Marine Weather and Tide Forecast for George Mason, VA

KEY MESSAGES
- 1) High pressure brings near normal temperatures through Tuesday.

- 2) Hot, humid conditions and scattered thunderstorms return late this week.

DISCUSSION
KEY MESSAGE 1...High pressure brings near normal temperatures through Tuesday.

Clouds continue to thin out this evening as boundary layer mixing decreases and the high continues to drift southward. It's possible some clouds could become banked up against the central Virginia Blue Ridge and Alleghenies, although high level clouds will be increasing overnight as well. Dew points will reach their minimum tonight, so temperatures will be more comfortable in the 50s compared to the rest of the week.

The high will drift east off the Mid Atlantic coast on Tuesday while a shortwave trough approaches from the west. There will likely be a lot of mid and high level clouds through the day.
Combined with the residual airmass from the offshore high, temperatures in most places will be limited to the mid 80s, with dew points only gradually climbing through the day. The shortwave may combine with orographic lift and some weak instability to produce a few showers and thunderstorms across the Allegheny Mountains during the afternoon.

KEY MESSAGE 2...Hot, humid conditions and scattered thunderstorms return late this week.

A warm front will lift across the area Tuesday night into Wednesday. The isentropic ascent combined with the gradual passage of the shortwave trough may mean some showers and isolated thunderstorms move across the area Tuesday night. There might be a bit of subsidence behind the wave Wednesday morning, but continued moisture advection will likely result in a good deal of cloud cover and possibly some showers. The amount of cloud cover may make the difference as to whether temperatures stay in the 80s or top 90. It will definitely be more humid though, and some steeper lapse rates aloft may result in some notable instability building by afternoon. Forcing mechanisms remain in question, but most guidance has some potential for more showers and thunderstorms. Shear will be modest, but can't totally rule out some stronger storms.

Low-level southwesterly flow will advect a very hot and humid airmass into the area for the end of the week, with temperatures climbing into the 90s and dewpoints reaching into the upper 60s and lower 70s. This will result in heat indices climbing into the upper 90s to low 100s on both Thursday and Friday afternoon.

Upper level ridging is expected to build overhead on Thursday, with several models also showing a shortwave disturbance passing through the top of the ridge. How this disturbance evolves will have a large impact on our forecast locally. If the disturbance passes through early in the day, we could have large scale subsidence and relatively low coverage of showers and thunderstorms. If it were to approach at peak heating, we could have a much greater coverage of thunderstorms. Upstream convection will likely have a large impact on how that disturbance evolves, so confidence in the forecast details on Thursday is lower than normal. What models are in good agreement about, is that the background environment will be highly unstable (CAPE values likely in excess of 3000 J/kg). There will also be enough dry air in the mid-levels to support strong downdrafts (DCAPE in excess of 1000 J/kg), and just enough shear (around 20 kt) to give storms some weak organization. Such an environmental setup is common in many of our more impactful summer severe thunderstorm events. As a result, there appears to be a conditional threat for severe thunderstorms on Thursday. That threat for severe thunderstorms may continue on Friday as a shortwave disturbance passes to our northwest through the Great Lakes causing the upper ridge to break down and a surface cold front to approach from the northwest. With greater synoptic scale forcing, confidence in the occurrence of storms is higher on Friday, but instability might be slightly lesser. Machine learning guidance is very bullish on the severe thunderstorms threat for both Thursday and Friday. We will continue to monitor this potential threat over the upcoming days.

A cold front will move through Friday night, advecting drier low- level (dewpoints dropping to around 60) and mid-level air into the region. While it will still be hot, conditions are expected to stay remain dry during the day Saturday. Forecast uncertainty begins to increase substantially by Sunday, but most solutions favor dry conditions. For now, the forecast has around a 30 percent chance for afternoon thunderstorms across much of the forecast area.

AVIATION /00Z TUESDAY THROUGH SATURDAY/
While a low probability, it's possible the residual moisture could bank along the central Virginia Blue Ridge tonight, which may bring some borderline MVFR ceilings near CHO. Easterly winds may occasionally gust 15-20 kt into this evening before becoming light and southerly by daybreak Tuesday.

VFR conditions are expected Tuesday with southerly winds. A few gusts could reach 20 kt by the afternoon. A warm front will lift through the area Tuesday night into Wednesday. While the exact details are uncertain, there may be some sub-VFR ceilings and scattered showers during this time. Some thunderstorms are also possible Wednesday.

Prevailing VFR conditions are expected on both Thursday and Friday, but temporary restrictions may occur either afternoon as thunderstorms move through. Winds will generally be out of the southwest on Thursday, and then south on Friday.

MARINE
Cancelled SCA early with on the lower side of forecast.

Winds become a bit lighter and more southeasterly tonight into Tuesday morning, before a prolonged period of southerly flow/channeling brings more gusty conditions Tuesday afternoon through Wednesday night. It's borderline whether any advisories will be needed Tuesday afternoon, but they appear more probable by Tuesday night. Some showers or thunderstorms may reach the waters late Tuesday night, with a greater chance developing Wednesday.

Sub-SCA level winds are expected on both Thursday and Friday. Winds will generally be out of the southwest on Thursday, and then out of the south on Friday. Special Marine Warnings may be needed on both Thursday and Friday afternoon as thunderstorms move over the waters.

TIDES/COASTAL FLOODING
A somewhat prolonged period of southerly flow will result in rising tidal anomalies Tuesday through Wednesday night. The typically more aggressive guidance (CBOFS, SFAS) shows potential for solid minor flooding at Annapolis by mid week, with minor flooding possible along other vulnerable shoreline areas (Havre de Grace and Alexandria, for example).

The higher guidance may be warranted in this case given onshore flow through tonight pushing water into the Chesapeake Bay, then southerly flow holding it/pushing it northward into our neck of the woods through mid week.

Despite the favorable flow pattern, relatively lower astronomical tides due to a third quarter/waning gibbous today and relatively modest wind magnitudes should keep the threat for moderate tidal flooding low.

CLIMATE
Temperatures are expected to soar to as much as 15 to 20 degrees above normal Thursday and Friday. This approaches or exceeds daily record values at some sites.

Below is a list of record daily high and warm low temperatures for June 11th and 12th (Thursday and Friday).

================================================================= June 11th Record Daily Highs and Warm Lows ================================================================= Site Record High Record Warm Low DCA 101 F (set in 1911) 74 F (set in 2020 +6 others)
IAD 95 F (set in 2016) 72 F (set in 2005)
BWI 99 F (set in 1911) 75 F (set in 1914)
DMH 100 F (set in 1984) 79 F (set in 1984)
NAK 96 F (set in 2000) 79 F (set in 1973)
HGR 97 F (set in 1911) 73 F (set in 2005)
MRB 101 F (set in 1911) 71 F (set in 1927 and 1922)
CHO 99 F (set in 1911) 76 F (set in 2020)

================================================================= June 12th Record Daily Highs and Warm Lows ================================================================= Site Record High Record Warm Low DCA 95 F (set in 2017 +6 others) 77 F (set in 2015)
IAD 96 F (set in 1986) 72 F (set in 1986)
BWI 96 F (set in 1986 and 1914) 77 F (set in 1947)
DMH 96 F (set in 2025 +2 others) 77 F (set in 2017 and 2015)
NAK 98 F (set in 1914) 77 F (set in 2000 and 1973)
HGR 92 F (set in 2017 +5 others) 71 F (set in 2010 +5 others)
MRB 97 F (set in 1938 and 1933) 73 F (set in 1914)
CHO 98 F (set in 1914) 72 F (set in 1947 +2 others)

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