Marine Weather and Tide Forecast for Williamsport, MD

KEY MESSAGES
- 1) Severe thunderstorms return today.

- 2) A return to warm and humid conditions and the potential for strong to severe thunderstorms Thursday.

DISCUSSION
KEY MESSAGE 1...Severe thunderstorms return Sunday.

A sw will rotate around the base of an UL trof today. Ahead of the wave, southerly flow will usher in anomalous moisture with PWs nearing 2" and TDs near 70F. The sw will bring height falls aloft near peak heating and overlap with increasing wind shear.
The combination of increasing instability, shear, and large scale forcing for ascent ahead of the shortwave and an approaching cold front will lead to the development of widespread thunderstorms during the afternoon, some of which could be severe.

There's still a fair amount of spread in guidance with respect to the timing and exact placement of the storms, but as of now the threat looks to be greatest to the east of the Blue Ridge. General consensus is for isolated to scattered thunderstorms to form across the area during the early to mid-afternoon hours as large scale lift associated with the approaching sw increases. CAMs suggest that the convective mode may remain primarily cellular, which seems plausible given deep layer shear vectors are w-sw, and have a significant component oriented perpendicular to any prefrontal trough that may assist in initiation. With the cellular mode, the areal coverage of storms may end up being a bit lower than preceding days, which featured considerable upscale growth into linear structures. The background environment will be characterized by around 1000-2000 J/kg of MLCAPE and around 40-50 knots of effective bulk shear, so supercells may be possible. Model soundings indicate steep low level lapse rates (especially for the Mid-Atlantic) which will result in higher DCAPE values and therefore stronger wind gusts.
Damaging winds appear to be the primary threat tomorrow, with gusts of 60-70 mph possible in stronger storms. Very warm surface temps and poor mid-level lapse rates should limit the hail threat somewhat, but an isolated instance or two can't be ruled out, given the possibility for supercells. The tornado threat also appears to be very low, but non-zero, given predominantly straight hodographs with minimal low-level shear.
SPC currently has the entire forecast area outlooked in a Slight Risk, with damaging winds being the primary threat.

In addition to any storms that develop in the open warm sector during the afternoon, additional showers and thunderstorms are expected to form along the system's cold front in the Ohio Valley this afternoon. These storms will then track southeastward into the fa during the evening hours. The trend over time should be for these storms to weaken as they encounter a stabilizing boundary layer, but a low-end threat for a thunderstorm or two will continue after dark until the system's cold front clears the area later in the night.

The main threats with storms will damaging winds, large hail, locally heavy rainfall, and frequent lightning. SPC has maintained a Level 2 out of 5 (Slight Risk) with 30% wind probs (higher end slight risk). There was some discussion of upgrading to Enhanced, but some uncertainty remains in terms of coverage of storms. Will monitor trends this morning and coordinate with SPC on any potential upgrade.

WPC has a Level 1 out of 5 (Marginal ERO) for the metros, but progressive nature and prevailing drought look to limit the overall flood threat.

Much cooler, drier, and less humid conditions are forecast for Mon/Tue. Mostly sunny skies are expected with high temps in the upper 70s to around 80, dewpoints in the upper 40s to 50s, and a NW breeze.

KEY MESSAGE 2...A return to warm and humid conditions and the potential for strong to severe thunderstorms Thursday.

After trending somewhat drier at the start of the week, upper level moisture starts to move into the region on Wed, along with a trend upwards in temp as hotter & more humid conditions begin to take over. A stray shower or thunderstorm could develop later in the day Tuesday through early Wed, mainly east of the Blue Ridge, as a weak warm front slides northward from the Carolinas into VA.

Beginning Thu, a strong surface low will push east past the Great Lakes with a stemming cold front that will push across the Northeast and Mid-Atlantic. This cold front could result in multiple showers and thunderstorms throughout the region, with some becoming severe. There is already a 30%-45% severe prob noted in NCAR's AI model, and a 15%-30% severe prob noted in CSU's ML model. Timing and exact hazards are still the primary uncertainties being 5 days out, but early markers are showing an early widespread severe risk with this system.

This front will track towards the south by Fri, which could result in a few lingering showers across the southern portions of the region and along the central Chesapeake Bay. High pressure moves into the region on Sat.

AVIATION /06Z SUNDAY THROUGH THURSDAY/
S'ly winds and VFR conditions are expected through this afternoon. S'ly winds increase this afternoon, and may gust to around 20-25 knots. Thunderstorms are expected to develop across the area this afternoon/evening. Confidence is currently low on timing at individual locations, so have maintained PROB30s.
TEMPOs or prevailing groups will likely be needed as we move closer in time and confidence increases with respect to exact timing. The threat for thunderstorms will gradually wind down through the evening. Winds will shift to out of the NW behind a cold front tonight. Gusts to around 20-25 knots may be possible at times later tonight within NW'ly flow. VFR conditions and lighter NW winds are expected on Mon.

VFR conditions mainly expected Tue through Wed night. Winds light becoming southeast 5 to 10 knots Tue. Winds south 5 to 10 knots Wed.

MARINE
S'ly winds are expected over the waters today. SCAs are in effect for all waters through this evening for all waters, and tonight for southern waters. Thunderstorms will likely impact the waters this afternoon/evening, with SMWs likely being needed. Damaging winds will be the primary threat, but a stray waterspout or instance of large hail can't be ruled out. A cold front will move over the waters tonight, shifting winds around to out of the NW. Winds will remain out of the northwest on Mon, but are expected to drop below SCA levels by mid- morning.

No marine hazards expected Tue through Wed night. Winds light becoming SE 5 to 10 knots Tue. Winds south 5 to 10 knots Wed.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Small Craft Advisory from 11 AM this morning to 6 AM EDT Monday for MDZ008.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 11 AM this morning to 6 AM EDT Monday for ANZ530>534-537-539>541-543.
Small Craft Advisory from 11 AM this morning to 11 PM EDT this evening for ANZ535-536-538-542.