U.S. Severe Weather Forecast (Convective Outlook)

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000 
acus01 kwns 191252 
swody1 
Storm Prediction Center ac 191251 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0751 am CDT Wed Jun 19 2019 


Valid 191300z - 201200z 


..there is an enhanced risk of severe thunderstorms 
north-Central/Northeast Texas...northwest la...southwest Arkansas... 


..there is a slight risk of severe thunderstorms Lee of the Big 
Horn Mountains to the Black Hills... 


... 
Severe thunderstorms are most likely across north-Central/Northeast 
Texas and The Ark-la-tex region during the late afternoon and 
evening. Destructive hail and wind, along with a few tornadoes are 
possible. 


..TX to the MS/OH/TN valleys... 
Complex forecast with multiple episodes of severe storms anticipated 
during the period. Primary changes are to increase damaging wind 
(including sig) probabilities for the enhanced slight risk, expand 
marginal and slight risk areas in parts of la/MS/TX, and expand 
tornado probabilities into the lower/mid-MS valleys. An upgrade to 
moderate risk via wind and/or hail may be needed in later outlooks. 


A decaying mesoscale convective system is ongoing, recently splitting into two active areas 
of convection in the Ozarks and Ark-la-tex. Reintensification is 
possible with The Ark-la-tex complex as boundary-layer heating 
increases. Even if full decay occurs, redevelopment along remnant 
outflows is likely towards midday/early afternoon downstream of both 
areas across the lower/mid-MS valleys as the downstream air mass 
characterized by upper 60s to mid 70s surface dew points 
destabilizes. 25-35 kt 500-mb westerlies will support several 
multicell clusters with scattered damaging winds as the primary 
hazard this afternoon into the Ohio and Tennessee valleys. 


Remnant west/east-oriented outflow boundary in the wake of the 
morning mesoscale convective system should drift north across north-Central/Northeast Texas 
into perhaps southeast OK by late afternoon. South of this boundary, 
intense diabatic heating coupled with a plume of 70s surface dew 
points over East Texas will support a strong to extremely unstable air 
mass with MLCAPE in excess of 3500 j/kg. By late afternoon, ascent 
should increase downstream of a minor mid-level impulse that is 
currently approaching from the southern rockies. This should aid in 
convective initiation along the outflow boundary, as well as near 
the dryline bulge in the Texas Big Country. 40-50 kt effective shear 
with pronounced speed shear in the mid to upper-levels will support 
a risk for very large hail with initial supercells. This activity 
should consolidate into yet another mesoscale convective system during the evening, aided by 
a strengthening southwesterly low-level jet, with an increasing 
threat for severe wind gusts (a few could be significant given the 
large buoyancy). Tornado risk should be maximized during the first 
couple hours of supercell formation in a relatively narrow corridor 
near the outflow boundary. 


Later tonight, this mesoscale convective system may spread east or separate clusters will 
develop east as warm advection strengthens eastward into the Tennessee 
Valley. An isolated threat for severe hail/wind may persist along 
the eastern periphery of the elevated mixed-layer. 


Near the confluence of the MS/Ohio rivers, in the wake of early-day 
convection, a separate cluster of severe storms may develop towards 
early evening. This region will lie south of the primary surface 
cyclone that should consolidate and gradually deepen as it tracks 
east along the I-70 corridor. If adequate boundary-layer heating can 
occur in the absence of substantial overturning from the morning 
convective activity, a few supercells are possible with a risk for 
all hazards. 


..northern Wyoming to western South Dakota... 
Have upgraded to slight risk given the potential for a couple 
long-track supercells this evening into tonight. 


A shortwave trough will amplify from British Columbia across the 
northern rockies as a 50-60 kt mid-level jet spreads east across the 
northwest. This will strengthen forcing for ascent and yield 
sustained thunderstorm development by late afternoon along the Wyoming/Montana 
border. While boundary-layer moisture will be limited and the 
boundary-layer will not be particularly warm, increasingly elongated 
hodographs will favor potential for splitting supercells, a couple 
of which could be long tracked. A swath of severe hail with 
localized severe wind gusts appears possible. 


.Grams/Gleason.. 06/19/2019 


$$ 

Mesoscale Discussion


000 
acus11 kwns 191111 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 191110 
laz000-txz000-191245- 


Mesoscale discussion 1132 
National Weather Service Storm Prediction Center Norman OK 
0610 am CDT Wed Jun 19 2019 


Areas affected...portions of East Texas into northwestern la 


Concerning...severe potential...watch unlikely 


Valid 191110z - 191245z 


Probability of watch issuance...20 percent 


Summary...an ongoing line of storms may pose an isolated 
strong/gusty wind threat in the short term. Watch issuance remains 
unlikely. 


Discussion...two previously separate lines of storms (one from 
southern OK and the other from north-central tx) have recently 
merged across East Texas. A corresponding increase in radar 
reflectivity and cooling cloud tops have recently been noted. Strong 
inbound velocities are also present across East Texas along the apex of 
this line per kshv radar. These storms are encountering mainly 
elevated instability, with MUCAPE likely ranging from 1000-2000 j/kg 
from latest mesoanalysis estimates. However, the low-level inversion 
across East Texas and northwestern la is likely shallow (about 800-1000 
ft agl) based on rap forecast soundings. There is some potential for 
strong/gusty downdraft winds to breach the low-level inversion and 
reach the surface given the strong velocities occurring on radar. 
Observed gusts from various stations have generally ranged from 
35-40 kt across East Texas over the past hour or so. But, isolated 
strong to perhaps damaging winds could still occur. Watch issuance 
remains unlikely in the short term, but convective trends will 
continue to be monitored. 


.Gleason/grams.. 06/19/2019 


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


Attention...WFO...shv... 


Latitude...Lon 32009535 32289490 32709449 32989431 32989339 32839273 
31919270 31459326 31329427 31799532 32009535