Marine Weather and Tide Forecast for Friendship, MD

NEAR TERM /THROUGH TONIGHT/
Mid-morning update: Thinking still remains largely in line with the previous discussion. One trend of note in model guidance is that the three most recent HRRR runs (10,11,12z) have been consistently producing a north-south oriented stripe of 4-8 inches of rain through later this evening from roughly just northeast of Charlottesville northward to around or just south of Winchester (centered on Madison, Rappahannock, Page, and Warren Counties). At the moment, these solutions are outliers relative to the rest of the guidance (incoming 12z 3km NAM and FV3, along with all other previous guidance have significantly less), but have certainly caught our eye, as it would lead to significant flooding issues if it were to come to fruition. The HRRR solutions try to initiate and then continually regenerate convective cells on the edge of the incoming dry slot over Central Virginia, where it intersects a zone of low-level convergence near the western terminus of a southeasterly low- level jet. Those cells then track northward and train along the low- level convergence zone, leading to the heavy rainfall totals. These HRRR runs have been initiating with much deeper convection than is currently on radar, so hopefully these solutions are consistently wrong, as opposed to consistently right. In terms of timing, the HRRR runs are trying to produce the heaviest rain during the late afternoon and evening hours.
We'll continue to monitor trends over the coming hours. Previous discussion follows...

Closed upper level low is lifting into the Tennessee Valley this morning. At the surface, the warm sector has moved ahead to eastern North Carolina, where thunderstorms and heavier convection are occurring. For the most part, rain has been light to moderate but efficient as precipitable water values have risen above 1.5 inches east of I-81. A corridor of heavier rain is likely to pivot northward through the morning hours driven by a low level jet, which will lift toward the northern half of the area this afternoon. Locations which are under heavier rain elements the longest and have seen more rain recently will have a greater chance of seeing some localized flooding. Locations along the eastern slopes of the mountains remain favored for the highest rain totals due to the upslope lift of the southeasterly low level jet. A Flood Watch is in effect for much of the area. While low level stability will likely prevent the jet from fully mixing down, some gusts in the 20-30 mph range are possible today. Even those these speeds aren't too strong, weak water- laden tree branches can still break in this type of set-up.

Meanwhile, a dry slot will start to work northward toward the area by this afternoon. Showers may end or become lighter across southwestern parts of the CWA We'll have to monitor two potential areas of thunderstorms. First, storms may develop in the dry slot to our southwest where instability will develop.
These may lift northward into central Virginia and the central Shenandoah Valley during the mid to late afternoon. This area may have greater instability but weakening shear. Second, a triple point low will be lifting northward along the coast, possibly bringing the warm sector toward southern Maryland by mid/late afternoon. Instability will be limited, but there will be increased low level shear. Both areas may carry an attendant marginal severe weather risk, but it is uncertain if/how far the threat extends north into the forecast area, as widespread low clouds and rain will keep low levels stable. Temperatures will be held in the 60s to near 70.

Rain will last longest tonight near and northeast of the Potomac, where the low level jet will only slowly exit. Showers will tend to taper off to the southwest. With light winds, stratus clouds have a higher chance of lowering into fog in this area. Lows won't fall far with the elevated dew points...in the upper 50s to mid 60s.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/
The upper level low will begin opening as it approaches Wednesday. While cloud breaks might be limited, especially across the northern half of the area, some low level drying may begin to take place as the steadier showers pivot off to the north. Instability will build in this area to the southwest, and with little inhibition, widespread showers and scattered thunderstorms are expected to develop by afternoon. This activity should gradually spread northeastward, but perhaps with lower intensity as it encounters weakening instability. Shear will be marginal, around 20-30 kt, but this could support a few stronger storms with gusty winds being the primary threat. Storm motions will also be somewhat slow with unidirectional wind profiles. Precipitable water values will be lower, but isolated flooding will be possible with any heavier convection that moves over sensitive areas from previous rainfall. Temperatures should push into the 70s for most areas, warmest in the southwest. Showers will gradually lift to the northeast Wednesday night.

The weakening trough axis will be overhead Thursday. More breaks of sun are likely, which will allow temperatures to rise toward 80. While forcing is somewhat nebulous, dew points will still be well into the 60s, so at least some scattered showers and thunderstorms will be possible during the afternoon. Late Thursday night, eyes will turn to the northwest as some guidance has remnant convection along a warm front moving toward the area. If this does occur, storms may be maintained by steepening lapse rates aloft and elevated instability.

