You need to be aware that the threat for extremely heavy rain coming late Tuesday into late Wednesday will cause widespread flooding in many areas — and not just locations which are prone to flooding. In the elevated terrain, rainfall amounts could become extreme with widespread erosion roads being washed out with whole fields being eroded or heavily damaged by extreme excessive rains falling on already saturated ground conditions.

The cause of these excessive rains is the tropical storm FRED which has made landfall on Florida Panhandle Coast. As WxRisk said last week , Fred did NOT reach Hurricane status. The latest information shows FRED’s track is bending a little to the right (northeast). This means that once FRED makes landfall, instead of passing up the west side of the Appalachian Mountains and perhaps dropping its heaviest rains in eastern Tennessee, eastern Kentucky, West Virginia and Ohio, the new data shows that the heaviest rains will fall on the eastern side of the Appalachian Mountains. This is bad news for areas such as the western half of the Carolinas, southwest Virginia, the Shenandoah Valley, the eastern portions of West Virginia, western and central Maryland, and central Pennsylvania.

Complicating this forecast is the fact that we already have seen several days of widespread areas of showers and thunderstorms throughout the Mid-Atlantic region. As of August 10, moderate drought conditions had developed in much of the Shenandoah Valley, as well as northwest portions of North Carolina, southwest Virginia, West Virginia, eastern Kentucky, eastern Ohio, and western Pennsylvania. But during the past few days, there have been areas of significant rainfall because of a series of weak cold fronts which have stalled across the Mid-Atlantic region. These fronts have been focusing mechanisms for the extremely humid air mass to produce widespread moderate to severe thunderstorms with widespread heavy rains in many locations.

This image shows recent rainfall totals from the past seven days. While there have still been some gaps in the central portions of the Shenandoah Valley and eastern portions of West Virginia, generally western North Carolina and Virginia has seen good rainfall amounts of 1 to 4 inches.

The reason why we are focusing on recent rainfall amounts is because the model data shows that the track of the remains of tropical storm Fred will bring excessive if not extreme rain to the entire Appalachian mountain range from northern Georgia into western portions of North Carolina, South Carolina, the entire Shenandoah Valley into western and central Maryland and into central Pennsylvania.

This image shows the early Monday morning British model total rainfall over the next five days. The burgundy color and white colors on this map represent rainfall amounts between 9 to 14 inches of rain which according to the data will fall in a 48-hour interval starting on Tuesday afternoon and continuing into Wednesday and Wednesday night.

Another aspect to this tricky forecast is the interaction of the tropical moisture upon the elevated terrain in the western Carolinas, West Virginia, and the Shenandoah Valley regions. The British model is clearly the wettest of all the models and presents the worst case scenario. The American or GFS model is not nearly as ominous with the rainfall amounts but the European model is trending towards the British model.

I know this is particularly bad news for Harvest during the weekend FRED had fallen apart and had been downgraded to a tropical depression. Because the storm was weaker the rainfall potential for the interior portions of the Middle Atlantic and the mountain regions were also decreasing.

WxRisk’s concern Is that because so many of the weather apps that people use as well as weather from different various websites or TV stations are all based upon the GFS model, that the threat of this sort of extreme Heavy Rain is being underplayed and not getting enough attention. This implies that a lot of people are going to be caught unaware and raise the risk of a significant public forecast disaster from this of the sources if the British model turns out to be correct .



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DT Wxrisk

DT Wxrisk

Meteorologist ... Atheist.. Dyslexic ..Baseball.. Fat tail distributions ..Good Judgement Projection… Black Swans/ Taleb …Choas / non Linear Dynamics… ENTP