After all the panic, no snow fell in DeKalb. Tuesday saw a rather nasty day of mist to light rain conditions. According to the National Weather Service out of Romeoville, Illinois (the Chicago office), there was some pea-sized hail in the region.
Throughout the day Tuesday, I mostly walked in light rain. On my way back from my morning class, I did see some snow-like precipitation, but very little. I saw a few small flakes (probably about 5-10 in total), and a little frozen precip, but for the most part it was rain.
Conditions are currently sunny and warming. Currently it is 59 degrees, and temperatures in the low 80's could be seen Friday and Saturday. I am getting this straight from the National Weather Service today, as I am a little time crunched. However, we will be entering a 500 mb ridge, which should keep our weather nice. I'd better wrap this up, because I still have a lot to do before the end of the week. I'll get another post up as soon as I can.
Wednesday, April 22, 2009
Monday, April 20, 2009
S-S-S-Snow!!!! In Late April?!
This seems to be a fairly popular topic in DeKalb lately. There is a fair chance of seeing some late April snow. This has left some people panicking, however, it seems to really be nothing.
As always, let's get ready to do some map analysis! Current 500 mb maps show an upper level low parked on top of DeKalb. This is sitting in a pretty nice trough. A look at the surface map shows a low pressure located in northern Michigan. Now it is time to look at more features. At 850 mb, We can see a freezing line in central Illinois. This level is around 1250-1500 meters above the surface. If we were to look at another upper air tool, called a sounding, we can look at temperatures in a vertical profile. I am going to use the Davenport, Iowa sounding from 0000Z, which is the evening sounding.
I have added a thick blue horizontal line to indicate the freezing line. The vertical red line indicates temperature with height, and the vertical green line indicates dew point with height. Where they are close, the atmosphere is moist. This is a pretty moist profile, extending up to about 600 mb. So, most of the moisture is above the freezing line in this profile, indicating that if precipitation falls, it will fall frozen. Below the freezing line, it will more than likely melt.
So, what is going to cause the snow? It appears that the low in Michigan will be the problem. Motion around a low is counterclockwise. So, the precipitation forming around a mid-latitude cyclone will follow this motion. Areas north of the warm front are cooler, in this case cool enough for snow. The snow will follow the motion around the low, driving the snow and cool temperatures towards DeKalb.
As for accumulation, I don't think we will see any. Forecast soundings indicate that surface temperatures will not reach freezing. Both the GFS and NAM models are in fair agreeement that the nighttime lows will be around 36 degrees into Tuesday morning. Tuesday highs should be around 46, with Tuesday night/Wednesday morning lows being around 36 again. There is about a 70-80% chance of precipitation. We will also be having northerly , turning into westerly, surface winds around 15-20 miles per hour Tuesday, which will keep the air feeling cooler. With highs expected in the 40's, I would expect to see some rain as well.
To sum it all up, yes we may see snow in DeKalb. However, it will proabably have rain mixing in as the day progresses, and we probably won't have an accumulation. If we do end up with accumulation, it will be minimal, and probably won't last long.
As always, let's get ready to do some map analysis! Current 500 mb maps show an upper level low parked on top of DeKalb. This is sitting in a pretty nice trough. A look at the surface map shows a low pressure located in northern Michigan. Now it is time to look at more features. At 850 mb, We can see a freezing line in central Illinois. This level is around 1250-1500 meters above the surface. If we were to look at another upper air tool, called a sounding, we can look at temperatures in a vertical profile. I am going to use the Davenport, Iowa sounding from 0000Z, which is the evening sounding.
I have added a thick blue horizontal line to indicate the freezing line. The vertical red line indicates temperature with height, and the vertical green line indicates dew point with height. Where they are close, the atmosphere is moist. This is a pretty moist profile, extending up to about 600 mb. So, most of the moisture is above the freezing line in this profile, indicating that if precipitation falls, it will fall frozen. Below the freezing line, it will more than likely melt.So, what is going to cause the snow? It appears that the low in Michigan will be the problem. Motion around a low is counterclockwise. So, the precipitation forming around a mid-latitude cyclone will follow this motion. Areas north of the warm front are cooler, in this case cool enough for snow. The snow will follow the motion around the low, driving the snow and cool temperatures towards DeKalb.
As for accumulation, I don't think we will see any. Forecast soundings indicate that surface temperatures will not reach freezing. Both the GFS and NAM models are in fair agreeement that the nighttime lows will be around 36 degrees into Tuesday morning. Tuesday highs should be around 46, with Tuesday night/Wednesday morning lows being around 36 again. There is about a 70-80% chance of precipitation. We will also be having northerly , turning into westerly, surface winds around 15-20 miles per hour Tuesday, which will keep the air feeling cooler. With highs expected in the 40's, I would expect to see some rain as well.
To sum it all up, yes we may see snow in DeKalb. However, it will proabably have rain mixing in as the day progresses, and we probably won't have an accumulation. If we do end up with accumulation, it will be minimal, and probably won't last long.
