Discussion-
...Ohio Valley into the Mid Atlantic...
A broad and slow moving mid/upper level trough will result in
scattered to widespread convection today from the Ohio Valley into
the Mid Atlantic. The environment will be conducive for very heavy
rainfall rates. PWs are above the 90th percentile, and wet bulb
zero heights ranging from 12-14k AGL are pretty much as high as
you will see in early June over this region. Thus efficient warm
rain processes will likely dominate today/tonight. Instability is
likely a limiting factor for depth/intensity of cells...however
the aforementioned moisture parameters would still favor shallow
low topped cells capable of very heavy rain rates. The other
limiting factor is longevity of cells at any one location...as
cells should generally pulse up and down rather quickly. The weak
instability potentially restricting the coverage of heavier cells,
and the short lived nature of most cells, may prevent a more
widespread flash flood risk today/tonight. However slow cell
motions and heavy short duration rates will likely still be enough
to result in scattered flash flooding.
There is certainly some potential for a more widespread and
significant event today over portions of WV and VA given the
efficient environment in place. A backdoor front dropping
southwestward will be a convective focus today, potentially
helping sustain a corridor of cell mergers...as it interacts with
terrain induced cells and slow moving cells downstream of the
front. The event today/tonight has Moderate risk potential over
portions of WV/VA...but a bit too much uncertainty on the
coverage/magnitude of impacts to go with the upgrade at this
point. At the minimum we are expecting isolated to scattered flash
flooding today. At the worst we could be dealing with more
numerous flash flooding, some of which could be locally
significant. We will continue to monitor trends through the day.