More rain is heading into the Tennessee Valley. The developing issue is the potential for widespread very heavy rainfall. Forecast models are showing widespread rainfall on the order of 1.50" to 2.00" of rain. Based on other data we have in the WAAY 31 Severe Storm Tracking Center, higher amounts are possible. Locally, up to 3.00" of rain can fall in spots, though those highest amounts will not be as widespread. With rain like that, flash flooding can become an issue Wednesday morning. That is especially true in poor-drainage areas. If you know of a particular spot that floods frequently, it may be best to avoid that spot.
Areas of light rain can develop tonight after midnight. That rain will clear out by the Tuesday morning drive. An isolated, brief light shower is possible through noon. Showers will gradually grow more numerous and heavier from noon through midnight, then heavy rain will become widespread after midnight.
The heaviest rain is tricky to time because the showers may influence the evolution of this storm system. The timing can change, but right now the heaviest rain looks to pick up between midnight and 4 AM early Wednesday across the Shoals west of I-65. The heaviest rain will track eastward across I-65 through Huntsville and Madison between 1AM and 5 AM Wednesday. The eastward track will bring heavy rain to Sand Mountain from 2 AM to 6 AM Wednesday. The rain will come to an end across the Shoals from 6AM to 8AM Wednesday. It ends around Huntsville, Fayetteville, and Decatur from 7 AM to 9AM. The end comes across Sand Mountain from 8 AM through 10 AM. Some small adjustments are possible with the ending, but all indications right now are the rain will end before noon.
This evening will be clear.
Temperatures this evening will drop through the 40s and into the 30s. Clouds will increase overnight. The increase in clouds will likely bump up the temperatures after midnight, and some light rain can come from those clouds after midnight. Tomorrow morning will be mostly cloudy but mainly dry. Temperatures will be in the lower 40s.
More rain, and perhaps some thunder, will move through the Tennessee Valley on Saturday and Sunday.