U.S. Severe Weather Forecast (Convective Outlook)

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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 
SC/NC... 


..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. 


..Midwest/Ohio Valley... 
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. 


.Jewell.. 03/30/2017 


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. 


..Great Basin... 
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. 


$$ 

Mesoscale Discussion


000 
acus11 kwns 302241 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 302240 
kyz000-inz000-tnz000-302345- 


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 
western/middle Tennessee 


Concerning...Severe Thunderstorm Watch 103... 


Valid 302240z - 302345z 


The severe weather threat for Severe Thunderstorm Watch 103 
continues. 


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 
watch issuance. 


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. 


.Picca.. 03/30/2017 


..please see www.Spc.NOAA.Gov for graphic product... 


Attention...WFO...lmk...ohx...ind...pah...Meg... 


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