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

KEY MESSAGES

-1) A strong cold front will slowly push across the region this evening bringing gusty winds and severe thunderstorms capable of producing significant damaging winds, heavy rain, and tornadoes.

-2) A period upslope snow showers are expected along and west of the Allegheny Front tonight into Tuesday.

- 3) Below normal temperatures are expected Tuesday and Wednesday before seasonable weather returns for the remainder of the week.



DISCUSSION
KEY MESSAGE 1.. A strong cold front will slowly push across the region this evening bringing gusty winds and severe thunderstorms capable of producing significant damaging winds, heavy rain, and tornadoes.

Our initial wave of strong to severe thunderstorms continues to work along and east of I-95 this afternoon. This activity will exit toward the Chesapeake Bay over the next 1-2hrs. Several reports of wind damage have been noted as this line pushes east of the Blue Ridge earlier this afternoon and up across central portions of MD this afternoon. Behind this line, is a lull in the activity with the cold front still lagging back across central WV and far western VA.
Some uncertainty remains to if there will be re-development between the initial line of storms and the front back toward the west. You can start to see the evolution of the next line of storms building northward from far southwest VA down into western NC/SC. This line should start to lift northward starting down around KCHO/KMRB around 21-23z/5-7pm before advancing eastward toward the metros between 00- 03z/7-10pm. There will be notable increase in wind (50-60 kts/60-70 mph) directly along the front and behind it as the wind abruptly switches from the south/southwest to the west and northwest.

Tornado Watches have been cancelled with a 3-5 hr lull window before the front pushes through. Ample 0-6km shear remain anywhere between 50-70kts with 0-1/0-3km helicity in excess of 200-300 m2/s2. This will lead to a continued threat for isolated tornadoes outside of the damaging wind gusts with the main line expected to push through this evening between (5-10pm). Any storms will be fast movers with progressive storm motions likely to reduce flooding. Even with that said, high PWATs on the order of 1-1.2 inches coupled with low 60 degree dewpoints will lead to efficient rain producers. SOme ponding and nuisance flooding has been noted particularly in urban/poor drainage areas this afternoon. Any convection will quickly exit east of the bay after 9pm-midnight as the cold front pushes through.

Outside of convection, conditions will be gusty today as a deep surface low tracks across the Great Lakes. Increased southerly flow may gusts to 30 to 40 mph, with gusts closer to 50 mph in the mountains. Additionally, this also could occur in northeastern Maryland given this region stays in the warm sector longer and perhaps free of convection. Wind Advisories are in place across these areas which may see 50 mph gusts outside of any convection.
Eventually a powerful cold front will usher in a cold and blustery air mass to the region. Gusts may be strong enough in the mountains to support additional Wind Advisories.

Have multiple ways to receive hazardous weather information from the National Weather Service. When it comes to Tornado and Severe Thunderstorm Warnings, know where your safe place is and remain there until the storm has moved through and alerts have ended.

KEY MESSAGE 2...A period of upslope snow showers are expected along and west of the Allegheny Front this evening into Tuesday.

Behind the powerful frontal system, a period of upslope snow showers are expected for those along and west of the Allegheny Front. From this evening into Tuesday morning, 2 to 4 inches of snow will be possible over Garrett Co. MD and western portions of Highland, Grant and Pendleton counties. Locally higher totals are possible over the higher elevations above 3000 feet. Winter Weather Advisories have been issued to encompass this threat. As temperatures, come crashing down through the evening and night, there will be a flash freeze potential as lows plummet into the teens. This comes with wind chills dropping into the lower single digits.

While some of this snowfall spreads downstream off the terrain (toward the Catoctins/, the dry nature of the air mass to the east should limit any resulting snow accumulations.

KEY MESSAGE 3...Below normal temperatures are expected Tuesday and Wednesday before seasonable weather returns for the remainder of the week.

It will feel like a cold and blustery winter day Tuesday in the wake of the strong cold front with upper troughing overhead. High temperatures will be 15 to 20 degrees below normal across much of the area. Wind chill values will be in the 20s and lower 30s. The latest forecasts for wind gusts would fall in the 30 to 40 mph range, but can't rule out some stronger gusts closer to Wind Advisory criteria in the mountains. It will also be mostly cloudy across much of the area, with some occasional upslope snow showers in the Alleghenies. Tuesday will be the coldest night of the stretch as winds drop off and high pressure builds overhead. Forecast lows range from the mid teens to mid 20s.

