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Forecast Discussion



... Complexes of thunderstorms will track from the Midwest into the Mid Atlantic and central Appalachians several times through the end of the week before a cold front moves into the region by the weekend. Humid conditions continue all week.

NEAR TERM /THROUGH TODAY/... As of 1045 PM EDT Tuesday...

Minor changes to the forecast for tonight. Fog has developed where it rained today and this will be the forecast challenge overnight.

As of 725 PM EDT Tuesday...

Quiet for the remainder of tonight, then more storms tomorrow...

Main line of storms has moved south into central TN and NC. We are mostly dealing with stratiform showers behind this line, but these are also shifting south. We had numerous reports of downed trees as well as heavy rainfall leading to urban and small stream flooding.

The remainder of the night will be quieter with lows in the 60s and 70s, with isolated showers possible for the mountains, but no thunder. Tomorrow expect storms entering from the northwest by mid morning and spreading/developing farther southeast for the afternoon and early evening, similar to today. The severe weather threat tomorrow looks perhaps better to our west and also to our south, but some severe storms will be possible again tomorrow for our area. Again damaging winds and heavy rainfall leading to flooding are the main concerns.

As of 215 PM EDT Tuesday...

The chance of showers and storms, some with locally heavy rains and strong/damaging winds, continues this evening and returns Wednesday.

Scattered thunderstorms have been moving into the region from the northwest this afternoon and growing in coverage as the local airmass grows more unstable in the heating of the day. A concern continues this afternoon and evening for a few of the stronger storms to increase to severe levels and generate some damaging winds. The potential for this should increase as the showers and storms progress into Southside Virginia and neighboring sections of north-central North Carolina. Downdraft CAPE values have a maximum in this area between 1000 and 1500 J/Kg. Also, while the precipitation is moving around 20 to 30 mph, localized flooding could become a concern in areas where multiple heavy showers or storms cross the same location in a short period of time.

Given the convection is more than just diurnally driven, we do not expect an immediately dissipation of the activity once sunset arrives. While there will be a general trend downward in coverage, it is likely to be more gradual with the last of the precipitation ending around midnight.

Overnight, while lower clouds are expected to dissipate for most locations, there will be a concern for fog development, especially in those area which receive the most rainfall this afternoon and evening. Also, mountain and river valleys will be good candidates for fog development as well. Some lingering lower clouds may also be possible over portions of southeast West Virginia.

On Wednesday, we will continue within the same pattern as today. Isolated to scattered showers or a few storms may be in or close to the northwestern sections of the region around sunrise. As the day progresses, coverage increases with the potential for a thunderstorm complex to head southeast toward/into the area from the Ohio Valley. Again, there will be the concern for the strongest storms to generate strong/damaging winds, and locally heavy rains could generate some localized flooding.

The combination of heat and humidity may allow the heat index to reach the 100 to 105 range for a couple of hours across the far eastern and southeastern sections of the area tomorrow afternoon.

Humidity levels will remain high and temperatures will generally be above average for this time of year.

Confidence in the above weather scenario is moderate to high.


Thunderstorms each afternoon and evening this week...

The main driving feature of this period's weather will be an upper ridge situated over the southeastern CONUS. We are placed in northwest flow on the ridge's eastern side, downstream of the Great Lakes and OH River Valley regions. Shortwaves embedded around the ridge will be advected through those regions where thunderstorm-producing systems will form and grow, eventually reaching our forecast area. Several of these systems are expected to cross through our area, with exact timing still uncertain. The greatest likelihood is that each afternoon/ evening seems primed for thunderstorm activity, and these upper disturbances are likely to maintain thunderstorm activity well into the overnight hours.

The threat for any flooding with this activity appears to be in the form of localized flash flooding, with better chances where rainfall impacts any areas multiple days in a row. Precipitable water values across the lower Mid-Atlantic will increase to 1.75 inches or higher, a sign of deep moisture in the atmosphere to work with. Strong instability with afternoon heating may also result in high rainfall rates in the stronger storms. However, storms should remain moving for the most part, and given some areas haven't received rainfall in over a week, much of our region can handle at least some excessive rainfall.

Temperatures will be a few degrees above normal for this forecast period. Dewpoints will be high, so heat indices could reach 100 degrees in parts of the Piedmont and Southside VA Thursday and Friday.


Weekend front keeps showers around for most of the weekend...

A cold front associated with a strong shortwave will approach our area late Friday. As with many summer frontal boundaries, it will gradually lose southward momentum and eventually stall against subtropical ridging this weekend.

As the boundary remains near the Mid-Atlantic and the Carolinas through most of the weekend, it will keep showers in our region through Sunday. As higher pressure and ridging comes east into our area by Monday, precipitation coverage will then diminish for early next week, allowing temperatures to regulate a bit closer to normal by the end of the period.