Heavy Rain And Flash Flooding Possible This Week.

Good Morning! It is Monday September 20th, 2021. It is the 263rd day of 2021. There are 102 days remaining in the year. Sunrise today was at 7:14am and the sun will set at 7:02pm. Today has the same amount of daylight as March 21st. We are quickly losing daylight and the sun will set before 7:00pm in just three days.

We are going to start this week off on an unsettled note before a cold front moves through and dries us out going into late week and the weekend. Our eastern slopes will rack up the highest rainfall totals but everyone should receive a good helping of rain.

High pressure will slowly lift North today while strengthening. Clockwise flow around that high pressure will drag moisture West off of The Atlantic Ocean. As the moisture comes west it will be lifted by the topography of the land. As that moisture is lifted up the east slopes of the Blue Ridge, the topography will ring out the atmosphere’s moisture. This could mean trouble. To better understand where we sit with rainfall right now here is the flash flood guidance. This guidance takes into account the amount of rain that has fallen already, stream flows, and how saturated the ground currently is. It tells us how much rain it would take to initiate flash flooding.

  • 1 Hour Flash Flood Guidance:
  • Alexander: 2.5 – 3.0 inches
  • Burke: 2.0 – 2.5 inches
  • Caldwell: 2.0 – 2.5 inches
  • Catawba: 2.5 – 3.0 inches
  • Cleveland: 2.5 – 3.0 inches
  • Lincoln: 2.5 – 3.0 inches
  • McDowell: 1.5 – 2 inches
  • Rutherford: 2.0 – 2.5 inches
  • 3 Hour Flash Flood Guidance
  • Alexander: 3 – 4 inches
  • Burke: 3 – 4 inches
  • Caldwell: 3 – 4 inches
  • Catawba: 3 – 4 inches
  • Cleveland: 3 – 4 inches
  • Lincoln: 3 – 4 inches
  • McDowell: 2.0 – 2.5 inches
  • Rutherford: 3 – 4 inches
  • 6 Hour Flash Flood Guidance
  • Alexander: 4 – 5 inches
  • Burke: 4 – 5 inches
  • Caldwell: 4 – 5 inches
  • Catawba: 4 – 5 inches
  • Cleveland: 4 – 5 inches
  • Lincoln: 4 – 5 inches
  • McDowell: 2.5 – 3 inches
  • Rutherford: 3 – 4 inches

It is important to remember that these numbers are moving targets. The more it rains, the more these numbers go down. Upslope flow is already underway. Cloudy skies persist this morning but the low levels remain pretty dry due to the proximity of the high pressure. As that high drifts further north, surface and mid level dewpoints will increase tonight. Right now it looks as through the heaviest rain will start after 2:00am. These upslope flow events thrive on evolving during the nocturnal hours. See study: https://www.weather.gov/mrx/heavyrainclimo

Overall expect rain to start this afternoon. It will be sporadic early but should become more widespread as the night goes on. We expect heavy rainfall by the time you wake up Tuesday Morning, especially near the eastern slopes. We will have a forecast map out this afternoon with totals. If you live in an area where flash flooding occurs, please have multiple ways to receive warnings starting tonight. Apps, weather radio, or anything that will alert you to possible danger.

Forecast Rainfall: Outside and away from the mountains we think that general 2 – 4 inch total can be expected. This is generally in Catawba, Cleveland, and Lincoln Counties.

Close to the mountains we expect numerous 3 – 6 inch totals. In the South Mountains though a few totals could reach 4 – 8 inch range. In the eastern slope of the Blue Ridge 6 – 10 inches with a few higher amounts cannot be ruled out. If those areas do in fact exceed a 6 to 7 inch mark within 60 hours then flash flooding and landslides will be possible.

Alexander County will see a wide range of totals. In southeast Alexander 2-4 inch totals are expected. In northern Alexander, near the Brushy Mountains, 3 – 6 inch totals. I think Central and Western Alexander County could see 2 – 6 inches.

Again a map will be developed based on the afternoon model’s data. That will be released this evening. The NWS may issue a flash flood watch sometime this afternoon for potions of the area. Below is a look at the average rainfall projection with all of the model data averaged out.

  • Caldwell County

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