Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Mon Mar 19 2018
Valid 191200Z - 201200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS PARTS OF
TN...NORTHEAST MS...NORTHERN AL...AND NORTHWEST GA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
ENHANCED RISK FROM THE TENNESSEE VALLEY TO THE SOUTHEAST STATES...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK FROM THE MID-SOUTH AND SOUTHERN KY TO NORTHERN FL...
...SUMMARY...
Tornadoes (some strong), very large hail, and damaging winds are
expected across parts of middle Tennessee into northeast
Mississippi, northern and central Alabama to western Georgia.
Severe storms will be possible into southern Georgia and northern
Florida.
...Synopsis...
A compact closed cyclone and attendant shortwave trough will weaken
this forecast period as this system remains progressive, reaching
the lower Ohio and Tennessee Valleys by 20/00Z and into the upper
Ohio Valley by 12Z Tuesday. Meanwhile, a pair of shortwave troughs
and accompanying midlevel jets is expected to phase across the
southern Plains this afternoon into the evening, with further
amplification of this trough into the middle Mississippi Valley to
the northwest Gulf Coast region. A surface low, attendant to the
lead trough, will track from northeast OK to western middle
Tennessee by late this afternoon (by 21Z), with a cold front
extending southwest through northeast MS to southern LA. At 12Z
today, a warm front should extend through central AR and MS into
southern AL/GA. An increase in southwesterly winds across the lower
Mississippi and Tennessee Valleys to the Southeast States will
result in a moistening warm sector as the warm front advances to the
northeast. This boundary should extend from the surface low in
middle TN south-southeast through northern and central AL to
south-central GA by mid-late afternoon, before advancing farther
northeast tonight.
...TN/northeast MS/AL/northern and western GA...
Elevated showers and thunderstorms are expected to be ongoing at the
start of D1 within a zone of warm advection and strong forcing for
ascent attendant to a strong southwesterly low-level jet and the
lead compact shortwave trough moving through southern MO and AR. As
the deep-layer ascent spreads east into the lower Tennessee Valley
this morning to early afternoon, the early day convection will shift
into the Mid-South, likely delineating the northwest extent of
stronger destabilization. Surface dew points in the 60s and
steepening lapse rates will result in moderate instability across
the warm sector.
New storm development is expected by mid afternoon in western middle
TN into northeast MS as the surface low and cold front reach these
areas. This will coincide with strong forcing for ascent spreading
across the western extent of moderate instability. Strengthening
deep-layer winds (westerly at 50-70 kt in the 500-700-mb layer and
southwesterly at 40-50 kt at 850 mb shifting across MS into AL) this
afternoon will prove favorable for supercells. Given effective SRH
will exceed 300-400 m2/s2, a strong tornado or two will be possible
from parts of middle TN into northeast MS, northern AL and northwest
GA late this afternoon into the early evening, as the cold front
advances east. The favor thermodynamics and strong bulk shear will
support very large hail, as well.
Farther south across central into southeast AL, organized storms
including supercells will prove favorable for all severe hazards as
activity forms along the warm front this afternoon.
...Southern and eastern GA into northern FL...
Weak height falls across this region where the environment should
become moderately unstable may prove favorable for thunderstorm
development. Strengthening deep-layer westerlies across this region
will result in favorable shear for organized storms producing all
severe hazards into the early evening.
