Update: 2:30 pm
Rather than update the timeline set in place. I will do my
best to interpret and evaluate the models output that has been presented in
terms of how Tuesday Night into Wednesday looks for this region and the rest of
the Mid-Atlantic/Northeast.
A large 500 mb trough is stretched out across the entire
country and with it brings in high pressure with a large amount of upper level
divergence. This trough is expected to move through the Midwest and Ohio Valley
Tuesday night into Wednesday. A separate cold front will move across our region
late today into tonight which will cool down temperatures. Once the cold air
starts to interact with the warmer waters of the Atlantic, a low pressure
starts to form. Where this low forms and how it interacts with the cold air
along its track up the coast is key with forecasting the precipitation forecast
of the storm. There are several different situations that could occur that
leave us with several different situations. I will do my best to explain each
one and the probability of each of them occurring Tuesday Night through
Wednesday night.
The low pressure system rapidly deepens off the Atlantic coast and moves in a nearly parallel pattern to the East Coast. Temperatures on Tuesday Night into Wednesday will remain in the middle to upper 30’s throughout most of the metropolitan region with higher ranges towards the western suburbs and warmer closer to the water. Precipitation will begin as rain during the late night/early morning hours on Wednesday. Soon though during the mid-morning hours into midday there will be a changeover to snow. Most likely this change over will occur at around the 11:00 am mark with the accumulation beginning around 1 pm. While dew points will be at freezing or below, surface temperatures will remain above freezing during the early afternoon hours. This will slowly change though as a small amount of cold air advection will bring in enough cold air to cool off the entire region leading to the changeover to snow. When and how this occurs throughout the day is truly dynamic so the difference between accumulation or not is really a matter of a minuscule shift in the rain snow line. Within this model, we could very well see all rain and just snow showers showing up midday without accumulation on the surface.
Situation #1:
Accumulation amounts: For the western suburbs, especially right
near the Blue Ridge, accumulations will be in the 3-6 inch range with higher amounts possible depending on when the changeover to all snow occurs. For the
immediate metropolitan region though, a dusting to 1 inch of snow is expected
with around a quarter to half an inch of rain expected also. This will be very
wet snow also meaning it will melt fairly quickly due to the dew point being
right near the freezing mark.
Impact (Low, Medium, High)-For our region I will put this
situation as a Low impact as the amount of snow expected is nothing to warrant
any concern. Using caution while traveling is definitely important in this situation,
especially those who are traveling to the North and West where totals are
forecasted to be higher and heavier due to colder temperatures. Traveling along
the 95 corridor, expect minor delays mostly due to high volume, but weather
shouldn't be an impact at this time.
Probability: Very likely. I will say this is about 80-90% chance
of occurring.
Timing: While precipitation will start Tuesday night into
Wednesday morning, the models are in agreement that the heaviest amount will
occur between 9 am and 4 pm Wednesday. Most of the snow will move out by Wednesday
night with lingering snow showers mostly to our west possible early Thursday.
Situation #2:
The models are not exactly in agreement over the snowfall
amounts. There is a true possibility that this could be a Low to Medium impact
storm even though it is relatively early in the season. Within the situation we
are looking at right now, where temperatures are right near the freezing mark
and a large swath of moisture from a low in the Atlantic will bring in
precipitation (rain or snow) for the entire region, the probability of a “busted”
forecast is very high. The GFS model right now has the low being much closer to
the Atlantic coastline than the NAM and the Euro model has us getting more snow
than both of those models.
It is really tough to forecast so far out from a winter
storm even as there are so many variables that need to be set into place to
properly say with any kind of certainty that snow will occur.
In this scenario of higher precipitation, the rain/snow line
moves over the DC area early and temperatures fall near the freezing mark
earlier than expected, thus leaving the amounts of snow higher. Roadways could
begin having slush on them by the 3-4 pm time-slot and if snow stays in the
region, rush hour will be also affected.
Accumulation: In this situation, the 95 corridor will be
more affected by snow covered roads and the 3-6 inches of snowfall will shift to the
East while higher amounts (6-10 inches) will remain to the North and West and
lower amounts to all rain will be likely in the East of our region (trace-2
inches).
Impact: Low to Medium-Roads will be slippery in this
situation, not high enough impact that you should plan on changing travel
plans, but allow more time to reach your destination and anticipate backup and
accidents along major roadways.
Probability: Not very likely 10-20% chance.
