December 16 Afternoon Winter Storm Analysis: Heavy Snow And More Ice

1 PM Wednesday December 16 2020

The snow arrived early. For many it is already HEAVY!!!

That was the headline this morning that I was able to update on social media, (but not here on the website). I have more in depth look at this set up as we are in “Nowcasting Mode”. This is when we can compare the set up to how the models are performing or adjust ahead.

The roads are bad! 

I had mentioned in my reports that it would get heavy in a hurry. It has! Snow in some parts of central Maryland has been falling at the rate over 1 inch per hour. A quick few inches on the front end…

At 1 PM, I heard (unofficially) that Howard County Police  was working over 40 active accidents!

 

 

I Stand By My Forecast!

I believe this early hit, and the end hit tonight will verify for most areas. I will show that map again below.

The only concern I have now will be more icing this evening and tonight in between.  We’ll get to that.

 

Quick Note About Change Over:

If you see BIG flakes, that is often a sign of warmer air at cloud level. They partially melt and then stick together on the way down.

Your thermometer may hold, but the clouds will warm.  Then sleet and freezing rain may be the concern.

 

Faster Arrival

At 11 AM, Doppler Radar showed the snow, and numerous reports confirmed this snow falling was reaching the ground. This meant we did not get the ‘virga’, and the system was ahead of schedule.

Compare the Doppler To the HRRR (Short Range Model)

 

DOPPLER 11 AM

 

 

HRRR 11 AM

 

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Analysis at Noon

(sorry it may be a little old. It took 2 hours to work these maps, write up, and publish)

Have you heard of a cold air dam?  It is cold dense air that spreads down the eastern US and sandwiched between warm air along the coast and on the other side of the mountains. That is common with winter storms and can do two things:

• Hold The Cold longer
• Disrupt the forecast with more ice in transition zones

 

Here we see that reflected on the Surface Analysis AND Temperatures

Mesoscale Analysis at Noon

This may be just a little SouthEast of forecasts. That may play a role in how far the warm air can push inland.

I’ve highlighted the Surface Low AND the surface wind direction.

Two things I have pointed out in almost all reports:

• Respect the Warmth from the water
• Wind Direction is Key!

 

Temperatures at Noon

This reflects the Cold Air Dam. The low dense air can be hard to budge and many models ofter push it out too soon.

Meanwhile the freezing line and warmer is right around I-95.

 

 

 

Reminder:

Warnings and Advisories

 

Evening Forecast

I DO NOT TRUST MANY MODELS AT THIS POINT

The Cold Air dam can be hard to move, so where it is cold it may hold longer. This can lead to sustained snow and ice, even on the edge where it is forecast to turn to rain.

The Wind Direction is KEY!

That will determine how much warmer air can mix it. It will warm the clouds, but at the surface just west and north of I-95 there may be extended icing. Farther inland it can be snow longer.

Where will this be?  That can vary from a few miles to 20 miles.  Sadly that is the most densely populated in Maryland.

 

GFS Model

Wind Forecast Map

This shows a more northerly component at 10 PM. That will battle any warming just inland from I-95!

But, warm air will fight farther inland at cloud level. That is why we can expect icing.

 

Why did I jump to this time?

Because this should be the peak of heavy mix or rain, and just before the cold comma head swings back through.

But, if the location is wrong and this verifies east, it will allow the cold air to hold in many more urban areas.

 

 

GFS Forecast

 

 

European Model Forecast

I still am not 100% confident this is addressing the cold air dam correctly.

10 PM

This Low is WAY WEST of earlier assessments.  I have trouble accepting this. 

But look at the tight ice and snow just west of the cities.

If this verifies just a little east, it should keep the ice and snow for immediate suburbs longer.

 

 

1 AM

Again. I am not sold on this location of the Low.  But I am all in for the ‘comma head’ and heqvy snow swinging back through. This may have rates of 1”-2”/hour.  That is the ‘Thump’ of snow to end this thing.

 

 

 

 

4 AM

Moderate to heavy snow from Baltimore and north. Again, this may bring the bulk of accumulation.

 

Thursday Morning Conditions

What is on the ground and untreated will be icy!  Widespread below freezing temps

 

My Final Call For Snowfall From Yesterday!

I did not panic and change this. If anything the mixing might aim for the low end of the zone. But I will not hide from what I told you and you can grade me when this is done.

 

 

 

 

Also see:

 

 

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