Marine Weather and Tide Forecast for Upper Marlboro, MD

KEY MESSAGES
- 1) Near-Blizzard conditions expected in the Alleghenies late this morning through Saturday morning

- 2) Extreme cold and strong winds will result in dangerous wind chills this weekend.

- 3) Temperatures should start to increase on Monday, with a chance for mixed precipitation later in the week.

DISCUSSION
KEY MESSAGE 1...Near-Blizzard conditions expected in the Alleghenies late this morning through Saturday morning.

Morning Update: Snow showers are already noted on KLWX making their way east of the Alleghenies, with snow observed around Hagerstown and over the Shenandoah Mountains. There has also been some freezing drizzle reported just west of our forecast area in southwest PA and WV.

A Special Weather Statement has been issued along and west of the Blue Ridge and Central VA for a dusting to around 1 inch of snow possible as these showers increase in coverage this afternoon. Brief periods of heavy snow are possible with the strongest showers. Additionally, a Winter Commuting Hazard Statement has been issued along the I-95 corridor for this afternoon as these showers move through. The higher accumulating snow totals look to be over central VA and west of the Blue Ridge. The northern Blue Ridge (Shenandoah NP) could end up with 1-2" of snow.

Previous Discussion: A Winter Storm Warning remains in effect from 10AM this morning to 7AM Saturday morning with near- blizzard conditions expected across the western portions of the Alleghenies. Snow totals of 6 to 7 inches, with locally higher amounts along the western favored ridges are expected. Further east in the Alleghenies, Winter Weather Advisories remain in effect beginning this afternoon through the overnight. Total snow accumulations between 2 and 4 inches are expected.

As an Arctic front moves across the Alleghenies tonight, heavier bursts of snow showers are expected. During this time, snow squalls are possible within the Winter Storm Warning.

In addition to accumulating snowfall, gusty northwest winds as high as 50 to 60 mph will result in blowing and drifting snow.
This will yield reduced visibilities as low as 1/4 mile across roadways.

Outside of the Alleghenies, guidance continues to show snowfall further east Friday afternoon. Accumulations from a dusting to a few tenths are expected across much of the area, with accumulations of an inch possible along the Blue Ridge.

Synoptic discussion: A series of mid/upper troughs will traverse the area today into Saturday, bringing several intense periods of snow to the Alleghenies. The leading shortwave arrives this morning to afternoon, then the main upper trough and Arctic front cross the area Saturday morning.

The strong trough crossing the northern Mid-Atlantic will provide ample lift to generate heavy snow showers across the mountains today into Saturday. In addition, increasing instability through the DGZ Friday evening and very high SLRs will generate squalls. Travel disruptions are likely along I-68/US-40 west of Frostburg, MD, US-219 from the PA/MD line south to the WV line, US-48 west of Moorefield, WV, US-33/WV-28 west of Franklin, WV, and US-250 west of Monterey, VA.

Strengthening winds will also lead to significant blowing and drifting snow. The strongest winds on Saturday don't overlap with the best lift and instability, so don't see a need for a Blizzard Watch. Squalls will likely continue through the day Saturday given the strength of the low- level flow and high Froude numbers.

KEY MESSAGE 2...Extreme cold and strong winds will result in dangerous wind chills this weekend.

Morning Update: The Extreme Cold Warning has been expanded south to the DC Metro Area and Anne Arundel County. This is due to the prolonged nature of wind chills at and below zero, as well as the coldest wind chills right around -10F Saturday morning. We cannot stress enough how dangerous these wind chills will be for anyone outside for a prolonged period of time.
Frostbite can occur in as little as 30 minutes on exposed skin.
It is recommended you limit your time outdoors on Saturday, and if you do go outdoors be sure to dress in multiple layers and cover most, if not all, exposed skin (especially your face, ears, and hands). Additionally, the wind chills are now expected to get down to or just below 0 degrees in all of Central VA, so the Cold Weather Advisory has been expanded to cover that area.

Previous Discussion: A strong low pressure system located offshore paired with arctic high pressure moving in from Canada will yield a tight pressure gradient over the forecast area today into Sunday morning. Additionally, an upper level trough digs across the east this weekend, with a low level jet intensifying over the forecast area Saturday morning.

Model soundings continue to show mixing up to around 925mb, with a stout inversion located just above that level between 850-900mb. The strongest winds are maximized just above the inversion, but there is still around 50-60 kt of wind just below that inversion. The strong synoptic setup (with breaking lee waves off the Alleghenies) will allow these strong winds to mix down to the surface. A sudden onset of strong winds is expected right right as the Arctic front passes through. There is high confidence for widespread, persistent gusts in the mid to upper 40kt range (50-55 mph), with occasional gusts to 50-55kt (60-65 mph) possible.

High Wind Warnings and Wind Advisories have been issued across the forecast area with the exception of Orange and Spotsylvania Counties. Wind headlines go into effect tonight and persist through Saturday evening. Cold temperatures from the Arctic front combined with gusty winds will yield dangerously cold wind chills. Therefore, the Extreme Cold Watch was converted to Extreme Cold Warnings and Cold Weather Advisories for much of the forecast area.

KEY MESSAGE 3...Temperatures should start to increase on Monday, with a chance for mixed precipitation later in the week.

Once this weekend's upper trough moves to the northeast starting Sunday night, a general zonal flow pattern will encompass a large portion of CONUS early next week. Winds should generally ease up, and temperatures will steadily start to warm up on Monday.
Temperatures reaching the upper 40s could be seen in areas south of the I-66 corridor on Tuesday. Starting sometime mid-next week, models are showing a possibility for a weak low to move across the Great Lakes approximately by Wednesday. Depending on how far north this low tracks, this could result in some wintry mixed precipitation in the region, although temperatures are still trending warmer by then.

