UPDATE ON OCT 27-28 MIDDLE ATLANTIC COASTAL LOW
STARDATE 201810.26 0030 EDT ** BE SURE TO CLICK ON MAPS TO SEE FULL IMAGE ***
The weather models on Wednesday evening are in pretty good agreement and do not show any big changes with regard to the coastal storm / Nor'easter for this weekend-- specifically for Friday and Saturday. All the models STILL show the LOW will hug the coast at least as far northern as the Delaware and southern New Jersey. This will drive the DRY SLOT deep into central and eastern VA Saturday morning...and probably into NJ.
WHAT IS THE DRY SLOT ?
All large and deep LOW pressure areas whether they are on the East Coast or the Midwest or the Plains .. or in Europe or in China ... all have an area where there is very little precipitation along with weaker winds and sometimes even breaks the clouds. This feature is refer to as THE DRY SLOT which is a weather term used by meteorologists to describe in section of a large of well develop LOW pressure area that is all usually in the southwest portion of the storm. The DRY SLOT develops when intense LOW pressure area's large circulation pulls drier air and sometimes cooler air from locations hundreds or thousands of miles away. This drier air gets pulled into the LOW pressure area of like a giant fist and punches its way into the clouds and the precipitation usually on the southwest side of the system.
These two images shows a schematic of how the typical LOW pressure area with a well developed D RY SLOT t will look like on the radar (left) and the satellite picture right). When forecasting East Coast storms whether its a rain storm or snowstorm.. it is very important to understand the track of the proximity of the actual main LOW pressure area to the coast. The track of the Main LOW determines where this important DRY SLOT feature is going to develop.
When the main LOW pressure area is on the coast and or just inland ...the "dry slot" portion of the LOW pressure area develops over portions of eastern North Carolina ...eastern or southeastern Virginia ...into the Delmarva and sometimes as far north as New Jersey... NYC or Connecticut . The heaviest precipitation is then forced to stay to the north and west of LOW pressure area so areas such as the Shenandoah Valley .. western North Carolina ..West Virginia southern Central Maryland western and central Pennsylvania see the heaviest precipitation.
BUT when strong LOW pressure area is off the coast (as in the case with a true nor'easter) ... this "dry slot" feature also stays off the coast and the heaviest precipitation is no longer over the mountains but over the Piedmont and coastal areas. This is one the reasons why the classic winter storm nor'easter often brings blizzard conditions to the East Coast from Richmond to Boston but a coastal storm .. where the Low is ON the coast ...will often have snow going over to rain with a heavy snows over the mountains or inland locations.
I am mentioning this DRY SLOT feature because this Low will have significant DRY SLOT which is going to make a difference with respect to how long the rain lasts and how much will fall and where. .
Most the data shows that the heavy rain which moves in on Friday midday will continue Friday night into Saturday morning. Most areas of North Carolina... Virginia ...Maryland ...eastern portions of West Virginia ...all of Delaware ....central and eastern Pennsylvania ...New Jersey up into New York City will see significant rain. The rain will continue for good portion of Saturday over some of these areas.
As you can see you can see from the weather models they are taking the track of the main LOW very close to or over the coast. Indeed some models ate the main LOW into the Delmarva and southern New Jersey. If this is correct it means that the dry slot is going to appear over eastern half of North Carolina and eastern and southeastern Virginia as well as the Delmarva and up into New Jersey
The one significant change on all the models is that this system is moving much faster. This means that the rain will clear or push through most of the lower Middle Atlantic region the southern half of VA... NC... the Delmarva ...WVA by Saturday midday . In fact over eastern VA...NC.. and the Delmarva the data continues to show that the sun may actually come out in the afternoon hours.
With any sort of coastal Low/ Noreaster one of the bigger concerns are winds. This is especially true along the coast. For the lower half the Middle Atlantic region this particular system will only produce winds of 40-60 mph over the northern Delmarva as well as the Delaware Bay.. the NJ Coast / NYC / y Long Island and the coastal areas of southern New England . Those strongest winds that will be mainly on Saturday morning and afternoon. For most of the Chesapeake Bay... and coastal areas of Southeast Virginia ..and western North Carolina and southern Delmarva.. the winds with this particular system are not going to be that impressive.--generally in the 25-40 mph range.
The other significant change has to do with a new system that comes from the Ohio valley. A strong piece of energy in the jet stream which race across he Ohio Valley into WVA VA MD DEL on Sunday afternoon. Sunday night... into Monday morning. This feature will bring intervals of moderate rain late Sunday and Sunday night in these areas. The rain will be gone by Monday morning however but gusty north winds will bring colder air and snow showers are possible over portions of eastern WVA... western MD and far Northwest Virginia.
With respect to the timing of this event there are no significant changes here. The only change is that the cause the system is moving a little faster the rainfall amounts might not be as heavy
The Black line= edge of Moderate rain. The RED line = the edge of heavy rain