Area Forecast Discussion

WHAT HAS CHANGED

Severe Thunderstorm Watch has been cancelled for approximately the SE 2/3 of the CWA in VA (from much of metro RIC and pts SE) given that the end time of the Watch is 10 PM.

KEY MESSAGES

1) A lull in convection for the next 2-3 hrs, with additional strong to severe thunderstorms and heavy rain possible/redeveloping overnight.

2) The threat of severe thunderstorms will linger into Wednesday and the potential for torrential rainfall to produce scattered instances of flash flooding will also increase through Wednesday night and Thursday.

DISCUSSION

As of 815 PM EDT Tuesday...

KEY MESSAGE 1...A lull in convection for the next 2-3 hrs, with additional strong to severe thunderstorms and heavy rain possible/redeveloping overnight.

Latest WX analysis indicates a lull in the convection this evening as the initial batch has weakened/moved offshore. Have therefore cancelled the SVR Tstm Watch (that had been in effect through 10 PM) for much of central and SE VA as there is little to no threat for additional storms of significance over the next 2-3 hrs. Have left the Watch in effect to the N/NW in case some of the stronger storms across the I-81 corridor hold together as they reach into the CWA between 9-10 PM. Low level lapse rates have diminished significantly over the past 1-2 hrs as the airmass has been worked over with numerous showers/storms, but shear remains strong at 35-45 kt.

The Severe threat overnight is somewhat uncertain as the instability has waned, but with the continued strong shear, additional strong to severe storms will certainly be possible and an additional SVR Watch may be needed. Probably of higher confidence is that additional heavy rain and a hydro threat will redevelop and persist overnight given the PWAT values of 2.00-2.25" and the potential for training/backbuilding storms, as the front slows overnight (and eventually Wednesday/Wednesday night). An initial Flood Watch has been issued from central VA to the lower Eastern Shore covering the threat tonight into Wednesday. This will eventually need to be expanded SE to cover the later Wednesday/Thursday time period.

KEY MESSAGE 2...The threat of severe thunderstorms will linger into Wednesday and the potential for torrential rainfall to produce scattered instances of flash flooding will also increase through Wednesday night and Thursday.

The severe threat likely continues into Wednesday, but with the higher probabilities shifted to the south and east ahead of the aforementioned southward-moving cold front. How convection evolves today/tonight will also influence the degree of cloud cover and destabilization potential on Wednesday. That said, the flow aloft is forecast to remain rather strong (40-50kt at 500mb). SPC has the Slight Risk outlined for our entire CWA (lvl 2/5).

Despite the ongoing drought conditions, Wednesday into Wednesday night is showing an increasingly confident signal for localized flooding, especially in urban and poor drainage areas. WPC has most of the area in a Slight Risk ERO again Wednesday with PW generally 2- 2.4", and a small Moderate Risk area will be issued for SE VA into NE NC. Additionally, a small Moderate Risk area will be introduced including NE NC Thursday. Decent flow aloft should keep individual cells moving but training storms on top of the rainfall received today/tonight could cause scattered instances of flash flooding. A Flood Watch will eventually be needed for SE VA and NE NC based on the latest data. All total, the QPF forecast through Thursday has generally 3-5", with locally higher amounts of rain from Richmond and Emporia eastward to SE MD and NE NC.

Some drier air finally moves back into northern portions of the region Thursday and Friday but some showers and storms will remain possible, mainly across the southern and southeastern portions of the area. Trending drier with below average temperatures by the weekend.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

As of 743 PM EDT Tuesday...

Most of the terminals are clear of convection for now, but another round is expected overnight. The expected timing of convection tonight through tomorrow evening is a little tough, as we now wait to see what the second round of storms do tonight which will likely have an impact on what happens tomorrow. There is more confidence at the southern terminals for the afternoon convection, so have included PROB30 at PHF, ORF, and ECG to account for this. CIGs are forecast to come down overnight into tomorrow morning, with most terminals (except for ECG) seeing at least a few hours of MVFR CIGs, with a few hours of brief hours of near IFR CIGs possible at RIC and maybe SBY. Winds outside of convection will gust to 15-20 kts from the SW through the TAF period.

Outlook: Additional rounds of storms are possible through Thursday, and intermittent flight restrictions are likely. Rain and storm chances shift south by late week, but could still impact KORF/KPHF down to KECG.

MARINE

As of 255 PM EDT Tuesday...

- Small Craft Advisories are in effect for the local waters from this afternoon into Wednesday.

- Strong thunderstorms are possible today and Wednesday, primarily during the afternoons and evening.

SW winds behind the warm front that moved across the area early this morning are just short of Small Craft Advisory criteria this afternoon at 15-20 kt in the Ches. Bay and 20-25 kt in the coastal waters. Winds will continue to gradually increase into the overnight as the pressure gradient tightens with winds peaking at 15-20 kt with gusts to 25 kt in the Ches. Bay, tidal rivers, and Currituck Sound, and 20-25 kt with gusts to 30-34 kt in the coastal waters. A few gusts around 35 kt will be possible past 20 nm, especially for the southern zones. These conditions continue into Wed morning, then diminishing Wed afternoon and evening. SCAs are in effect for all marine zones (excluding the 20-60 nm zones where SCAs are not issued) through 1 PM Wed for the Ches. Bay, Currituck Sound, and tidal rivers and 6 PM for the coastal waters. A surge of northerly winds is possible Wed night into early Thurs with gusts to 20 kt in the Ches. Bay, which could need another SCA. Lighter NE winds are likely Thurs afternoon and into the weekend.

Multiple rounds of thunderstorms are expected from today through Thurs morning. Some storms may be severe with strong, erratic winds. The highest risk is today through overnight across the VA and MD waters. Additional strong to severe storms are possible Wed into Thurs.

Seas build to 3-4 ft by this evening as the winds pick up with waves in the bay increasing to 2-3 ft. Seas of 4-5 ft for southern nearshore waters and 5-6 ft for the northern nearshore waters are forecast overnight (6-7 ft offshore). Waves up to 4 ft expected in the bay overnight. 5+ ft seas may linger as late as Wednesday night.

AKQ WATCHES / WARNINGS / ADVISORIES

MD...Flood Watch through Wednesday afternoon for MDZ022>025. NC...None. VA...Flood Watch through Wednesday evening for VAZ048-060>062- 065>069-076>090-092-099-100-509>520-522>525-528. MARINE...Small Craft Advisory until 1 PM EDT Wednesday for ANZ630>637- 639. Small Craft Advisory until 6 PM EDT Wednesday for ANZ650-652- 654-656-658.