As the National Weather Service in Birmingham, Alabama put it this afternoon in their latest discussion, we have a "smorgasboard" of weather to talk about over the next several days.
Before we get into the nitty gritty of the next few days, I hope you've enjoyed the very refreshing last two days we've had across east Mississippi. The transition from winter to spring went seamless, as we had a plethora of sunshine both days with comfortable temperatures into the mid 60s with a refreshing north breeze. But as we know how the weather can behave in Spring around here, changes are right around the corner...
This map shows vorticity at 500mb valid Thursday evening at 7 PM, and we like to look at the advection of this vorticity because that can lead to areas of rising air. Here, a few maxima of vorticity are noted, most notably over central Arkansas. This coupled with warm air advection in the lower levels, especially 850mb, will help create widespread precipitation across the Mid-South beginning Thursday afternoon initially over parts of Arkansas and southern Missouri that will spread into western Tennessee and the northern half of Mississippi during the overnight hours of Thursday.
The next challenge is to determine precipitation type. The above is a modeled skew-t sounding for Thursday evening for Memphis. Notice the red and green lines almost on top of one another from the surface through around 600mb; this means the atmosphere is saturated throughout this layer. Plus, the temperature stays below freezing throughout the entire column and the area around -12 C / dendritic growth zone/ is also saturated. Therefore, it is expected that some snow will fall in around the Memphis area into extreme northern Mississippi Thursday afternoon and lasting into the overnight hours. It should be noted that this precipitation may initially begin as a rain/sleet mixture before transitioning to all snow by Thursday afternoon.
For this reason, the NWS in Memphis has hoisted a winter storm watch for the counties in dark blue. This does include Memphis and Jonesboro. Here, it is not out of the realm of possibility that 1-2" of snow/sleet could accumulate!
This is a modeled sounding for the Starkville area valid at the same time, 7 PM Thursday evening. Notice the large amount of dry air below 700mb (much different than the above sounding), but saturated above that. We here in east Mississippi will actually undergo moistening from the "top-down" throughout the day Thursday and into the evening. We will also undergo some evaporative cooling, which may actually allow for a period of light sleet Thursday afternoon as precipitation begins, despite temperatures being in the 40s. However, we will not be able to evaporatively cool far enough to get any snow here. Therefore, after the column saturates, we will likely just experience a relatively cold rain with temperatures in the upper 30s or low 40s.
The weather roller coaster continues Friday as we begin a gradual warming process. As the image above depicts, another lobe of energy is progged to move across the area Friday afternoon and evening. Expect more rain showers and even some elevated thunderstorms Friday afternoon/evening with the main threat being some hail. These storms will not have any tornado threat because they are elevated, i.e. rooted above a stable surface layer.
This image is the forecast upper level wind pattern by the 12z GFS for Saturday evening at 7 PM. This would suggest a severe weather setup as the LMRV would be positioned favorably in the broadly diffluent upper-level flow, which would favor enhanced surface lift. Sufficient instability at the surface would aid in the development of thunderstorms, some of which could be quite strong or severe.
On the other hand, here's the 12z ECMWF for 12z Sunday. This model shows the surface low near Demopolis, AL with any severe weather threat confined to southeast Alabama, southern Georgia, and into the Florida Panhandle, keeping us here in Mississippi (with the exception of coastal areas) likely clear of any severe weather issues.
The bottom line is that forecast confidence is very low after Friday evening. One thing is for certain, however, and that is Spring in the Southeast always poses weather surprises!
Have a great week, and God Bless!!
IW
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