textproduct: Wakefield

WHAT HAS CHANGED

Updated full discussion. Increasing confidence for severe storms Tuesday afternoon and evening.

KEY MESSAGES

1) Typical summer weather today with scattered thunderstorms near the coast from early afternoon through early evening.

2) Widespread showers and thunderstorms expected Tuesday afternoon with the potential for damaging wind gusts and hail.

3) Isolated showers and storms are possible on Wednesday, with mainly dry weather to end the week. Temperatures drop to slightly below average late this week.

DISCUSSION

As of 240 AM EDT Monday...

KEY MESSAGE 1...Typical summer weather today with scattered thunderstorms near the coast from early afternoon through early evening.

Northwest upper/mid level flow continues to prevail over the forecast area early this morning with strong ridging over the central/southern CONUS and troughing over New England and offshore. A weak surface boundary is bisecting the area while an upper shortwave tracks over us at the same time. These features have been responsible for the storms we have seen in the Piedmont since last evening, with some very impressive storms in Louisa County and near Farmville. The kinematic environment remains strong with 40 kt of effective shear even though instability is modest given the loss of daytime heating. Expect storms to persist (mainly west of the bay) for the next few hours before gradually weakening as we head toward sunrise.

That weak boundary settles near the coast today with NW flow aloft continuing. Scattered tstms are expected to initiate along sea breeze boundaries by early afternoon, and persist through early evening before dissipating by 10-11 PM. Storm timing today should be closer to climatological norms when compared to the very late timing yesterday. Storms will likely spread slightly inland during the late aftn/early evening, but will struggle to make it to the I-95 Corridor. With the NW flow remaining in place, 25-30 kt of bulk shear, and moderate sfc-based instability, a few stronger storms are possible with the main threat being damaging winds, though large hail can't completely be ruled out. In addition to the severe threat, localized flooding is possible as the storms will be somewhat slow moving and will likely impact the urban areas of SE VA. The HREF ensemble has 30% probs of 3" of rain in 3 hours across SE VA/NE NC, with at least 10% probs for 3"/3 hours in other coastal areas.

KEY MESSAGE 2...Widespread showers and thunderstorms expected Tuesday afternoon and evening with better potential for severe weather. The main threat is damaging wind gusts with large hail also possible.

The set-up Tuesday continues to suggest that this will be the best shot at thunderstorms, with a decent chance for severe weather. An anomalously strong upper trough and sfc low are progged to deepen over the Northeast CONUS. In fact, the low could deepen to 993mb with -2 to -3 sigma height anomalies over the northern Mid- Atlantic/Northeast. The synoptic features are impressive especially considering it is late July. There will be a belt of 40-50 kt 500mb winds on the SW side of the trough that may move over the local area during the aftn. At the same time, the low will drag a cold front toward the area. Where there is a slight chance of showers and storms in the morning, the main window of concern is expected to be from 2-10 PM. Storms likely initiate near our northern CWA border during the afternoon before potentially moving SE through the area during the evening. Storms move offshore Tuesday night as the front moves through and winds become NW. Given the 500mb flow, impressive shear by July standards, and mid level lapse rates up to 6.5C...there could be a robust damaging wind and hail threat. Can't completely rule out a brief tornado near the coast as LLVL winds will be more backed here. SPC has maintained the Slight Risk (Level 2/5) for severe wx across the entire area. While the parameters look decent for severe wx, we will have to watch upstream overnight/morning MCS activity which is the main thing that could result in a lower severe threat than anticipated (especially across north and northeast portions of the FA). Highs Tuesday look to be in the upper 80s to around 90F, along with humid conditions with dew points in low-mid 70s. Storms will be moving quickly, which will act to limit flooding, but cannot rule out localized flash-flooding, mainly in urban/flood prone areas.

KEY MESSAGE 3...Isolated showers and storms are possible on Wednesday, with mainly dry weather to end the week. Temperatures drop to slightly below average late this week.

The low pressure system at the surface and aloft is progged to linger over the Northeast CONUS from Wednesday-Friday. With the closer proximity of the upper low, there cold be some showers/storms on Wednesday (mainly late in the day). Thursday through Friday looks mostly dry, with near to slightly below average temperatures, as LLVL flow will continue to be out of the NW.

AVIATION /06Z MONDAY THROUGH FRIDAY/

As of 110 AM EDT Monday...

VFR in place across the region with isolated tstms W and NW of the terminals. These should remain away from all terminals except perhaps SBY through 12z. Otherwise, some BR and MVFR stratus is possible at PHF/RIC between 09-13z. There is a low chc of IFR, but not confident enough to include this in the TAFs. VFR with SCT-BKN cumulus quickly develops by late morning. Main concern today is scattered sea breeze convection which is expected to develop by 16-18z and persist through 21-23z. Added PROB30 groups for TSRA at all terminals except RIC. Could see brief gusts to 30-40 kt in the stronger storms. Light and variable winds become SSE (inland) or SE 5-10 kt today.

Outlook: There is a higher chance for storms Tuesday aftn/evening as the next front approaches the region from the NNW. Some of the storms could be severe on Tuesday. Isolated showers/tstms are possible Wednesday but PoPs are much lower than on Tuesday.

MARINE

As of 240 AM EDT Monday...

- Sub-advisory conditions prevail with southerly winds today.

- A cold front approaches on Tuesday, which could bring a period of low-end SCAs with S-SW winds.

Weak sfc high pressure is now offshore with S-SE winds around 10 kt early this morning. Seas are 2-3 ft with 1-2 ft waves in the Bay and rivers. Benign marine conditions with light winds are expected today outside of aftn/early evening tstms which could result in a few SMWs. S to SW winds increase by a few knots this evening-tonight (w/ gusts of 15 kt possible). The gradient is expected to tighten on Tuesday ahead of the next front. S and SW winds are forecast to increase to 15-20 kt in the Chesapeake Bay, and 20 kt w/ gusts to 25 kt offshore. Local wind probs for sustained 18 kt winds have increased to 50-70% from 1-7 PM Tue on the bay. SCAs on the ocean are a bit more uncertain as local probs for 25 kt gusts are below 50%, this is a WAA regime, and seas may struggle to get to 5 ft if the flow becomes more SW than S. The main weather concern Tuesday is the better chance of strong to severe storms over all of the waters during the afternoon and evening with gusty winds the primary threat. In the wake of the front, winds will decrease to 5-15 kt and shift to the NW. NW winds may increase with low-end SCAs possible Wed night into Thursday but a lot of uncertainty remains at this range.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...None. VA...None. MARINE...None.