Easy to miss one on a clear “still” night in this part of the country. Varied terrain, all the hills, ridges, valleys, you name it.
Long, long time ago, before I was lucky enough to get in the USWB/NWS, I was already a “weather geek.” One clear, cold night, I installed minimum thermometers in these areas of Jefferson County with two teenage neighbors to help me:
…..at the base of the Forest Service lookout tower on the highest part of Shades Mountain
…..at the base of another Forest Service tower atop Rock Mountain west of McCalla in SW Jefferson County.
…..at the base of Rock Mountain just a short distance west of the tower (about 1/4 mile) and the spot that the three of us camped in sleeping bags overnight.
Next morning, these lows:
* 42 at the base of the tower on Rock Mountain
* 32 with heavy frost at our campsite only 1/4 mile away
* 54 at the base of the Forest Service Tower on Shades Mountain
* 28 in Pinson (official NWS coop station)
That was an amazing 26 degree difference between Shades Mountain and Pinson less than 15 air miles apart!
It was another big temperature inversion somewhat like last night.
We forecast 39 for last night and this morning. At times, like last night, we have to walk a tightrope in coming up with a min temperature. We have to estimate if the high pressure ridge will be east of us, thus allowing a light SE wind to set in. Also yes or no on any clouds.
Birmingham Airport is in a wide open area with no trees. The official weather sensing equipment is out in the middle of the airport because it is crucial that pilots know up-to-the-minute wind conditions near the runway. In the middle of the night, it is easier for the wind to suddenly go from calm to about 5 or 7 mph than it is in places like Pinson, in a better protected valley with lots of trees. On certain nights, there can even be a 5 or 6 mph “drainage wind” off the Red Mountain ridge east and NE of the Airport and hills on the NW side.
The 39-degree decision for last night was about right, considering all the variations in the area. At the Shelby County Airport the low this morning was 44. However, the morning upper air sounding, launched at about the time of the lowest temperature, showed a very sharp inverson not far off the ground where the temperature was about 55.
A BIG SCARE: By the way, on that cold night long, long ago when we were bedded down in the woods at the base of Red Mountain, about 3 am, we heard a motor running. It was a full-moon night and we were still-as-a-mouse as a pickingup truck (stole that expression from the late Justin Wilson) slowly passed about 30 yards away. They had their lights off and they did not see us. From what they had on the truck, I am 99.987% sure they were bootleggers. If they had seen us, we would probably have been “expired” and I would not be writing this story today!
