However, warning were just issued for an area just northwest of us to expect 4-7 inches of rain from this storm as a result of heavy downpours from the passage of a train of thunderstorms. This is a remarkable amount of rain to come out of such a system, from a historical perspective. The 24-hour rainfall record at Reading is about 8.5 inches, set during the landfall of Hurricane Agnes in 1972. It is conceivable that some localities in this region may set new single-day rainfall records today. And eastern Pennsylvania is not alone in its experience of this storm. The storm totals (see below), as of 3 pm today, exceed 6" in parts of North Carolina and exceed 4" in wide areas of North Carolina and Kentucky and some additional rain is possible in those areas.
Several flash flood and flood warnings have been issued for our region and stream and river hydrographs are rising very rapidly. No major flooding is expected, thankfully, but there is clearly a lot of moisture in this system.
The occurrence of more frequent, more extreme rainfall events is the flip side of the occurrence of more frequent more extreme droughts, as both are driven by a warming atmosphere. As Earth warms, more liquid water can evaporate into the atmosphere. As the low pressure system forms, and air is drawn in and cooled, the balance between evaporation and condensation shifts and condensation increases, eventually resulting in rain. Since there is more vapor available, more rainfall can occur (thanks to the Bad Meteorology blog for helping me get this straight). Hurricanes are famous for their ability to delivering drenching rainfall in large part because they collect water vapor into their circulating air over very warm tropical seas. As temperatures increase everywhere, we should expect more non-tropical systems to deliver deluges and this is in fact what climate modelers have been predicting to come from a warming world. All of which leads me back to the title question... Is this just a singular isolated event, or is this now the weather we can expect on a regular basis, the new normal?
