TULSA, Oklahoma - The National Weather Service is expecting some flooding this weekend, with heavy rain expected, especially in southeast Oklahoma.

They're monitoring the water with a network that gives them almost real-time information about rainfall and river levels.

Clouds like this figure into the forecast for river flooding.

Because long before the rivers might be impacted, hydrologists are looking at what's expected in the watershed.

At the river forecast center - part of the national weather service, hydrologist James Paul is forecasting a weekend with a threat of flooding.

"The rivers right now in eastern Oklahoma aren't doing too badly as far as being in the elevated state, but because of the rainfall we've had, the ground is saturated, so any rainfall will get will run off and make it into the rivers," Paul said.

The forecast here includes both expected rainfall - and what's already on the ground.

They monitor all that with a network of gauges scattered up and down rivers, and along local streams in heavily populated areas.

There are hundreds of boxes in Oklahoma which collect data that, within 15 minutes or so, arrives at the forecast center.

If the water is rising, they can tell.

If the rain might create a problem downstream, they can predict it.

"Once it hits the ground, we have a good idea of where it rained and how much it rained and our hyrdologic models do a pretty good job of figuring out how much of that will reach the rivers, so at that point we're doing pretty good,” Paul said. “It's still the forecast rainfall that we have the most issues with."

The hydrologists make the forecast, the monitors gauge what's happening on the ground and computers calculate the impact.

For example, a chart shows what they're predicting for the Illinois River this weekend.

"We would look at a 3-foot rise at Tahlequah and that would get it bank full," Paul said.

It's still a forecast, but it's backed up with a flood of data coming in.

The monitors allow very specific river forecasts that usually only get attention from boaters.

This weekend, it could be the key part of the severe weather forecast.