All Weather News

This Weekend: Snow, Rain, And Possibly – Gasp – Freezing Rain

12 Dec 2012, 10:58 am

We’ve been keeping a close eye on a storm system working its way around the Pacific.  It started out over the western coastlines of Washington and Oregon.  Now it’s marching southward into the desert Southwest regions – bringing the “heat” in the way of lower elevation rain and higher elevation snowfall.  Places like the Los Angeles  region and San Diego could pick up anywhere from a couple tenths of an inch of rainfall to even more than that!  Much needed rain for many in southern California.

Here is a look at some of the snowfall potential that could take place in Nevada over the next several days (higher elevations, of course):

 

Nevada Snow Potential
Nevada Snow Potential: 1-2 Feet Possible

 

Now if you continue into the forecast, the system starts to curve to the Northeast heading into Friday, Friday night, and Saturday.  As that happens it will start to drag colder air down from Canada – which brings us to the big question marks associated with this system.

This is a look at the ECMWF (European Model) forecast for early Saturday morning.  Notice the blue line in the middle of the Midwest.  That *could* be the rain/snow line.  Under certain circumstances, however, that line can fool you into falsely predicting snow… so we’re going to take a closer look:

 

Saturday Morning ECMWF
Saturday Morning ECMWF

Regardless of what falls from the sky – you can tell just from looking at that image that something is brewing.

Where will snow happen, and where will rain happen? 

Right now it is looking like places like Iowa, Nebraska, Missouri will likely miss snow – and it will be rain.  But what about those places to the north?  Well, we pulled out a program called Bufkit (click on the name for more information, if you are a “weather geek” like us!) that we use for in-depth point forecasting.  Here are some of the highlights from an overview (think of this as a timeline – from the start of the storm to the finish), starting with the potential for rain/freezing rain:

 

Rain/Freezing Rain Potential
Rain/Freezing Rain Potential

 

Keeping in mind that this is only one computer model, and using the point location of Minneapolis, you can see the area circled indicating a decent amount of rain – rather than snow.  Notice, though, how the colors change to blue on the far right hand side of that graphic.  The low pressure center would look to pull in colder air from Canada – and that would change things to snow:

 

Snow Potential
Snow Potential

 

The big question, then, is *when* the cold air will arrive.  That will decide everything.  With all snow, this is the type of tally we could be looking at, as per the ECMWF model:

Midwest Snow Potential
Midwest Snow Potential

 

Over Minneapolis, the NAM WRF (a more “short-term” model) is showing close to 0.6″ of liquid-equivalent precipitation – which would be no big deal if it fell as all liquid rain.  Freezing rain = trouble (as you likely are aware).

Here is a close-up view of the vertical sounding of the atmosphere, which is basically if you were to launch a weather balloon and measure the temperature and dewpoint with height:

 

ZR_Sounding
ZR (Metar code for freezing rain) Sounding

 

If you look closely at the diagonal line extending from the number zero at the bottom, you can see there are red and green colors that cross that line in both directions.  The red line is temperature – and notice how it dips slightly to the right of the zero line.  That indicates freezing potential – and that is after a fairly robust period of the temperature line being to the left of the zero line – indicating above-freezing temperatures.  The end result could end up being freezing rain/drizzle.  Let’s hope for all above-freezing or just straight snow (if you’re a fan of snow).

Stay tuned over the next couple of days, because this forecast will likely change in some regard!

WeatherNation Meteorologist Aaron Shaffer @ashafferWNTV

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