U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 210039 
Storm Prediction Center ac 210037 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0737 PM CDT Sat Oct 20 2018 

Valid 210100z - 211200z 

..no severe thunderstorm areas forecast... 

thunderstorms will be possible this evening into the overnight 
across parts of the upper Ohio Valley, northern Florida, southeast 
Georgia and across parts of the Desert Southwest. 

An upper-level trough will move eastward across the eastern Seaboard 
tonight. Thunderstorms will be possible near the trough axis in the 
upper Ohio Valley this evening. A few thunderstorms will be possible 
this evening along a cold front in northern Florida and southeast 
Georgia. Thunderstorm development will also be possible across parts 
of the Desert Southwest through tonight ahead of an upper-level 
system just off the West Coast. No severe thunderstorm activity is 
expected across the Continental U.S. This evening or tonight. 

.Broyles.. 10/21/2018 


Mesoscale Discussion

acus11 kwns 201608 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 201608 

Mesoscale discussion 1588 
National Weather Service Storm Prediction Center Norman OK 
1108 am CDT Sat Oct 20 2018 

Areas affected...Southern Lower Michigan 

Concerning...severe potential...watch unlikely 

Valid 201608z - 201815z 

Probability of watch issuance...5 percent 

Summary...strong damaging gusts (40-50 mph) are possible over the 
next several hours as a broken convective line with embedded cells 
moves east across Southern Lower Michigan. 

Discussion...visible satellite imagery shows a cumulus field 
developing over Southern Lower Michigan where surface temperatures 
are rising into the middle 50s degrees f. Radar imagery shows a 
low-topped convective line with embedded cells showing weak 
organizational characteristics located in a south-southwest to 
north-northeast line immediately east of Grand Rapids. As a potent 
mid-level shortwave trough continues to pivot southeast over the 
central Great Lakes this afternoon, large-scale forcing for ascent 
will maximize coincident with peak heating. 

Modifying rap soundings over Southern Lower Michigan for middle 50s 
surface temperatures yields a nearly 9 degree c/km 0-3 km lapse rate 
because of very cool mid-level temperatures (-25 degrees c at 500 
mb). Although winds in the lowest 3 km are 40 kt or lower per kgrr 
VAD data, it seems plausible as the convection slowly organizes, 
potential for strong gusts via horizontal momentum transport may 
occur. The main threat with the strongest storms is localized wind 
damage due to 40-50 mph gusts. 

.Smith/guyer.. 10/20/2018 

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


Latitude...Lon 42988486 43008346 42568268 41878309 41788398 42048531