Finally, the promised man vs. machine contest! For even more fun, the Storm Prediction Center has issued a slight outlook. So, for this forecast, the focus point will only be on Alton, IL. Why? Because I am here and can make observations here, physically. For the DeKalb viewers, I will put a forecast for DeKalb following. Remember, the situation is that I will forecast only based on observations, radar, and satellite. Unfortunately, I am not having luck loading my hand analyzed maps to this post. So, to give an idea I will use the same old links.
So the situation at
500 mb is a trough over the western and central United States, with ridging starting in the east. Wind speeds at 500 mb around the region range from about 70-75 knots from the southwest. The surface map has shown chnge in roughly 4 hours. My 1500 Z (10 am) surface placed the low in north-central Missouri, with a warm front just north of St. Louis. The cold front trailed back west of Springfield, MO. The following
surface map is form the Hydrometeorological Prediction Center. Remember these links will change as time progresses.
Based on the surface map, I would predict that the low will track towards the north, northeast, following up the cold side of the warm front. This will swing the cold front around closing in on St. Louis and Alton. Currently in Alton, the temp is 78, with a dew point of about 57. Conditions are cloudy, preventing surface heating, which in turn, lowers the amount of instability. However, radar indicates storms north of the area. We will have moisture and lift (thanks to the cold front). The Lincoln, IL sounding from 1800Z (1 pm), was the closest recent sounding. There was a small amount of CAPE (Convective Available Potential Energy), a measurement of instability, in this sounding. It appears even though small, there was enough instability for convection to begin with the lift of the cold front.
It does appear that storms will occur in this area in the late afternoon into the evening as the cold front passes over. The current storm system is pretty much linear (due to the front), so the greatest threat is damaging wind, but given the set up, I do not believe we will see any of this in Alton.
As for temperatures, I will examine temps and dew points behind the front. Dews that should come in the area should be in the lower thirties/upper twenties. Looking at clearer areas behind the cold front, temperatures are around 40 degrees.
Putting it all together now;
Alton should see some storms push through this evening. They will probably go quick as the system begins to move out of the area. I would expect clearer skies tomorrow. As for tonights lows, probably around 29 degrees (based on dew point). With the clearer skies, one would expect to see similar temperatures in clear regions behind this front. I believe the high will be around 40 tomorrow. With this system moving through pretty quick, and with lighter rains in this system, I don't think we will see more that .25 inches.
Alright there was the "man" forecast, now for the "machine forecast":
GFS(Global Forecast System):
Low: N/A
Hi: 46
Chance of Precip (tonight): 58%
Chance of Precip (tomorrow): 0%
Tomorrow: Clear
Precip Total <.10"
NAM(North American Model):
Low: 28
Hi: 41
Chance of Precip (tonight): 87-67% (Decreasing over time)
Chance of Precip (tomorrow): 1-5%
Tomorrow: Clear
Precip Total: 1" or greater
