HOUSTON -

The National Weather Service has issued a Flash Flood Watch for our western and northern counties.

The watch will be in effect from 7 p.m. Monday until 1 p.m. Tuesday. The nine counties affected are: Austin, Brazos, Burleson, Colorado, Grimes, Houston, Madison, Waller and Washington.

Rainfall should average 2 to 4 inches in the watch area, with isolated 5 inches or greater totals.  Thunderstorms that train over the same area will be the most likely culprit for the flooding.  In such cases, the exact location at most risk for flooding is highly uncertain. The Local 2 Weather team will be watching radar closely over the next 24 hours.

Chief Meteorologist Frank Billingsley says we are expecting rainfall throughout Southeast Texas, but flooding should not be expected in the Houston metropolitan area at this point.

Forecast models not in agreement

Forecast models are still not in total agreement of what will be taking place where.

Areas northwest of a Columbus-to-Trinity line will average about 1.00 to 3.00 inches. Isolated amounts could reach between 3.00 to 5.00 inches as some storm training is expected.

East of the Columbus-Trinity line, it is anticipated that rain amounts will be much lighter, especially closer to the coast.

As of now, it appears the heavy rain could affect our morning commute.

However if the front slows down, it will make it's way to the Houston metro area by midday.

We could receive 0.25 to 1.00 inch of rain in Harris County through Wednesday morning. According to the latest advisory from the National Weather Service the front could fall apart just before reaching or when it is over Houston.

Looking at model data, precipitable water is 1.70 inches. Precipitable water tells us how much liquid water in a column of air would condense out.

When that value nears 2.00 inches, like it is possible with this system, we could get street flooding in Houston.

There is a second scenario based on different forecast models. This one is not as favorable.

In this forecast, a mesoscale convective system (MCS) will develop Monday night. A MCS is an organized system of thunderstorms.

We would still get heavy rain as a cluster of showers and thunderstorm sweep into the region.

The cold air behind it however would push the system southward faster clearing Houston by midday Tuesday. Once the storms passes, the rain chances will likely end instead of lasting through Wednesday.

This scenario still has the system weakening before making it to the coast.

Rain Chances

A line of storms started developing in Central Texas early Monday afternoon.

The front the storms were developing on will be pushing southeast affecting the northwest counties first, including College Station.

Models are still inconsistent on how far this front will push southward across our region, but the coastal region appears to have the lower chances of seeing rain.

For instance, College Station has an 90 percent chance of storms Monday night and an 80 percent chance Tuesday.

Comparing that to the coast, Galveston has a 30 percent chance of rain and thunderstorms Monday night with a 50 percent chance Tuesday.

Also, Galveston is not expected to rack up as much rain because the system is expected, as of now, to fall apart before reaching the coast.

Angleton may accumulate a 0.50 inch of rain by Tuesday night. But Galveston rainfall amounts are forecasted to be below 0.25 of an inch.

Staying Safe

North and Central Texas are under flash flood watches.

The National Weather Service is looking at whether our Northwest counties -- Houston, Trinity, Madison, Walker, Burleson, Brazos, Washington, Grimes, Colorado, Austin, Waller -- need to be added to the flash flood watch.

If the heavy downpours do kick start street flooding, it is important to remember Turn Around, Don't Drown.