A major outbreak of tornadoes and severe thunderstorms continues to appear likely for this afternoon & evening. The highest risk of tornadoes, some of which are likely to be strong and with long tracks, will be across the pink and red shaded areas on the image above. In addition, very large hail and damaging winds can be expected with severe storms that form across this region.
At midday, a strong upper level storm system was spinning over the central and southern Rockies (red circled area on water vapor satellite image below):
It is accompanied by a very strong band of winds in the middle and upper levels of the atmosphere (as shown by the red arrow around the base of the system in the above image).
This system, and the strong band of jet stream winds, is forecast to lift out East/Northeast into the Plains this afternoon and evening. As this occurs, thunderstorms will explode along a surface dryline near the western border of the highest risk areas, most likely between 2 and 3pm.
Based on current surface, computer model and satellite data, the series of images below shows how this situation is likely to unfold from mid-afternoon through mid-evening (click to enlarge):
The above is based on current trends, and could obviously change. I will say that all available data has been very consistent over the last few hours in that the above estimates will be pretty close. Also, the data has become even stronger at suggesting that one or more significant tornadoes (i.e., very damaging with a long track) are likely across this region this afternoon & evening.
Please note that the above hour by hour, regional outlook only applies to the region with the higest risk for strong, long track tornadoes. There will be additional activity both to the North and South of these areas as well.
Due to the potential magnitude of the situation today, I would look for the SPC to issue Tornado Watches well in advance (perhaps an hour or more) of actual thunderstorm development in the affected areas. The good news if you live in the Eastern half of the outlook area is that you will have plenty of time to track storms as they move and develop to the West, so we will be able to refine/adjust the forecast and give plenty of advance warning.
If you live anywhere within the pink or red outlined areas in the image at the top of the post, please take this situation very seriously - your life may literally depend on it! Remain on a high state of alert this afternoon (starting 2pm in the Western portions of that region) and evening.
There still appears to be the potential for a significant tornado threat after dark further to the East across portions of western Missouri and western Arkansas. If you live in this region and do not have a weather radio or some other means of obtaining a warning at night, please go out this afternoon and buy one. They cost between $20 and $40 and are available at most major chains such as Radio Shack, Wal-Mart, Target, etc. DO NOT depend on an outdoor warning siren to alert you at night (or any other time of day). These sirens were designed for OUTDOOR warning, not indoors or in vehicles as you may not always be able to hear them in those settings.