As you know, overnight bog temperatures can drop dramatically if skies clear or if the wind level drops. Cloud cover and wind speed are, unfortunately, sometimes difficult to forecast with high accuracy. Furthermore, bogs in more sheltered areas will typically experience lower average wind speeds and will tend to run colder. So a regional forecast may not always apply well to specific bog sites within that region.
To give you an idea of how cold a bog could get overnight, we run a couple different bog forecasts representing three different overnight meteorological scenarios:
When you first bring up the forecast Web page for your region, you see both the "best-guess" and "clear-sky" forecasts:
The "best-guess" forecast is plotted in solid lines, and the "clear-sky" forecast is plotted in dashed lines. You can see how the clouds (which disappear close to sunrise) keep the bog temperatures warmer overnight.
Note that if the current forecast is for clear skies, these two temperature plots will coincide and you will see only solid lines.
If your farm is in a more sheltered setting, you may be very interested in seeing how the forecast behaves under low-wind conditions. To view a worst-case scenario assuming both clear skies AND calm winds overnight, simply depress the checkbox button next to "Overnight winds are calm", then click on "Apply".
Low wind speeds near the bog surface inhibit the mixing down of warmer air from above and can result in very low bog temperatures.