Over three days. Hat tip: Don Paul.

Tornado With tornadoes, 5% is the significant probability threshold. Fifteen percent is a highly elevated risk. The hatched area is where violent (≥F-2) tornadoes are predicted to occur. Damaging Thunderstorm Winds With damaging winds, 15% is the significant threshold. Forty-five percent is very high. The hatched area is where gusts of 75 mph or higher are expected. If you live in these areas, please monitor local weather information. Safety rules are here . 

The most cogent analysis I have read.

Scroll through the information below for complete update on the Plains winter storm. Reminder: I tweet @usweatherexpert. There is some possibility of a tornado or two during the night in the brown area. If you live in the brown area, please monitor local weather information. This is the last update for this evening. Coverage will resume tomorrow morning.  This is brought to you by Mike Smith Enterprises, LLC . Copyright 2013. We provide professional presentations on weather risk mitigation for business and society and popular books on weather and its effects .

Here is an update on the snow. We are talking about snow only  here, not any ice that may have fallen before the snow (see postings below): Forecast snow depths for noon CST Saturday: Snow depths for 10pm Saturday evening. This is the 00Z NAM model: This is the type of thing that drives meteorologists crazy. The difference between no snow and 10+ inches is 25 miles. The computer model could easily be 30 mi. off in either direction.  The snow band could also be a bit wider than forecast. Here is the European model's snow forecast for the same time: As I have been discussing with this storm, with regard to travel in this region tomorrow earlier is better. How much snow will fall at your home?  Take the two models and they should give you a reasonable forecast range.

Update 8:40pm: A segment of I-35 in central Oklahoma has been closed due to the ice and numerous accidents. I suspect there will be more closings during the night.  ORIGINAL POSTING: Radar at 7:55pm. The purple in Oklahoma is freezing rain. In Kansas, it is light freezing drizzle. There is a 15-car pileup in downtown Oklahoma City. More than a quarter-inch of ice is coating surfaces in the southwest Oklahoma town of Duncan. This is the forecast radar at 4am CST Saturday. The dark blue line is the forecast 32°F line. Some areas will have coatings of ice more than ¾ inches. Power failures are likely. See below for suggested preparation ideas.

Here is the 9pm forecast radar from an experimental mesoscale meteorology model: Here are the forecast temperatures as of  9pm: Heavy ice accumulation is expected during the late evening and overnight hours as the rain moves to the northeast. There will even be some isolated lightning strikes. Power failures are quite possible with this storm. The highest probabilities of power failures are in the areas with 0.25" or more ice coatings forecast. When power failures are possible it is a good idea to: Go to the ATM and make sure you have plenty of cash Make sure your car is filled with gas and that essential errands are run before the freezing rain arrives Have an inverter you can plug into your car's cigarette lighter so you can keep your cell phone and/or laptop charged UPDATE: Here is the pair of 4am forecasts. The dark gray is light freezing drizzle.