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Nicole will race in the DC region on Friday, with rain and possible tornadoes

Nicole will race in the DC region on Friday, with rain and possible tornadoes

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Unusually warm and moist air is returning to the Mid-Atlantic ahead of the remnants of Tropical Storm Nicole, which will pass through the region on Friday. While Thursday is quiet, Friday will see more rain through the morning, with occasional flurries during the day.

Major impacts to the DC area will include periods of heavy rain that could lead to isolated flash flooding and gusty winds from the south and southeast.

Given the high atmospheric spin associated with the remnants of Nicole, a tornado threat may also develop. Chances for twisters are slightly higher south and southeast of Washington, toward southern Maryland, Richmond, and the Virginia Tidewater.

Tropical Storm Nicole has made landfall in Florida, preparing to make landfall in the eastern part of the US

The National Weather Service Storm Prediction Center located the DC area and Level 1 out of 5 risks for tornadoes, while areas to the south are in a 2 out of 5 level risk zone.

In addition, the meteorological service has placed the region in ua Level 1 of 4 risk of excessive precipitation. Chances for heavy rain will increase to the west and northwest of the DC area.

Timing: Shower chances increase during the predawn hours on Friday, especially southwest of the area, and become likely by sunrise. Additional waves of rain pass through the day. The rain should stop late Friday night.

Coverage: Expect occasional showers, coming in waves, and possibly thunder. Showers will be quick but could be quite heavy at times.

Dangers: The primary concerns are heavy rain, gusty winds, and the risk of an isolated tornado or damaging wind gust. The chance of flooding is quite low as the area has been quite dry lately.

Rainfall Projections: A wide spread of 1 to 1.5 inches is most likely. Up in the mountains, 2 to 3 inches could fall. Southern Maryland and the Delmarva Peninsula are likely seeing closer to a half inch to an inch.

How Nicole will impact the region

On Friday morning, the center of weakness of Nicole will be over central Georgia, as shown below, with showers working north through the mid-Atlantic.

A storm is characterized by a very large wind circulation. High pressure moving northward will help sharpen the pressure gradient across the Mid-Atlantic, increasing wind speeds. Expect frequent gusts of 20 to 30 mph on Friday and potentially stronger in the case of thunderstorms.

As Nicole transitions from a tropical storm to a higher midlatitude storm, a warm front will form (red dashed lines above) that could be the focus of any tornado activity. Meanwhile, a strong cold front and a deep drop in the jet stream will approach the East Coast from the Ohio Valley.

The center of Nikola’s remnants will merge with that front, perhaps near the spine of the Appalachians, as a plume of deep tropical moisture moves northward to the east of the storm. Strong upwelling on the western side of Nikola’s remnants will interact with tropical moisture to create a patch of potentially very heavy rain over the Appalachians, with more showers to the east.

By Friday evening, Nikola’s remnants will quickly move northeast, and skies could begin to clear by midnight.

Why high winds and tornadoes are a danger

While the fuel for the types of storms that can generate tornadoes will be limited in the DC area, wind shear (the change in wind direction and/or speed with height) will be significant. That combination of ingredients can set the stage for low-top rotating storms. Those cells, in turn, can bring damaging wind gusts (50-60 mph) to the surface in a few places, as well as generate brief tornadoes.

Inland tornadoes generated by tropical debris tend to be short-lived and weak, but these characteristics also make them difficult to detect by radar, hindering the issuance of timely warnings.

At this time, the Storm Prediction Center thinks the biggest tornado threat will be south of DC. However, we warn that this zone could extend further north if the air mass remains unstable in the late afternoon and early evening hours.

Rain totals will depend heavily on the track. For now, about an inch total in Washington seems reasonable. Moving the forecast farther east would bring higher totals closer to that area. The region has been quite dry recently, so the limits of rain causing local flooding are high.

Overall, the predicted track of Nikola’s remnants has shifted westward, somewhat reducing potential rainfall in the immediate vicinity.

Here are the amounts provided by the different models:

  • European (ECMWF): 0.50-1 inch+
  • US (GFS): 0.75-1.5 inches
  • American (NAM): 0.50-1 inch
  • Canadian (GEM): 0.75-1.5 inches
  • ICON: 0.75-1.5 inches

Additional track movements are possible, which would affect the precipitation forecast. But we don’t expect much change now that we’re within a day of the event.





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