AVIATION /15Z FRIDAY THROUGH TUESDAY/
VFR conditions continue across the terminals this morning with light winds expected. Snow showers are possible across all terminals this afternoon, with little to no accumulation expected. The main hazard expected with snow showers will be slightly increased gusts and reduced visibilities. Currently have -SHSN in PROB30 groups as guidance continues to shift south. For the 12Z TAFs, will likely include in prevailing groups, especially at KMRB where confidence is highest. Periods of heavier snowfall are possible, leading to potential IFR or LIFR conditions. Additionally, the frontal passage will result in a wind shift to northwest winds.

A powerful Arctic front crosses the area early Saturday morning.
Light winds will rapidly increase from the northwest around daybreak Saturday, with gusts of 40-50 kt ensuing and lasting through the afternoon. A few gusts above 50kt are possible at times, but the majority will likely be in the mid to upper 40kt range. Winds begin to decrease in the late afternoon, but still gusting 30-35 kt into the evening.

Once this weekend's low passes through, winds should be fairly benign for the early portion of next week. Winds will likely shift SE overnight on Monday, and generally stay at 5-10 knots until a potential Wednesday low increases gust potential. VFR conditions likely for Monday and Tuesday, although a southern pressure gradient may cause some lower CIGs Monday night at KMRB.

MARINE
Light winds and non-hazardous marine conditions continue through late this evening. Snow showers are possible over the waters, possibly resulting in reduced visibilities and sporadic gusts near SCA criteria. Otherwise, benign conditions over the waters expected today.

Tonight, a potent Arctic front pushes across the forecast area with a rapid onset of Gale Force Winds expected. A Gale Warning is in effect for tonight, with increasing winds leading to a Storm Warning being in effect beginning Saturday morning.
Northwest wind gusts up to 50 knots are expected. Additionally Gale Warnings are expected Saturday night through Sunday morning. Winds diminish on Sunday with SCA criteria winds expected over the open waters through late Sunday evening.

NW winds ranging 10-15 knots are expected for most of the day Monday, and SCAs are not out of the realm of possibility as winds continue to decrease after Saturday's major arctic frontal event.
Gusts up to 20 knots are possible. By Tuesday, winds and gusts should be fairly low, ranging 5-10 knots with a southeastern directional shift occurring overnight Monday.

TIDES/COASTAL FLOODING
Blowout tides are expected late Friday night through Sunday night. Water levels as low as -2 ft MLLW are possible. Low Water Advisories are likely to be issued. The ice covered waters of the northern/middle bay and tidal Potomac could result in the potential for damage to docks, moorings and boats, especially when blowout tides result in significantly lower water levels.

LWX WATCHES/WARNINGS/ADVISORIES
DC...Extreme Cold Warning from 4 AM Saturday to 10 AM EST Sunday for DCZ001.
High Wind Warning from 4 AM to 7 PM EST Saturday for DCZ001.
MD...Gale Warning from 2 AM to 6 AM EST Saturday for MDZ008.
Extreme Cold Warning from 4 AM Saturday to 10 AM EST Sunday for MDZ006-008-011-013-014-018-501-503>510.
High Wind Warning from 4 AM to 7 PM EST Saturday for MDZ003>006-008-011-013-014-016>018-502>508.
Storm Warning from 6 AM to 6 PM EST Saturday for MDZ008.
Cold Weather Advisory from 4 AM Saturday to 10 AM EST Sunday for MDZ003>005-016-017-502.
Winter Weather Advisory until 7 AM EST Saturday for MDZ501.
High Wind Warning from midnight tonight to 10 PM EST Saturday for MDZ501-510.
Winter Storm Warning until 7 AM EST Saturday for MDZ509-510.
Wind Advisory from midnight tonight to 7 PM EST Saturday for MDZ509.
VA...Extreme Cold Warning from 4 AM Saturday to 10 AM EST Sunday for VAZ053-054-501-503>508-526-527.
High Wind Warning from 4 AM to 7 PM EST Saturday for VAZ025>031-053-054-501-504>506-526-527.
Cold Weather Advisory from 4 AM Saturday to 10 AM EST Sunday for VAZ025>031-036>040-050-051-055>057-502.
Winter Weather Advisory until 7 AM EST Saturday for VAZ503.
High Wind Warning from midnight tonight to 10 PM EST Saturday for VAZ503-507-508.
Wind Advisory from 4 AM to 7 PM EST Saturday for VAZ036>040- 051-055-057-502.
WV...Extreme Cold Warning from 4 AM Saturday to 10 AM EST Sunday for WVZ501-503-505-506.
High Wind Warning from 4 AM to 7 PM EST Saturday for WVZ050>053-055-502-504-506.
Cold Weather Advisory from 4 AM Saturday to 10 AM EST Sunday for WVZ050>053-055-502-504.
Winter Weather Advisory until 7 AM EST Saturday for WVZ503.
High Wind Warning from midnight tonight to 10 PM EST Saturday for WVZ501-503-505.
Winter Storm Warning until 7 AM EST Saturday for WVZ501-505.
MARINE...Gale Warning from 2 AM to 6 AM EST Saturday for ANZ530>543.
Extreme Cold Warning from 4 AM Saturday to 10 AM EST Sunday for ANZ530.
High Wind Warning from 4 AM to 7 PM EST Saturday for ANZ530.
Storm Warning from 6 AM to 6 PM EST Saturday for ANZ530>543.
Freezing Spray Advisory from 6 AM Saturday to 6 AM EST Sunday for ANZ532-533-542.
Heavy Freezing Spray Warning from 6 AM Saturday to 6 AM EST Sunday for ANZ534-537-543.