Marine Weather and Tide Forecast for Ashton-Sandy Spring, MD

NEAR TERM /THROUGH TONIGHT/
Cold continues to grip the area today as the main story, with high temperatures topping out in the teens and 20s, and single digits in the mountains. While winds are expected to overall diminish in comparison to yesterday, as high pressure moves overhead tonight, clear skies will allow temperatures to drop hard. A pressure surge is anticipated around the time of lowest temps as well, allowing winds to pick up and resulting in lower wind chills. Lows tonight are expected to be single digits-- essentially above zero east of the Blue Ridge and below zero to the west. The metros may be able to hang onto the low teens.
Even just a 5 mph wind very late tonight into tomorrow morning will bring wind chills down to near zero and below across the board, and -10s and -20s in the mountains. Cold Weather Headlines remain in effect for most of the area today, and begin for the entire area late tonight.

Beyond the cold temperatures, Tuesday continues to be interesting as an upper trough swings overhead. Guidance continues to show subtle frontogenesis in the mid-levels (600-700mb), coinciding with weak ascent ahead of the trough.
Snow showers along the Alleghenies is fairly certain, but there is the potential for flurries to scattered snow showers gradually advancing east late this morning through the afternoon and into the evening hours. With the persistent cold, even a quick coating or inch could become impactful for those traveling. The main concern is the timing of any snow with the evening commute. Guidance currently suggests the better forcing aligning near the/just south and east of the DC metro area near the end of our typical evening commute (around 7-8pm). Earlier in the day, moist advection will be fighting low level dry air.
We'll gradually become more saturated in the low levels through the afternoon. However, dry air will also be working its way into the mid-levels, around the time of the evening commute.
There could be a brief window where the entire column is saturated enough and Fgen forcing and synoptic ascent allows for a quick snow shower or two around the metro. 0z guidance suggests this window has shifted slightly south and east of the metro area, but we will continue to monitor closely for potential impacts.



SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/
Cold air continues to envelope the region Wednesday with a broad upper trough encompassing most of the CONUS and high pressure building in at the surface. High temperatures are expected to top out in the teens to mid-20s (single digits to teens in the mountains). Low temperatures will range from single digits in the mountains to near 10-15 in far southern Maryland. While winds are expected to lighten as high pressure builds in, it won't take much to bring apparent temperatures to near or just below zero early Wednesday morning for much of the area. Cold Weather Headlines are in effect through Thursday morning across the area.

As surface high pressure slides east, southerly return flow will result in very welcome WAA on Thursday, allowing temperatures to rise into the upper 20s to mid 30s. Dry conditions and mostly sunny skies are expected, outside of the mountains, where a passing disturbance will bring continued cloud cover and possible upslope snow Thursday afternoon and evening.

LONG TERM /FRIDAY THROUGH MONDAY/
The Arctic chill is expected to continue Friday through Saturday night as an area of high pressure builds in from the west and northwest. Temperatures will be about 10 degrees below average with highs in the lower 30s and lows in the lower to middle teens. Dry conditions expected for the most part. We can't rule out a few snow showers in the Appalachians Friday and Friday evening as the building high produces an upslope component. There could even be a snow shower or two spill over into parts of the Shenandoah Valley late Friday based on the 00z GFS model.

As we look into Sunday, a cold front is expected to move from the Great Lakes into the mid-Atlantic. This front could be moisture- starved, thus most of any precipitation could be focused over some of the highlands as snow showers and would occur where an upslope light wind materializes ahead of or behind the front. Temperatures Sunday into Sunday night look to be more closer to average for late January. Highs in the lower 40s and lows in the middle 20s.

While models tend to agree on a cold frontal passage sometime on Sunday, they tend to disagree as to whether or not an area of low pressure develops on the tail-end of the cold front Sunday night and into Monday. The GFS does form a low and moves it across our region, bringing some light wintry. Then, it wants to form another low pressure system along the cold front of the first developed low.
This second low would bring us more precipitation and more likely snow. The EURO forms a low and keeps it well to our south Sunday night and does not want to form a second low along the front of the first low. It also pushes everything off of the East Coast and out to sea later Monday. Looking at the perspective of a model blend for the extended period, particularly Days 6 and 7, we will have a chance for a little snow in the north, a chance for a little rain and little snow mix in central areas, and a chance for a little rain in our southern zones. As we get closer to next weekend, we will get a better feel of the potential for dual low pressure systems with precipitation or low pressure systems that stay to our south.

AVIATION /08Z TUESDAY THROUGH SATURDAY/
A disturbance will cross the area Tuesday, resulting in mid- level ceilings. There is a low chance for MVFR conditions and a few snow showers or flurries during the afternoon and evening.
Winds will be light from the west to southwest.

VFR conditions are expected Wednesday and Thursday. N/NW winds may gust 15-20 kt in the morning but should quickly diminish.
Winds turn SW/W on Thursday.

VFR conditions Friday through Saturday night. Winds northwest 5 to 10 knots Friday and Friday night. Winds becoming southwest 5 to 10 knots Saturday and Saturday night.



MARINE
A Small Craft Advisory remains in effect early this morning, with a few locations still observing gusts 18-20 kts. N/NW winds gradually diminish through the day. SCAs may be necessary again tonight into Wednesday morning as a pressure surge moves through with a passing disturbance aloft. Winds diminish again through the day Wednesday as high pressure moves through, then turn W/SW on Thursday.

No marine hazards expected Friday through Saturday night at this time. Winds northwest 10 knots Friday and Friday night. Winds becoming southwest 10 knots Saturday and Saturday night.

LWX WATCHES/WARNINGS/ADVISORIES
DC...Cold Weather Advisory until 10 AM EST Thursday for DCZ001.
MD...Cold Weather Advisory until 10 AM EST Thursday for MDZ003>006- 008-011-013-014-502>508.
Small Craft Advisory until 5 AM EST early this morning for MDZ008.
Extreme Cold Warning until 10 AM EST Thursday for MDZ001-501.
Cold Weather Advisory from 10 PM this evening to 10 AM EST Thursday for MDZ016>018.
VA...Cold Weather Advisory until 10 AM EST Thursday for VAZ025>031- 038>040-051-053-054-501-502-505-506-526-527.
Extreme Cold Warning until 10 AM EST Thursday for VAZ503-504- 507-508.
Cold Weather Advisory from 10 PM this evening to 10 AM EST Thursday for VAZ036-037-050-055>057.
WV...Cold Weather Advisory until 10 AM EST Thursday for WVZ050>053- 055-502-504.
Extreme Cold Warning until 10 AM EST Thursday for WVZ501-503- 505-506.
MARINE...Cold Weather Advisory until 10 AM EST Thursday for ANZ530.
Small Craft Advisory until 5 AM EST early this morning for ANZ530>534-536>543.
Freezing Spray Advisory until 10 AM EST this morning for ANZ533-534-541-543.