A dangerous severe weather outbreak is setting up for Christmas Day for much of Mississippi and Alabama. For our area specifically, violent, long-track tornadoes are possible. Damaging winds in excess of 80 mph and large hail are also possible. One wave of rain will wash over our area around mid-morning. Following that back of rain, supercell thunderstorms could begin developing. Most models indicate increasing instability throughout the late morning, but it looks like the storms will begin firing around or just after noon. Very heavy rainfall will accompany this system, which means there is a threat for flash flooding. It also means many tornadoes will probably be wrapped with rain and you will not see them until they are right on top of you. Never try to see a tornado. If your area goes under a warning, move to your place of safety. The passage of the cold front, which should clear east of our area by midnight will mark the end of the severe weather threat. So the greatest threat for severe weather looks to be from around noon until around midnight, though it will begin ending as early as 9-10 pm for our western areas. Otherwise, try to not focus too much on times. Similarly to April 27, 2011, this system will be mainly made up of supercell thunderstorms that are developing over us rather than a squall that we track from the west.
Technical discussion: A mid-level low pressure swirl is dropping out of the Rocky Mountains and into the Plains. Surface pressure along the eastern edge of the Rockies is falling quickly, indicating low pressure is developing at the ground as the mid-level swirl drops down the eastern side of the mountain range. The system is baroclinically driven, meaning it is fueled by temperature differences ahead of it and behind it. As the low pressure organizes and takes control of its own environment, it will begin drawing deep moisture and warmth northward from the Gulf of Mexico. This process will increase the temperature difference that drives this system, helping to intensifying the low pressure circulation. Christmas morning, relatively weak low pressure will intensify and move from northern Texas across northern Louisiana and into Mississippi. East of the low pressure a warm front will slide north. The shallow lift along the warm front should generate a wave of rain over East Mississippi and West Alabama. Behind the warm front, a strong surge of warm air and deep humidity will lift north beneath diffluent (spreading out) and very strong jet stream. That strong jet stream with wind that spreads out suggests a high potential for long-lived updrafts. Those storms that produce tornadoes will have the ability to last long, and we may have tornadoes grow very strong and they could be on the ground for long distances. Once the cold front clears through, temperatures fall and take away the instability and the severe threat will quickly come to an end. The cold front should clear our far western areas around 9 PM and then clear east of our West Alabama area by midnight or shortly after. That means severe supercell thunderstorms will be developing from noon to midnight for our area. The strong jet stream and deep moisture also means that heavy rain is likely. Rainfall totals of over 2 inches are possible in spots. This also increases the risk for rain-wrapped tornadoes.
After the cold front, expect another wave of deep cold for probably the better part of the next week.
TONIGHT: Becoming cloudy with areas of fog after 2 AM. The low will be near 53. The wind will be from the east at less than 5 mph. Sunset is at 4:56 PM.
TOMORROW: Heavy rain and thunderstorms likely. Some storms will be severe with strong tornadoes, damaging wind in excess of 80 mph, and hail. Rainfall totals of up to 2 inches are possible. The high will be near 67. The wind will be from the south/southeast at 9-18 mph and gusty. Sunrise is at 6:54 AM.
WEDNESDAY: Cloudy, cold, and windy. The morning low will be near 40. The afternoon high will be near 48.
THURSDAY: Becoming sunny. The morning low will be near 27. The afternoon high will be near 52.
FRIDAY: Mostly sunny. The morning low will be near 30. The afternoon high will be near 54.
SATURDAY: Cloudy with cold rain. The morning low will be near 39. The afternoon high will be near 52.
SUNDAY: Becoming sunny. The morning low will be near 33. The afternoon high will be near 52.
MONDAY: Mostly sunny. The morning low will be near 28. The afternoon high will be near 55.