Saturday January 28 2020

10:10 AM Update

Ice is on the way sooner and it may impact more areas. We are in the lull we discussed, but hard to call it that if you did not see the Part 1 snow. It may seem like a bust, but don’t lose track that there is still some messy weather on the way.

The snow arrived this morning, but most ‘south of the Pennsylvania line’ missed it. While the radar showed a pronounced band of snow, the cold air was so dry that could not reach the ground (sublimation). This apparent false radar is called Virga, but those flakes did help to saturate the mid levels, so that next next part will do what is expected.

Here is a look at the radar earlier this morning, but compare to the most recent conditions and radar below. The computer modeling has not handled this well, so we are up to nowcasting the start of Part 2. The icing through the day may be a little more extensive. The storm itself and impact is still far from a complete bust.

Radar for Part 1

 

Why Did The Snow Not Reach The Ground?

Dry air!  The temperatures were cold enough, but the Dew Point was too low!  The Dew Point is the true measure of moisture in the air.  When it was 11ºF, that means it has to be that cold to saturate the air.

Regardless of how hard it was snowing above, it was like a thunderstorm over the desert that can produce lightning and a rain shaft, but nothing hits the ground.

 

Conditions at 10 AM

Temperatures

Baltimore at BWI is up to 30ºF but the 20s surround the airport.

 

Dew Point

Baltimore at BWI is up to 16ºF, which is still dry but climbing.  These numbers will get closer to the actual air temperature as the air saturates to support the snow and ice reaching the ground.

 

Doppler Radar

There is still some virga to consider, but the moisture will break through soon.

 

Mesoscale Analysis

The High Pressure that was responsible for keeping our air so dry this morning is moving away. This will allow the next batch (Part 2) to saturate the air and reach the ground.

 

What To Expect

Snow and ice will return in the metro area between Noon and 2 PM, then last the rest of the day.

The dry air will saturate, but strengthen the cold column above. This will hold the cold longer, and perhaps include Washington DC to Anne Arundel County (away from the water).

Watch the thermometer: If you pay close attention, you may see the temperature drop one to three degrees just before or as the precipitation returns. This is from the evaporative cooling. Then it will slowly bump up and try to hold steady for a few hours. That is the column of air holding the cold near the surface while warmer air flows at cloud level.

I am NOT going to show a simulation slider. The models did not identify the snow and ice one radar now and have NOT been able to handle this storm well. It is all nowcasting at this point. I will provide frequent updates on social media. Note that Twitter does a better job with new posts. On Facebook the algorithm mixes up new posts and you may miss them. But I will do my best to provide updates on the temps and radar to track the icing.

 

 

 

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