Sunday December 8 2019

It is going to snow this week. FIFT! There is high confidence now that following heavy rain Monday and Tuesday, colder air will move in and the storm will end with a few hours of snow. In fact, a surge of energy will ride up along the front and should keep snow falling through a good part of Wednesday for most of our region. But how will it impact you and of course will teachers and kids get time off of school?

The confidence in the snow comes with all prime computer models showing it. Here is the comparison of the Canadian GEM, GFS (American), and ECMWF (European) models at 7 AM Wednesday here.

Snow on the Canadian GEM Model

Snow on the GFS Model

Snow on the European ECWMF Model

 

The challenge for how it will impact the region will be:

• Snow arrives a day after temps will be near 60ºF
• Water temps near the Bay are still in the 40s
• The freezing line at the surface will lag behind the freezing line at cloud level.

Snow could be heavy at times Wednesday morning. But will it be enough to overtake the warmer ground for stickage, or will it melt?

Do you recall me mentioning the error in the computer models? This includes timing being faster. The latest package of outer model guidance has sped up the transition to snow to Tuesday night. So that by Wednesday morning the snow could be flying over all metro areas and possibly into southern Maryland.

Let’s take a closer look snow timeline on the European Model. After getting over 1 inch of rain and temps reach around 60ºF Tuesday, the transition to the snow will spread overnight.

It looks like snow will reach the western suburbs between 10 PM and 1 AM.  Then across metro areas by morning.

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Temperatures Wednesday Morning

At 7 AM, this is the best indication of where the impact for snow may be.

This is the European Model projection for temperatures Wednesday morning. I’ve highlighted the freezing line, which appears to set up for the typically colder suburbs west and north of Baltimore. Places most likely to get snow to stick includes:

Germantown, Frederick, Mt. Airy, Westminster, Hereford, and York PA.

This does not rule out stickage in metro Baltimore or Washington. It just makes it more challenging.

 

My Thoughts

• If you see a snowfall map from a computer model it is most likely wrong! The models often over estimate the snow AND do not account for melting flakes.
• Howard, Baltimore, Harford, Cecil, metro Washington, and Anne Arundel Counties: For snow stickage (on the roads) we need to fine tune the intensity of the snow before sunrise. If rates reach 1/2″ or 1″ per hour, then it could overtake the warmer ground… even a day after they reach 60ºF with rain. 
• The temperature at cloud level (850mb) where the snowflakes form can also determine how long it can survive before melting on the way down.

I will post more insight on timing and areas likely to be affected in my Monday evening report. 

 

Storm Animation (GFS Model)

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