Marine Weather and Tide Forecast for Washington, DC

KEY MESSAGES
- 1) Tranquil weather conditions are expected tonight through THursday as high pressure builds over the region.

- 2) Showers and thunderstorms possible this weekend ahead of an increase in temperatures.

DISCUSSION
KEY MESSAGE 1...Tranquil weather conditions are expected tonight through Thursday as high pressure builds over the region.

The Severe Thunderstorm Watch for southern MD and the northern neck of Virginia has been allowed to expire early as remaining convection exits the Delmarva coast. This thunderstorm activity was in association with a strong cold front that will continue to sag south and east of the region tonight into Wednesday morning. Meanwhile, high pressure will build in from the Ohio/Tennessee River Valleys bringing tranquil weather conditions and lower humidity for the middle of the workweek.

It will be a break from Summer Wednesday with wake up temps in the upper 50s and low 60s and highs in the mid 70s to low 80s (cooler mountains). Comfortable conditions continue into Wednesday night as the high slides overhead. High pressure will slide offshore Thursday allowing for southerly return flow back into the region. This will push temperatures back toward 90 degrees east of the Blue Ridge Thursday afternoon along with a slow uptick in humidity.
Any rain chances look to hold off until the end of the workweek and into the upcoming weekend.

KEY MESSAGE 2...Showers and thunderstorms possible this weekend ahead of an increase in temperatures.

A strong cold front with a center low forming over the Great Lakes will track across the Mid-Atlantic late this week, bringing additional chances for showers & thunderstorms this weekend.
Precipitation onset could begin Friday and into Saturday as the cold front slowly meanders offshore, with some thunderstorms having the potential to become severe.

However, timing of this front remains uncertain as the position of the center low to the north still shows some variance. ML probabilities still show a low-end chance for thunderstorms through the end of the weekend, with some members showing an either Friday or Saturday cold front arrival while other members show it arriving slightly later. Movement of the center low to the north will be critical for tracking the movement of the corresponding front to the south. The latest 12Z deterministic models generally show the front arriving within the Friday & Saturday timeframe, with the low transitioning offshore by Sunday. Widespread rain & thunderstorm chances thus remain elevated through this period.

Once the front moves offshore early next week, expect high pressure to move in and a potentially extended period of upper-level ridging over the Mid-Atlantic near the end of the forecast period. This will allow temperatures to gradually increase, with high temperatures potentially reaching back into the 90s across the metros by next Monday. With upper-level ridging potentially extending across a large area of CONUS, this gradual warming could persist into the long-term along with reduced precipitation chances once this weekend's front moves offshore.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/
Prevailing VFR conditions are expected overnight as clouds continue to clear with high pressure building into the region.
Northerly winds will gusts up to 15 kts through this evening before becoming light and variable overnight. Northwest winds are expected Wednesday at 5 to 10 kts. High pressure will settle overhead Wednesday night before sliding offshore Thursday allowing for VFR conditions to continue. Winds will shift from the west and northwest Wednesday back to the south Thursday at less than 10 kts.

A strong cold front bringing showers and thunderstorms could bring temporary flight restrictions across the area Friday and Saturday.
Conditions gradually improve Sunday as the front transitions offshore. Southwesterly winds shift northwesterly by Saturday night before returning to southerly flow Sunday night in the wake of the front.

MARINE
SCAs remain in effect for all waters outside of the northern bay, northern tidal Potomac, and Baltimore Harbor through 11am Wednesday morning. High pressure builds overhead on Wednesday with winds forecast to drop below Small Craft Advisory criteria. Sub-SCA levels winds will continue through THursday morning with SCAs potentially needed Thursday afternoon and night due to southerly channeling.

Winds drop back below SCA thresholds Friday into the weekend.
Southerly winds transition northerly winds Saturday evening before shifting southerly again by Sunday night in the wake of a potential cold front. Shower and thunderstorms will accompany this front Friday through the weekend. SOme storms could be strong to severe, leading to the potential of SMWs each afternoon. Confidence in this is low at this time based upon timing and placement of surface features.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Small Craft Advisory until 8 PM EDT this evening for MDZ008.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ530- 535-536-538-542.
Small Craft Advisory until 11 AM EDT Wednesday for ANZ531>534- 537-539>541-543.