Marine Weather and Tide Forecast for Bel Air South, MD

KEY MESSAGES
- 1) Turning warmer this weekend with multiple opportunities for showers and thunderstorms.

- 2) Frost/freeze expected Monday night west of the Blue Ridge, followed by moderating temperatures and returning rain chances.

DISCUSSION
KEY MESSAGE 1...Turning warmer this weekend with multiple opportunities for showers and thunderstorms.

Early morning analysis shows a surface low near Lake Superior and a shortwave trough moving through the Ohio Valley. While a surface warm front is ill-defined, warm and moist advection will take place through the day. Showers ahead of the shortwave are approaching western Maryland. Based on trajectories of the upstream echoes and CAMs, showers will be possible throughout the morning hours mainly near the I-68/70 corridors. There is still low level dry air in place, so rain rates will be light.

There will be a lot of mid and high level clouds throughout the day as the shortwave trough approaches. As such, most models have decreased instability forecasts (and surface dew points in the upper 40s and 50s won't help). The shortwave will still be responsible for shower development along with possible thunderstorms this afternoon as it crosses the area (highest chances for the northern half). However, the meager instability will likely limit the severe weather threat. Gusty winds will be the main threat with any stronger thunderstorm, and perhaps some small hail. SPC has maintained the Marginal/Level 1 Risk in case a trend toward greater afternoon heating emerges. Any convection will quickly depart to the east during the early evening. Afternoon highs are progged to be in the upper 60s to mid 70s, but values could be lower should thicker low level clouds develop. Light winds tonight could lead to some fog development.

Much of tonight and Sunday morning should be dry. After that, a cold front will slowly settle in from the northwest, eventually pushing to the south on Monday morning. Temperatures on Sunday will rise into the 70s and lower 80s with more sun than today, and surface moisture will continue to return northward.
Instability forecasts have trended upward in some guidance, with multiple solutions now showing scattered thunderstorms developing Sunday afternoon, particularly across the northern half of the area. Similar to today, instability will be the limiting factor, as bulk shear will again be over 40 kt.
Will have to monitor these trends for potential of gusty thunderstorms.

Showers will fill in along the frontal zone Sunday night. A wave of low pressure will form along the boundary as stronger troughing digs southeast from the Great Lakes later Sunday night into Monday. This could ultimately bring a steadier rain to parts of the region, but these details remain uncertain. After Sunday evening, thunderstorms will be unlikely as we end up on the cool side of the boundary. Temperatures Monday will be in the lower to mid 60s, if not upper 50s. Any lingering rain will exit the area Monday afternoon. Unfortunately this system won't offer much drought relief, as probabilities for greater than a half inch of rain are generally 30 percent or less.

KEY MESSAGE 2...Frost/freeze expected Monday night west of the Blue Ridge, followed by moderating temperatures and returning rain chances.

High pressure will quickly build in from the west Monday night. This will result in light winds and favorable radiational cooling conditions. Frost or near freezing temps could result in the sheltered valleys near and west of I-81. This could be rather impactful given the fact that we are approaching mid-May at this point which is a couple weeks to a month past the median last freeze for these areas.

The high pressure will drift offshore Tuesday marking return flow and moderating temperatures. The warming trend will be more noticeable heading into Wednesday as a warm front lifts into the region, followed by a cold front and wave of low pressure Wednesday night into Thursday. This frontal system will bring a chance of showers and a few thunderstorms mid week.

Temperatures will actually trend warmer in the wake of the frontal system at the end of next week as large scale height rises commence.

AVIATION /07Z SATURDAY THROUGH WEDNESDAY/
A warm frontal zone will lift through the area this morning with lowering mid level cloud bases. Some light rain showers may affect MRB at times but appear less likely to affect the other TAF locations. There is a higher likelihood of isolated to scattered showers/thunderstorms this afternoon and evening between 18-23z/2- 7pm as an upper level disturbance crosses the area. While some thunderstorms may produce gusty winds, instability forecasts have been trending downward, which would result in more benign showers.
Have thus left the mention as PROB30. A few southerly winds gusts to 20 kt could also occur throughout the day.

Uncertainty increases tonight as winds become light and variable in the wake of the showers. The typically moist models (e.g.
NAM) indicate fog and/or low clouds developing in this environment, especially east of the Blue Ridge. However, am not confident given the background south or west wind direction, so am only adding a SCT MVFR cloud group for now due to the uncertainty.

VFR conditions can be expected after sunrise Sunday. However, a cold front will drop into the area during the afternoon.
Scattered thunderstorms could develop ahead of the boundary.
More widespread rain showers can be expected as this front traverses the region, especially Sunday night into Monday morning. Expect MVFR or IFR ceilings and visibilities during this time. Northwesterly wind gusts may reach 20 to 25 knots in the wake of the front Monday as ceilings lift.

VFR Tue-Wed with N winds gusting 15-20 kts Tue AM becoming light S Tue PM. Gusts of 15-20 kts out of the S are possible Wed as a frontal system approaches, with at least brief sub-VFR possible in showers or a few thunderstorms.

MARINE
A Small Craft Advisory remains in effect for all waters through 6 PM this evening due to enhanced southerly flow. However, the forecast has trended toward more clouds and less mixing today, so there could be some breaks in the gusts, especially over the northern bay and upper Potomac. Isolated to scattered t-storms may affect the waters this afternoon and early evening, which may prompt SMWs due to gusty outflow winds. However, this threat may be trending downward somewhat based on the latest data.

While it's possible some gusts linger over southern Maryland during the early evening, overall lighter winds are expected tonight into Sunday. The chance for a few gusty thunderstorms may be trending up Sunday afternoon and evening, especially for the northern bay and upper Potomac. More widespread showers along a cold front will likely cross the waters Sunday night into Monday morning. This front will cross the waters Monday morning with a shift to northwesterly winds gusting up to 20 to 25 knots. SCAs will likely be needed late Sunday night through Tuesday morning, although the latest guidance shows a break between two separate surges.

Winds will become lighter as high pressure builds overhead Tuesday. Winds will turn to the south Tuesday night into Wednesday as high pressure moves offshore, with Small Craft Advisory conditions possible Wednesday morning through Wednesday evening.

TIDES/COASTAL FLOODING
Southerly flow will persist through tonight. Channeling has piled water into the northern bay with anomalies rising to 1-1.5 feet. Given little change to the expected water level through the morning, issued a Coastal Flood Advisory for Annapolis for this morning's high tide. Wind direction may be a bit more variable tonight into Sunday evening introducing further uncertainty to the tide forecast, though models indicate a general downward trend. However, elevated water levels are plausible until a cold front crosses Sunday night into Monday.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Small Craft Advisory until 6 PM EDT this evening for MDZ008.
Coastal Flood Advisory from 9 AM this morning to 1 PM EDT this afternoon for MDZ014.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ530>543.