Marine Weather and Tide Forecast for Calvert Beach, MD

KEY MESSAGES
- 1) Monitoring potential for localized urban flooding tonight into Wednesday morning as a warm front lifts north.

- 2) Daily shower and thunderstorm chances are expected from Wednesday into early next week.

DISCUSSION
KEY MESSAGE 1...Monitoring potential for localized urban flooding tonight into Wednesday morning as a warm front lifts north.

While the earlier frontal boundary is currently down in southern Virginia, broad ascent atop this frontal zone is yielding multiple areas of convection. The latest KLWX WSR-88D radar imagery depicts one such wave bringing some light showers to areas just north of I-64 in central Virginia. Being at the leading edge of the instability gradient, this storm cluster is not terribly organized and has continued to weaken. However, in the wake of these storms, a more concentrated axis of heavier showers and thunderstorms have begun to develop around the Richmond metro area. These are slow moving and already yielding Flash Flood Warnings in central Virginia. Looking further south, additional slow moving cells are forming over the Virginia Tidewater region. As the warm front lifts northward in time, all of this convection shifts focus toward the local area by tonight into early Wednesday morning. How this evolves over the next 6 to 12 hours will dictate the degree of impact to the region.

Besides the showers moving near/just east of Charlottesville, the weather has been tranquil across the remainder of the area.
Aside from some shallow fair weather cumulus fields, skies remain mostly sunny this afternoon. Being north of the frontal zone, mean surface winds are largely out of the east to northeasterly direction. Overall temperatures are holding steady in the low/mid 80s, with mainly 70s across mountain locales.
This comes with dew points in the 60s which are supporting heat indices in the mid 80s to low 90s. Expect clouds to increase into tonight as the warm front lifts poleward. Forecast lows will be in the 60s to low 70s, with increasing shower chances.

Looking a bit more closely at the threat for overnight heavy rainfall, the 12Z high-resolution models are not showing the strongest of signals. However, there are a number of meteorological conditions which warrant this situation to bear watching. This includes: (1) Precipitable water values (PWAT)
increasing from 1.50 to around 2 to 2.25 inches, (2) An uptick in warm advection with the approaching front, and (3) Enhanced lift with vorticity swinging northward from an upper low across the Mid-South. Where the heavy rainfall sets up will dictate the degree of impact. If this impacts the urban sprawl around the D.C. metro, poor drainage will support a risk of flash flooding.
Will continue to monitor the situation and 00Z/18Z guidance to determine if any Flood Watches will be needed.

KEY MESSAGE 2...Daily shower and thunderstorm chances are expected Wednesday into early next week.

In the wake of what morning convection materializes, the models do show a brief lull in the action. The northward pushing warm front eventually stalls nearby before shearing out. Likewise, the upper low across the Mid-South region begins to fill although the reflection of this circulation still shows up across southern West Virginia on Wednesday. Remaining perturbations around this mid/upper low should help fire off some afternoon/evening thunderstorms. A number of models depict anomalous moisture lingering across the region with PWATs over 2 inches for those of the Blue Ridge. While no clear signal exists, slow moving cells could produce a few instances of flash flooding. However, the longstanding drought conditions could easily curb that threat.

Seasonably warm temperatures and typical early August humidity remain a fixture in the forecast for the foreseeable future. A broad subtropical ridge in the mid/upper levels will continue retrograding from the western Atlantic back toward the Eastern Seaboard. At the same time, while the strongest jet energy remains tied to the northern tier states, the quasi-zonal flow aloft will steer a myriad from weak to modest shortwaves toward the northeastern U.S. As usual, these types of features are of low confidence given the mesoscale nature of the convective elements. As such, will continue to maintain a risk of strong to severe thunderstorms as well as isolated instances of flash flooding each day. At this point, Friday presents the most active looking day of the period. However, this could easily change as global models continue to waver from run to run.

AVIATION /18Z TUESDAY THROUGH SUNDAY/
Showers continue to weaken while pushing to the vicinity of KCHO. Given closer proximity to the frontal zone, activity near Richmond is likely to impact the Charlottesville area first.
This TAF site should bring the most likely period for restrictions as storms move in from the southeast. Elsewhere, VFR conditions continue through the evening and early overnight hours. This is accompanied by mainly light easterly winds.
However, lowering ceilings will support restrictions across all terminals tonight into Wednesday morning. Locally heavier rainfall could impact the D.C. metro area terminals. Some improvements are expected by midday before another round of storms could impact the area. PROB30 groups accompany this threat, particularly in the 20Z-00Z window on Wednesday.

Winds shift to mainly south to southwesterly for the foreseeable future as a Bermuda high pressure system persists across the western Atlantic. Daily convective chances each afternoon and evening will support convective-driven restrictions. With little change in the upcoming pattern, this sort of forecast will likely hold for the next several days.

MARINE
While today largely presents tranquil weather across the waterways, this will change for the mid to late week period.
Diurnally driven showers and thunderstorms should increase the risk of hazardous conditions for boaters and swimmers. Special Marine Warnings would accompany any of the stronger storms, with any cell capable of producing frequent lightning and gusty winds. In terms of gradient winds, a few periods of southerly channeling may warrant some short-fused Small Craft Advisories.
Most notably, this would include Wednesday evening into Thursday, as well as Friday evening into the night.

TIDES/COASTAL FLOODING
Tidal anomalies continue to remain on the lower end as northeast to easterly winds persist. Southerly winds will return tonight behind a warm front that lifts north through the area. Anomalies climb again mid to late week in response to return southerly flow. Additional periods of coastal flooding are possible at times of high tide at sensitive locations.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.