Marine Weather and Tide Forecast for North Chevy Chase, MD

KEY MESSAGES
- 1) Additional heavy rainfall is possible this afternoon and evening, mainly south of I-66.

- 2) Additional shower and thunderstorm chances persist through this weekend.

DISCUSSION
KEY MESSAGE...Additional heavy rainfall is possible this afternoon and evening, mainly south of I-66.

The earlier upper low across the Ohio Valley has now shifted just north of Lake Ontario while becoming more elongated in nature. At the same time, this has pushed the parent frontal boundary along I-81 where it has generally stalled. The forecast calls for this frontal system to slowly drop southward in time.
The front is going to be the main focus for another round of showers and thunderstorms. The main uncertainty is the exact placement of this boundary, with most high res guidance showing it south of I-66 where low-level convergence is more focused.
This is where most of the rain chances (50-70 pct) will be for today, with mostly dry conditions to the north/west.

It is still going to be warm and muggy areawide as highs reach the mid to upper 80s. Thunderstorms once again are going to be efficient rain makers with a deep warm cloud layer and PWATs above 2". A few instances of flash flooding are possible if any heavy thunderstorm develops and moves slowly over regions of poor drainage. The frontal boundary completely crosses the area this evening, ushering in drier conditions for tonight. Slightly lower dew points allow temps to drop to the 60s for most locations (upper 50s in the mountains).

The boundary attempts to lift north as a warm front Tuesday, but only makes it to around I-64. This means most of the area remains dry.
Isolated showers and thunderstorms are possible in the afternoon along and south of a line from Staunton to Fredericksburg. The dry spell is going to be short lived as the warm front lifts north across the entire area on Wednesday, bringing the return of an active weather pattern that persists through the weekend.

KEY MESSAGE 2: Additional shower and thunderstorm chances persist through this weekend.

Showers and thunderstorms will focus in the afternoon & evening hours each day. Increasing humidity will allow for PWATs ranging from the 75th-90th percentile, indicating potentially increased flooding concerns with any thunderstorms that do materialize. Severe thunderstorm probabilities continue to indicate the potential for severe thunderstorms during the Thursday-Sunday timeframe, with machine learning outputs remaining in the 15%-30% range. Still, that remains uncertain given the lack of defined synoptic support and abundant cloud cover over the region that limits instability.

As this synoptic pattern persists, temperatures gradually increase back to summertime normals, with elevated humidity contributing towards heat indices that will approach 100F across the metros late into the week. Looking ahead, deterministic models do show some signal for this front transitioning offshore towards the start of next week with drier air moving in from the west, potentially providing some relief from the humidity. For now, the primary weather feature remains as humid & rainy, along with increasing heat.

AVIATION /13Z MONDAY THROUGH FRIDAY/
A mix of MVFR to near-IFR CIGs continue to impact some terminals, but general improvements have been noted during the past couple of hours.

VFR conditions return this afternoon as a front slowly moves south across the area. Another round of showers/thunderstorms are likely this afternoon, except at KMRB that will be north of the boundary. Dry and VFR conditions tonight through Wednesday morning. Daily shower and thunderstorm chances return Wednesday afternoon as that frontal boundary lifts back north across the area as a warm front.

Sub-VFR conditions will likely continue to be intermittent at terminals throughout the week as daily shower and thunderstorm chances persist, particularly in the afternoon & evening timeframes.
South to southwesterly winds flow Wednesday through the end of the week.

MARINE
Southerly channeling this morning is going to produce SCA conditions, especially the main channel of the southern Chesapeake Bay. A weak front slowly moves south across the waters today, though not before another round of showers and thunderstorms develop this afternoon. Special Marine Warnings are likely needed again today, especially south of the Bay Bridge and over the lower Tidal Potomac. Wind gusts in excess of 35 knots are the primary threat to mariners, in addition to lightning strikes.

The front pushes south of the waters this evening. Dry conditions and sub-SCA winds expected Tuesday into Wednesday morning. The stalled boundary lifts back north over the area as a warm front by Wednesday afternoon. Southerly flow returns, and could approach SCA levels over the central Chesapeake Bay. Wednesday also brings with it the return of daily afternoon showers and thunderstorms.

Southerly channeling over the waters are anticipated to produce SCA conditions Thursday afternoon through Friday. Showers & thunderstorms remain possible over the waters during this period (especially in the afternoon/evening hours) due to a stalled front nearby.

TIDES/COASTAL FLOODING
Tidal levels remain elevated this morning, but minor tidal flooding has begun to subside at Annapolis behind high tide.
Other sensitive locations likely top out at Action Stage. A brief period of lighter winds is expected Tuesday and that should prevent minor tidal flooding at all locations. Southerly flow returns Wednesday through the end of the week, bringing the possibility of additional periods of coastal flooding.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Small Craft Advisory until 11 AM EDT this morning for MDZ008.
Coastal Flood Advisory until 10 AM EDT this morning for MDZ014.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 11 AM EDT this morning for ANZ530>534-537>543.