U.S. Severe Weather Forecast (Convective Outlook)

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999 
acus01 kwns 190605 
swody1 
Storm Prediction Center ac 190603 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0103 am CDT sun Apr 19 2015 


Valid 191200z - 201200z 


..there is an enh risk of severe thunderstorms over parts of the S-central 
states... 


..there is a slight risk of severe thunderstorms from the southern Great Plains to 
the southeast... 


..there is a marginal risk of severe thunderstorms surrounding the slight risk and 
including the lower Ohio Valley... 


... 
Scattered severe thunderstorms are expected over parts of the 
south-central states mainly this afternoon and evening...with very 
large hail...damaging winds...and a few tornadoes. Isolated severe 
storms may also occur over parts of the southeast states through the 
period. 


... 
A broad upper trough will gradually shift east and amplify over the 
central Continental U.S. With a few embedded shortwave impulses. Of particular 
convective interest is an impulse currently over the Central High 
plains that should reach the confluence of the MS/Ohio rivers early 
Monday. Convectively induced impulses from East Texas to the northern Gulf may 
evolve NE within the broader cyclonic flow regime. Meanwhile...an 
intense upper-level jet will become centered from northwest Mexico 
bisecting Texas and into la. A complex surface evolution is expected 
given the multitude of middle-level impulses. A weak surface cyclone 
should track along the Red River today while large-scale 
cyclogenesis should occur primarily late in the period over parts of 
the Midwest. A dryline will likely mix east into East Texas and be overtaken 
by a cold front that should reach the lower MS valley to Texas Gulf 
Coast by 12z/Mon. 


..S-central states... 
In the wake of decaying early morning convection and ahead of the 
Central High plains shortwave impulse...diabatic heating should be 
pronounced. With a gradually eastward-expanding eml plume atop residual 
60s surface dew points emanating from S TX/la...a moderately to 
strongly unstable air mass should develop by late day in the 
arklatex area. Initial diurnally driven thunderstorm development will 
probably occur immediately ahead of the shortwave impulse over parts 
of central OK with the main hazard being severe hail. Additional 
storms should develop along the dryline near the weak surface 
cyclone by late afternoon as mlcin weakens. Setup should yield 
initially discrete supercells with primary hazards of very large 
hail and a couple tornadoes. Strengthening 700-500 mb west/swlys during 
the evening and predominant veered low-level winds should tend to 
favor upscale growth and bowing structures with a correspondingly 
increase in the damaging wind risk towards the lower MS valley. 


..southeast states... 
Widespread cloudiness and abundant showers with embedded thunderstorm 
activity are expected to be ongoing at 19/12z...aided by large-scale 
height falls and a few middle-level vorticity maxima. This along with 
poor middle-level lapse rates sampled by 19/00z radiosonde observations across the region 
will hamper diurnal destabilization. Nevertheless...a belt of 
strengthening low-level slys from the Florida Panhandle towards the central 
Appalachians should yield enlarged low-level hodographs and 
potential for a couple tornadoes and isolated damaging winds. 
Greater diabatic heating is anticipated farther west over parts of 
MS/Alabama where a remnant mesoscale convective vortex from a decaying mesoscale convective system over East Texas may focus 
afternoon/evening thunderstorm development and provide sufficient deep shear 
for organized updrafts. 


.Grams/cohen.. 04/19/2015 






Mesoscale Discussion


000 
acus11 kwns 190756 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 190756 
msz000-laz000-190930- 


Mesoscale discussion 0373 
National Weather Service Storm Prediction Center Norman OK 
0256 am CDT sun Apr 19 2015 


Areas affected...central/eastern la into western MS 


Concerning...severe potential...watch unlikely 


Valid 190756z - 190930z 


Probability of watch issuance...20 percent 


Summary...locally damaging winds/small hail will remain a 
possibility with eastward-moving quasi-linear convection across 
central la into portions of eastern la/western MS. Current thinking 
is the scenario will remain relatively marginal overall...but 
convective trends will continue to be monitored. 


Discussion...a 100+ mile north-south extensive squall line currently 
over north-central la will continue an east-northeastward 
progression overnight into additional portions of 
east-Central/Northeast la and western MS. In association with this 
squall line...measured 38 knots wind gusts were noted over the past 1-2 
hours in western la at both Shreveport and Beauregard. This 
quasi-linear convection appears to be aided by an mesoscale convective vortex...aside from 
the increasing influences of an upstream synoptic-scale trough/warm 
advection. Mesoscale convective vortex-related winds/rear inflow do not appear to be overly 
strong per WSR-88D vwp data from Shreveport/feet Polk. 
However...sufficient forcing/vertical shear will help sustain this 
relatively well-organized squall line east-northeastward toward 
western MS. Particularly since the boundary layer has cooled little 
over the past few hours...relatively weak inhibition/modest buoyancy 
will continue to support stronger updrafts/downdrafts within the 
line. Locally damaging winds will be a possibility. 


.Guyer/Edwards.. 04/19/2015 


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


Attention...WFO...Jan...lix...lch...shv... 


Latitude...Lon 32409314 32629241 32429066 31639059 30619214 30579312 
31469282 32409314