Wednesday will be slightly warmer and with much less wind, but temperatures will still be below normal. A weak wave could bring some upslope snow showers to the Alleghenies Wednesday or Wednesday night.

Temperatures will continue to moderate for the latter part of the week with near normal temperatures Thursday and above normal Friday.
A low pressure system will pass to the north toward the weekend, but it's uncertain if it will bring any rain, as well as whether there is a return to colder temperatures behind it or not.



AVIATION /19Z MONDAY THROUGH SATURDAY/
It's a mashup of VFR conditions and MVFR to IFR conditions across the area. The initial line of convection continues east of the I-95 corridor terminals with a 3-5 hour lull expected until this evening as the cold front pushes in. The evolution of this front has been noted across central WV down into far southwest VA. In between the initial line of exiting storms and the front remains on and off shower mainly impacting terminals east of the Blue Ridge mountains.
These showers could lead to MVFR cigs/vsbys at times.

The main show comes in this evening between 22-03z/6-10pm as the front comes through. Strong south to southwest winds ahead of the front will abruptly switch to the west/northwest behind it. Gusts of 40-50 kts are possible directly along the front and behind it as it pushes through. The front should push toward KMRB/KCHO between 22- 00z before advancing into the IAD/BWI/DCA corridor between 00-03z/7- 10pm. SOme snow may mix in with the front pending how much precip lingers especially from IAD west as the colder air catches up. No accumulation is expected at the corridor terminals at this time.

Outside of these storms, increased southerly flow will bring gusts to around 30 to 35 knots. Winds shift to west-northwesterly behind the cold front by the early/mid evening hours. VFR conditions are likely to return later tonight, but with blustery northwesterly flow.

VFR conditions are likely Tuesday through Thursday. Northwest winds gust around 25-30 knots for much of Tuesday morning to afternoon, then winds diminish Tuesday night. Light southerly winds are expected Wednesday and Thursday.

MARINE
Gale Warnings are in effect for all waters through tonight. While mild air on top of cooler water is not ideal for vertical mixing, the robust wind field certainly could mix down at times. On the convective side of things, it will be an active weather day over the region.

Severe thunderstorms are possible during the evening hours, many of which will require Special Marine Warnings. Given the degree of vertical shear in place, waterspouts will be possible as well with any supercells or waves in the approaching QLCS. To ensure safety, conditions will be very hazardous today and spending time on the water is not recommended.

Behind the cold front, winds abruptly shift to west-northwesterly which will necessitate Small Craft Advisories later tonight into Tuesday. A high end scenario would be close to gale conditions.
Winds will diminish Tuesday night as high pressure builds overhead.
Sun-SCA level light south winds are expected Wednesday and Thursday.

TIDES/COASTAL FLOODING
A Coastal Flood Warning remains in effect for Anne Arundel Co. for this afternoon's high tide cycle. Coastal Flood Advisories are in effect for Baltimore and Havre de Grace as well.

Increasing southerly winds ahead of a powerful cold front will cause a quick rise in tide levels across the Chesapeake Bay and tidal Potomac River. Sensitive locations are likely to reach or be close to minor flood during this afternoon/evening's high tide. Annapolis is forecast to be well within minor flood stage, and could reach moderate flooding if southerly flow is stronger as some of the model guidance suggests. Water levels quickly drop tonight as offshore winds take hold behind the front.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Gale Warning until 1 AM EDT Tuesday for MDZ008.
Wind Advisory until 10 PM EDT this evening for MDZ006-008-011- 507-508.
Coastal Flood Advisory until 9 PM EDT this evening for MDZ011.
Coastal Flood Warning until 10 PM EDT this evening for MDZ014.
Coastal Flood Advisory until midnight EDT tonight for MDZ508.
Wind Advisory until 11 AM EDT Tuesday for MDZ509.
Winter Weather Advisory from 7 PM this evening to 11 AM EDT Tuesday for MDZ509-510.
VA...Winter Weather Advisory from 7 PM this evening to 11 AM EDT Tuesday for VAZ503.
Wind Advisory until 2 PM EDT Tuesday for VAZ503.
Wind Advisory until 2 AM EDT Tuesday for VAZ507-508.
WV...Winter Weather Advisory from 7 PM this evening to 11 AM EDT Tuesday for WVZ501-505.
Wind Advisory until 2 PM EDT Tuesday for WVZ501-505.
MARINE...Gale Warning until 1 AM EDT Tuesday for ANZ530>543.
Wind Advisory until 10 PM EDT this evening for ANZ530.