Marine Weather and Tide Forecast for Riva, MD

KEY MESSAGES
- Heavy showers and strong thunderstorms, a few of which may produce damaging winds and flash flooding, are possible this afternoon and evening.

- Heat and humidity return for the middle and second half of next week.

- Scattered thunderstorm development is anticipated during the the second half of next week in a moderately unstable and sheared environment.

DISCUSSION
KEY MESSAGE 1...Heavy showers and strong thunderstorms, a few of which may produce damaging winds and flash flooding, are possible this afternoon and evening.

As of 3 PM, radar imagery shows several areas of showers and thunderstorms scattered about the area. Showers that have developed in the vicinity of the bay breeze have struggled to mature. They have yet to produce lightning, and aren't showing signs of intensification at the moment.

Additional showers and storms are present along and west of the Blue Ridge. These storms have formed downstream of an MCV approaching from the Ohio Valley. These storms should continue to slowly drift off toward the south and east through the remainder of the afternoon and evening.

Finally, a third area we continue to monitor is up to our north in PA/NJ. A cold front has sparked the development of showers and storms from southern NJ northwestward into central PA.
These storms will drop southward into our forecast area during the evening hours. With an unstable airmass in place, these storms may persist well after dark from the DC Metro southward to southern MD, until the front finally clears the area later tonight.

Forecast soundings show an environment with saturated profiles through the vertical, around 1000 J/kg of MLCAPE, 400-600 J/kg of DCAPE, and around 20-30 knots of mid-level flow. While this environment isn't overly favorable for strong downbursts, an instance or two of damaging winds can't be completely ruled out.
SPC has much of the forecast area outlooked in a Marginal Risk (level 1 of 5) for severe thunderstorms.

With the saturated profiles, deep warm cloud layers (around 14k ft), and precipitable water values approaching 2 inches, storms today should be very efficient heavy rainfall producers.
However, ample flow in the mid to upper levels should enable storms to be somewhat progressive. The weak low-level jet and lack of focused areas of stronger low-level convergence should also limit backbuilding to a degree. However, it's possible that there could be an isolated instance or two of flash flooding if localized storm mergers are able to prolong the period of heavier rain. The best chance for this to occur may be later this evening along the I-95 corridor from DC southward, where there could be some potential for outflows moving in from the west to collide with the front and associated storms moving in from the northeast. At this time, the threat for flooding appears to be low (not rising to a threat level worthy of a Watch), but non- zero. We'll continue to monitor trends over the course of the day. WPC currently has much of the area outlooked in a Marginal Risk (level 1 of 4) for excessive rainfall.

As the front weakens and progresses southward, it will struggle to scour out low- level moisture. As a result, we'll have another threat for showers and thunderstorms tomorrow afternoon, primarily to the southwest of the Potomac. The background environment doesn't appear to be overly favorable for severe thunderstorms or flash flooding, but an isolated instance of flash flooding can't be ruled out across Central Virginia or the Central Shenandoah Valley. WPC has those areas outlooked in a Marginal Risk (level 1 of 4) for excessive rainfall on Sunday.

KEY MESSAGE 2...Heat and humidity return for the middle and second half of next week.

Upper high centered over the Dakotas early in the week is expected to expand eastward cresting over the area Tue evening. This will support high temperatures in the upper 90s, but dewpoints will not be terribly too high in the 60s. By Thu and Fri, low level moisture returns into the area with dewpoints in the upper 60s to near 70 resulting in heat indices near 100 degs which is still below heat advisory criteria. While it will be hot, it won't be as hot as it was during the first weekend of July.

KEY MESSAGE 3...Scattered thunderstorm development is anticipated during the the second half of next week in a moderately unstable and sheared environment.

During the second half of next week, the upper ridge centered over the Dakotas early in the week will build westward with time while the eastern Canada trough digs southward. This results in moderately strong flow aloft across the area with the synoptic pattern becoming favorable for thunderstorm clusters or MCSs that form over the upper Great Lks and upper Midwest to track southeastward into the OH Valley and Mid-Atlantic states. The earliest we could see thunderstorms it seems to be Thu, but with higher probs of thunderstorms Fri into Sat and likely extending it beyond that.

AVIATION /00Z SUNDAY THROUGH THURSDAY/
Prevailing light winds and VFR conditions are expected through the remainder of the day, but showers and thunderstorms are expected across the area this afternoon into this evening.
Confidence is low on both timing and coverage of the storms, so PROB30 groups have been maintained for now. MVFR ceilings appear possible late tonight, with IFR even possible near CHO. MVFR ceilings may linger through tomorrow morning, before improvement back to VFR is seen during the afternoon. Additional thunderstorms may be possible near CHO, but drier conditions are expected elsewhere. Winds tomorrow will be out of the east. VFR and dry conditions are expected on Monday, along with east to southeasterly winds.

Fair weather is expected through mid week.

MARINE
Sub-SCA level north to northeasterly winds are expected over the waters today into tonight. An SMW or two can't be ruled out as storms move over the waters. Winds will turn out of the east tomorrow. Small Craft Advisories have been issued for the Lower Tidal Potomac and our southernmost Bay zones late Sunday afternoon through much of Monday night. Lighter winds are expected further north.

Great boating weather is expected Monday through mid week with no thunderstorm potential. SCA conditions are likely Monday, but winds will be diminishing by Monday evening.

TIDES/COASTAL FLOODING
Elevated water levels will persist for the next couple of days with minor coastal flooding becoming increasingly likely Monday into Tuesday as southerly flow strengthens.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 5 PM Sunday to 4 AM EDT Monday for ANZ534-537-543.