Friday's frost forecast, Sept 16
If we see frost tonight it could come two weeks earlier than the average first frost dates for Michiana. Usually the 36°F mark is the threshold we look for when forecasting frost. The reason while the air temperature at the recording sight is above freezing, other areas nearby or close to the ground could fall below the freezing mark and produce frost if conditions are favorable ( clear skies,calm wind, temperatures falling to a subfreezing dew point)
With tonight's forecast dropping temperatures into the upper 30s, we will be in the borderline criteria for frost development, most areas will be to mild. Areas shaded in blue (see image) are the most likely to see frost as they are low lying, inland rural zones. Why is that important? Because those areas will allow the coldest air to pool close to the ground.
Shaded in Orange (see image) is the Lake Zone, this is a milder temperate zone where lows are almost always warmer than the surrounding area due to the waters of lake Michigan. This is a big reason why there are so many orchards and vineyards in Berrien County, because of the more favorable climate. The lakes impact will keep this zone in the 40s for lows.
The major urban areas; South Bend, Mishawaka, Elkhart and Goshen are not included as cities tend to hold more heat, as paved surfaces, houses, trees etc tend to act as insulation.
Finally extreme southern areas of Michiana look to reach into the 60s during the day, the high temperatures should aid in keeping the low temperatures just out of the frost range.
In the area prone to frost development overnight, and worrying about what you can do to keep your plants alive? Check out Monica's Blog!