Tuesday, December 08, 2020

Snow or Rain for Christmas week?

As of this writing (December 8) with a week removed from our heavy snowfall, the overall pattern across the US and North America has been somewhat stale. No major snow.  No major rainfall.  No extreme temperatures either way. Look at the morning lows Tuesday December 8th. No major cold.

Temperatures each day this week look fairly typical for early December. A brief period of milder air Friday and Saturday then back to near normal.

Is this "stale" pattern going to continue over the next 14 days as we approach Christmas week?

Back on December 3rd, the pattern strongly suggested a short-lived, "mid-month-ish" break from the cold with an active panhandle storm track (see the "L" on the picture below). The warmth is going to peak Friday the 11th, a few days early. 

So far, the storm track seems pretty good with primarily rain this weekend for Ohio with the majority of the snow staying across Missouri, Illinois and parts of Michigan. Snow is close but not close enough if you're a snow lover. (see animation below)

Historically, we receive at least ONE INCH or more of snow between December 24-26. Most recently 2.6" in 2018.  Who remembers the BIG snow in 2002?

Northern Pacific pattern is starting to give us BIG hints on Christmas week.  1) LOW just west of the dateline 2) Edge of high pressure south of the weak Aleutian Islands which stretches to the west coast. 3) Trough in the southwestern US which continues to promote panhandle low development

Animation from December 7 to December 23

The Southern Oscillation Index region also gives us big clues.  Recall that the SOI is an index that measures pressure changes between Australia and Tahiti. 

When we look at the southern oscillation index (SOI) data , there is a 10 point drop around December 3rd.

We can check what the pattern was like during similar SOI changes in La Nina early winters 18-22 DAYS AFTER the SOI changes. This is what those composite periods look like below.  Notice the colder colors signify CLIPPER TYPE storm systems and brief cold periods. See how quickly they move across the Great Lakes.  Also look how the southern high pressure centers quickly bounce back...

Let's not forget about the lack of significant BLOCKING around the arctic and northern Atlantic.  We look for warmer colors which signify HIGH PRESSURE around Greenland. Not much blocking currently. There are some indications that this could be changing in the upcoming week. 

This strongly suggests that the active storm track Clipper systems (NW to SE) AND panhandle systems (SW to NE) seems fairly strong over the next two weeks heading into early Christmas week. The big question is where specifically: 

Will the storm track trend more from St. Louis to southern Michigan or more east from Louisville, KY to Pittsburgh?

Early Christmas week, I see another storm system developing in the central US similar to what we have already seen. Given the east coast ridge is stronger, I think this will create a storm track more from St. Louis to Michigan vs more east.  

Temperatures across Ohio will briefly warm into the 40s at the start of Christmas week

I think we will see a better chance of rain not snow Christmas week for northern Ohio. Timing of rain (brief mix) is closer to WEDNESDAY/THURSDAY, DECEMBER 23-24.

I'm watching Greenland for potential COLDER changes

 If I had to put money on it, chances for light snow on the ground Christmas Day are around 30%.