Friday, February 27, 2009

Snowfall possibilities

Now that the thunderstorm possibilities have diminished, we can turn our attention to more important matters - snow! (Side note: rain moves back in tonight with the chance of some thunder, but nothing like last night.)

A low pressure system currently over the Upper Midwest/Northern Plains is moving southeast and bringing with it some very COLD air. As it nose-dives just to our west tomorrow, showers will break out by late morning as temps hover near 40. By mid-afternoon, the cold air aloft will push into the region and surface temps will also fall into the 30s. This combo will begin changing the rain over to snow.

One model (GFS) actually makes this transition earlier in the afternoon (maybe around noon), while another (NAM) is closer to 3pm. The other model differences are in precipitation amounts after the changeover. The GFS believes amounts will be fairly light, but with the earlier transition we could see an inch by the time it ends. The NAM is more bullish and actually gives us closer to 2-3" even with the later transition - most of this falling in the evening hours. Both move the precip out by midnight. The NAM has done exceptionally well with cold air intrusions this winter and I tend to favor it's timing, but think that the precip amounts from it might be overdone. Thus, I think the transition will be ~3pm with an inch of accumulation possible between 3-9pm. I do believe that areas north and east of Memphis, such as Dyersburg, Jackson, Selmer, etc. could see up to 2". I'll look for the models to come into more agreement and update the forecast tonight or early Saturday.

Cold weather will continue Sunday and it will be a windy weekend, so wind chills will be pretty cold (teens to 20s). Dry weather wand a warming trend will commence for the first week of March, which will come in like a lamb!

2 comments:

jacksonweather said...

What are your thots about the 12z guidance my friend?

MWN/Erik said...

Guidance I used this morning was the 12Z NAM and 06Z GFS. Don't see much change in the 12Z GFS from the 06Z. I think you have a better chance of accum. than we do, and I still think GFS is a little quick with the changeover. NAM temps have been hard to beat on cold air situations this winter. I'm sticking with it. Here's to one last snowfall! --Erik