Wednesday Morning Update On Approaching Storm System

A strong storm system with a history of producing severe weather is heading toward the East Coast today and Thursday. Rain has been moving into southwest Virginia early this Wednesday morning, and will gradually expand north and east into central Virginia this afternoon and tonight.

I do not expect rain to reach the Richmond Metro area until after dark, closer to 9 p.m., and then rain overnight into most of Thursday.









A Flood Watch is in effect for the green counties highlighted on this map, where the highest accumulations are possible (because it will rain the longest here):

However, here is a snapshot of the potential rainfall accumulation in central Virginia by late Friday night as the rain ends, which shows most locations should receive at least 1"-2" of rainfall (dark blue shade):

In addition to the potential for heavy rainfall, we'll also have the threat for severe weather. Thursday afternoon and evening, conditions will be ripe for strong to severe thunderstorms in part of central and southeast Virginia (yellow on this map below):

The primary threat will be damaging straight-line winds (like what we saw on Sunday), but the environment will also have enough wind shear to potentially produce brief tornadoes. A potent upper vorticity maximum will dig into the region, producing significant lift and instability in eastern North Carolina and into Virginia:

At the same time, strong southerly flow will force moisture to surge northward into the Mid-Atlantic ahead of the system's cold front Thursday. This moisture (look at the bright green shades on the map) will serve as fuel for storms:

The warmer air mass that will also surge northward into the Commonwealth Thursday afternoon will combine with the wind shear and moisture to generate instability, shown below in purple as CAPE (Convective Available Potential Energy):

The areas in purple, you can see, align closely with our yellow Slight Risk map above. This is the part of the region most likely to receive severe weather Thursday afternoon and evening because of this optimum combination of factors.

After the heavy rain ends late Thursday night, the James River will rise Friday and Saturday higher than it did on Tuesday night as a result of Sunday's heavy rainfall. Click here for the latest James River forecast for Richmond-Westham. You can also check the level a little farther downstream at Richmond Locks by clicking here.
--Carrie--

More Heavy Rain Likely Wed-Thur

More heavy rain is likely Wednesday and Thursday from a storm system developing Tuesday morning in the Southern Plains. A Flood Watch is already in effect in advance of this storm system for the Virginia counties highlighted in green on the map below:

The center of the storm system (the L for low) will track to our north, pulling in moisture and warmer temperatures from the south.

Rain should be nearly constant for western parts of the state Wednesday and Thursday, which is why they will be able to accumulate the highest rainfall amounts.

But Thursday the rest of central Virginia will have a shot at some heavy downpours and thunderstorms as a result of the instability generated ahead of the approaching surface cold front and the ample moisture and warmer temperatures in the 60s surging northward into the Commonwealth.

Instability, as shown below by the CAPE value (Convective Available Potential Energy), should be sufficient to support strong to severe thunderstorms in central Virginia Thursday afternoon and evening. Damaging straight-line winds (of the likes we saw Sunday in parts of the state) will be our primary threat again on Thursday. However, the Tidewater region of Southeast Virginia may also have the threat for a few tornadoes.

By the time the rain ends from west to east late Thursday night, one to three inches of accumulation looks likely for much of central and western Virginia.

Flood Warning for James River in Richmond

Sunday's heavy rainfall (see previous blog entry for a summary), especially in western Virginia, is heading downstream. The James River is expected to swell above the 12.0 FT flood stage (Richmond-Westham gauge, near the Huguenot Bridge) Tuesday morning and max out at 13.2 FT at about 10 a.m. Tuesday.

At that level, about 20 acres of lowlands near the gauge will flood, but no residences in the vicinity will be affected along the river. You can check the latest River level and forecast by clicking here. With the rising level, and likely debris that will be coming downstream, activity in the James is discouraged in Richmond until the river falls back below flood stage Wednesday morning. Extra caution is also advised along the riverbanks as erosion can occur.