Scary sky, little rain

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Rainfall has been relatively unimpressive through Thursday night, but there is still a chance of additional rain through the day on Friday.  It looks pretty spotty, though! Check out the impressive wall cloud on the single, solitary thunderstorm over Northwest Alabama’s Lauderdale County on Thursday evening just after 7 PM:

NOAA defines a wall cloud like this:

It is formed in a supercell thunderstorm. A localized, persistent, often abrupt lowering from a rain-free base. Wall clouds can range from a fraction of a mile up to nearly five miles in diameter, and normally are found on the south or southwest (inflow) side of the thunderstorm.

Even though this cloud is lowering, it remains attached to the rain free cloud base of the thunderstorm. It is usually located south or southwest of the visible precipitation area, and marks the strongest updraft in the thunderstorm. The wall cloud develops as the strong updraft draws in surface moisture from several miles away.

Eventually, this updraft will pull air from the rain cooled area of the thunderstorm. Since the rain cooled air is very humid, it will quickly condense in the updraft at a lower altitude than the rain free cloud base. When seen from within several miles, many wall clouds exhibit rapid upward motion and cyclonic rotation.

However, not all wall clouds rotate. Rotating wall clouds usually develop before strong or violent tornadoes, by anywhere from a few minutes up to nearly an hour. Wall clouds should be monitored visually for signs of persistent, sustained rotation and/or rapid vertical motion.

More showers and a few storms are possible, but there is very little threat of severe weather through Friday.

More rain needed! Back around Christmas it seemed like the rain would never stop. Since January, we have had a small rainfall deficit. It stands at -1.57" at Huntsville International as of April 21st. It is -2.82" in The Shoals through Thursday morning.

It's been very dry since March 1st all things considered. March, April and May are among the wettest months of the year, and that rain is crucial for agriculture and recreation (think levels along the Tennessee River). We need about an inch of rain per week in the growing season to stay out of drought/abnormally dry conditions. Unless something changes dramatically, we expect drier-than-normal weather on the the whole through the rest of April and on into the first part of May.

"Drier-than-normal" does not mean "no rain at all." It just means we expect to fall short of that one inch per week benchmark that we need to keep the grass green and the gardens growing.

Next week's outlook: Even with the dry outlook, we see a more active pattern for a few days next week that almost certainly brings heavy rain nearby. The question is just how far south it can get. A series of strong spring storm systems move from the Plains across the Midwest toward the Atlantic Coast next week bringing wave after wave of rain and stormy weather. There's a good chance we will get some rain, but how much is very much in doubt at this point.

See our Forecast Discussion at WHNT.com/Weather for the latest ideas about the unusually dry Spring and how things will change over the next few weeks.

-Jason
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