Saturday, April 26, 2014

Significant Tornado Outbreak Expected Sunday, Monday

A significant tornado outbreak is expected on Sunday and Monday, with strong to violent tornadoes expected on these two days.

The Storm Prediction Center has issued a moderate risk of severe weather for northeast Texas, northern Louisiana, eastern Oklahoma, southern Missouri, and most of the state of Arkansas. This moderate risk comes as a strong upper level low brings moisture and other destabilizing factors up to the Plains, likely resulting in one of the more significant tornado events in recent memory. The Storm Prediction Center has indicated that long-tracked and strong tornadoes are possible if this event comes to fruition, and an upgrade to the agency's highest risk level, the High Risk, will come tomorrow if model guidance continues to hone in on this severe weather event.

The image above shows the East WRF-ARW model forecast for maximum updraft helicity over its entire 48 hour forecast period. The idea of highlighting the maximum updraft helicity values is to identify where potentially tornadic supercells may strike for this severe weather event. A look at this image, showing maximum updraft helicity for the Sunday event, gives a clear indication of what we could be facing with this situation. This particular model shows multiple long-tracked, rotating supercells moving northeast from Texas into Arkansas. Based on the high helicity values, it looks like some of the most intense cells may be able to put down some strong tornadoes, but it will take another round of model guidance to confirm or reject this idea.

A look at the Storm Prediction Center's SREF (short range ensemble model guidance) projection for the probability of strong tornadoes only worsens this threat. We see the chance of a significant tornado at or above 75% in Arkansas, but there's a very small speck in the middle of Arkansas, where it seems to increase another contour level. The next contour level above 75% is 90%, meaning that this model run indicates there is a 90% chance of a significant tornado in central Arkansas. Predicting tornadoes is a very difficult endeavor, but this graphic gives us an idea of where the worst tornado threat may be.

On Monday, we see another moderate risk area, now located just to the east over northeastern Louisiana, much of Mississippi, and western Tennessee. This moderate risk area also has the potential to be upgraded to a High Risk, as many of the same dynamics that look to produce a potentially deadly environment on Sunday will be in place again on Monday. If you or someone you know resides in the moderate risk area for either Sunday or Monday, please alert them to this severe weather. This outbreak may be one of the more significant ones of the last few years, and should be dealt with with extreme caution.

The SPC SREF projection for the probability of significant tornadoes is also startlingly high for the Monday evening event, as the graphic above shows. We see the highest probabilities placed in far northeastern Mississippi into northwest Alabama, located a bit east of the current Monday moderate risk area. While this forecast may see slight adjustments in the near future, the trend of a significant tornado event on Sunday and into Monday remains clear.

To summarize:
• A significant tornado event is expected Sunday and Monday.
• Long-tracked, violent tornadoes may occur on either of those days.
• Anyone in either of the moderate risk areas on Sunday or Monday should immediately prepare for potentially extreme weather, which may threaten lives and property.