SPC Mesoscale Discussion

SPC MD 310

MD 0310 CONCERNING SEVERE POTENTIAL...WATCH LIKELY FOR SOUTEAST IA...NORTHEAST MO...AND MUCH OF WESTERN AND CENTRAL IL

Mesoscale Discussion 0310
NWS Storm Prediction Center Norman OK
0146 PM CDT Wed Apr 08 2020

Areas affected...souteast IA...northeast MO...and much of western
and central IL

Concerning...Severe potential...Watch likely 

Valid 081846Z - 082045Z

Probability of Watch Issuance...95 percent

SUMMARY...Thunderstorm development is expected in the next couple of
hours near southeast IA/northeast MO/west-central IL. Very large
hail and damaging winds will be the main threat associated with
these storms.

DISCUSSION...Strong heating across southeast IA into MO/IL ahead of
a surface low and cold front has resulted in weak to moderate
destabilization this afternoon. Strong boundary layer mixing has
been noted across IL, where morning dewpoints had been in the mid
50s F, generally are now in the mid 40s to low 50s F. Further south
across MO toward southern IL, dewpoints from the low 60s to upper
50s F were being maintained. Aloft, a plume of very steep midlevel
lapse rates has continued to spread eastward across the mid-MS
Valley, with 18z regional RAOBs showing 8-9 C/km lapse rates in
place. Cumulus development near a quasi-stationary boundary from
southeast IA into IL has been increasing, while additional deepening
of midlevel CU near the MO/IA border continues. Stronger height
falls have been noted recently across SD/NE into southern MN and
western IA as a lead shortwave impulse begins to eject across the
area ahead of the main upper trough. This is expected to provide
adequate forcing for thunderstorm development in the next couple of
hours. 

Initial development is expected to be semi-discrete, higher-based
supercells. Forecast hodographs continue to indicate long, straight
hodographs with speed shear increasing with height. In conjunction
with very steep lapse rates, large hail (some greater than 2 inches
in diameter) is expected. Low level lapse rates also are steep
across the region due to ample heating and mixing. This should act
to enhance downdrafts, and damaging wind gusts also are expected. As
frontal forcing increases later this evening, and through storm
outflow interactions, upscale growth into one or more bowing
segments is expected across parts of southeast MO into central IL,
further enhancing the damaging wind threat. Given generally dry low
levels resulting in higher-based storms, at least initially, the
tornado threat is expected to be rather marginal.

..Leitman/Guyer.. 04/08/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...LOT...ILX...LSX...DVN...SGF...DMX...EAX...

LAT...LON   41029220 41159207 41289159 41359108 41259048 41128995
            40938931 40628849 40138781 39788757 39568758 39328769
            38838828 38358943 38019044 37879151 37949201 38459236
            39509241 40759227 41029220 

SPC MD 309

MD 0309 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR FAR SOUTHEAST ARKANSAS...CENTRAL MISSISSIPPI...AND CENTRAL ALABAMA

Mesoscale Discussion 0309
NWS Storm Prediction Center Norman OK
1213 PM CDT Wed Apr 08 2020

Areas affected...Far southeast Arkansas...central Mississippi...and
central Alabama

Concerning...Severe potential...Watch possible 

Valid 081713Z - 081915Z

Probability of Watch Issuance...60 percent

SUMMARY...A cluster of storms moving out of southeast AR and into
central MS will continue to intensify through early afternoon.
Additionally, new storm development is likely across parts of
central MS and AL.

DISCUSSION...Recent satellite and radar trends show a cluster of
storms moving out of southeast AR and into central MS. Although
storm interactions have largely limited storm growth, a gradual
increase in storm intensity is likely through the early afternoon as
this cluster moves into central MS where negligible MLCIN and
1500-2000 J/kg MLCAPE are noted in recent SPC Mesoanalysis. Despite
weak low level winds, strong upper level flow has allowed for 45-55
knots of effective bulk shear and elongated hodographs that will
support organized convection, including discrete to semi-discrete
modes. In this environment, these storms will pose a risk for severe
hail and strong winds. 

Across central AL, visible satellite imagery shows a field of
agitated cumulus developing in response to boundary layer
destabilization. This destabilization is being driven by modest
northeastward low-level warm/moist advection and increasing daytime
heating - two factors that will continue through mid afternoon.
Although exact timing remains somewhat uncertain, convective
initiation is expected within the next 1-2 hours. As with the AR/MS
cluster of storms, any storms that develop in this region will pose
a risk for hail and wind (barring destructive interactions from
neighboring storms). A watch may be needed.

..Moore/Guyer.. 04/08/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...TAE...BMX...MOB...MEG...JAN...LZK...SHV...

LAT...LON   33439213 33749170 33849050 33878901 33848713 33858610
            33688558 33448535 33018527 32628514 32098510 31848525
            31598550 31548644 31538707 31548801 31608925 31759028
            31999091 32369137 32709175 32989206 33439213