Weather Alert Day: Heavy rain returns Thursday night into Friday

An ABC17 Stormtrack Weather Alert Day is in effect for storms that primarily bring a flood threat Thursday night through noon on Friday. A Flood Watch is in effect from 1 p.m. Thursday through 7 a.m. on Friday.

A stalled front will be stationary over the region Thursday through Friday. An upper-level wave will enhance an area of low pressure along the boundary that will slide in on Thursday night. This wave will be responsible for widespread showers and thunderstorms that pose a threat of flooding.

Precipitable water values will be quite high, reaching near 2 inches between those two days. Precipitable water is the amount of liquid that would fall if all of the water vapor in a column of air from the top of the atmosphere to the ground were condensed. Viewed as an index, 2 inches is significant because it indicates high atmospheric moisture, even for early summer. This 2-inch mark, however, is not a direct indication of how much rain we expect to fall. In other words, a precipitable water value of 2 inches doesn't necessarily mean we'll get 2 inches of rain.

A big part of how much rain we are forecasting has much to do with how long it rains. A low-pressure system working in from the northwest will drag a slow-moving cold front into the area on Wednesday. It stalls out, allowing waves of energy to move through the jet stream along the boundary, triggering rounds of storms between Thursday and Friday. When storms repeatedly move over the same area, they're known as "training" storms, sort of like a line of cars on a locomotive moving along a straight path. Our "train track," so to speak, is the stalled front. Training storms often bring appreciable rainfall and flooding concerns.

The Weather Prediction Center has much of the state in a slight risk for excessive rainfall on Thursday into Friday. A range of 1-3 inches of rain is possible for all, with isolated totals of 3-4 inches possible along Highway 50. This axis of heaviest rain may shift in the forecast, as a dift north or south is still possible.

As storms move in south of the front on Thursday evening, strong winds may be possible from our strongest storms.

Rain and storms come to an end on Saturday as the front lifts back north, shifting our focus from flooding to dangerous heat. A dome of high pressure builds to our south, drawing in moisture-rich air from the south as dew points rise into the 70s and highs spike into the 90s. No Weather Alert Days are yet active for next week, but the potential for dangerous 105+ degree heat indexes has us closely monitoring for that possibility.

The heat index is currently forecast to reach the triple digits with readings between 100-105 degrees through early next week.