U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 231950 
Storm Prediction Center ac 231949 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0249 PM CDT Mon Apr 23 2018 

Valid 232000z - 241200z 

..there is a marginal risk of severe thunderstorms across portions 
of the Central High plains... 

..there is a marginal risk of severe thunderstorms across parts of 
the southeast... 

A few strong to severe storms are possible across parts of Georgia 
and South Carolina, and over the Central High plains. 


No large-scale changes are required for severe probabilities this 

However, have lowered thunder probabilities across much of Wyoming to 
better reflect large-scale forcing/baroclinic zone progression 
across this region. A few strong wind gusts may accompany convection 
as it spreads into the NE Panhandle this afternoon. 

Thunderstorm probabilities have also been lowered along the Florida Gulf 
Coast into southeastern Alabama where large-scale subsidence is now 
predominant. Otherwise, a few strong storms have developed over 
portions of central Georgia and this activity could generate gusty winds 
per 5% severe probs across this region. 

.Darrow.. 04/23/2018 

Previous discussion... /issued 1117 am CDT Mon Apr 23 2018/ 

A persistent upper low is centered over west TN, with 
west-southwesterly mid level winds across the southeast states. The 
primary occluded surface low is beneath the upper low, with an 
occluded front extending southeastward into Georgia. The primary region 
of concern for a few strong/severe storms today will be in vicinity 
of a warm front extending from its intersection with the occluded 
boundary into SC. 

Visible satellite imagery shows breaks in the clouds along and south 
of the warm front, where dewpoints in the mid 60s will yield 
afternoon MLCAPE values around 1000 j/kg. This should result in 
scattered thunderstorm development this afternoon. Forecast 
soundings suggest that mid-level lapse rates will be rather weak, 
limiting updraft strength and overall severe threat. However, 
sufficient deep layer shear will promote organized storm structures 
capable of hail and/or gusty winds. This threat should diminish a 
few hours after sunset. 

The strongest low-level shear profiles will be in vicinity of the 
warm front over central/eastern SC. Storms in this area would also 
have some potential for isolated/brief tornadoes. Current 
indications are that the overall setup is sufficiently covered by 
the ongoing marginal risk category. 

Water vapor loop shows a progressive shortwave trough moving into 
western Wyoming. Lift associated with this feature will begin affecting 
eastern Wyoming and northern Colorado this afternoon. Surface dewpoints will 
only be in the upper 30s to lower 40s. However, strong heating will 
combine with very steep lapse rates to yield just enough cape for 
thunderstorms later today. Cold temperatures aloft and favorable 
effective shear suggest a few rotating storms or bowing structures 
capable of hail and/or gusty winds. 


Mesoscale Discussion

acus11 kwns 232000 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 231959 

Mesoscale discussion 0286 
National Weather Service Storm Prediction Center Norman OK 
0259 PM CDT Mon Apr 23 2018 

Areas affected...portions of central/eastern Georgia and far 
southern South Carolina 

Concerning...severe potential...watch unlikely 

Valid 231959z - 232100z 

Probability of watch issuance...20 percent 

Summary...a few thunderstorms may be capable of locally damaging 
winds, marginally severe hail, and perhaps a brief tornado through 
this evening. Watch issuance is not expected. 

Discussion...given considerable insolation and boundary-layer 
moistening, isolated to widely scattered thunderstorms have 
gradually developed over parts of Georgia this afternoon. These 
cells have organized within confluent bands extending southwest of a 
warm front, where the air mass is characterized by MLCAPE values 
upwards of 1000-1500 j/kg. Although mid-level lapse rates are not 
particularly steep, effective shear around 35-45 kt may yield 
marginally severe hail in the strongest cores. Pockets of dry 
mid-level air and steepening 0-3km lapse rates could favor localized 
damaging wind gusts into the early evening as well. Lastly, weak 
background low-level winds (and related storm-relative helicity) 
should limit the tornado threat; however, locally backed surface 
flow near the warm front could focus a small corridor of brief 
tornado potential into this evening. 

.Picca/Hart.. 04/23/2018 

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


Latitude...Lon 32698447 33198448 33438442 33678423 33788387 33808308 
33618202 32898066 32558036 32438051 32358058 31298141 
31358214 31748371 32298444 32698447