Summary: Tonight's storm is enroute but going to act differently than I earlier thought. Many areas will still see good snow tonight, but the focus will be on central and southern Colorado. Additionally, heavy snow is likely from midnight through midday Sunday for the front range and eastern foothills from Boulder south to the Palmer Divide. The storm will clear out by Sunday night, then another weak storm will move in on Tuesday into Wednesday. Drier weather is likely for the first 7ish days of March.

Today will be on the drier side with snow showers increasing toward afternoon and evening.  I wouldn't expect much or any accumulation until later.

The storm is powerful and has already dropped lots of snow on the Pacific Northwest over the past 24 hours.

The big change to the forecast is that the storm IS going to drop south and west, just as the European model indicated days ago. However, the main American model (the GFS) originally thought the storm would stay further north and make a direct hit, and only yesterday flipped and agreed with the European. The GFS was steady in its forecast so I gave it some credit, but the European model is often more correct and proved to be more accurate yet again. Here's how the American GFS model flipped. 

Part of the reason the storm is diving further south could be a very strong storm over the northern Pacific Ocean southwest of Alaska. Everything in the atmosphere is connected, so a stronger storm out there can create a strong ridge over the north Pacific (the flow goes further north), and then the pattern further compensates by going further south to the east of the ridge over the western US (our storm). The atmosphere is just a bunch of waves that all play off of each other, and when one gets stronger, other waves can follow suit.

The cold front will come through tonight, later than I earlier thought. Probably between about 6pm in the northern and western areas and 10pm for areas further east. Since the storm is diving further south, I think the longest lasting and heaviest snow will likely be in the southern half of the state from Aspen down to Irwin and the San Juans. Monarch will also do well. I am more pessimistic for the I-70 area, but let's hope for the best.

Another issue will be heavy snow east of the divide, starting around midnight and lasting through midday to afternoon Sunday. Since the storm is diving further south, the counter-clockwise winds around it will create upslope flow and strong winds on the plains and foothills. I imagine that travel will be a real pain Sunday morning through midday in the foothills and plains from Boulder south to the Palmer Divide.

By early Sunday morning, the storm will develop a circulation somewhere over central Colorado and this will play with the wind direction which will affect where the heaviest snow will fall. I'll keep an eye on this and update things this evening if anything changes. My best estimate of the snowfall accumulation is here.

We'll dry out Sunday night, then another weak storm will move through on Tuesday into Wednesday. Then it looks like we dry out and warm up for the first week or so of March...

JOEL GRATZ