U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 311628 
Storm Prediction Center ac 311627 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1127 am CDT Monday Aug 31 2015 

Valid 311630z - 011200z 

..there is a marginal risk of severe thunderstorms this afternoon/evening for 
central Arizona... 

Isolated damaging winds may occur this afternoon and evening across 
parts of Arizona. Otherwise...scattered thunderstorms are expected 
across the central rockies and High Plains...and along parts of the 
Gulf and Atlantic coasts...as well as the Ohio and middle Mississippi 

A midlevel shortwave trough will continue to eject east-northeastward from ND/southern 
Manitoba to western Ontario...well to the east of a low-amplitude trough 
that will approach the Pacific northwest. A monsoonal moisture plume and 
associated diurnal convection will persist from the central rockies 
to the desert SW. Farther east...a diffuse trough will persist from 
the Ohio Valley to Texas with embedded vorticity centers over 
Indiana...AR...and S Texas. A separate vorticity maximum will slowly 
weaken eject northeastward/east-northeastward over the middle Atlantic coast today...with a 
tropical moisture plume accompanying this system near the SC/NC 
coasts along a stalled front. Scattered thunderstorms are expected 
with the embedded vorticity maxima...but the severe storm risk will 
be limited by poor lapse rates and/or weak vertical shear. 

..central Arizona this afternoon/evening... 
A low-end transition-type event is underway as a weak southern stream 
shortwave trough translates slowly eastward to the lower Colorado River 
valley...with SW flow aloft over central and western Arizona. Boundary layer 
dewpoints in the 60s remain across S central Arizona...and the modified 
12z phx sounding supports afternoon MLCAPE at or above 1500 j/kg with dcape 
near 1500 j/kg. Scattered thunderstorm development is expected this 
afternoon over the rim with other storm development possible into 
the lower deserts on convective outflow. The environment will favor 
substantial precipitation loading and strong downdrafts in a steep 
low-level lapse rate environment...with the potential for isolated 
damaging outflow winds. 

.Thompson/Mosier.. 08/31/2015 

Mesoscale Discussion

acus11 kwns 310715 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 310715 

Mesoscale discussion 1755 
National Weather Service Storm Prediction Center Norman OK 
0215 am CDT Monday Aug 31 2015 

Areas affected...eastern SC and adjacent eastern Georgia coastal area to 
southeast NC 

Concerning...severe potential...watch unlikely 

Valid 310715z - 311015z 

Probability of watch issuance...5 percent 

Summary...the overall severe weather threat will remain quite low 
through 10-11z. However...the environment near a surface boundary 
extending northeast through eastern SC into southeast NC will remain 
supportive for a potential non-zero/brief tornado threat during the 
rest of the overnight period. 

Discussion...a shortwave trough...currently tracking to the north-northeast 
across western SC into southwest NC per water vapor imagery...will 
begin to stall and weaken into NC during the pre-dawn/early 
morning...resulting in weakening deep-layer winds. Despite this 
weakening/decaying system...there appears to remain sufficient 
forcing for ascent on the eastern periphery of the trough for 
additional attempts of sustained updrafts/thunderstorm potential. The 
greatest likelihood for this occurrence should remain in vicinity of 
a boundary extending from the Georgia coast into southeast SC at a weak 
area of low pressure attendant to the midlevel trough...and then 
extending to the northeast inland and generally parallel to the 
SC/NC coast. 

The weakening kinematics suggest the overall potential for organized 
storms will remain quite low into the early morning /10-11z/. 
However...high moisture content air /pw values at or exceeding 2 
inches per 00z soundings along the southern Atlantic coast/ combined 
with effective srh of 100-200 m2/s2 near the surface boundary will 
continue to promote a non-zero tornado threat. 

.Peters/Mead.. 08/31/2015 

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


Latitude...Lon 31588121 31988122 32808090 33378039 33817977 34557897 
34717849 34557802 34127826 33817892 33497946 32918006 
32708039 32418061 31608066 31348078 31588121