Hey all,
This being New Year's Eve, this will be the last post of 2010. I originally planned on writing a forecast for tomorrow, but my plans were changed this morning. I got online to look at weather, seeing that most of the St. Louis area was under a tornado watch. Within minutes, there were tornado warnings posted. I jumped into "Severe Weather Mode" which kept me glued to radar and the skies. After the reports are completed, I'll put them up here for you to see. The severe weather mostly stayed south of Alton, so no cool pictures from me this time.
On a slightly different topic, with the new year coming, I am wondering if there are anythings you would like to see on the blog in 2011. I've been leaving forecast verifications in the comments section starting this year. If there are anythings you would like to see (that are reasonable), I'll see what I can do on putting them on this blog. Also, if you are just an occasional reader, but would read more often if there was some improvements, please let me know. Anything that helps spread the word on the weather. So please, if you would like to see changes, write a comment in the comments section, and I'll see what I can do.
Well, I'm going to keep this short and sweet. Have a safe and happy new year! I'll write to you all in 2011!
Friday, December 31, 2010
Saturday, December 25, 2010
Snowfall Update
Hey all,
Here's the latest update on snowfall totals. I really cut it close on the Alton forecast. While areas in St. Louis were recording 4 inches or greater, I measured 3 inches in Alton. Just clipped my upper limit on that forecast! Other reports from around St. Louis.
I was just a bit too low on DeKalb, as the official report was 5.1 inches. Looks like the snow to liquid ratio was a bit higher than I expected, but that is weather for you. Here are the reports from around Chicago.
I hope everyone enjoyed their day! Merry Christmas!
Here's the latest update on snowfall totals. I really cut it close on the Alton forecast. While areas in St. Louis were recording 4 inches or greater, I measured 3 inches in Alton. Just clipped my upper limit on that forecast! Other reports from around St. Louis.
I was just a bit too low on DeKalb, as the official report was 5.1 inches. Looks like the snow to liquid ratio was a bit higher than I expected, but that is weather for you. Here are the reports from around Chicago.
I hope everyone enjoyed their day! Merry Christmas!
Thursday, December 23, 2010
I'm Dreaming....
'Tis the season of giving, so today I am giving a double forecast. With Christmas being just 2 days away (really seems like the year went fast), there is always the conversation of whether or not there will be a white Christmas. There is a nice set-up out in the West, and it is heading for the Midwest. It's time to see if Alton and/or DeKalb will have a white Christmas!
Let's start by looking at the system. The jetstream has a very nice trough out west, with the trough axis in central Utah as of 1200Z (6 am CST). This trough will continue its eastward journey, and by midday tomorrow (Christmas Eve) the trough axis should be around the Oklahoma Panhandle. Current forecast models show that the trough will then track across Illinois, and moving out of Illinois Christmas morning. As this trough approaches Illinois, the lower level winds (at 850 mb), will begin to flow from the south, bringing in some moisture from the Gulf of Mexico. This will contribute in forcing precipitation from this system. After this trough passes, Illinois will be sitting under a fairly large ridge.
Normally, I would be getting ready to blame some surface feature for the possibility of precipitation. This time, it appears there will be another forcing mechanism for the snow. The low in Colorado is looking like it will take a southern turn, and come evening Christmas Eve, the low should be crossing Texas. With a ridge following in the jet stream, Illinois will mostly be seeing high pressure at the surface after this event.
Currently, the cause of possible snow, seems to be isentropic forcing. This will take a bit of explanation, and I will do the best I can to explain it. Please remember, I am trying to explain a complex process as simply as I can.
In meteorology, we have a variable known as potential temperature. This is the temperature that an unsaturated parcel of air would have if you brought the parcel adiabatically to 1000 mb pressure. Here's the big deal about it for purpose of this discussion: Parcels like to "ride along" on this temperature. The parcels basically treat this as a sort of "ski lift." I'll bring in a chart soon which should help you visualize this.
Here is the cross section of the atmosphere between Slidell, LA (left) and Green Bay, WI (right) (conveniently right through the forecast area!) The red lines are lines of potential temperature (in meteorology, commonly called "theta", since that is the variable used in calculations.) Notice, as the potential temperature lines approach Green Bay, they go up in height. Remember, parcels are riding along this line of potential temperature. As the parcels rise, their actual air temperature decreases, and brings it closer to the dew point. When the air temperature and the dewpoint temperature reach the same temperature, you have saturation. As the atmosphere reaches saturation, you begin to form clouds and can form precipitation.
Basically, isentropic forcing is when you get this type of situation, where parcels are "riding" lines of potential temperature and forcing out precipitation. There is a whole lot involved in this process, but I am really trying to give a very simple explanation for something that is not very simple. However, this appears that it will be the culprit for any snow caused on Christmas Eve and into Christmas day.
Now for the fun part, which is snowfall accumulation. So I'll start with Alton, and then I'll finish with DeKalb.
