One Shot at Light Snow Tonight, Another on Friday

At the moment, it doesn't look like any major storms are in our near future.  The best chance we had of a moderate storm was Friday but at this point, the storm looks like it will be weaker and will not produce all that much precipitation.

Let's look at where we are - first with tonight's event.

A weak "clipper" system is poised to move over our area overnight - probably after midnight and into the hours around dawn.  The GFS and the NAM both show this clipper and show a decent amount of energy (for a storm like this) passing over our region.  We can expect a dusting to perhaps an inch and the enjoyment of watching snow fall if you're up late enough (or early enough).  The track is far enough south that areas around Fredericksburg could see the most snow - but even there, an inch or so is about as good as it will probably get.

GFS model output showing light band of snow across the region overnight.  Liquid equivalent precipitation forecasts are around 0.05 - 0.1 inches which translate to around an inch of snow.

Because of the very cold airmass that is currently locked in our region, the snow ratios should be higher than the standard rule-of-thumb 10-1.  So even though the amount of available moisture is small, the chances of snow accumulation are pretty good.  I'd say in the DC metro area we stand a 60-70% chance of seeing around an inch of snow tonight. 

If the snow should continue into the morning rush hour, expect the NWS to put out Winter Weather Advisories.

This is a fairly narrow band of energy (as you can see from the model output above) so if we don't see much of anything on the ground and just a few flurries flying, I wouldn't be that surprised.

 On to Friday:

The models are slowly coming into agreement and the news for snow-lovers isn't that good.  The phasing I discussed in my previous post seems unlikely to happen as the southern stream energy gets shunted south and sheared apart.  That means the northern stream energy has to work with whatever moisture it has and since it's continental in origin, that's not much.

Also, the storm will be a Miller B type scenario.  Miller B storms are characterized by a primary low moving over land that weakens and transfers energy to a secondary low - usually off the coast.  Sometimes this is a really good thing.  For example, the Snowmageddon storm was a Miller B.

But.

In that case the energy transfer happened earlier and the southern stream low pressure system was much stronger (and had its origins in the Gulf Coast).  As the storm moved up the coast, it actually almost stopped to our east before proceeding up the coast because of blocking patterns.

Radar composite image from February 5-6, 2010 showing strong southern stream low receiving energy from a weaker low over the Tennessee Valley before moving up the coast.

In this case, however, the southern stream energy is weak and the energy transfer may happen right over our area.  These are bad things.  If the energy transfer happens directly over us, we could be caught in the middle - what meteorologists call a "snow hole".  That would result in us seeing very little snow at all.

The models are still in a bit of disagreement as to the path and the amount of moisture available to the system.  At this point, it's unlikely that the storm will be anything to get excited about but we'll see how the models look this afternoon.

For now, there's a pretty good chance of light snow on Friday that could maybe result in 1-3 inches of snow if we're lucky.