• Tue. May 21st, 2024

Significant Severe Weather Event Today Including Possible Strong Tornadoes South Mississippi

The deep mid level closed low over the central Plains will be slowto push east and into the upper MS Valley by this evening and as
this occurs the trough will begin to pivot taking on a neutral andeventually a negative tilt. The cold front which is currently slowly
moving into the Lower MS Valley will continue to be slow thismorning but will respond and begin to accelerate across the Lower MS
Valley and into the southeastern CONUS late this afternoon and thisevening. As the trough begins to pivot we expect to see the line of
convection really begin to slow up (possibly pause/stallmomentarily). Additional development may begin ahead of the line and
it is at that point that the severe and heavy rain threat starts toincrease especially the farther west this pause in movement occurs.
Scattered to numerous showers and thunderstorms will thendevelop/redevelop along and ahead of the line late this morning and
as this starts to congeal into a QLCS the overall forward motionshould begin to speed up once again. The line is expected to be in
coastal MS be late afternoon/early evening and should finally pushinto AL late tonight.

Overall the severe threat is impressive. With the main line expectedto slow down there will be time for the area to heat up and become
quite unstable. MLCAPE of around 2000 J/kg and 0-3km cape of 150J/kg or greater for much of the northern half of the area is
expected. Showalters will be around -3 while LI`s could be around -6to -7. Mid level lapse rates will be around -6.5 C/km. The dynamics
will be strong with this system. Mid level winds will slowlyincrease with 50-60kts nudging in around late morning and through
the afternoon but the impressive feature will be a strengthening LLjet of 50-60kts right over the CWA. In addition we will be under the
RRQ of the upper jet with very strong diffluence collocated with theLL jet. The increase in the wind field will also lead to a very
favorable shear environment. Both 0-1 and 0-3km SRH look to bearound 200-350 m2/s2 while 0-6km Bulk shear of 40-50 kts will be in
place. A lot of these features appear to occur around the same timeframe of 15-21/0z especially along and north of the 10/12 corridor
and east of a line from Baton Rouge to Amite county.

We expect the line of convection to begin to redevelop as this LLjet starts to strengthen late this morning. Additional storms out
ahead of the main line are possible as well. It is the initialredevelopment of the line and any storms out ahead that pose the
greatest concern. These storms will be in the best shear environmentand capable of producing tornadoes some of which could be strong. We
do expect things to slowly combine into a QLCS as it pushes throughSELA and into coastal MS late this afternoon. As the convection
evolves into a QLCS the straight-line wind threat will become the dominant concern however there will still be more than sufficient
shear in place for embedded tornadoes. Even if storms don`t develop out ahead of the main line I am quite concerned with the low level
cape combined with the high 0-1 to 0-3 SRH. If the line redevelops quickly becoming the dominant feature the combination of the LL cape
and high shear values could enhance the risk of seeing tornadoes within the line.

We remain concerned with the heavy rainfall threat possibly leading to flash flooding and river flooding. Again we are expecting the
main line to pause as this happens there will be a window for multiple storms to move over the same area. These storms will have a
very rich moisture environment to work with as PWs could be just under 2". That combined with the strong LL jet pumping high h85
theta E values and strong diffluence aloft will lead to very efficient storms. Overall we are still expecting widespread 2-4" of
rain with locally higher amounts possibly exceeding 6". A flash flood watch is already out and will not make any adjustments to it.

Due to the strengthening LL jet winds will be quite gusty at the sfc. This is especially so along the coast where strong winds will
come in right off the water. With that NWS has issued a wind advisory
for all coastal ounties in Mississippi.

All convection should finally exit coastal MS during the evening hours with much drier and cooler air quickly filtering in. The
trough axis will be east of the area by midday tomorrow and we will then move under northwest flow for the next 48 hours. This will keep
use cool and dry with temps well below normal Sunday and Monday morning. Highs Sunday and lows Monday morning could be 15 to almost
20 degrees below normal in some locations. We will begin a slow moderation Monday night and Tuesday with weak ridging aloft late
Tuesday and Tuesday night. Another weak cold front will approach Wednesday night as a strong disturbance moves across the central
Plains and into the Upper MS Valley. That said the front will likely hang up and with pretty much zonal flow aloft we will not see much
if any impact from this.

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