24 June 2008 Severe Weather Outbreak

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A relatively clear-cut mixed case event occurred on 24 June, with a sea breeze providing the focus/trigger for severe convection in RI and SE MA, supported by upper dynamics  associated with a well-defined upper-level impulse and upper-level cold pool.

Convection was expected across the northeastern
U.S., but the questions were:  When and where would the convection be initiated?  The first evidence of sea breeze convergence was at around 14-15Z, and was the remnants of a weak cold front.  Surface plots and mesoscale analyses showed a theta-e ridge and dew point pooling over southeastern New
, with light southwest to southeast winds along the RI and SE MA coasts, converging with light northwest winds inland.

Thunderstorms initiated around noon in southern RI and SE MA, eventually becoming widespread thunderstorms with severe hail through the afternoon, as more storms from southern NH and central MA merged with the activity, resulting in some wind damage as well.

Attached are some 12Z soundings, surface plots with mesoscale analyses, radar, satellite and a couple of text products from NWS Taunton, MA (BOX).  It is interesting to see how the weather evolves, and the NWS BOX forecasts and thought process.  The Storm Prediction Center (SPC) issued a Mesoscale Discussion at 1207 PM EDT, did not identify the sea breeze role in the convection beginning to initiate, and eventually chose not to issue a watch box.  SPC had our region in "See Text" all morning, then put much of
New England in a slight risk at 1215 PM EDT, as was stated in their Mesoscale Discussion, and coincidentally when BOX began issuing warnings.

Once the convection formed, the warnings were definitely flying, and virtually all severe weather was warned with good lead times.  There is no doubt that these are some EXTREMELY subtle features and were EXTREMELY difficult to resolve in real time, but it is good to see that this event behaved in a manner consistent with the research.




Figure 1.  Skew-T Log-P display of 12Z 24 June raobs from a) Albany, NY, b) Chatham, MA and c) Upton, NY.




Figure 2.  a) MSAS station plot and surface dew points for 15Z 24 June, b) MSAS wind barbs and Theta-E for 15Z 24 June, and c) MSAS station plot, surface Theta-E and surface dew point for 18Z 24 June.




Figure 3.  Satellite imagery from 24 June depicting a) water vapor imagery from 1415Z, b) visible imagery with lightning overlay at 1601Z, and c) visible imagery from 1815Z with lightning overlay.




Figure 4.  Radar reflectivity from a) 16Z, b) 18Z, c) 20Z and d) 22Z.


Hail size key


a) b)


Figure 5.  Hail swaths through Rhode Island, eastern Massachusetts and southern New Hampshire on 24 June.




Figure 6.  Text products from NWS Taunton, MA depicting a) Area Forecast Discussion from 1010 AM 24 June, b) Area Forecast Discussion from 1146 AM 24 June, and c) Hazardous Weather Outlook from 446 AM 24 June.




Figure 7.  Nowcasts from NWS Taunton, MA from a) 1105 AM 24 June, b) 1205 PM 24 June, c) 105 PM 24 June and d) 405 PM 24 June.



Severe weather reports for individual NWS offices, courtesy of The Iowa Environmental Mesonet division of Iowa State University Department of Agronomy


NWS Albany, NY



NWS Taunton, MA



NWS Upton, NY