Man vs. Machine, Day 4

So far the day 3 forecast is shaping up beautifully. Everything is almost spot on. There have been some stronger than expected winds, but that hasn't affected the forecast by that much at all. That being said, let's move on to day 4 of the contest. Once again, the forecast is for Alton, IL , with the forecast period being 7:00pm CST March 10-7:00pm CST March 11.

The 500 mb jet stream is still showing a strong trough, but it is over the Ohio Valley. Illinois is now west of the trough axis, and the ridge is on the way. Time for a little weather lesson. Once again, the actual event is more complicated. In order to get the general point across of why this is important, it will be simplified. Our location is next to a jet streak (which is a speed increase in the jet stream). We are located on the left entrance region, which is where one expects to find convergence. An area of convergence in the upper atmosphere helps push air down, while an area of divergence helps lift air up. (It all deals with vorticity or spin.) So what does this all mean for the weather forecast? Really simply, it means is air is being "pushed" down from the upper atmosphere, which helps create an area of higher surface pressure. With high pressure, you generally get nicer weather. For our area, the upper atmospheric forcing will be a big contributor in having nicer weather.

At 850 mb, there really isn't anything that should affect our area too much. There is a bit of cold air advection, which might impact temperatures, but that is about it. It's not strong, but it is there.

On the surface map, the low we just had is pushing out of the United States. Most of the continental United States is under an area of high pressure. The only other low pressure I have on my map is in British Columbia.

The last satellite images I looked at were promising for our area. The clouds were pushing out, and it looks like they will be gone within a few hours. We'll be able to see the sun tomorrow, which is a nice break from all the cloudiness as of late. Also, nothing on the radar. There was a little bit of drizzle last night around midnight, but no accumulation occurred.

With not too much to discuss, it is time to put this forecast together. No clouds tonight means we lose our "blanket" over the area. This means temps can fall tonight. I'm forecasting the low to be at 33 degrees. Tomorrow we will actually see the sun, and that means we can warm up the surface a bit. Provided the winds don't kick up too high, I will forecast my high to be at 48 degrees, through the use of a temperature correction chart. I'm not sure if we'll get a big warm up, but temps should start to rise.

Man vs. Machine Day 4 forecasts:

Man:
Low: 33
High: 48
Weather: Clear skies
Precip: 0.00"

GFS:
Low: 27
High: 51
Weather: Clear skies
Precip: 0.00"

NAM:
Low: 28
High: 53
Weather: Mostly Sunny (it calls for clear skies and partly cloudy skies, leaning more towards clear)
Precip: 0.00"

Another NWS Comparison:
Low: 28
High: 61
Weather: Sunny

Well, every forecast agrees on precip, but the high and low remains to be seen. Major gap between myself at 48 and the NWS at 61. The models are putting it right around 52. I just think the cold air advection at 850 mb will keep temps cooler. Like always, time will tell who is closer. Find out tomorrow!