CORPUS CHRISTI, Texas — Wednesday's cold front will make for not only a cold Halloween (highs in the upper 50s), but a cold night/Friday morning; the coldest of the season so far. The reason: Radiational Cooling.
Radiational cooling is a fancy way of saying, the Earth loses heat rapidly/efficiently at night. Radiational cooling happens when skies are clear, winds are calm, and humidity is low; especially after cold fronts. I usually describe it as the three C's: Clear, Calm, and Cold.
Nature's blanket (clouds) will leave the area today, allowing for the heating that happens today (highs in the upper 50s) to escape efficiently into the atmosphere after sunset. This process is enhanced by light winds (they'll be at 5-10 mph overnight) and low humidity. Humidity plays a role in how low temperatures can go because air temperatures cannot get any lower than the dew point. Tonight, dew points will be near 30°. Theoretically, temperatures COULD get into the low 30s if there was absolutely no wind, but that won't be the case. With a 5-10 mph north breeze in place, temperatures will dip into the middle and upper 30s/low 40s overnight in the Coastal Bend. I don't think we observe a freeze, but it will be close in portions of Bee/Live Oak Counties.
If clouds were to stay put tonight (they won't), they'd trap some of the Earth's heat, keeping overnight lows milder. If dew points were higher (like the 50s), temperature would not cool below the 50s. And if winds were breezy, the atmosphere would stay 'mixed up', keeping warm air from escaping into the atmosphere efficiently.
