Saturday February 3 2018

A Winter Weather Advisory has been issued for Sunday beginning at 10 AM for parts of central and western Maryland and Pennsylvania. This is a very tricky situation and I will do my best to try and explain the set up. I think more areas than shown on this map will be affected at least a little in northern Baltimore, Harford Co in Maryland and York and Lancaster in PA. There will also be a battle between the wintry mix of snow, sleet, and freezing rain with daylight solar energy on the roads. The daylight hours should help roads maximize their ability to stay wet.

*Some of my school clients have already delayed their Sunday events, and reevaluating in the morning will be best.

I am really torn between this going to a cold rain quickly or the colder NAM solution I am showing below. Since there is just a small adjustment in temperatures, I think it is best to be prudent and just show the worst case and plan around that.

Here’s the set up:

After a cold day with most areas staying at or below freezing, the ground is currently cold enough to support any stickage. That means it will be able to hold any snow or sleet that falls early Sunday. The timing will be key as solar energy gets absorbed by the roads during the morning and icing is less likely with anything falling after 10 AM. That may confuse you with the

Overnight

The HAM 3 Km Model is a little aggressive, but I can not ignore the light wintry mix it is suggesting overnight. A little drizzle or sleet could be a hazard. But I need to mention the GFS and HRRR models are dry for this time frame.

3 AM Sunday Morning

The freezing temps should dominate our region overnight. Even on Delmarva

Why A Mix and Not All Snow?

There There is warmer air moving in thanks to a shift of the winds to the east from the water. Warmer, moist air will move up and over the colder air at the surface and can make the clouds warmer than what we have on the ground.

I expect the energy from the approaching system on Sunday to help generate its own cold air and drag down colder temps to change over to snow for a few hours. There may be sleet or rain at the onset that changes to snow as it gets heavier… See that in the slider…

Winds will be light, but this afternoon time plot highlights the direction. That wind usually thaws metro areas

10 AM

This is the time plot that helps prove why a subtle variation of a degree or two can make a huge difference in the weather we get.

Compare the colder NAM model to the HRRR. Also, the HRRR Model shows the first drops of rain reaching Baltimore and moving northeast while the NAM has us wet for a few hours.

NAM = COLDER: Freezing Temps near Westminster, York, and Frederick

HRRR Model = Milder: No Freezing nearby at this time

But, there is a thaw in the cities and I-95 at this time?

I see the 34ºF line along I-95, but as the precipitation increases, the temperatures should drop just a few degrees. The inland areas that are normally colder are most likely to have the problems.

Timeline 11AM to 6 PM: More Snow, Sleet, Ice and Then Rain

—> slider

Shows the mix fully engulfing our region and turning over to more snow (inland of I-95) between 10 and 11 AM

[metaslider id=57559]

Evening Temperatures

The thaw line should be moving north during the afternoon and evening.

This is ALWAYS tough to forecast with precise time. Please be alert in colder areas for the potential of the thaw window to develop over a few hours before or after 6 PM.

I do NOT have a snow forecast since areas that get snow will likely just a coating. The real issue will be just a few degrees and ice Vs rain. My main point is that either way, I see the timing during the day as a benefit for traveling since solar energy should help roads get warmer sooner.

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