textproduct: Blacksburg

SYNOPSIS

Remnants of Chantal will move north out of North Carolina this evening and into Virginia tonight, then east of the area on Monday. Rain, heavy at times, will fall mainly east of the mountains. A daily chance of rain and thunderstorms is expected beginning Monday, continuing through the weekend.

NEAR TERM /THROUGH MONDAY/

As of 130 PM EDT Sunday...

Key Messages:

1) Remnants of Chantal move through the area this afternoon through tonight.

2) Potentially heavy rain across portions of the Piedmont of Virginia/North Carolina.

Chantal is now a tropical depression, currently centered over central North Carolina. Chantal will continue to weaken as it slowly lifts north through tonight. Forward speed will begin to increase once it begins to move across Virginia and should be east of the area by sunrise on Monday.

Will see increasing rainfall later this afternoon as the center moves closer and appears to track from Caswell County north through Halifax and Charlotte Counties. The heaviest rainfall zone will be rather compact and will be closely associated with the low pressure center of the remnants. HREF rainfall probabilities seem to be pinpointing Caswell County in North Carolina and north into Southside Virginia for the heaviest rain between 8PM and midnight. Precipitable Water values also continue to increase and are expected to exceed 2" which will result in the increased potential of very efficient tropical downpours capable of localized flooding issues overnight. Will expand the current Flood Watch north to include a few more counties in Virginia to account for the increasing flood potential.

Outside of heavy rainfall, a low tornado threat exists across Southside Virginia and north Central North Carolina as a few feeder bands rotate through within a modestly unstable and sheared environment.

Remnants of Chantal will finally lift northeast out of the area on Monday with gradual clearing expected. Winds shift westerly behind the system and downsloping subsidence will result in temperatures in the 90s from Roanoke and east. A few afternoon/evening thunderstorms are possible, but westerly flow may prevent any widespread storm development.

SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/

As of 130 PM EDT Sunday...

Key Messages:

1) Multiple rounds of showers and thunderstorms after Tropical Depression Chantal's passage.

2) Marginal Risk for damaging wind gusts and excessive rainfall on Tuesday.

An active weather week is ahead regardless of the impacts of Tropical Depression Chantal. By Tuesday morning, Chantal will be well outside of the area. There may be a very brief calm period before a long frontal system arrives in the area to bring daily chances of showers and thunderstorms. The frontal system still looks to stall and meander about the Mid-Atlantic. Even so, the moist and hot conditions this week will be enough to support pulse storms similar to what was experienced in late June. Dew points are expected to be between the mid-60s and mid-70s and high temperatures are likely to be from the lower 80s up to the lower 90s. The heat index may reach up to 100 degrees for counties east of the Blue Ridge.

Two upper level ridges are to form over the southwestern CONUS and the Deep South. The southwestern CONUS ridge is forecast to be stronger and robust while its sister counterpart is expected to weaken as the week progresses. An upper level trough develops in between these ridges over the Great Plains and begins to stretch a little south as the Deep South ridge degrades. As a result, the Mid- Atlantic will find itself under the downstream portion of this trough. The overall upper level pattern supports the transportation of multiple shortwaves into the region to assist in thunderstorm development. While effective bulk shear struggles to get above 25 kts, the atmosphere will be unstable enough to support severe wind gusts on Tuesday for most of the region. The Storm Prediction Center has issued a Marginal Risk for Tuesday due to this hazard potential.

With the multiple opportunities of showers and thunderstorms, there is a concern for localized flooding. Because of how isolated this hazard could be, it is difficult to narrow down where the most rain can be expected later this week. The Weather Prediction Center has issued a Marginal Risk of Excessive Rainfall for areas (generally) north of I-81 for Tuesday, but this will be closely monitored for any future changes.

LONG TERM /THURSDAY THROUGH SATURDAY/

As of 130 PM EDT Sunday...

Key Message:

1) Weather pattern of daily showers and thunderstorms continues.

Active weather continues for the rest of the week into early next week with daily showers and thunderstorms. A frontal system just to our north is expected to continue to stall and subtlety move around. A boundary line left by Tropical Depression Chantal may assist in the initiation of storms regardless of where the front ends up moving. Dew points in the mid-60s to mid-70s and warm temperatures (highs between the mid-70s to mid-80s) will still provide an unstable atmosphere for afternoon showers and thunderstorms each day. Meanwhile, an upper level ridge over the southwestern United States will continue to maintain its strength while a weaker ridge over the Deep South is forecast to degrade and move into the Gulf. A trough over the eastern CONUS will provide the weather pattern to pass multiple shortwaves through the Mid-Atlantic from the Great Plains and support thunderstorm development. While severe potential currently looks low and uncertain, PWAT values between 1.5-2.0 inches raise the concern for flooding. However, since many of these storms may be pulse based, the flood threat is too localized and adds additional challenges to the forecast.

EXTENDED AVIATION OUTLOOK

The forecast area then transitions back into a typical summertime weather pattern with daily chance of showers/storms during the peak heating hours each day. Morning fog possible each day, especially at LWB and BCB.

RNK WATCHES/WARNINGS/ADVISORIES

VA...Flood Watch through Monday morning for VAZ043>046-058-059. NC...Flood Watch through Monday morning for NCZ004>006. WV...None.