Image above from the National Weather Service website

Tropical Storm Helene is expected to develop into a hurricane, and hit Georgia by Thursday, bringing with it the possibility of widespread flash flooding. A flood watch will take effect at 2 p.m. Wednesday, September 25, and last through Friday.

The National Weather Service issued a hazardous weather outlook for Cobb County and other parts of north and central Georgia due to the possibility of isolated storms hitting the county by Wednesday morning and more severe weather as Helene approaches.

In this article, you will learn:

1. What is in today’s National Weather Service alert
2. What counties are included in the alert
3. What is meant by the terms “isolated” and “scattered”
4. About the National Weather Service and what it does

What is in the statement?

The statement gives the following details:

This Hazardous Weather Outlook is for portions of North and Central Georgia.

.DAY ONE…Tonight…

Isolated thunderstorms are possible along and north Georgia

tonight.

.DAYS TWO THROUGH SEVEN…Wednesday through Monday…

A Flood Watch has been issued for north and central Georgia from

Wednesday afternoon through Friday afternoon.

Between Wednesday afternoon and Thursday morning the greatest

flooding risk in expected along and north of Interstate 85.

Localized rainfall total near or above 4 inches may result in

flash flooding or river flooding.

The arrival of tropical cyclone Helene on Thursday and Friday will

allow the flooding threat to expand to all of north and central

Georgia. By Friday evening widespread rainfall totals in the 3 to

5 inch range and localized amounts in excess of 8 inches are

expected. Due to this rainfall flash flooding and river flooding

may occur. Additional concerns for Thursday and Friday include gusty

winds which may result in tree and powerline damage, and an

isolated tornado risk in eastern Georgia.

What counties are affected?

The following counties are included in the hazardous weather outlook:

Baldwin, Banks, Barrow, Bartow, Bibb, Bleckley, Butts, Carroll, Catoosa, Chattahoochee, Chattooga, Cherokee, Clarke, Clayton, Cobb, Coweta, Crawford, Crisp, Dade, Dawson, DeKalb, Dodge, Dooly, Douglas, Emanuel, Fannin, Fayette, Floyd, Forsyth, Gilmer, Glascock, Gordon, Greene, Gwinnett, Hall, Hancock, Haralson, Harris, Heard, Henry, Houston, Jackson, Jasper, Jefferson, Johnson, Jones, Lamar, Laurens, Lumpkin, Macon, Madison, Marion, Meriwether, Monroe, Montgomery, Morgan, Murray, Muscogee, Newton, North Fulton, Oconee, Oglethorpe, Paulding, Peach, Pickens, Pike, Polk, Pulaski, Putnam, Rockdale, Schley, South Fulton, Spalding, Stewart, Sumter, Talbot, Taliaferro, Taylor, Telfair, Toombs, Towns, Treutlen, Troup, Twiggs, Union, Upson, Walker, Walton, Warren, Washington, Webster, Wheeler, White, Whitfield, Wilcox, Wilkes, Wilkinson

What is meant by “isolated” and “scattered”?

The NWS defines “isolated” as follows:

A National Weather Service convective precipitation descriptor for a 10 percent chance of measurable precipitation (0.01 inch). Isolated is used interchangeably with few.

“Scattered” has the following definition:

When used to describe precipitation (for example: “scattered showers”) – Area coverage of convective weather affecting 30 percent to 50 percent of a forecast zone (s).

Isolated thunderstorms and scattered thunderstorms are two terms used to describe different distributions of thunderstorm activity within a particular area. The main difference lies in the extent of coverage and how the thunderstorms are spatially distributed:

1. Isolated Thunderstorms:
   • Isolated thunderstorms are relatively rare occurrences that happen sporadically and are generally confined to a limited area.
   • These thunderstorms are often characterized by being few and far between, with significant gaps between individual storm cells.
   • Typically, isolated thunderstorms cover less than 20% of the forecast area.
   • Despite their isolated nature, these storms can still be intense and may produce heavy rain, lightning, gusty winds, and possibly hail.
2. Scattered Thunderstorms:
   • Scattered thunderstorms are more widespread than isolated thunderstorms and cover a larger portion of the forecast area.
   • In a scattered thunderstorm scenario, numerous individual thunderstorms develop, but they are not continuous or widespread enough to be classified as a “line” or “cluster” of storms.
   • Scattered thunderstorms generally cover between 30% to 50% of the forecast area.
   • Although scattered thunderstorms are more widespread, they still leave considerable gaps between storm cells, and not everyone within the forecast area will necessarily experience a thunderstorm.

In summary, isolated thunderstorms are fewer in number and more localized, covering a smaller area with significant gaps between storms, while scattered thunderstorms are more widespread, covering a larger area with numerous individual storms occurring somewhat randomly across the forecast area.

About the National Weather Service

The National Weather Service (NWS) is a part of the National Oceanic and Atmospheric Administration (NOAA).

The NWS describes its role as follows:

“The National Weather Service (NWS) provides weather, water, and climate forecasts and warnings for the United States, its territories, adjacent waters and ocean areas, for the protection of life and property and the enhancement of the national economy. 

“These services include Forecasts and Observations, Warnings, Impact-based Decision Support Services, and Education in an effort to build a Weather-Ready Nation. The ultimate goal is to have a society that is prepared for and responds to weather, water and climate events.”

>>> Read all the Cobb County Courier climate and weather coverage by following this link.