U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 211959 
Storm Prediction Center ac 211958 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0258 PM CDT Sat Apr 21 2018 

Valid 212000z - 221200z 

..there is a slight risk of severe thunderstorms over a small part 
of North Texas... 

..there is a marginal risk of severe thunderstorms over portions of 
Texas into Louisiana... 

Isolated severe thunderstorms are possible from 
northwest/north-central Texas this afternoon to East Texas and 
northern Louisiana tonight. 

For short-term details across northwest/north-central Texas this 
afternoon, please see mesoscale discussion 280. Elsewhere, no significant changes 
were made to the previous outlook. 

A sporadic lightning strike will remain possible this afternoon 
across northwest Montana in association with an upper-level impulse, 
where large-scale ascent has contributed to scattered showers. 
Coverage is expected to remain below 10 percent. 

.Bunting.. 04/21/2018 

Previous discussion... /issued 1049 am CDT Sat Apr 21 2018/ 

An upper low is centered today over eastern Colorado/western KS, with 
band of strong westerly flow around the south side of the low across 
Texas. A large area of showers and thunderstorms is affecting much of 
OK and north-central Texas within the strong low-level advection 
regime. This activity should spread northeastward and away from 
North Texas by mid afternoon. 

In the wake of the morning activity, some heating/destabilization is 
expected west of ftw, leading to an area of sufficient cape and 
low-level convergence for isolated thunderstorm development. 
Low-level shear will decrease through the day as winds veer/weaken, 
but the consensus of 12z cam solutions suggests 1 or 2 strong/severe 
storms will develop in this small area, capable of large hail. The 
threat should focus in the 22-02z period. After that, storm 
intensities are expected to diminish but overall mesoscale 
organization may increase as storms become oriented into a line. A 
marginal risk of gusty winds or hail will persist through much of 
the night as storms spread into East Texas and northern la. 


Mesoscale Discussion

acus11 kwns 211841 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 211841 

Mesoscale discussion 0280 
National Weather Service Storm Prediction Center Norman OK 
0141 PM CDT Sat Apr 21 2018 

Areas affected...north-central Texas 

Concerning...severe potential...watch unlikely 

Valid 211841z - 212115z 

Probability of watch issuance...20 percent 

Summary...a severe threat is expected to develop across parts of 
north-central Texas this afternoon. Large hail and damaging wind 
gusts will be possible with the strongest of storms. However, the 
severe threat should remain isolated and weather watch issuance 
appears unlikely. 

Discussion...the latest surface analysis shows a 1008 mb low over 
the Low Rolling Plains of West Texas. A warm front extends eastward 
from the low across north-central Texas. South of this boundary, 
surface dewpoints are generally in the upper 50s and lower 60s f. 
This is contributing to a narrow corridor of weak instability from 
the Texas Hill country northward into the Low Rolling Plains where 
MLCAPE values are estimated in the 250 to 500 j/kg range according 
to objective analysis. 

Surface-based convection has initiated to the northwest of Abilene, 
Texas over the last hour. This convection is located just to the west 
of the strongest instability and near a pronounced vorticity Max 
analyzed by the rap. The Abilene WSR-88D vwp shows strong deep-layer 
shear with 0-6 km shear estimated to be from 50 to 55 kts. In 
addition, forecast soundings suggest an area of steep mid-level 
lapse rates exists near the instability Max. These factors should be 
supportive of strong updrafts capable of producing hail. Isolated 
large hail could occur with any storm that develops persistent 
rotation. An isolated wind damage threat may also develop mainly 
after convection matures later this afternoon especially if a short 
line segment can organize. Isolated storm coverage and the small 
affected area make weather watch issuance unlikely. 

.Broyles/Hart.. 04/21/2018 

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


Latitude...Lon 32329942 31869804 31829722 32269689 32779688 33209734 
33319801 33339919 33259969 33099984 32829984 32329942