- Day Three
acus01 kwns 302051
Storm Prediction Center ac 302050
Day 1 convective outlook amend 1
National Weather Service Storm Prediction Center Norman OK
0350 PM CDT Thu Mar 30 2017
Valid 302043z - 311200z
..there is an enhanced risk of severe thunderstorms across parts of
the Ohio Valley and Midwest...
..there is a slight risk of severe thunderstorms from the Midwest
southward into the Florida Panhandle...
..there is a marginal risk of severe thunderstorms over a large
part of the Midwest into the southeastern states including coastal
..there is a marginal risk of severe thunderstorms across parts of
the eastern Great Basin...
Amended for NC/SC area late tonight
Scattered severe storms are most likely across the Midwest and Ohio
Valley this afternoon into evening, with other severe storms along
the central Gulf Coast. Damaging winds, isolated weak tornadoes, and
hail will be possible in these areas.
Isolated cells currently exist across central Indiana near a sharp
E-W oriented warm front. Locally backed surface winds along this
front may enhance tornado potential briefly for any storms
interacting with it, before they cross over into the cooler more
stable air. Otherwise, scattered storms continue to evolve along the
main cold front to the west, from southern Illinois into the lower MS
valley with wind and marginal hail threat. Tornado threat looks to
be reduced across much of Kentucky and Tennessee due to strong boundary-layer
mixing which both reduces moisture and truncates the lower parts of
the hodograph. For more information see mesoscale discussion 379.
..Alabama into the Florida Panhandle...
A renewed cluster of cells has developed across southern Alabama in a
region of strong heating and where lapse rates are quite steep along
with long hodographs favorable for supercells and large hail. These
cells were ahead of an approaching MCS, which continues to surge
eastward across southern Alabama and into the western Florida Panhandle. While
hodographs are long, low-level shear is not particularly strong,
suggesting low end tornado threat. However, the orientation of the
deep-layer shear vectors are largely parallel to the approaching
line of storms, such that it remains possible that a brief/weak
tornado could still occur. Otherwise, hail would appear to be the
main threat. For more information see mesoscale discussion 380.
..coastal eastern SC and southern NC late tonight...
Visible satellite imagery shows a boundary extending eastward from
southern SC with mid 60s dewpoints to the south of it. As the upper
trough approaches later tonight, this moisture will move farther
inland, an Orient with an increasing low level jet with 30-40 kt at
850 mb. Several cams show the potential for isolated supercells to
form, perhaps over the water and move northward through early Friday
morning. Instability will not be strong but perhaps sufficient to
support a localized severe risk. Forecast soundings show favorable
hodographs for supercells, and perhaps a localized tornado threat.
Thus, have upgraded the tornado probabilities in this area.
Previous discussion... /issued 1150 am CDT Thu Mar 30 2017/
..Midwest and Ohio/Tennessee valleys...
A closed mid/upper-level low will continue a slow general eastward
progression from the lower MO valley and Ozarks toward the lower Ohio
River valley through tonight. A related surface low will continue to
develop east-northeastward from east-central MO into central IL,
while a warm front advances northward across eastern Illinois and much of
in/OH. Overall buoyancy will remain modest today and cloud cover has
remained semi-prevalent into midday across the warm sector. However,
some cloud breaks are noted near/just east of the MS river with
mid/upper 50s and some lower 60s f surface dewpoints otherwise
expected to expand northward in tandem with the warm front.
As gradual air mass destabilization occurs, storms may first
intensify across far eastern MO into southern Illinois just ahead of the
surface low and in concert with the aforementioned cloud breaks at
late morning. Additional warm sector or near-warm-frontal-related
development should also occur this afternoon into in/Ohio this
afternoon, while other storms should form near the cold front across
KY/TN. While buoyancy will not be robust in most areas, long/largely
unidirectional hodographs, albeit with some near-1km above ground level hodograph
curvature, will support a mixed Mode including supercells and fast
northeastward-moving bows. Severe hail and damaging winds will be
possible, with a least some tornado risk as well, particularly near
the warm front where low-level srh will be maximized.
..Gulf Coast states/lower MS River Valley...
12z upper-air data and contemporary surface observations/visible
satellite imagery show that considerable convective overturning has
occurred across parts of the region via an overnight/early morning
mesoscale convective system. Ahead of a slow-moving convective cluster across southeast MS
and coastal eastern la at late morning, the main severe risk should
be confined to far southeast MS into southern Alabama/Florida Panhandle and
eventually southwest Georgia. For additional short-term details, see
mesoscale discussion 377.
Farther west, in the wake of the early-morning MCS, some additional
development may occur near the north/south-oriented cold front this
afternoon. However, persistent cloud cover, modest
moisture/buoyancy, and limited near-frontal convergence all imply
that any near-frontal severe risk later this afternoon/evening
should remain limited across the lower MS valley vicinity.
A band of showers and isolated storms is expected to form along a
strong cold front attendant to an amplifying shortwave trough.
Although buoyancy will be scant, well-mixed thermodynamic profiles
ahead of the front should support downward momentum transport of
robust flow aloft and may yield isolated severe wind gusts.
acus11 kwns 302241
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 302240
Mesoscale discussion 0383
National Weather Service Storm Prediction Center Norman OK
0540 PM CDT Thu Mar 30 2017
Areas affected...portions of the Ohio Valley southward to
Concerning...Severe Thunderstorm Watch 103...
Valid 302240z - 302345z
The severe weather threat for Severe Thunderstorm Watch 103
Summary...a broken band of thunderstorms will push eastward out of
the current Severe Thunderstorm Watch this evening. While a marginal
damaging-wind risk may persist downstream of this watch,
thunderstorms should remain disorganized enough to preclude new
Discussion...strong to briefly severe thunderstorms across portions
of the Ohio Valley southward to western Tennessee are progressing
eastward early this evening. While relatively strong southerly
Uni-directional flow aloft and mixed low-level profiles may favor an
isolated damaging-wind threat through mid evening, convection should
remain relatively disorganized. This expectation is based on the
observation of veered near-surface flow noted in regional
observations and vwp data ahead of the line, as well as the narrow
buoyancy observed in the 20z ohx sounding and various forecast
soundings. Additionally, efficient diabatic cooling will reduce
surface-based buoyancy through this evening. In turn, updraft
accelerations should suffer from weak low-level convergence and
considerable dry-air entrainment, likely precluding greater
convective organization and the need for a downstream watch.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 36718825 38438760 38568701 38698587 38588539 36928554
35698634 35448798 35778856 36718825