U.S. Severe Weather Forecast (Convective Outlook)

Day Three

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Storm Prediction Center ac 210043 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0743 PM CDT Wed Jun 20 2018 

Valid 210100z - 211200z 

..there is a marginal risk of severe thunderstorms portions of 
central and eastern Oregon...central Illinois...coastal 
Carolinas...and the Florida Big Bend... 

A few strong to locally severe thunderstorms are this evening from 
parts of the coastal Carolinas, central Illinois, Florida Big Bend, 
and Oregon. 

A mid-level low over NE this evening will slide slowly southeast to 
the Iowa/MO border by daybreak while a mid-level anticyclone is 
centered over the northern Gulf of California. A weak impulse evident in 
evening water-vapor imagery is moving through south-central or. 
Scattered thunderstorms will likely persist into the late evening. 
A few of the stronger storms may be capable of a strong to locally 
severe gust and marginally severe hail. This activity will weaken 
coincident with diurnal cooling this evening. Farther east, a 
couple of thunderstorms embedded within clusters and propagating on 
outflow over the coastal Carolinas and the Florida Big Bend may pose a 
risk for gusts in the 45-60 mph range --capable of damage-- for the 
next 1-2 hours before weakening. 

Elsewhere, a weak squall line over the middle MS valley continues to 
move into a less unstable airmass over northern Illinois and the 00z ilx 
radiosonde observation showed a tropospheric profile nearly saturated from the surface 
to 500mb but with 2600 j/kg MLCAPE. A strong gust or two may occur 
before this activity also weakens during the next 1-2 hours. 

.Smith.. 06/21/2018 


Mesoscale Discussion

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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 202341 

Mesoscale discussion 0808 
National Weather Service Storm Prediction Center Norman OK 
0641 PM CDT Wed Jun 20 2018 

Areas affected...northeast la...southwest Arkansas 

Concerning...severe potential...watch unlikely 

Valid 202341z - 210045z 

Probability of watch issuance...5 percent 

Summary...a brief tornado or two is possible over the next hour or 
so across northeast la and southwest Arkansas. 

Discussion...despite calm surface winds, high Theta-E airmass 
(characterized by temperatures in the low 80s and dewpoints in the 
mid 70s) is contributing to strong low-level cape (i.E. 0-3 km 
MLCAPE over 75 j per kg based on the latest mesoanalysis). 
Additionally, a narrow corridor of relatively confluent, slightly 
stronger low-level likely exist across northeast la and southwest 
Arkansas. This slightly enhanced low-level flow is likely contributing to 
a maximum in low-level shear and storm-relative helicity. Latest 
mesoanalysis estimates 0-1 km bulk shear is near 25 kt and 0-1 km 
srh is over 150 m2/s2. This favorable low-level shear coupled with 
the very moist, tropical airmass and strong low-level instability 
may result in a brief tornado or two. Marginal and isolated nature 
of the threat precludes the need for a watch. 

.Mosier/grams.. 06/20/2018 

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


Latitude...Lon 32989406 33479295 33279247 32839255 32369342 32429426