotating more quickly and have an "eye" in the middle as it intensifies. These systems can cause severe flooding because of the tremendous amount of water that evaporates from the warm ocean surface of ther Gulf of Mexico  in the atmosphere




Current satellite imagery
You will be able to see how this tropical system dies out as it makes it way northward and its moisture and cloud gets advected and dispersed (that is to say transported blown) eastward in the mid-latitude westerlies. A little guide to the imagery is provided below. Note that blue indicates cold cloud tops (the colder the higher) while red generally represents surface temperatures.   You should be able to see the cloud and precipitation due to the moisture of this system if you are in Southern New England.

Link to satellite imagery.

Temperatue and weather at LSC weather station

Weather summary for Wed. March 4, 2009 at LSC indicates the following high and low
Hi temp: 22.2F (-5.4C) at 13:55
Low temp: -11.7 F (-24.3C) at 06:10

Overnight temperatures were falling continuously (blue) before the low at 6:10 AM shortly before sunrise. This indicates a relatively clear night in which outgoing longwave radiation (OLR) was able to radiate into outer space without clouds interfering.

The sharp 30 degree rise in temperatures during the morning hours (red) indicates strong solar warming associated with clear skies and higher noontime solar angles.

Finally, temperatures in the early afternoon (green) are relatively constant in the lower 20's after about noon . Indeed, a slight dip in temperatures can be observed at around noon. The pressure trace shows a very slight dip (about 2 or 3 mb) in the pressure trace.

Comparison to temperature and pressure data shows a clear morning with light winds and a sudden appearance of snow over Burke Mountain around noon. This corresponds to pressure fall and constant afternoon temperature. Click here to retrieve larger image at webcam archive.

Wednesday's WeatherCam

The above WeatherCam image is for Wed Feb 18, 2008. The time in UTC is displayed at the top right of the animation. A larger animation can be viewed at the LSC Meteorology site webcam archive. It documents a weak storm system moving into the NEK and most of New England from the southwest. The camera faces eastward from the college campus towards Burke Mountain. Clouds moving into the page therefore mover from west to east, and those moving from right to left move form south to north.

The day begins with clear conditions and occasional high level cloud moving across the region from the northwest. Around 11 AM (16 Z) a mid level deck of cloud (at about 5 km or 15 000 feet)moves in from the west with the jet stream. Around 18Z. a lower, thicker deck of clouds moves in rapidly from the south. By sunset around 5 PM (22Z), this deck has lowered to the top of Burke Mountain (about 4000 ft). Snow begins to fall and obstruct the view of the mountain in the final few frames of the animation.

Local data

LSC data for Wed. 11 Feb. 2008 is posted in the image at right. the temperature reached a balmy 52.2 F (11.2C) at 14:45 in the afternoon. The dewpoint (purple line) rose consistently throughout the day as the air became more humid. The temperature (red line) fell and relative humidity (green line) rose abruptly at around 4 PM *(16:00 EST) . The dewpoint and temperature met at about 35 F as the relative humidity hit 100%, an indication of fog and precipitation.

The approach of the upcoming storm is announced by the increasingly sharp drop in pressure (blue line). The total drop in pressure appears to be about 15 mb for the day. Winds actually appear to have died down in the evening after peaking in the late afternoon.

Data from Littleton/Whitefield Airport, NH (HIE) confirms a high of 52.0 F and the onset of rain and fog at about 5 PM EST. A similar plunge in sealevel pressure is also observed. The rain gauge detected 0.10 inches of precip before 0Z (7PM EST).

February showers

Today's rain is associated with a low pressure system and associated warm front moving in from the southwest. On the surface analyses for 12 Z (7AM) Wednesday 11 February, 2008 (left) the low pressure system was located over the center of the U.S. A warm front extended northeastward into West Virginia. A south-southesterly flow ahead of the storm system (red arrows) transports warm, humid air from the Gulf towards the warm front. Meteorologists refer to this flow as a vapor channel. The humidity falls as precipitation to the north of the front (black circle). This is typical of of midlatitude winter storms. Light to moderate precipitation typically falls in broad regions north of warm fronts to the northeast of the low pressure center.

By 00Z Thursday 12 Feb. 2008, the storm center has moved into the Ohio valley. The vapor channel from the Gulf of Mexico is cut off by the cold front moving eastward across the southeastern states. Moist air from the Atlantic continues to stream northward ahead of the storm system (red arrows). Precipitation continues to fall ahead of the warm front (shown as a stationary front over northern New England (black circle).

This precipitation occurs because warm humid air overruns the cold air ahead of the front when it reaches the front. This leads to cloud formation and precipitation. This falls ahead of the front as frozen precipitation if the surface temperature is below freezing and rain of the surface is above freezing. See "Precipitation along warm front" tutorial for more information.