SPC AC 181626
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1126 AM CDT Mon Mar 18 2024
Valid 181630Z - 191200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
ACROSS CENTRAL FL AND MUCH OF THE FL ATLANTIC COAST...
...SUMMARY...
Isolated large hail and wind damage is possible this afternoon
across central Florida and along much of the Florida Atlantic coast.
...Central and eastern Florida Peninsula...
Morning water-vapor imagery indicates a shortwave trough over the
middle MS Valley digging southward into the base of a larger-scale
trough. This evolution will allow a related cold front to continue
southward across the central/southern FL Peninsula today. While the
FL Peninsula will generally be displaced from the associated
midlevel height falls/large-scale ascent, afternoon storm
development will be aided by ascent along the shallow frontal zone
and diurnal heating of a moist boundary layer amid leftover outflow
boundaries from morning convection.
The development of 40-50-kt effective shear (characterized by a
long/mostly straight hodograph) will support a mix of organized
multicells and transient supercells along/ahead of the
southward-moving front and mesoscale boundaries over the warm
sector. These storms will be aided by relatively steep midlevel
lapse rates atop a moist/destabilizing boundary layer. A deep CAPE
profile (with moderate surface-based buoyancy) and the
aforementioned hodograph will support large hail up to 1.75 inches
and locally severe gusts near 60 mph with any sustained/organized
storms. Additionally, a brief tornado cannot be entirely ruled out
along the east coast, where locally backed flow may contribute to
slightly more low-level hodograph curvature. However, veered
low-level flow ahead of the front (along with a lack of large-scale
ascent) and deep westerly flow may both limit the coverage of
organized storms, and convective residence time in the most
favorable environment -- warranting the maintenance of the Marginal
risk.
...Arizona and southern California...
A mid/upper-level low centered over west-central AZ will move slowly
westward into southern CA today. On the eastern periphery of this
feature, 25-30-kt midlevel southeasterlies combined with cold
temperatures aloft/steep midlevel lapse rates could favor a couple
strong/loosely organized storms capable of mainly small hail and
locally strong gusts. Along the northern and western periphery of
the upper low, a stronger belt of midlevel flow (around 45 kt)
accompanying a westward-moving impulse will overspread west-central
AZ into southern CA this afternoon. Over parts of southern CA
(particularly west of the Desert), upper 40s/lower 50s dewpoints
beneath the steep lapse rates will contribute to more substantial
buoyancy amid 30-40 kt of effective shear. While convective
evolution/sustenance is uncertain given offshore/downslope flow
across this area, there is a conditional risk of near-severe hail
and gusty winds if any longer-lived storms develop. Overall,
confidence in this scenario is too low to add unconditional
5-percent hail/wind probabilities with this outlook.
..Weinman/Goss.. 03/18/2024
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