U.S. Severe Weather Forecast (Sääkatsaus)

Tänään
Huomenna
Day Three

000 
acus01 kwns 200535 
swody1 
Storm Prediction Center ac 200534 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1234 am CDT Fri Jul 20 2018 


Valid 201200z - 211200z 


..there is a moderate risk of severe thunderstorms from western Tennessee 
to southern in... 


..there is a slight risk of severe thunderstorms from lower Michigan to 
MS and Alabama... 


... 
Severe thunderstorms will develop across the Ohio and Tennessee 
Valley region into the mid-south Friday. Very large hail, damaging 
winds, and a few tornadoes can be expected. Isolated severe storms 
are possible across the Central High plains. 


..OH/Tennessee valleys into the mid-South... 


Strong mid-level jet, in excess of 60kt at 500mb, is forecast to dig 
southeast across the mid-MS valley region Friday as primary 
mid-level circulation settles into the Southern Lake Michigan area during 
the latter half of the period. With 500mb high centered over the 
southern High Plains, pronounced mid-level diffluence will extend 
across a good portion of the Ohio Valley into the central Gulf states. 
This large-scale regime will prove favorable for robust convection 
along the eastern plume of Southern Plains heat dome. 


Early this morning a substantial Reservoir of instability exists 
from the Central Plains into the lower MS valley. Several pockets of 
strong/severe thunderstorms have evolved within a warm advection 
corridor across southern Kansas/northern OK and ahead of the larger 
trough over WI/IL. This activity is not currently expected to grow 
upscale prior to daybreak. As a result, extreme buoyancy is expected 
to develop across the mid-south into southern in within 
southwesterly low-level flow where surface temperatures are expected 
to warm rapidly ahead of synoptic front. The aforementioned 
mid-level jet will dig into this region during the day enhancing 
shear profiles and venting aloft for robust updrafts. 


Current thinking is stronger forced regions of in/lower Michigan will 
easily convect by early afternoon and a possible squall line could 
evolve after 18z where mid-level backing and height falls are more 
evident. However, more intense thunderstorms are expected to develop 
toward 21z farther south across western KY, then into western Tennessee by 
late afternoon. Forecast soundings across the MDT risk region are 
quite impressive regarding buoyancy with SBCAPE on the order of 
5000-6000 j/kg and sfc-6km shear approaching 60kt. Environmental 
parameters strongly favor supercells across this region and very 
large hail could accompany this activity. In addition, tornado 
threat will be greatest with these discrete storms that will 
propagate strongly southeast around 25kt. If this region is not 
convectively contaminated prior to mid afternoon there is some 
concern that a higher tornado threat may be embedded in this region. 
Will monitor mesoscale details and address this concern in later 
outlooks. Otherwise, multiple severe thunderstorm clusters should 
evolve across the mid-south during the evening which should 
propagate across northern MS/Alabama with an attendant threat for large 
hail/damaging winds. 


..Central High plains... 


Weak isentropic ascent may generate convection early in the period 
across portions of the High Plains. Several cams suggest this 
activity could grow upscale as it propagates southeast along a 
corridor of warm advection toward southern Kansas. However, confidence 
in this scenario is not particularly high. Of more concern will be 
the region of eastern Colorado/western Kansas later in the day. Easterly 
upslope flow and strong boundary-layer heating should allow at least 
isolated thunderstorms to evolve across this region as temperatures 
warm into the upper 90s. Deep-layer shear will be more than adequate 
for sustaining organized updrafts and a few supercells could evolve 
that would pose a threat of large hail/damaging winds. 


..Southeast Arizona... 


Higher-precipitable water air mass is expected to be maintained across northwestern 
Mexico into southern Arizona through the upcoming day1 period. Deep 
convection will once again develop over the higher terrain and then 
should propagate toward lower elevations during the early evening 
hours. Gusty winds are the primary risk with this activity. 


.Darrow/Bentley.. 07/20/2018 


$$ 

Mesoscale Discussion


000 
acus11 kwns 200443 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 200443 
inz000-kyz000-ilz000-200615- 


Mesoscale discussion 1095 
National Weather Service Storm Prediction Center Norman OK 
1143 PM CDT Thu Jul 19 2018 


Areas affected...south-central Illinois into southwest Indiana 


Concerning...Severe Thunderstorm Watch 286... 


Valid 200443z - 200615z 


The severe weather threat for Severe Thunderstorm Watch 286 
continues. 


Summary...a few strong to severe wind gusts remain possible across 
ww 286 and perhaps into southwest Indiana. 


Discussion...a complex of thunderstorms, now largely linear in Mode, 
continues to travel rapidly southeastward across Illinois. Measured winds 
have generally been in the 30-40 kt range, with little if any hail 
potential. These storms are expected to weaken over the next few 
hours with eastward extent as the air mass becomes less unstable. 
However, southern portions of the line will remain in closer 
proximity to the instability axis which will be maintained by a 20 
kt southwesterly low-level jet, suggesting isolated severe 
potential. 


.Jewell.. 07/20/2018 


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


Attention...WFO...ind...pah...ilx...lsx... 


Latitude...Lon 38698974 38918977 39258952 39498912 39518890 39338828 
39078791 38678772 38318749 37938776 37858818 37918875 
38108928 38698974