U.S. Severe Weather Forecast (Previsión convectiva)

día tres

acus01 kwns 191952 
Storm Prediction Center ac 191950 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0250 PM CDT Wed Sep 19 2018 

Valid 192000z - 201200z 

..there is a marginal risk of severe thunderstorms over parts of 
the Central Plains and upper Mississippi Valley... 

A few severe storms, mainly with a threat for hail and damaging 
winds, are possible across parts of the north-Central Plains to 
upper Mississippi Valley. 

For the 20z update, we extended the existing 2% tornado area 
westward along/north of the outflow boundary in NE, where several 
more hours of heating will continue to destabilize the air mass, and 
where low level shear is conditionally favorable for a supercell. 
However, warming aloft may have a tendency to counteract the 
otherwise favorable factors. A storm or two may eventually form 
later this afternoon, with hail most likely, but with a conditional 
threat of a brief/likely weak tornado. 

.Jewell.. 09/19/2018 

Previous discussion... /issued 1101 am CDT Wed Sep 19 2018/ 

..Central Plains to upper Mississippi Valley... 
Morning water vapor loop shows an expansive upper ridge across the 
central/southern US, with the southern fringe of stronger westerlies 
extending from Wyoming into parts of NE/IA/IL. Multiple rounds of 
convection have resulted in a complex zone of surface boundaries 
from Colorado to IA, which will aid in the initiation of storms later 
today. It appears likely that a few clusters of strong to 
occasionally severe storms will intensify during the peak-heating 
hours this afternoon and evening, with hail and locally damaging 
wind gusts possible. Sufficient deep-layer shear will promote a few 
rotating cells, but the overall organization of the clusters will 
likely be limited. Thus will maintain the ongoing marginal risk 


Mesoscale Discussion

acus11 kwns 190848 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 190847 

Mesoscale discussion 1479 
National Weather Service Storm Prediction Center Norman OK 
0347 am CDT Wed Sep 19 2018 

Areas affected...north-central to eastern South Dakota and adjacent southwest 

Concerning...severe potential...watch unlikely 

Valid 190847z - 191145z 

Probability of watch issuance...5 percent 

Summary...isolated large hail should be the primary risk with the 
ongoing storm moving to the east-southeast through north-central 
South Dakota, and with any additional sustained storms that can 
develop and move into northeast and east-central South Dakota to 
southwest Minnesota through the early morning. 

Discussion...trends in mosaic radar imagery indicated mainly 
discrete storms and one that has evolved into a linear Mode across 
north-central South Dakota (dewey County into Potter county). These storms 
were elevated, given their presence well north of the southern NE to 
northern MO synoptic boundary, with easterly surface winds across 
South Dakota/Minnesota and temperatures and dew points in the 50s to lower 60s f. 
Forcing for ascent appears to be primarily associated with a 
transient midlevel impulse tracking east across South Dakota overnight and 
into Minnesota after 12z, while accompanying stronger westerly 500-mb 
winds/shear and steep lapse rates are supporting the threat for 
large hail. 

The track of the Dewey/Potter counties storm indicated that it began 
to accelerate around 0730z while moving through northern Ziebach 
County, and has a current movement at 0840z toward the 
east-southeast at 45 kt. Although this storm and others that 
develop will be elevated, the potential may exist for a locally 
stronger wind gust to reach the surface. Similar to early yesterday 
morning (prior to sunrise), there likely exists dry air in the 
sub-cloud layer above the stable boundary layer per modified 00z unr 
sounding. Downdrafts penetrating this dry air layer could be 
enhanced such that higher-momentum air could reach the surface. 
Short-term guidance does not provide very much confidence in the 
forecast of the ongoing storms, though consensus of href members 
would suggest overall coverage of sustained and potentially severe 
storms should be isolated into this morning as convection spreads 
toward eastern South Dakota and adjacent southwest Minnesota. 

.Peters/Edwards.. 09/19/2018 

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


Latitude...Lon 45180113 45590016 45589871 45569747 45559590 45039580 
44349596 44089629 44069756 44189889 44520031 45180113