Area Forecast Discussion

WHAT HAS CHANGED

No significant forecast changes.

KEY MESSAGES

1) Typical summer weather today and Monday with near average temperatures and late afternoon-evening showers/storms.

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

3) Some uncertainty regarding the forecast for Wednesday, then mainly dry and near normal temperatures through the weekend.

DISCUSSION

As of 330 PM EDT Sunday...

KEY MESSAGE 1...Typical summer weather tonight and Monday with near average temperatures and late afternoon-evening showers/storms.

Northwest upper/mid level flow has set up over the forecast area as the axis of a seasonably deep trough shifted offshore this morning. This is typically a favorable set-up for severe weather across this area, and will likely be a factor in making up the the slightly cooler than normal temperatures acting to limit some instability, especially today/tonight. The NW flow will work in tandem with a shortwave that is progged to move across the area this evening into tonight. This will help enhance the environment and bring good kinematics to help sustain storms when they develop. With the lowering heights, drier air aloft, and modest deep-layer shear, this evening could bring a mix of a wind threat and potentially a hail threat. Hi-res guidance is depicting a late start to thunderstorm development, and this, paired with the best environment due to slightly higher dew points and better instability, will generally keep the best chance for severe weather to the west of I-95 this evening into tonight. The farther east these storms progress, they will enter a less favorable environment, but isolated to scattered showers and thunderstorms are still possible across most of the area through tomorrow morning.

Another round of scattered storms is expected Monday, but with an earlier initiation time and coastal areas being included in the action. The NW flow will remain in place, and when combined with about 30kt of bulk shear and 1500-2000 J/kg of CAPE, could help produce stronger storms. Will note that some hi-res guidance has lesser coverage and is more focused on the sea-breeze initiation. This will be dependent on the evolution of the storms through tonight and how the environment recovers, especially in the piedmont.

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

The set-up Tuesday continues to suggest that this will be the best shot at thunderstorms, with a decent chance for severe weather. SPC currently has a Slight Risk (2/5) The Mid-Atlantic will still be under NW flow as a cold front sweeps through at the surface. Global models continue to depict a strong upper trough becoming a cut off low somewhere over the upper Mid-Atlantic or Northeast, but differences in the exact location of this low and subsequent surface boundary will impact timing. Regardless, confidence is increasing in a strong synoptic set up for severe weather. Shear looks impressive by July standards, and the models mostly depict decent instability and even mid level lapse rates up to 6.0-6.5C, which would support a robust damaging wind and hail threat. As always though, timing of the storms will be important to how much severe weather occurs, though there is good consensus that storm initiation will in the mid- late afternoon. 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...Some uncertainty regarding the forecast for Wednesday, then mainly dry and near normal temperatures through the weekend.

There is some uncertainty in regards to rain chances in the wake of the cold front on Wednesday. With the closer proximity of the upper low, there cold be some showers on Wednesday. Blended guidance still has low PoPs, but this may be adjusted depending on the location of the upper low to our area. Thursday through the remainder of the weekend looks mostly dry, with seasonable temperatures.

AVIATION /19Z SUNDAY THROUGH FRIDAY/

As of 150 PM EDT Sunday...

VFR conditions prevail at all terminals this afternoon. Heading into this evening, there is potential for thunderstorm develop in the piedmont that could move over RIC, so have included a PROB30 for now. While there is a chance that other terminals could see some showers/thunderstorms during the TAF period, confidence was too low to include at this time. Winds will be light and, for the most part, variable through tomorrow morning, though the sea breeze influence at PHF and ORF has kept winds between 5-10 kts. Winds will shift to the south at most terminals tomorrow, remaining light.

Outlook: Isolated to widely scattered late aftn/evening showers/storms are possible both tonight and Monday, with a higher chance for storms Tuesday aftn/evening as the next front approaches the region from the NNW. Additional SHRA/TSRA possible Wednesday.

MARINE

As of 330 PM EDT Sunday...

- Sub-advisory conditions prevail with easterly winds shifting to the S-SE overnight and Monday.

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

Weak sfc high pressure has started to settle across the local waters this afternoon, allowing winds to shift from N to E at 5-10kt. Seas are 2-3 ft, with waves in the Bay 1-2 ft or less. The pressure gradient remains fairly weak overnight and through Monday as the sfc high becomes centered just offshore. Light S-SE flow is expected with seas 2-3 ft and mainly 1 ft waves in the Bay and rivers. The gradient is expected to tighten on Tuesday ahead of the next front. S and SW winds are forecast to increase to ~15 kt w/ gusts to 20 kt in the Chesapeake Bay, and ~20 kt w/ gusts to 25 kt offshore. A few strong storms are possible Monday aftn/evening, though a better chance is expected Tuesday 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.

A moderate rip risk continues into this evening for the southern beaches due to seas around 3 ft. The rip current risk drops to low for all beaches on Monday and Tuesday.

AKQ WATCHES / WARNINGS / ADVISORIES

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