Marine Weather and Tide Forecast for Annandale, VA

KEY MESSAGES
- (1) A cold front crosses overnight into Sunday morning.

- (2) High pressure moves in early next week, with persistent cool temperatures and fire weather risk.

- (3) Warming temperatures late next week.

DISCUSSION
KEY MESSAGE 1...A cold front crosses overnight into Sunday morning.

An upper-level trough and corresponding strong surface cold front will cross the Mid-Atlantic tonight into Sunday morning. There is not the best overlapping synoptic setup with the surface cold front being displaced from upper-level trough. Despite this, there is a decent signal for strong low-level convergence and modest moisture advection. This leads to intermittent showers through Sunday morning, exiting east of the Chesapeake Bay by Sunday afternoon. Cannot rule out a few thunderstorms through this evening mainly west of the Blue Ridge/Catoctin Mountains. SPC does have a Marginal Risk (level 1 of 5) for these areas, with a Slight Risk (level 2 of 5) clipping far western Maryland. The main threat is gusty winds given steep low-level lapse rates and moderate flow a few thousand feet AGL, but the threat is somewhat conditional on if/when convection organizes into a band over the Ohio Valley. Areas further east are more stable given onshore flow off nearby cooler waters, lowering thunder chances. Guidance continues to show some elevated instability early Sunday morning resulting in the potential for a few downpours or a clap or two of thunder. Still favoring a gusty line of showers with the front itself early Sunday morning with a notable wind shift from S/SE to W/NW; gusts of 40-45 mph are possible (with around 50 mph possible on the ridges) in a 1- to 3-hour window immediately in the wake of the front.

Once precipitation moves out, NW CAA will bring breezy conditions Sunday afternoon into evening. High temperatures on Sunday will be reached early in the day, and are expected to be 15 to 25 degrees cooler than Saturday - a stark contrast to the recent spell of record heat.

Depending on how much rain falls and how quickly humidity drops, a fire weather threat could develop mainly west of I-95 Sunday afternoon. See the Fire Weather section below for details.

KEY MESSAGE 2...High pressure moves in early next week, with persistent cool temperatures and fire weather risk.

Following a secondary cold front Monday, a strong upper-level trough and shortwave will pivot overhead. Very cold air at 850-500 hPa will result in very steep lapse rates, with deep inverted-V profiles noted in forecast soundings up to 8-12 kft.
This will result in wind gusts of 20 to 30 mph as dry low-level air moves in. Given mid-level moisture and the shortwave, some cloud cover and a few sprinkles or even a light/brief graupel shower can't be ruled out.

High pressure builds overhead Monday night into Tuesday leading to lighter winds. The cold, dry airmass, clear skies and light to calm winds Monday night into Tuesday morning are likely to result in widespread frost/freezing temperatures.

As the high moves offshore Tuesday, winds turn out of the south beginning the end of the early-week cool spell. Another cold front will begin approaching from the north late Tuesday night into Wednesday, but with little moisture to work with.

KEY MESSAGE 3...Warming temperatures late next week.

Temperatures begin to warm to the 70s and 80s in the later half of next week, with a warm front on Friday pushing highs back into the mid-80s range for much of the area. Some residual showers may be possible on Wednesday stemming from low surface pressure to the north. Thursday and Friday will see significant upper- level ridging over the region, allowing for relatively light winds and low rain chances.



AVIATION /18Z SATURDAY THROUGH THURSDAY/
Winds will remain S/SE into this evening with 15-20 kt gusts at times. Winds may become a bit lighter and more E especially further north and east for a time, and LLWS is possible as a LLJ pivots overhead. SHRA and perhaps TS approach KMRB as early as 00Z, with lesser thunder chances east as precip moves in mainly after midnight.

An abrupt wind shift to the northwest is expected 06Z-12Z Sun with FROPA. Some MVFR is possible Sun AM. Gusty winds of 30 to perhaps 40 kts are possible for a brief time right after FROPA.
Gusts of 20 to 30 kts then linger through Sun eve before lighter winds overnight. A secondary cold front likely results in 20 to 30 kt gusts again heading into Mon with a spotty shower possible.
Otherwise, VFR Sun night through Tue. Winds shift to S by Tue.

Southerly winds shift northeast by Wednesday night as low pressure passes to the north and a cold front drops in. Gusts up to 15 knots are possible across terminals on Wednesday before gradually decreasing overnight. Northerly winds are expected on Thursday with VFR conditions across the area.

MARINE
Southeast flow will remain gusty this evening, with a bit of a lull for a time overnight for most waters. Winds will likely remain elevated over the wider waters off southern MD, though.
An abrupt shift to the northwest is expected between 4 AM and 8 AM Sunday from northwest to southeast, with gusts of 30-40 kts for a brief time likely necessitating Special Marine Warnings even if there is little to no precipitation as a strong cold front crosses the waters.

Showers and gusty winds (SCAs) linger behind the front, with drying expected by Sunday afternoon. Winds become lighter Sunday night then increase again Monday with a secondary front. Light winds Monday night turn southerly Tuesday with additional SCAs possible by Tuesday night.

Small Craft Advisories may be needed Wednesday morning as winds flow southerly with gusts up to 20-25 knots before gradually decreasing later in the day. Winds shift to northerly overnight with winds on Thursday likely falling below SCA criteria.

FIRE WEATHER
While some rain is expected late this evening into Sunday morning, amounts of a tenth to two tenths on average will not be sufficient to wet fuels significantly. It should be noted some hi- res guidance does have localized amounts near a half an inch, but pinpointing the exact locations of these spotty amounts is very difficult. Strong gusty winds of 35 mph with potential for gusts as high as 45 mph will create renewed fire weather concerns despite marginal humidities and the overall light rainfall Sunday into Monday. Given the short duration of precipitation (6 hours or less for most), the 100-hour fuel moisture values aren't likely to rise much at all. The 10-hour fuel moisture likely rises considerably, but drops quickly through the day Sunday due to the drying effects of strong winds and rapidly lowering humidity especially west of the Blue Ridge and Catoctin Mountains.

Much cooler temperatures are expected Monday and Tuesday with a moderating trend in temperatures expected during the middle and second half of the week. Strongest winds look to be on Monday out of the northwest with gusts to 25 mph (30 mph over ridges). For the rest of the week, winds will be on light side thanks to high pressure overhead, but humidities will be marginally low to near critical levels. A dry pattern seems likely to continue with little to no rainfall.

TIDES/COASTAL FLOODING
SE flow will cause tides to rise to around or a little over one foot above normal through early Sunday morning ahead of a strong cold front. Minor tidal flooding is possible at several sites especially for the waters around central to southern MD, with near moderate flooding possible in a high-end scenario at Annapolis (though a wind shift to the northwest right around high tide should prevent that).

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Coastal Flood Advisory from 3 AM to 10 AM EDT Sunday for MDZ014.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ530>533-535-536-538>542.
Small Craft Advisory from 6 AM to 6 PM EDT Sunday for ANZ530>533-535-536-538>542.
Small Craft Advisory until 6 PM EDT Sunday for ANZ534-537-543.