1/5: Thoughts on Tuesday's Clipper

Monday, January 5th 5:30am

Yesterday I mentioned the very cold air on the way this week along with the clipper system potential. Today I'll focus on our first clipper since it's now under 24 hours away.  

First things first...the southern trend of the vorticity maximum (or vort max for short) continued overnight.  A few days ago it looked like it would swing across northern Pennsylvania.  It now looks quite possible that it may dig all the way south of the Mason Dixon line.  This is important because the most snow with a clipper system usually occurs in a band right along to 100 miles north of the track of the vort max with a sharp moisture cutoff just to its south where the amount of lift fades quickly.  This trend leads me to believe that the entire Shenandoah Valley now at least has a shot to see flakes with the better chance for light accumulations the further north and west you go.  

6z NAM 500mb vort max track

A few notes for Tuesday's system:

• Clippers don't typically have all that much moisture to work with. Although this disturbance is pretty potent..still only expecting a shallow swath of 0.10-0.25" of liquid to fall.
• With that said, they usually pack pretty high snow-liquid ratios (15:1 or 20:1 as opposed to 10:1) resulting in a dry, powdery snow.  This can cause that 0.10-0.25" of liquid to pile up quite nicely.
• The western facing slopes are at a big advantage because the mountains help wring out precipitation as air flows over them...so this will be where greatest accumulations occur.
• For the Shenandoah Valley..5-10am Tuesday looks like the snow window.
• I think the central and southern Valley will see anywhere from some flakes in the air up to a coating..with the potential for a bit more up towards Woodstock and Winchester
• A few leftover snow showers/streamers may persist Tuesday night into Wednesday as northwesterly flow continues to pour cold air into the region...not expecting additional accumulation with these outside western mountain areas. 

Here are my current thoughts for the clipper in map form.  Since such a small jog north or south makes such a big difference with these systems, will update this evening as needed.