Marine Weather and Tide Forecast for George Mason, VA

KEY MESSAGES
- (1) Showers and thunderstorms expected this weekend as a cold front approaches at the end of the week.

- (2) Increasing heat and humidity are expected next week.

DISCUSSION
KEY MESSAGE 1...Showers and thunderstorms expected this weekend as a cold front approaches at the end of the week.

An upper trough and associated surface low will develop over the Great Lakes and move into the northeast CONUS through Friday.
The trailing cold front will slowly sag south into the region through Saturday. Isolated to scattered showers and perhaps a thunderstorm will return to the forecast late today or this evening for northern and western MD into eastern WV before dropping south into the rest of the region Friday morning.
Overall, the risk of thunderstorms today seems low given lack of deep moisture (i.e. 850 mb dewpoints less than 10C) and 850-700 mb ridging and associated mid-level capping seen on model soundings, but some shallow convection is possible west of the Blue Ridge Mountains. In the vicinity of western MD, slightly deeper moisture and better lift ahead of an approaching cold front as well as strong mid-level flow could lead to a strong to severe storm or two this evening as convection shifts east across the OH Valley/lower Great Lakes.

Moisture deepens Fri into Sat with 850 mb dewpoints rising above 10C Fri and over 15C on Sat. This when combined with increasing temperatures should result in a more unstable environment. 850-700 mb height falls are progged after 18Z Fri associated with an approaching secondary shortwave-trough from the mid MS River Valley. This should prove more than sufficient to generate sct-nmrs deep convection. Fri poses the greater risk of some severe wx/downburst winds due to hot air mass and mid-level dry air, while Saturday poses a bigger risk for heavy rainfall due to deeper moisture and nearly moist adiabatic/skinny CAPE profiles. The front finally starts crossing the area Saturday night, but it will be a slow gradual process.

KEY MESSAGE 2...Increasing heat and humidity are expected next week.

There is some uncertainty with how far south the front makes it Sunday. However, it will likely be a relatively cooler day with the front over or south of the area. There may be a lingering shower and thunderstorm chance. The front will likely start losing its definition Monday as weak high pressure builds in. Thus expect lower rain chances and a slight uptick in temperatures.

Heat will likely ramp up Tuesday and Wednesday with the building upper level ridge over the Ohio Valley, although there is still a fairly large spread in ensemble high temperature data, ranging from the mid 80s to near 100. Humidity will also likely be elevated, so heat index values could top 100 if the hotter solutions verify. The strength and position of the ridge will determine if subsidence wins out, or if there might be an opportunity for diurnal thunderstorm development.

AVIATION /12Z THURSDAY THROUGH MONDAY/
VFR/dry conditions are expected through the TAF period (18Z Fri), though can't totally rule out a pop up shower near MRB 01Z-05Z.
Winds will be southerly (more SE at MTN) 9-12 kts with gusts 15-23 kts with the highest gusts most likely 21Z-03Z.

After 18Z Friday, SHRA/TS chances increase markedly. A boundary will slide slowly southward across the area with moisture advection overrunning it, and this is expected to cause scattered to numerous showers and a few thunderstorms.
Additional activity is possible through Friday night, with a chance of remnant TS activity approaching from the OH Valley late into Saturday morning. Additional activity and lower CIGs are possible through Saturday as a front slowly slides south.
Wind direction may be a bit variable between S and NW depending on the placement of the front, but should be generally light outside of convection.

There may be a lingering shower or thunderstorm chance Sunday depending on how quickly the cold frontal zone moves south. VFR/dry conditions are more likely Monday.

MARINE
SCAs are in effect for all the waters through tonight. Southerly winds pick up this afternoon, peak this evening, then gradually diminish through Friday morning. Sct-nmrs convection Fri afternoon and evening may pose a risk of strong winds, which may require Special Marine Warnings. Convection Saturday will pose a bigger threat for intense rainfall rates and poor visibility at times.

Light northerly winds are forecast Sunday with a cold front gradually pushing to the south. A thunderstorm could remain possible if the front is slower. Weak high pressure builds across the area Monday with light east to southeast winds.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 2 PM this afternoon to 3 AM EDT Friday for ANZ530-531-538-539.
Small Craft Advisory from 2 PM this afternoon to 8 AM EDT Friday for ANZ532>534-537-540>543.
Small Craft Advisory from 5 PM this afternoon to 3 AM EDT Friday for ANZ535-536.