Good morning, here is your 5:30 AM update:
High impact Nor’easter still slated to slam the Washington Metropolitan Area this evening through Tuesday. Thunder-Snow and sleet is possible overnight with gusty winds (40 mph +) and snowfall/sleet rates of one to two inches per hour during the overnight hours!
The exact snow/snow-sleet/sleet-rain line is still in question but it is important to remember that where this line sets up, one won’t have to travel too far to go from lighter accumulations to significant accumulations. This is why it is prudent to be prepared for this major high-impact winter storm (the potential loss of power) than to focus too much on any slight shifts back and forth between where this line sets up. Please continue to monitor the official forecast from the National Weather Service as those of you under Winter Weather Advisories could still be upgraded to a Winter Storm Warning later today.
As of 5AM No changes to my snowfall map:
- After looking at the all-important European Model I am sticking with this for now. Any update to this map won’t be made until this afternoon.
- The area of highest uncertainty in my opinion continues to be those of you located in the “4 to 8” and “1 to 4” zone in the map below. I can see a situation where this zone gets shrunk very close together meaning the short west to east distance from Woodbridge, VA to Waldorf, MD could see a snowfall gradient of 10″ or more!
This storm has a lot of moisture to work with:
If we were to melt down the snow and sleet… the map below shows incredible precipitation amounts with a solid inch of liquid to work with. Snow ratios will range from 9:1 where the snow is heaviest to 12:1 Tuesday morning as temperatures begin falling into the middle to upper 20s. 10:1 ratio simply means that 1″ of liquid would equal 10″ of snow. This is drought relief at its best.
Last nights European Snowfall Forecast has remained relatively steady for the big cities here in the Northeast (Mid-Atlantic/DC/Baltimore/Philly/NYC & New England/Boston):
The short range forecast models indicate that snow will begin to fall between 5 and 7PM (5PM across central Virginia and closer to 7PM in DC, later north of there). Please continue to follow the NWS graphics (http://www.weather.gov/lwx/winter) as they will be updating their precipitation onset times (the image below courtesy NOAA and will be updated):
Latest “most likely snowfall accumulation map” from NOAA:
Latest National Weather Service National Digital Forecast Database Snowfall Forecast (images courtesy WxBell):
- Notice the extremely tight snowfall gradient across the District of Columbia between SE DC and NW DC…. 4 to 8″!
- The trip from Tyson’s Corner to New Carrollton (9 or 10″ of Snow to 4″ of snow) shows a very tight snowfall gradient and where this actually sets up can change with future model runs and may shift east during the day!
- Snowfall ratios will increase pre-dawn Tuesday across the northern and western suburbs… so don’t be shocked to see snowfall totals of a foot or more the further north and west you go in the typical colder outer suburbs (Germantown, Leesburg, etc.)
Model Trends Overnight:
Global Forecast System (GFS) trends for 8AM Tuesday (12z Tuesday):
- The GFS has shifted west in track bringing an extremely impressive 990mb low (category 2 hurricane equivalent) just offshore the DEL-MAR-VA coastline 8AM Tuesday.
- Beach erosion, Tropical storm force winds and wind-driven rain will cause considerable damage to the coast of the Mid-Atlantic and New England!
- Heavy Snow (according to the model below) continues to threaten the 95 to 81 corridor with snowfall rates of 1 to 2 inches per hour and thunder snow/sleet possible!
Canadian Trends for 8AM Tuesday (you are looking at the last 5 runs of the same operational Canadian Model showing you how it has adjusted track west and then slightly back to the east):
Why am I showing you this model? Because look at the shifts west and then back east (in the last frame)… any shift even of 25 miles back to the east is going to be a game changer along interstate 95! Do not let your guard down… this storm means business in areas that are going to be right along the all-snow/mix line!
The North American Model (latest operational just out):
Please remember that even though today’s highs will make it into the middle 40s… the dew points are sitting in the single digits to lower teens at the surface and even lower as you gain altitude in the boundary layer (the layer of the atmosphere where weather occurs). This very dry are in the lower to mid-levels of the atmosphere will allow for evaporation cooling (that is initially the snow will evaporate once it reaches the dry layers of the atmosphere which will cool the column). As the precipitation (a mix of rain and sleet or graupel) develops during the tail end of the rush hour… the mix will quickly go over to heavy snow. Stay off the roads… plan accordingly to be home before the precipitation begins to allow road crews the ability to do their jobs (so you don’t get stranded in snow-covered roadways… all it takes is one inch in this area on the roads… and 500 accidents can turn an hour commute into 9 hours).
The time stamp on the image below takes you from 8 PM this evening (00z) to 7 PM Tuesday (23z)
I will update my snowfall map one more time this afternoon if needed.