Thermal Updraft Velocity

TUV at Cranberry Marsh

Thermal Updraft Velocity (TUV) is only monitored at Cranberry marsh and only since the year 2000.

TUV is measured in ft./min., the range being from 0 to 700+ ; the higher the reading the greater the possibilities for a significant hawk migration or for predicting the same “very soon”. To get a TUV value for the day click here.

We see the most birds when the TUV is on the order of 400 feet per minute.

Importance

TUV may be even more important than wind direction or barometer change. The following 3–dimensional graph shows “skyscrapers” where many birds are seen.

The height of each bar or “skyscraper” on the left side scale shows the count of total birds seen over the study; the scale across the bottom of the graph shows barometer change with values of Falling, Rising, and Steady, each of which is subdivided into eight wind directions; the right side scale is Thermal Updraft velocity values in feet per minute.

The tallest of the “skyscrapers”, shown here in purple, is located where the barometer is Rising during a North East wind with a TUV of 400–499 feet per minute. The second highest (mauve) bar is a Rising barometer in a North West wind with TUV of 100–199 feet per minute.

In general the largest number of birds are seen when the barometer is Rising, the winds are generally from the North and the TUV is at least 100 feet per minute (but note that the heights of the bars are not corrected for the number of hours of observing time under each set of conditions).