Many people woke up to a Mother Nature alarm clock Friday morning. Heavy rain and gusty winds rolled in as a big cold front pressed eastward. This is part of the same system that brought severe storms to the Midwest and Mississippi regions earlier this week. Severe storms were not our concern, it was the flooding. Two features combined to dramatically increase our flooding potential… movement and intensity.
In a “typical” summer-like storm or cold front passage we can get very heavy downpours (like today) but they tend to move relatively quickly. Even with rainfall rates of 2”+ per hour (like today’s cells) if the storms move quickly they may only leave 1/2” in the rain gauge. Today’s system was a slow mover, allowing more time for rain to fall. Plus we had a training set up, that is when storms or heavy downpours tend to follow each other like train cars on a track. So that 2” per hour rainfall cell gets repeated over the same location again and again. The result… a lot of rain in a relatively short amount of time.
The movement of these cells was a bit unique too. Each individual downpour was basically sliding north along or in front of the cold front. The cold front was very slowly drifting east. This general motion can be seen in our rainfall totals “bulls eye”. The highest rain falling from Edenton to Chesapeake/Norfolk/Portsmouth to the Eastern Shore (the areas in green).
Downtown Norfolk topped the charts with just shy of 6” of rain. Most of that fell within a three hours span Friday morning. Portsmouth wasn’t far behind with about 5.5”. A few unofficial reports of 5” came in from portions of Gates and Chowan Counties in North Carolina.
An interesting side bar is the issue of tidal flooding. It is not uncommon for parts of Norfolk and Portsmouth to see flooding on a clear day due to tidal flooding (basically extra high, high tides). This usually occurs when we have a coastal low, Nor’easter, or strong winds from the east. That was not the set up today. We were approaching high tide as the cold front moved in which certainly did not help the situation but was also not the primary cause of the flooding.
Looking forward, rain will continue to move east this afternoon, with rain mainly hugging the coastline. Any flooded areas should see dramatic improvements as high tide approaches around 5pm for much of Hampton Roads. Like with most weather systems, we will be treated to some nicer weather behind it. Expect a nice mix of sun and clouds and highs in the 70s this weekend.
-Meteorologist Myles Henderson