April 20, 2012

Rain is Coming

Soaking rainstorm will unfold in at least part of the eastern United States this weekend.

However, there is also the potential for severe weather.

There is no doubt the region is in need of rainfall when gauging rainfall deficits, the number of wildfires, near-record low stream levels and late-summer ground water tables. The rain will foil some outdoor plans, sporting events and projects.

The storm will help some areas with their rainfall deficits. However, the overall scope, duration and intensity of the rain is still in question.

Some areas will receive over an inch of rain, while others may not get enough to greatly impact the building dry conditions.

During the weekend, a front will progress slowly eastward from the Midwest with a zone of rain. The rain may reach the Appalachians by Saturday midday and will progress toward the coast over the balance of the weekend.

For the Appalachians, it appears now that the front has the best shot delivering rain, instead of a storm that follows soon thereafter.

A modest storm delivered some needed rain to part of the south during the middle of the week.

However, the main storm we refer to will evolve over the South this weekend, then is forecast to migrate slowly northeastward during early next week.

This track opens up several options for the overall zone of rain and its behavior.

One scenario causes the rain to congregate along the Atlantic Seaboard then head out to sea Monday. With this setup, eastern New England would gather the most rain in the Northeast.

Another, less likely scenario spreads the rain westward with time back over part of the Ohio Valley and eastern Great Lakes and develops wet snow over the highest elevations. This idea would be a long-duration, unsettled event reaching into the middle of next week.

Both scenarios will drive unseasonably chilly air into the eastern half to third of the nation for at least a several-day stretch.
Severe Weather Risk

Both scenarios also appear likely to bring a round of severe thunderstorms to portions of the South during the first part of the weekend as the storm begins to take shape with rapid cooling of the upper atmosphere. This setup makes the atmosphere very unstable and favorable for tall and potentially damaging storms.The initial area of concern would be from the northeastern Gulf of Mexico waters to Florida and Georgia. Since storms may affect coastal waters, weekend boating interests should keep up to date on the situation.

Both scenarios also deliver generous rain to portions of the South.

If the storm system was to really get cranking, such as the case of the second scenario, then potentially violent thunderstorms and flash flooding problems could pivot up along the Atlantic Seaboard into the Northeast.

Chances are that the outcome of the storm's evolution and precipitation will be somewhere in between both scenarios, perhaps favoring the coastal track and part of New England and the Deep South receiving the most rain.

By Alex Sosnowski, Expert Senior Meteorologist  - Accuweather.com  April 20, 2012

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