Severe weather is expected in the Plains today and Tuesday, but Wednesday could steal the spotlight this week. Cold air from Canada, clashing with warm and moist air from the Gulf and combining with dry air from the Desert Southwest could combine to produce a potentially deadly and widespread severe weather outbreak by mid-week. “There is the potential for a significant weather event Wednesday,” Bill Bunting, Chief of Operations at the Storm Predication Center said.  Severe storms could spawn tornadoes, damaging winds and destructive hail across Oklahoma, Kansas and Missouri. The outbreak could continue into Thursday and Friday as the system punches eastward.

The Storm Prediction Center issues several forecasts highlighting the probability for severe weather several times a day. These forecasts are called Convective Outlooks. The outlooks highlight the probability that an area will experience severe storms up to eight days in advance. These probabilities fall into three categories: high, moderate and slight. High risk days usually indicate an extreme severe weather event is in the forecast. In most cases, it indicates a major tornado outbreak could occur.

Cold air from Canada, clashing with warm and moist air from the Gulf and combining with dry air from the Desert Southwest could combine to produce a potentially deadly and widespread severe weather outbreak by mid-week.

Weather forecast models were already coming into good agreement early this morning indicating a severe weather outbreak could happen by mid-week. It is unusual for most of the models to predict such a severe weather event this early. After seeing the models were in agreement, forecasters at the SPC decided to issue a moderate risk area for severe storms on Wednesday in this morning’s outlook. That’s three days in advance. Issuing a moderate risk for severe thunderstorms this far in advance is rare for the SPC.  Including the moderate risk area issued today, only five moderate risk areas have been issued three days in advance in the past 10 years during the month of April, said Bunting.

One of those times occurred in advance of the largest tornado outbreak in U.S. history. The outbreak commenced April 25, 2011. 358 tornadoes touched down across the U.S. during a 3-day period. Tornadoes and severe weather caused over 300 fatalities and approximately $11 billion in damages. During this outbreak, a large, violent tornado swept through Alabama, causing destruction in Tuscaloosa and the University of Alabama. The twister also caused 1,500 injuries and 65 fatalities. It was 1.5 miles wide when it crossed Interstate 65 and stayed on the ground for an astounding 80 miles.

Moderate risk areas issued three days in advance also occur outside of the month of April. In the past 10 years, 12 moderate risk areas have been issued three days prior to a severe weather outbreak. Moderate risk forecasts that are issued two days in advance are more common. In January of this year, a moderate risk area was issued two days before an unusually strong weather system triggered a severe weather outbreak that resulted in 57 tornadoes across the South and Midwest.

CNN Meteorologist Melissa Lefevre contributed to this report.