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

NEAR TERM /UNTIL 7 AM MONDAY MORNING/
The cold front continues to track across the forecast area with satellite view showing decreasing clouds in the wake of the front. The 12Z KIAD sounding shows dry air aloft with saturation at the mid levels. Expect cloud cover to linger ahead of the front ahead of dry air moving in overnight. No changes were made to the forecast with the previous forecast discussion below.

A weak and diffuse warm front has lifted north of the Mason Dixon line as best I can tell as of mid afternoon, as winds have shifted to out of the southwest and dew points have been steadily rising. Back over the Ohio River Valley, a cold front was trekking eastward. This cold front will reach the Appalachians late this afternoon, then cross the remainder of the Mid-Atlantic through this evening.

Broad ascent ahead of the cold front will continue to result in some spotty sprinkles (or light upslope rain), with a more pronounced area of light rain likely developing in the vicinity of southern Maryland through this evening as frontogenesis increases ahead of the approaching cold front. Any rain should exit by mid to late evening, though abundant cloud cover likely lingers through much of the night.

Temperatures may struggle to rise much this afternoon before steadily falling tonight in the wake of the cold front.

SHORT TERM /7 AM MONDAY MORNING THROUGH TUESDAY NIGHT/
High pressure will briefly build over the Mid-Atlantic Monday before lifting into New England Monday night. Although briefly in a favorable position, the high will be steadily retreating heading into Tuesday's precipitation event.

Low pressure developing over the Southeast will lift up off the Carolina coast and eventually toward New England heading into the middle of the week. Residual low-level cold air will result in precipitation beginning as a wintry mix especially west of I-95 late Monday night into early Tuesday morning. The latest guidance continues to trend toward a quicker onset time of precipitation due to a faster and more progressive/somewhat flatter low track. The southeast extent of wintry precipitation as well as specific timing of changeover and amounts remain uncertain given the transient cold air and residual spread in the track of the low. Areas in the vicinity of northern and western Maryland would be at greatest risk for accumulating snow, with those in eastern West Virginia into the Shenandoah Valley most at risk for ice. But again, the details remain a bit fuzzy at this juncture.

In terms of specific guidance, the ECMWF/EC-AIFS remain consistently on the southeast side of the guidance envelope, with the NAM12/ICON on the northwest side. The GFS and CMC are roughly in between, though the CMC guidance is notably colder with the residual wedge resulting in much more ice. Overall, guidance seems to be slowly trending toward the mean with a slight bias toward a faster/flatter low track.

Given that this will likely be the first wintry precipitation event of the season for much of the area, and coming off the heels of one of the busiest travel weekends of the year, it is prudent to check back for the latest at weather.gov/lwx/winter.

LONG TERM /WEDNESDAY THROUGH SUNDAY/
High pressure builds over the central Appalachians on Wednesday, then slides offshore through Thursday. Dry and cold conditions are expected during the middle of the week, with highs in the upper 30s to low 40s and overnight lows in the 20s. A strong cold front moves through the area Thursday night, and that could bring some upslope mountain snow showers. A very cold airmass settles over the region Friday into the start of next weekend. Thursday night lows drop to the teens in most locations, and highs on Friday are only forecast to be in the 30s. A period of wintry weather is possible Friday afternoon into Friday night as a wave of low pressure tracks south of the area. Current ensemble low tracks indicate the system could be over the Carolinas to the VA Tidewater.

AVIATION /01Z MONDAY THROUGH FRIDAY/
Any residual light rain or sprinkles should depart east of the TAF sites this evening leaving abundant VFR clouds in its wake as a cold front crosses. Transient lower CIGs should lift through 21Z (mostly affecting KCHO). Winds will shift from SW to NW 22Z-01Z with gusts of 15-20 kts (at least occasional)
lingering into the overnight. A few higher gusts are possible mid to late evening immediately in the wake of the front. Winds then turn more northerly with just a few mid/high clouds Monday.

The trend is for precipitation to move in quicker Monday night, particularly after midnight. A wintry mix is most likely near KMRB (SN/PL) and KCHO (PL/ZR), though a brief mix is possible into the metros (especially KIAD) early Tuesday morning. The temperatures should warm quickly to support plain rain in the metros Tuesday morning, and KCHO toward late morning. KMRB may hold onto wintry precip well into Tuesday depending on low track.
Precipitation will exit quickly heading into Tuesday evening.
Given the pattern, a period of IFR is likely early Tuesday morning through Tuesday afternoon. Southeast winds late Monday night into Tuesday will become northwest late Tuesday afternoon through Tuesday night with gusts of 15 to 25 knots possible.

VFR conditions are expected to prevail during the middle to late part of the week.

MARINE
Southwest winds will turn northwest heading into this evening with gusts of 15 to 25 knots likely through the night. A few gusts of 30 to 35 knots are possible this evening immediately in the wake of a cold front, but confidence was not nearly there for a Gale Warning. Can't totally rule out an SMW or two. Winds will shift to north, east, then southeast later Monday morning through Monday night at lighter speeds. Light southeast winds will linger through Tuesday afternoon before shifting to northwest and increasing possibly to gale force for portions of the waters late Tuesday afternoon through Tuesday night. Light rain this evening will exit overnight, with rain or a wintry mix possible late Monday night through Tuesday afternoon.

High pressure builds into the region from the west on Wednesday, then moves overhead Wednesday night into Thursday. Ongoing SCA conditions Wednesday morning will quickly diminish by early afternoon. Sub-SCA winds prevail through Thursday morning, then SCA conditions are possible again as winds turn south to southwest.

TIDES/COASTAL FLOODING
Gusty northwesterly winds will lead to possible blow out tides starting Monday morning. Low water levels are possible at Chesapeake City, Havre De Grace, Baltimore, Annapolis, and Solomons Island. Tidal anomalies begin rising Tuesday morning.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Small Craft Advisory until 8 AM EST Monday for MDZ008.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 8 AM EST Monday for ANZ530>543.
Gale Watch from Tuesday afternoon through late Tuesday night for ANZ533-534-537-541>543.