Marine Weather and Tide Forecast for Mount Vernon, VA

KEY MESSAGES
- 1) Active weather pattern persists through the middle of the week.

- 2) Dry conditions and seasonable temperatures are forecast for the end of the week.

DISCUSSION
KEY MESSAGE 1...Active weather pattern persists through the middle of the week.

The persistent cold air damming (CAD) wedge signature has remained a fixture in the forecast along much of the Eastern Seaboard. The latest surface analysis places the stalled boundary in a familiar position which stretches along the coastal Carolinas up along the Appalachian chain into the Ohio Valley. The combination of this frontal zone with a stout dome of high pressure across far eastern Canada into New England has supported continued north to northeasterly gradients. In the net, the GOES-19 visible satellite imagery depicts a clear picture of the impact of this setup. Low stratus remain over vast portions of the region, although some cloud breaks are evident along/west of the Blue Ridge Mountains. These breaks in the clouds have even sparked scattered showers over areas of Garrett and western Grant counties. Any strengthening will be dependent on further heating of the boundary layer.

The overall forecast package has brought high temperatures down relative to preceding shifts. As is common in CAD wedge setups, model guidance often does not capture the degree of cooling.
Consequently today's highs will largely top out in the 60s, accompanied by pockets of low 70s in central Virginia and along/west of the Blue Ridge. Winds should remain on the lighter side (10 mph or less) with a general onshore component.

Continued onshore flow coupled with light winds and saturated grounds will likely lead to another round of low clouds tonight.
In areas that are not actively precipitating, some patchy fog may develop in spots. The mentioned frontal zone is expected to approach from the south through the night. Isentropic lift atop this boundary should spread additional overnight showers to the region. Forecast lows will range from the mid 50s to mid 60s.

All signs point toward the boundary lifting north of the Mason- Dixon Line on Memorial Day. Thus, there will be a better chance for warming temperatures, but also with some increasing opportunity for showers and thunderstorms. As this boundary works in accordance with a southeastward pushing cold front out of the Ohio Valley, low-level convergence will begin to increase. High-resolution models show a decent footprint of heavier showers south of I-66, possibly over central Virginia into southern Maryland. Despite the ongoing drought, multiple days of rainfall has yielded some saturated soils. Spotty flooding cannot be ruled out where any of these stronger storms occur. The Weather Prediction Center has expanded the Marginal Risk area to cover this region of the forecast area.

Looking ahead to Tuesday and Wednesday, the frontal zone is largely going to be meandering north/south of the Mid-Atlantic states. As a mid-level subtropical ridge builds over the southwest Atlantic Ocean, additional mid/upper disturbances will track around the western side of this anticyclone toward the local area. Such impulses aloft will work in conjunction with the stalled boundary and daytime heating to produce additional rounds of showers and thunderstorms. How impactful these are is uncertain given this is still a few days out in time. Multi- ensemble temperature forecasts do shown an upward trend in numbers which makes for more seasonable highs through mid-week.

KEY MESSAGE 2...Dry conditions and seasonable temperatures are forecast for the end of the week.

The synoptic scale pattern is expected to hold relatively steady from Thursday into the upcoming weekend, with high amplitude ridging over central North America extending well into central Canada, and downstream troughing extending southward from Hudson Bay toward the Mid-Atlantic. Northerly winds at low levels will transport a much drier airmass into the region, leading to predominantly dry conditions. Seasonable temperatures will accompany the drier conditions, with highs in the 70s to lower 80s, and lows in the 50s for most.

AVIATION /18Z SUNDAY THROUGH FRIDAY/
A persistent CAD wedge remains a fixture in the pattern along the Eastern Seaboard. The continued onshore flow has maintained a semi-permanent thick stratus deck across all terminals. Most terminals are still seeing IFR ceilings (600 to 800 feet), although some improvements are underway at the D.C. terminals and KCHO. Such a shift is likely to be short lived as additional low clouds are expected tonight into Memorial Day morning.
Aviation guidance supports a mixture of IFR to LIFR ceilings tonight, which also comes with the risk of increasing showers for the second half of the overnight period. Winds will vary in direction at times but remain light in nature.

The Memorial Day forecast will see mainly IFR conditions through the morning with the potential for improvements to MVFR for the afternoon hours. A risk of thunderstorms is noted from the D.C.
terminals southward, particularly around 21-00Z. Otherwise, the meandering boundary remains nearby through mid-week which will certainly favor restrictions at times. Temperatures are to warm at the same time which suggests some loss of these persistent low cloud days.

VFR conditions are forecast for both Thursday and Friday. Winds are expected to be out of the north on Thursday, and then northwest on Friday.

MARINE
Despite the broad gradient formed by high pressure over far eastern Canada into New England and a frontal zone stalled across the southeastern U.S., winds remain weak across the area.
Sub-advisory caliber winds are expected for the early/mid portions of the week. The main caveats to note are a multitude of wind shifts which occur as the boundary meanders north/south of the waters. Additionally, daily shower and thunderstorm chances are expected which could lead to some hazardous boating conditions. Improvements in the active pattern eventually occur by later in the week.

Sub-SCA level north to northwesterly winds are expected on Thursday and Friday.

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