As I stated earlier when you try and change a pettern at the start of winter you get confusion among the model masses. What extremes we have showing up on the models for December 24-25. A lot of something will be falling from the sky Christmas Eve whether its presents, rain or snow expect it to be a bit wild at times.
MODELS MODELS MODELS
EUROPEAN (ECMWF) OPERATIONAL
The Euopean Operational Model shows a very big storm for the Midwest and East Coast. The track would bring lots of rain and wind to the I-95 area and even inland back to Harrisburg. Places like Chicago, Indianapolis and Cincy would get a white Christmas. The map on the right shows temps at 5500 feet and that is key for making snow. If you are in the green or yellow it's rain and blue is snow.
The 540 snow line on the left map shows the snow line from Harrisburg and west. This means most of the area would be wet not white for Christmas.
The Euro Ensembles (a blend of many variables) shows about the same as the operational on this run. The track has moved inland and most of the East gets wet not white. This would place the white Christmas in parts of the Ohio Valley and Midwest. We'll see how this might shift the next few days.
The storm is a little further east than the Euro model but also plays rain in the east for Chritmas Eve and Christmas Day. The key may be the placing of the NAO and AO during this timeframe. I still like the Dec 30-Jan 2 time slot for the best chance of a snowy nor'easter.
NAO AO STEP DOWN TO WINTER
WAIT FOR IT...
The good news is that we'll see winter we just have to take baby steps like you see on the NAO or North American Oscillation Index. The index shift the storm track and colder air back and forth from the Midwest to the East. On the Positive side it tends to make for Lake cutter or storms headed to the Midwest. The Negative side allows colder air to pour into the East and slow the areas of high pressure down over New England. This "blocking' pattern is like a weather traffic cop in Greenland. When the negative light comes on the cop says slow down you Highs and Lows. This creates the cold air to hang around longer for a possible nor'easter. It also allows big storm to move slower bring more snow and in some cases rain.
The Arctic Oscillation is the gate keeper of cold air and how it pours into the U.S. When it drops to -3 cold air is coming for the Midwest and East. The lower that number goes the deeper the cold air gets into the South. A -3 is a good number to supply cold air after the 24th or 25th. The timing may be off just a little bit near Christmas for a big east coast snowstorm but after that it's go time.
MY THOUGHTS ON
THE CHRISTMAS STORM
I like the moisture from the south..expect to see that all winter long. The key to the rest of the month is to time out the cold air that is coming down from Canada. For now it may be a day late and a dollar short to bring a white Christmas to many in the East. Sure the NAO and AO dip but with this type of pattern of maritime Pacific Ocean air it make take a few days to get the colder mojo into the mix. The odds are against us right now for a snowy Chritmas eve and Christmas but not all hope is lost.
We'll see how the models and pattern adjust the next few days and watch this evolve. They make adjustments all the time..the models just have to see where and when they want the polar party to join in.
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