Tuesday, January 15, 2008
A Glancing Blow
Remember my discussion about the dreaded 'Polar Vortex'? Well we are still going to see at least part of it and we will be feeling a real chill straight from the Arctic Circle. There's going to be a series of waves of low pressure that will move through the area finally bringing temperatures down into the single digits for the weekend. If you look at my forecast you will notice that I have temperatures down in the single digits and lows below zero. No one else has stepped in the that territory yet. (But is that really anything new!)If you look at the model which has performed best this winter it brings in -14 Farenheit temperatures by Saturday morning. If you account for some mixing which will take place and modify these temperatures a bit there's no other way to forecast it. One of my pet peeves is when forecasts keep changing, getting knocked down or up a notch each day. But my pet peeves could fill this blog each and everyday. So for right now it's going to be a 'glancing blow' of cold air which lasts just couple of days. Now, as you know this is not set in concrete, but I feel pretty confident we are going to see the seasons coldest air this weekend as the model I use most and is now becoming the model of choice for this event has been very consistant with the cold air. (As it's been all Winter so far).
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4 comments:
Greg,
I'm looking to go snowboarding later in the week, sometime between Fri and Monday, and I'm trying to determine which day would be the best - i.e. the day after we get the most snow.
Maybe you could give us laypeople a quick tutorial on how to get precipitation forecasts from that model...
Jeff,
I wish I could tell you an easy way to look at models and forecast snow. Truth is that their really is not an easy way to forecast snowfall totals. Let me give you some background to support my statement. Let's say you have about .25" of moisture coming in over a period of time with a weather system. Well if you figured snowfall on a 10:1 ratio then you'd have about 2.5". However, the temperature is falling because there is a polar front moving in and your ratio chages hour by hour. One hour it my be 15:1 and with extremely cold air it my go down to 25:1. It also depends on the track of the surface and 750 mb low.
The last large scale snow event we had our track was off by about 30 miles. So Syracuse had 18" of snow and Whitley county had about a foot. While Allen county was about 6 to 8". Folks thought I was nuts telling them we could see 12 to 22 inches of snowfall but that's exactly what the majority of the area received even if it was not exactly in your back yard.
I think snowfall out of this polar system on Thursday should be about 1 to 2" max with a 3 inch snowfall in an isolated area.
Sorry for the long post but I really wanted to explain to you why it would very difficult to take a page full of mathematical models with not output and try to forecast snowfall totals.
Greg,
Thanks but I don't think I made my question clear enough. I understand the relationship between moisture and snowfall.
I was really just confused about the mechanics of using the specific model you linked to...
Jeff,
We usually run a program from the models called 'bufkit'. This gives up numerical output to forecast snow totals. There are also a couple of other numeric solutions that I run at home and at the office to give me snowfall insight. Years ago, and I'm dating myself here we used to use something called the 'magic chart' for forecasting snow. This was before computers where faster and we were able to run our own numerical outputs. Here is a site that may help you as well. http://www.hpc.ncep.noaa.gov/html/fcst2.html I'm really not trying to dodge the question here, just trying to point out the complexities of precipitation forecasts.
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