U.S. Severe Weather Forecast (Przegląd konwekcyjny)

Day Three

acus01 kwns 260549 
Storm Prediction Center ac 260548 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1248 am CDT Wed Apr 26 2017 

Valid 261200z - 271200z 

..there is a moderate risk of severe thunderstorms across the 
arklatex region... 

..there is an enhanced risk of severe thunderstorms from northeast 
Texas to extreme southern Missouri... 

..there is a slight risk of severe thunderstorms from southern 
Louisiana to southeast Missouri... 

..there is a marginal risk of severe thunderstorms from the Upper 
Texas coast to Northwest Indiana... 

Severe thunderstorms are expected across the lower Mississippi 
Valley Wednesday. Tornadoes, large hail, and damaging winds should 
focus from northeast Texas across southern Arkansas and northern 
Louisiana primarily during the afternoon hours. Isolated severe 
thunderstorms may extend as far north as Illinois and into the 
central Gulf states during the overnight hours. 

..lower MS valley... 

Early-morning water vapor/radar imagery depict a well defined upper 
circulation over northeast nm shifting east-southeast in line with 
late-evening model guidance. High-level flow is increasing across 
the southern rockies and 500mb speeds on the order of 75kt will 
translate into central Texas later today. This feature will induce 
significant mid-level height falls across the lower MS valley and 
encourage strengthening low level jet over la/Arkansas by 18z. 

26/00z observed soundings across Texas depict very steep mid-level 
lapse rates, on the order of 8.5-9 c/km, and this lapse-rate plume 
should spread across the arklatex region prior to convective 
development. Current thinking is thunderstorms will struggle to 
develop across much of Texas due to significant cinh and this should 
allow air mass to destabilize across the MDT risk region as surface 
temperatures warm to near 80f with near 70f dew points. Forecast 
NAM soundings by early afternoon depict SBCAPE in excess of 3000 
j/kg across northeast Texas where convection should initiate prior to 
frontal passage. Shear profiles strongly favor supercells, though 
mid-level height falls and slightly backed mid-level flow could 
eventually lead to a more complex mesoscale convective system as the trough ejects toward 
the mid-south after dark. Very large hail could accompany the 
supercells across the arklatex region and tornadoes appear possible. 
Strong/severe convection should spread into the central Gulf states 
during the evening/overnight hours as entrance region of upper jet 
shifts into this region during the latter half of the period. 

..mid MS valley... 

Southwest-northeast oriented squall line has evolved from eastern OK 
into southwest MO early this morning. Models suggest this activity 
should be ongoing at the beginning of the period but possibly a bit 
farther east than deterministic data would suggest. This early-day 
convection will certainly disrupt and overturn buoyancy across much 
of the mid Mississippi Valley. It's not entirely clear how unstable 
MO/Illinois region will be ahead of this activity and forecast soundings 
suggest poor lapse rates and weak buoyancy. For these reasons have 
lowered severe probs across much of Illinois/MO due to limited 
instability. Otherwise, forced squall line could certainly produce 
isolated severe wind gusts but the more robust convection should 
remain across the Ozark Plateau and points south. 

.Darrow/leitman.. 04/26/2017 


Mesoscale Discussion

acus11 kwns 260643 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 260642 

Mesoscale discussion 0557 
National Weather Service Storm Prediction Center Norman OK 
0142 am CDT Wed Apr 26 2017 

Areas affected...eastern Oklahoma...northwest Arkansas...southern 

Concerning...Severe Thunderstorm Watch 160... 

Valid 260642z - 260845z 

The severe weather threat for Severe Thunderstorm Watch 160 

Summary...a severe threat is expected to continue for several more 
hour across southwest Missouri, northwest Arkansas and eastern 
Oklahoma. Wind damage and isolated large hail will be the primary 
threats. Severe storms may eventually affect areas just to the east 
of ww 160 but any severe threat should be too isolated for 
additional ww issuance. Local extension may be needed across parts 
of southern Missouri. 

Discussion...the latest radar analysis shows a nearly continuous 
line of strong to severe storms extending from southwest of 
Springfield, Missouri southwestward into southeastern Oklahoma. The 
rap is analyzing moderate instability ahead of the line with MLCAPE 
estimated from 1000 to 2000 j/kg. This combined with lift associated 
with a 40 to 55 kt low-level jet will help to maintain the line of 
storms for several more hours. In addition, forecast soundings early 
this morning across northwest Arkansas have moderate deep-layer 
shear profiles which will continue to be favorable for wind damage 
associated with bowing segments within the line itself. Isolated 
large hail will also be possible with rotating cells. The line of 
storms will continue to move eastward into south-central Missouri 
and across northwest Arkansas where a capping inversion atop a 
stable boundary layer. This should eventually help to weaken the 
line resulting in a more isolated severe threat. 

.Broyles/Edwards.. 04/26/2017 

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


Latitude...Lon 37629360 36369409 35419508 34979572 34629565 34429518 
34559365 35779238 36869186 37569224 37629360