Severe Weather Forecast

U.S. Convective Outlook

630 
acus01 kwns 170051 
swody1 
Storm Prediction Center ac 170049 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0749 PM CDT Wednesday may 16 2012 


Valid 170100z - 171200z 


..there is a slight risk of severe thunderstorms this evening across parts of 
central/northestern Massachusetts and southeastern New Hampshire into southwestern Maine... 


..cntrl Massachusetts into southeastern New Hampshire/southwestern Maine... 
Latest rapid refresh indicates that boundary layer cape remains 
moderately large along a lingering pre-frontal axis of stronger 
daytime heating. Perhaps aided by large-scale forcing for upward 
vertical motion associated with a significant short wave trough... 
the southern portion of which is shifting east of the Great Lakes 
region...vigorous convective development with large hail/damaging 
wind potential may persist into the 02-03z time frame...before 
conditions stabilize with frontal passage/loss of surface heating. 


..intermountain west/rockies/plains... 
Much of ongoing thunderstorm activity is expected to diminish by the 
03-05z time frame as boundary layer stabilization takes place with 
the loss of daytime heating. Even though moisture levels are rather 
low across the northern plains...models suggest that some additional 
thunderstorm development is still possible later tonight...in 
association with strengthening Lower/Middle tropospheric warm 
advection. Given the plume of very warm elevated mixed layer air 
advecting east northeast the north central rockies into the eastern 
Dakotas...the best chance for this may be across parts of 
northeastern South Dakota into parts of central/southern north 
Minnesota toward 08-12z...as a veering low-level jet finally begins 
to focus lift east of stronger middle-level capping. 


... 
With weak upper troughing contributing to convective potential... 
scattered vigorous thunderstorm activity continues across the South 
Atlantic coast states. However...given the generally weak wind 
fields and vertical shear...severe potential still seems 
low...particularly with continuing gradual boundary layer 
stabilization anticipated this evening. 


.Kerr.. 05/17/2012 






Mesoscale Discussion

216 
acus11 kwns 170042 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 170042 
mez000-maz000-nhz000-ctz000-vtz000-170145- 


Mesoscale discussion 0827 
National Weather Service Storm Prediction Center Norman OK 
0742 PM CDT Wednesday may 16 2012 


Areas affected...MA/NH/CT/western Maine 


Concerning...Severe Thunderstorm Watch 280... 


Valid 170042z - 170145z 


The severe weather threat for Severe Thunderstorm Watch 280 
continues. 


Summary...Severe Thunderstorm Watch 280 is scheduled to expire at 01z...but 
a localized wind damage/severe hail threat will continue in the 
short term /potentially outside of ww 280/ mainly across southern 
New Hampshire/adjacent Massachusetts and perhaps far southwest/coastal Maine. 


Discussion...a northeast-southwest oriented band of strong/severe 
thunderstorms continue to steadily progress eastward across southern 
New Hampshire/northern Maine as of 0030z. These storms will gradually encounter 
a relatively cooler/more stable boundary layer toward the coast as 
per the 00z observed Chatham Massachusetts sounding and observed surface 
temperature trends over the past 1-2 hours. Nonetheless...a 
localized wind damage/severe hail threat may continue over the next 
hour or so /beyond 01z/ given the existing thunderstorm 
organization/vertical shear...but likely on an increasingly marginal 
basis as thunderstorms otherwise eventually exit the southern New England 
coast. 


.Guyer.. 05/17/2012 


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


Attention...WFO...gyx...box...aly... 


Latitude...Lon 42387332 43217196 44687082 45306973 43567012 42057178 
41787325 42387332