Easter Severe Weather! "Dixie Alley" under Moderate Risk

There's like, no negativity here at all.

Everyone is generally so polite I can't believe it's the internet.

The NWS in Mobile has put out an statement on the severe threat. This is the first time they’ve identified an area that has the greatest potential

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1255 PM CDT Sat Apr 11 2020

.NEAR TERM /Now Through Sunday/...The bottom line during the
period is that there is the potential for a significant outbreak
of severe weather on Sunday especially north of the I-65 corridor
but this is contingent on overcoming a strong cap centered near
850 mb. A cut off upper low located near southern
Arizona/northwest Mexico transitions to a well defined shortwave
trof while advancing eastward across the south central states on
Sunday. A large northern stream upper trof meanwhile swings out of
western Canada into the northwest states and northern/central
Plains. In response to the shortwave trof and the northern stream
system, a surface low develops today to the lee of the Rockies
over the central Plains with a secondary surface low developing
near southern Texas. Due to the interaction between the northern
stream system and the shortwave trof, these two surface lows merge
to form one large surface low centered over Oklahoma Sunday
morning which progresses roughly along the Missouri/Arkansas
border through Sunday afternoon. Ahead of the approaching surface
low, a warm front advances northward across the north central Gulf
and nears coastal portions of Alabama and the western Florida
panhandle by daybreak on Sunday. The surface low brings a cold
front eastward across Texas and much of Louisiana during the day
on Sunday while the warm front continues northward through the
forecast area. Dry and relatively cool temperatures over the area
will be replaced with a moist and much warmer airmass in the wake
of the warm front, with surface dewpoints increasing to around 70
to the lower 70s across much of the area except for values of 65
to 70 over portions of south central Alabama.

Shear values increase dramatically through the period, with 850
mb winds of 20 knots this evening increasing on Sunday to 50 to 55
knots, with even higher values of 60 to 70 knots indicated in the
afternoon over portions of Wayne, Choctaw, northern Clarke and
Wilcox counties. SBCAPE values increase to around 2000 J/kg by
early Sunday afternoon across interior southeast Mississippi,
southwestern Alabama and the far western portion of the western
Florida panhandle while further to east values of 1000-1500 J/kg
are expected. These CAPE values with high anticipated shear values
result in potentially very high Significant Tornado Parameters
(SigTor) of 6.0 to 16.0 north of the I-65 corridor, with the
highest values seen over Wayne and Choctaw counties. High SigTor
values of 4 to 8 are also seen east of I-65. These conditions are
indicative of a potentially significant outbreak of severe weather
across the area on Sunday, especially north of the I-65 corridor.
That said, all of this is conditional on overcoming a strong cap
seen near 850 mb, the strength of which varies from strongest in
the NAM to becoming weaker and erodes in the afternoon per the
GFS and HRRR. The potential for the cap to be overcome looks to
be greatest north of I-65 and during the late afternoon hours on
Sunday. This coincides with when a squall line is expected to have
developed west of the area and will be nearing interior southeast
Mississippi and interior southwest Alabama (Choctaw county).

The Storm Prediction Center has a Moderate Risk of severe weather
across interior portions of southeast Mississippi and interior
southwestern Alabama with an Enhanced Risk of severe weather over
the remainder of the area. Would not be surprised is a High Risk
of severe storms is ultimately issued within the Moderate Risk
area. Stay tuned!!

Repeating this here from an earlier update: a Wind Advisory is in
effect for the entire area from 10 am Sunday to 4 am Monday due
to frequent gusts up to 45 mph. A Coastal Flood Advisory is in
effect as minor coastal flooding is expected along coastal
Alabama and coastal portions of the western Florida panhandle
which is in effect from 10 am to 10 pm Sunday. A High Surf Warning
is now in effect for coastal portions of Alabama and coastal
portions of the western Florida panhandle for surf heights of 7 to
10 feet and is in effect from noon Sunday to 4 am Monday. /29

Rolling along 287 up there in north Texas. Know every little town along that stretch. Watch where this resulting MCS ends up, as the farther north and west it ends up the bigger the warm sector will be tomorrow. 

Something of note on the CAMs that has stood out today is how different the NAM has the surface conditions vs the HRRR and some others. I'm going to show two soundings for the same time at the same location. 






Shear profiles are similar but look at the temperature at the surface. The NAMs have been keeping the cloud cover on, keeping the surface temps down. You get weaker lapse rates from the surface (closer to moist adiabatic with the saturation there) and maybe the boundary layer isn't really mixing? 1900hurricane (really smart dude) pointed this out on another forum this morning I think he has a  point. You can see how the lowest wind barb on the NAM has way more of an east component to it, and how it doesn't line up quite as well with the strong winds around 850 vs the HRRR here. The idea here is the NAM isn't mixing the surface boundary layer out and all the storms are showing up elevated vs surface based, which is why the NAM is not showing much supercell type activity. 

I'm not sure why it wouldn't mix with the wind and heat that will be pumping in from the gulf, but it's something I'm making a note of for watching things tomorrow.  

NAM tends to run cooler and HRRR warmer but there isn't a "better" really. It does tells us to watch those surface observations tomorrow and see how warm it's getting and what direction the wind is coming from.

Kind of an interesting tweet from Reed Timmer here.  Seems like this is one of those scenarios where the potential of an outbreak is high, but the potential for a bust is rather good too.  Someone correct me if I’m wrong.  Everyone should still be watching obviously in the southeast.  But hopefully this is one event where the potential is not reached.

Reading from the SPC and discussions from the weather service offices in Mobile and New Orleans, there are still plenty of questions. My amateur opinion is if we get a high risk on the Day 1 outlook, it won’t be on the first update.

Thermalwind, your detail and analysis are incredible. However, some of us have trouble following. Can you explain in layman's terms? Thanks.