textproduct: Blacksburg

WHAT HAS CHANGED

No significant change to the forecast. Daily threat of showers and thunderstorms. Primary hazard is localized heavy rain, but some potential for strong damaging winds across the Carolinas this afternoon.

KEY MESSAGES

1) There is a marginal risk of excessive rainfall for Virginia and the Carolinas today/tonight.

2) Unsettled weather will persist through the rest of this week with daily chances of showers and thunderstorms.

DISCUSSION

KEY MESSAGE 1...There is a marginal risk of excessive rainfall for Virginia and the Carolinas today/tonight.

A very moist airmass remains in place today with persistent easterly flow advecting deep moisture into the region. Surface analysis indicates that a stalled boundary is draped over the region, in addition to a wave of low pressure that is easily identifiable in the satellite water vapor imagery. The concerning factor is the low is nearly stationary which means steering winds will remain stagnant with little or no geographic change in the position of the surface front today. As such, expect persistent formation of showers and a few storms within the vicinity of the front, with heaviest of the rain today falling over southern Virginia and into North Carolina. This is where hi-res CAM guidance continues to pinpoint on the greatest coverage of heavy rainfall.

12z RNK RAOB shows an increase in Precipitable Water when compared to yesterday and current RAP analysis continues to increase these values, with some of the area now closing in on 2 inch values. This will result in very efficient rainfall which could lead to an increased potential for flash flooding through late this evening.

Away from the convergent zone near the surface front, not expecting a lot of shower coverage. However, heating of the day instability driven showers are still possible but they should not be as organized as what is expected along the actual surface front. The Storm Prediction Center has highlighted a small marginal risk area for strong to severe storms over western North Carolina...an area closer to the center of the upper low. Warming surface temperatures in the higher terrain will result in scattered convective initiation across the southern Appalachians. As instability peaks and low-level lapse rates become steep over the next few hours, an isolated wind-damage threat is expected to develop in the western Carolinas.

By tonight, loss of daytime heating should mitigate any severe threat, but a localized excessive rain hazard will linger. The surface front over southern VA should begin to lift north as the upper low begins to open up and shear out. This should reconfigure the axis of low level convergence with areas closer to the US 460/I-64 corridor targeted for the higher qpf overnight.

KEY MESSAGE 2...Unsettled weather will persist through the rest of this week with daily chances of showers and thunderstorms.

The upper low over the Mid-Atlantic will shear out and weaken Wednesday. Meanwhile a large upper level ridge builds over Bermuda and another upper level trough approaches the Great Lakes. Wind flow between these two features will maintain a persistent flow of moisture into the forecast area, enough to fuel daily showers and thunderstorms, most of which should coincide with the peak heating of the day favoring the afternoon and evening hours. We are not expecting anything severe, but a marginal risk for flash flooding will continue to be a hazard due to the potential for high rain rates which may lead to runoff issues.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Persistent easterly flow and a front within the vicinity has kept clouds over the region, with MVFR cigs quite common for most terminals. This will likely continue throughout the afternoon and evening, along with the potential for heavy downpours that could cause brief vsby reductions. Expecting deteriorating conditions overnight as clouds lower and fog develops...IFR/LIFR becoming more likely for most terminals. Slow to improve Wednesday morning with sub VFR possibly lingering again throughout much of the day.

Winds generally remain out of the east today...going light to calm overnight.

EXTENDED AVIATION OUTLOOK...

Scattered, mainly afternoon showers and thunderstorms are expected the remainder of the week. Abundant moisture favors MVFR ceilings at times along with patchy overnight fog.

HYDROLOGY

There is a marginal risk for excessive rainfall the next several days. Repeated chances of showers and thunderstorms amidst a moist air mass will persist the remainder of this week. Not a lot of confidence in the details for any particular location.

PWAT values expected to remain in the 1.50" to 2.00" range. High ambient moisture will produce very efficient rainfall rates which could exceed 2-3 inches per hour. Urban areas and along mountainous terrain will be particularly susceptible to flash flooding.

Antecedent soil conditions are gradually turning wetter across the area, but there are still considerable rainfall deficits across the Piedmont.

RNK WATCHES/WARNINGS/ADVISORIES

VA...None. NC...None. WV...None.