LONG TERM /FRIDAY THROUGH MONDAY/
The next mid-level low pressure system will move across the Great Lakes region with an associated surface low moving east across the Ohio Valley on Friday into Friday night. The surface low's affiliated cold front will drag across the region and bring another round of showers and thunderstorms Friday afternoon into the evening. Temperatures will be on the warm side once again. Deep layer shear and instability will support a severe thunderstorm risk Friday afternoon and at night.

The broad mid-level low to the north is forecast to track across the Great Lakes Saturday. A series of disturbances will move across the Ohio Valley and help to keep our region unsettled right into the weekend. Instability profiles may not be quite as potent as Friday.
There is still a threat for some strong thunderstorms Saturday, similar to Friday.

A drier more inactive day will be Sunday as high pressure works into the region. Highs should reach the upper 70s to lower 80s with lower humidity. This could continue into early next week.

AVIATION /14Z TUESDAY THROUGH SATURDAY/
Conditions are somewhat variable early this morning with intermittent showers and gradual moistening/lowering ceilings.
Eventually all locations should reach IFR and likely remain there most of the day save for short breaks. A period of steadier moderate to locally heavy rain will gradually work northward across the area through the day as well. This will be accompanied by a low level jet. It's uncertain how much of this wind makes it to the surface, but some 20-25 kt SE wind gusts are possible. As a dry slot slowly works north this afternoon and evening, some thunderstorms may develop. These are most probable at CHO, with decreasing chances toward MRB and MTN.

Showers continue into tonight, with ceilings lowering toward LIFR. Winds will lessen, and showers may begin to taper. CHO may have the stratus lower into fog.

We may see some improvement back to MVFR or even VFR for a time Wednesday, but drops back to IFR ceilings are expected again Wednesday night. Afternoon showers and thunderstorms are possible on Wednesday. On Thursday, mainly VFR conditions are expected by late morning, although there is an afternoon and evening risk of scattered thunderstorms.

Thunderstorms remain possible Friday and Saturday.

MARINE
Southeasterly winds will start to pick up toward daybreak and through the morning as a low level jet lifts northward. SCAs are in effect for all waters. A few models indicate that winds may even near low-end Gale levels late in the afternoon or evening, especially near southern Maryland. This would most likely be tied to thunderstorms. SCA conditions gradually lift toward the northeast tonight, with winds becoming lighter Wednesday. Light winds will continue through Thursday. However, a few thunderstorms are possible during the afternoon and evening each day.

Sub-SCA winds Friday with winds shifting from southerly to westerly Saturday, when winds may approach advisory levels.
There will be a risk of thunderstorms Friday and Saturday, particularly on Friday as stronger storms may impact the waters.
Special Marine Warnings may be necessary.

TIDES/COASTAL FLOODING
As a low pressure system slowly approaches through mid week, continued onshore flow will gradually build anomalies. Sensitive shoreline could approach minor tidal flood levels especially with the Wednesday and Thursday morning high tide cycles. Some uncertainty exists with the build up in the northern bay which may not be handled with the current bias correction of the model guidance. If this is the case, trends would favor water levels just shy or touching minor at Annapolis and Havre de Grace.

LWX WATCHES/WARNINGS/ADVISORIES
DC...Flood Watch through late tonight for DCZ001.
MD...Small Craft Advisory until noon EDT Wednesday for MDZ008.
Flood Watch through late tonight for MDZ003-004-501>504-510.
VA...Flood Watch through late tonight for VAZ028-031-050-051- 053>057-501-502-505-506-526-527.
Flood Watch through late tonight for VAZ025>027-029-030- 036>040-503-504-507-508.
WV...Flood Watch through late tonight for WVZ050>053-503-504.
Flood Watch through late tonight for WVZ055-501-502-505-506.
MARINE...Small Craft Advisory until noon EDT Wednesday for ANZ530-531- 539.
Small Craft Advisory until 6 AM EDT Wednesday for ANZ532-538- 540-541.
Small Craft Advisory until 6 AM EDT Wednesday for ANZ533-534- 537-542-543.
Small Craft Advisory until midnight EDT tonight for ANZ535.
Small Craft Advisory until midnight EDT tonight for ANZ536.