For Alton, IL, models seem to put the best time for snow to be in the afternoon into the evening on Christmas Eve, with snow falling overnight, and flurries on Christmas. MOS guidance shows probabilities of precipitation to be well over 70%, so it looks like Alton, IL will be having a white Christmas! As for amounts, based on what I am seeing, I feel confident that there will be about 1-3 inches of snow across the area, with local amounts reaching 4 inches.
For DeKalb, IL, everything seems to be pointing to similar conditions. It looks like the snow may begin around the middle of the afternoon on Christmas Eve, but these will more than likely be flurries. The snow should pick up into the evening hours, and it looks like there may be a few flurries on Christmas. MOS guidance isn't as high as Alton, but still shows around a 70% chance of precipitation on Christmas Eve. All in all, I believe DeKalb, IL will also be having a white Christmas! Based on the data, I am going with 2-4 inches of snow for DeKalb, with local amounts being up to 5 inches.
Well, that concludes this discussion. It looks like both areas will be having a white Christmas. If anyone is wondering what I'm wishing for, it would be a job (even part-time) or funding so I can go to graduate school in the fall, but that's another story, for another day. Have a safe and enjoyable holiday. Merry Christmas everyone!
Let's start by looking at the system. The jetstream has a very nice trough out west, with the trough axis in central Utah as of 1200Z (6 am CST). This trough will continue its eastward journey, and by midday tomorrow (Christmas Eve) the trough axis should be around the Oklahoma Panhandle. Current forecast models show that the trough will then track across Illinois, and moving out of Illinois Christmas morning. As this trough approaches Illinois, the lower level winds (at 850 mb), will begin to flow from the south, bringing in some moisture from the Gulf of Mexico. This will contribute in forcing precipitation from this system. After this trough passes, Illinois will be sitting under a fairly large ridge.
Normally, I would be getting ready to blame some surface feature for the possibility of precipitation. This time, it appears there will be another forcing mechanism for the snow. The low in Colorado is looking like it will take a southern turn, and come evening Christmas Eve, the low should be crossing Texas. With a ridge following in the jet stream, Illinois will mostly be seeing high pressure at the surface after this event.
Currently, the cause of possible snow, seems to be isentropic forcing. This will take a bit of explanation, and I will do the best I can to explain it. Please remember, I am trying to explain a complex process as simply as I can.
In meteorology, we have a variable known as potential temperature. This is the temperature that an unsaturated parcel of air would have if you brought the parcel adiabatically to 1000 mb pressure. Here's the big deal about it for purpose of this discussion: Parcels like to "ride along" on this temperature. The parcels basically treat this as a sort of "ski lift." I'll bring in a chart soon which should help you visualize this.
Here is the cross section of the atmosphere between Slidell, LA (left) and Green Bay, WI (right) (conveniently right through the forecast area!) The red lines are lines of potential temperature (in meteorology, commonly called "theta", since that is the variable used in calculations.) Notice, as the potential temperature lines approach Green Bay, they go up in height. Remember, parcels are riding along this line of potential temperature. As the parcels rise, their actual air temperature decreases, and brings it closer to the dew point. When the air temperature and the dewpoint temperature reach the same temperature, you have saturation. As the atmosphere reaches saturation, you begin to form clouds and can form precipitation.
Basically, isentropic forcing is when you get this type of situation, where parcels are "riding" lines of potential temperature and forcing out precipitation. There is a whole lot involved in this process, but I am really trying to give a very simple explanation for something that is not very simple. However, this appears that it will be the culprit for any snow caused on Christmas Eve and into Christmas day.
Now for the fun part, which is snowfall accumulation. So I'll start with Alton, and then I'll finish with DeKalb.
For Alton, IL, models seem to put the best time for snow to be in the afternoon into the evening on Christmas Eve, with snow falling overnight, and flurries on Christmas. MOS guidance shows probabilities of precipitation to be well over 70%, so it looks like Alton, IL will be having a white Christmas! As for amounts, based on what I am seeing, I feel confident that there will be about 1-3 inches of snow across the area, with local amounts reaching 4 inches.
For DeKalb, IL, everything seems to be pointing to similar conditions. It looks like the snow may begin around the middle of the afternoon on Christmas Eve, but these will more than likely be flurries. The snow should pick up into the evening hours, and it looks like there may be a few flurries on Christmas. MOS guidance isn't as high as Alton, but still shows around a 70% chance of precipitation on Christmas Eve. All in all, I believe DeKalb, IL will also be having a white Christmas! Based on the data, I am going with 2-4 inches of snow for DeKalb, with local amounts being up to 5 inches.
Well, that concludes this discussion. It looks like both areas will be having a white Christmas. If anyone is wondering what I'm wishing for, it would be a job (even part-time) or funding so I can go to graduate school in the fall, but that's another story, for another day. Have a safe and enjoyable holiday. Merry Christmas everyone!
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