Sunday, April 19, 2009
Update
I know I have not posted in a while (almost a month). School has really kept me busy these past couple of weeks, and the next two to three weeks look pretty full, especially with the semester ending. It may be a little while more before I can post a forecast. I really want to do another forecast discussion, but time is not on my side right now. With any luck, a time slot may open for a forecast discussion. Thanks for the patience.
Sunday, March 29, 2009
Storm Video/Pictures
Wow. It has been a while since my last post. Since then, there has been some pretty crazy weather. Here is some video and pictures to enjoy.
The first is from March 9. This was the day before the "Man vs. Machine" contest. I was on spring break, and what a way to start it with some severe weather. There was a tornadic storm roughly twenty miles northwest of Alton, IL. Here are the SPC Storm Reports from that day. From my house, I was standing in the inflow. It was relatively calm, and then strong sustained winds blew in the direction of the storm. I have a short video clip of the inflow.
Next, I have some pictures from DeKalb, IL. This is from the rather wicked snowstorm on March 28. These pictures were taken March 29 at around 2:15 pm. Unfortunately, the snow had started to melt, so I could not capture the full effect of the storm on camera. Earlier in the morning, the snow was much higher than what I caught on camera later in the day. I regret not getting some pictures of the higher snow, but I have some pictures nonetheless.
Well, that is all for this post. Just posting these few things for now. Hopefully another forecast will be coming up soon, but school has to take priority.
The first is from March 9. This was the day before the "Man vs. Machine" contest. I was on spring break, and what a way to start it with some severe weather. There was a tornadic storm roughly twenty miles northwest of Alton, IL. Here are the SPC Storm Reports from that day. From my house, I was standing in the inflow. It was relatively calm, and then strong sustained winds blew in the direction of the storm. I have a short video clip of the inflow.
Next, I have some pictures from DeKalb, IL. This is from the rather wicked snowstorm on March 28. These pictures were taken March 29 at around 2:15 pm. Unfortunately, the snow had started to melt, so I could not capture the full effect of the storm on camera. Earlier in the morning, the snow was much higher than what I caught on camera later in the day. I regret not getting some pictures of the higher snow, but I have some pictures nonetheless.
Well, that is all for this post. Just posting these few things for now. Hopefully another forecast will be coming up soon, but school has to take priority.
Thursday, March 12, 2009
Forecast Verification
Just as important as the forecast is the verification. In the man vs. machine contest, the only way to guage the results is to look at what actually happened.
Alton:
Tuesday Night:
Actual Low: 29
Forecast:
Man: 29
GFS: N/A
NAM: 28
Wednesday:
Actual High: 36
Forecast:
Man: 40
GFS: 46
NAM: 41
Actual Precip Total (for the forecast period): 0.16"
Forecast:
Man: less than 0.25"
GFS: less than 0.1"
NAM: 1.0" or greater
All three (man, GFS, and NAM) were correct on sky cover, as Wednesday was clear.
So, the results lay in the eye of the beholder. It really depends on what each individual believes. I believe I beat the computers. My low was spot on, I was off on my high, and a little high on precip totals. However, I believe my results were closer to the actual readings than the models.
My mistakes are explainable. For my high, I chose a target too far south, but at the time, it was the only area behind the front in sunlight. As for rain, I believed that there would have been heavier rain associated with the band of showers.
Well, that raps up this contest of man vs. machine. Hope you enjoyed it as much as I did!
Alton:
Tuesday Night:
Actual Low: 29
Forecast:
Man: 29
GFS: N/A
NAM: 28
Wednesday:
Actual High: 36
Forecast:
Man: 40
GFS: 46
NAM: 41
Actual Precip Total (for the forecast period): 0.16"
Forecast:
Man: less than 0.25"
GFS: less than 0.1"
NAM: 1.0" or greater
All three (man, GFS, and NAM) were correct on sky cover, as Wednesday was clear.
So, the results lay in the eye of the beholder. It really depends on what each individual believes. I believe I beat the computers. My low was spot on, I was off on my high, and a little high on precip totals. However, I believe my results were closer to the actual readings than the models.
My mistakes are explainable. For my high, I chose a target too far south, but at the time, it was the only area behind the front in sunlight. As for rain, I believed that there would have been heavier rain associated with the band of showers.
Well, that raps up this contest of man vs. machine. Hope you enjoyed it as much as I did!
Tuesday, March 10, 2009
A Happy Compromise
As stated, meteorologists should use models for guidance. Now, I will forecast DeKalb using model guidance. The pattern doesn't really change between DeKalb and Alton, except for the low pressure center and warm front between them. However, the cold front will pass over DeKalb as well. I am going to cut to the chase since I have already looked at the scenario, and quite frankly looked at this computer screen long enough.
Tonight's Low: 19
Tomorrow's High: 29
Should be clear skies.
60% chance of rain tonight, 0 % chance of precip tomorrow.
Sorry to be so breif on the forecast today.
Tonight's Low: 19
Tomorrow's High: 29
Should be clear skies.
60% chance of rain tonight, 0 % chance of precip tomorrow.
Sorry to be so breif on the forecast today.
Man vs. Machine
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
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
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