Marine Weather and Tide Forecast for Point of Rocks, MD

NEAR TERM /UNTIL 6 AM SATURDAY MORNING/
A persistent stratus shield extends into southwestern portions of the CWA (SW of Harrisonburg and Charlottesville) and has only been slowly expanding northward. Cloud bases here appear high enough that fog or other low visibility issues should not develop, except perhaps where the clouds intercept the highest ridges. Elsewhere, clear skies and light winds have allowed temperatures to plummet close to forecast lows in the mid 20s, so these values may need to be adjusted down slightly. However, at least mid and high clouds should increase the second half of the night, and a light south wind may develop as high pressure drifts off the Mid Atlantic coast. So the temperatures should level off or perhaps even rise in some locations the second half of the night.

SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/
A weak ridge of high pressure will become centered over the region on Saturday. Mostly cloudy skies and dry conditions are expected to the east of the mountains, with highs in the upper 30s to mid 40s for most. Meanwhile, much further to the west, the waveguide across North America will start to amplify as a system tracks toward the British Columbia coast. A ridge building event will ensue downstream over western Canada, which will cause a pre- existing upper low over the Upper Great Lakes to drop southeastward toward the Mid- Atlantic and amplify into a shorter wavelength open wave. As this occurs, large scale forcing for ascent will increase across the area late Saturday afternoon into Saturday night. Snow now appears as though it will start during the mid to late afternoon hours in the Alleghenies. This snow could be moderate to briefly heavy at times during the evening through the first half of the overnight. Winter Storm Warnings have been issued for western Garrett and western Grant counties, where 4-8 inches of snow is expected. Winter Weather Advisories have been issued for eastern Garrett, western Allegany, and western Pendleton Counties, where 2-4 inches of snow is expected.

With westerly low-level flow downsloping off of the Appalachians, precipitation will struggle to make progress to the east of the Allegheny Front for several hours. As the wave amplifies and approaches from the west, most models show a jet steak developing downstream, with forcing for ascent increasing within the equatorward entrance of the jet streak. Most solutions show the jet entrance region lining up right along I-95. Ascent within the jet entrance region may cause precipitation to jump eastward and develop in-situ along the I-95 corridor, largely skipping locations between the Allegheny Front and Blue Ridge.

Precipitation within the jet entrance region to the east of the Blue Ridge is expected to blossom during the mid-late evening hours, and then slowly drift southeastward through the remainder of the night. The precipitation may begin as a brief period of rain or mixed rain and snow, especially along and southeast of the I-95 corridor. This mix should be short-lived however, as much colder air rushes in behind an Arctic front that will move through over the course of the night. In terms of timing, some light precipitation could begin as early as the mid-late evening hours, but the bulk of the precipitation along the I-95 corridor is expected to occur between roughly 11 PM and 7 AM.

The band that will develop will be a relatively narrow feature, and will feature moderate to heavy snow at times. Snowfall rates within the band could near or potentially briefly exceed one inch per hour at times late Saturday night. With a narrow feature producing heavy precipitation, snow totals will be heavily dependent on the ultimate placement of this band. This, combined with the potential for a bit of mixing with rain at onset makes for a challenging snowfall forecast.

Probabilistically speaking, 12z guidance has focused in on the I-95 corridor from DC northeastward, and then eastward along US-50 toward the Chesapeake, with northeast Maryland southward toward Annapolis having the greatest probabilities for higher totals. As of this moment, a broad 1-4 inches from the vicinity of the I-95 corridor eastward appears like the most likely scenario, with embedded maxes of 4-7 inches possible where the band resides for the longest time period. Since there will be very sharp snowfall gradients on the edges of this band, and there's still a bit of uncertainty with respect to where this band will be, we've decided to hold off on issuing headlines to the east of the Blue Ridge for the time being. Headlines will almost certainly be needed eventually, and we'll continue to assess trends and refine the forecast through the remainder of the day. Snow will end from northwest to southeast a few hours either side of daybreak, with the back edge of the snow clearing southern Maryland by around mid-morning.

Strong cold air advection is expected behind the Arctic front through the day Sunday, with 850 hPa temperatures crashing to around -15 to -20 C by peak heating. This will cause temperatures to drop through the 20s over the course of the day.
Northwesterly wind gusts to around 35 mph will make it feel even colder, pushing wind chills into the single digits and teens.
After the snow moves out, dry conditions are expected to the east of the mountains. Upslope snow showers will linger in the Alleghenies over the course of the day. Cold and windy conditions will continue through Sunday night, with cold weather headlines likely being needed for portions of the area.

LONG TERM /MONDAY THROUGH FRIDAY/
Still very cold Monday, but not as windy with gusts up to 25 mph.
Arctic high pressure settles over the area Monday night.

Deep trough pattern lifts out early next week and replaced by largely zonal flow leading to a welcome moderating trend in temperatures mid week. An area of low pressure tracking north of the Great Lks will push a cold front through the area Thu night bringing a risk of rain showers and mountain rain/snow showers. High pressure builds again over the area to end the week. Overall, much warmer and tranquil weather middle and second half of next week than it had been the first two weeks of December.

AVIATION /01Z SATURDAY THROUGH WEDNESDAY/
VFR conditions will likely persist through the night at most of the terminals, although some MVFR clouds can't be completely ruled out near CHO. VFR conditions and light southwesterly winds are expected at all terminals during the day Saturday.

Lower ceilings and snow are expected to develop in place across much of the forecast area Saturday night. BWI, MTN, DCA, and IAD are most likely to experience the greatest impacts from snow, with a couple inches of accumulation possible during the second half of the night. The precipitation could also briefly mix with rain at onset. Chances for snowfall are a bit lesser at MRB, and the snow appears as though it will likely avoid CHO altogether.

Conditions are expected to improve back to VFR by mid-morning Sunday at all terminals. Northwesterly gusts to around 25-30 knots are expected throughout the day in the wake of a strong Arctic front.

Monday...NW wind gusts up to 25 kt. Light winds 10 kt or less Tue.

MARINE
Sub-SCA level southerly winds are expected over the waters for most of tonight. There could be a brief 2-3 hour window where gusts approach low-end SCA levels around daybreak. Sub-SCA level southwesterly winds are expected during the day Saturday. Winds will go light Saturday evening, before turning out of the northwest and picking up in magnitude during the second half of the night as an Arctic front moves over the waters. SCAs will likely be needed over the waters late Saturday night. Snow may also be possible over the waters the second half of the night into the first couple hours of Sunday morning.

Winds will further strengthen during the daylight hours Sunday.
Gale Watches are in effect for all waters from 11 AM Sunday through 6 AM Monday morning. Freezing spray may also be possible at times during the day Sunday.

SCA conditions expected Monday with gusts up to 25 kt, diminishing gradually through the day and night, and dropping below SCA threshold by daybreak Tuesday. Freezing Spray conditions are still possible Monday, but are more likely to occur Sunday with the stronger winds and colder temperatures.

Lighter winds Tue and Wed. Winds strengthen again during the second half of next week.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Gale Watch from Sunday morning through late Sunday night for MDZ008.
Winter Weather Advisory from 4 PM Saturday to 1 PM EST Sunday for MDZ501-510.
Winter Storm Warning from 1 PM Saturday to 4 PM EST Sunday for MDZ509.
VA...None.
WV...Winter Weather Advisory from 4 PM Saturday to 1 PM EST Sunday for WVZ503-505.
Winter Storm Warning from 1 PM Saturday to 4 PM EST Sunday for WVZ501.
MARINE...Gale Watch from Sunday morning through late Sunday night for ANZ530>543.