Saturday, April 21, 2012

Forecast for Sunday, April 22, 2012

Scattered showers and thunderstorms will move through the region this evening and tonight. The main threat from these thunderstorms will be cloud to ground lightning and locally heavy rainfall. There is weak instability in place and strong winds aloft and any thunderstorm could drag some of this wind to the surface and create some strong wind gusts. With the arrival of most of the activity after dark, the highest chances for any severe weather will be in our western suburbs.

Sunday Morning will likely be overcast. There could be some areas of fog along with patches of drizzle. However, a coastal storm will likely develop off the Carolina coastline along a stalled frontal boundary and move northward throughout Sunday Afternoon and Evening. Rain will develop and become heavy at times late in the morning into the afternoon. There is a slight difference between each of the computer models on the axis of heaviest rainfall. However, a general two to four inches of rain can be expected with locally higher amounts. The models right now point to late Sunday Afternoon and Sunday Evening for the heaviest rains. Even though it has been dry, this amount rainfall in less than twenty-four hours can certainly result in small stream, highway, and urbanized flooding. Even some of the flashier creeks may see significant rises.

The exact track will not only determine where the heaviest axis of rain develops, but also where the strongest wind field will exist. Most of the time, when you are east of the low pressure track, you find the strongest winds. Based on the latest guidance, there is a strong possibility that New Jersey and Delaware could be east of the center. If this is the case, sustained winds of 20 to 30 MPH with gusts to 50 MPH are likely over interior sections of New Jersey and Delaware with gusts of 60 MPH or greater along the coastal communities. West of the Delaware River may even see wind gusts to 35 or 40 MPH at times with the center passing close to Philadelphia. With many trees now near full canopy, this wind along with a ground that will be getting a soaking may be enough to knock down some trees and power lines. If 60 MPH gusts at the shore are realized, that is wind strong enough to cause some property damage. Sometimes such potent coastal lows around the Spring months can create brief tornadoes on the northeast quadrant. If New Jersey and Delaware fall on the eastern side of the storm track, there is a slight chance of a spin-up. If the model guidance nudges the track of the system closer to the coast in the late night runs, the strongest winds and tornado threat will be along the immediate coast and out over the ocean.

Coastal and tidal flooding will also be a concern, as it always is with Nor’easters. Widespread minor flooding with even some moderate severity flooding is expected. High surf and dangerous rip currents will also exist if you plan to venture out in the water. With the boating season probably off to an early start with the recent mild weather, you certainly may want to secure your belongings.

The low pressure area will meander around the Northeast on Monday and continue the chance for showers. Another round of gusty winds is anticipated as the low remains deep and high pressure tries to move in, creating a tight pressure gradient. A weak system may affect us mid-week.