July 9, 2014 Severe Weather

 

The initial Storm Prediction Center severe weather outlook had general thunder over the forecast area, but overnight staff coordinated a possible upgrade to a "See Text". The mid-morning outlook included the entire area in a "See Text" (Fig. 1a).  Considerations for an upgrade to a "Slight Risk" were how much instability was going to available, and would the weaker midlevel lapse rates limit any strong to severe thunderstorms ahead of the cold front. The early afternoon severe weather outlook (Fig. 1b) did upgrade the entire area to a Slight Risk with extensive details of the possibilities described in the outlook text (Fig. 2).  SPC issued a mesoscale discussion (Fig. 3) at 1653 UTC highlighting the increasing severe weather threat possibility for PA , NY (as far north as the Capital Region) and southern VT.  Convective initiation started toward the mid-afternoon between (19Z-20Z) with the first severe thunderstorms occurring in the Capital District including the Albany-Troy corridor. A Severe Thunderstorm Watch was issued until 10 pm that went from Schoharie, Albany, Rensselaer counties to southern Vermont and points south, and western New England (Fig. 4).

The focusing mechanism for the afternoon severe weather was another cold front with a few midlevel short-waves moving along the boundary. The morning 12Z soundings (Figs. 5a and 5b) indicated an atmosphere that was much more stable compared to the previous few days which made the potential severe weather threat more ambiguous, but enough low-level moisture, 0-6 km effective bulk shear and instability was in place for another round of severe thunderstorms for the southern half to two thirds of the forecast area (Figs. 6a and 6b).

A couple of thunderstorms quickly developed over the Capital Region around 4 pm (Figs. 7a and 7b) and produced downburst damage in Troy and its suburbs. A rainfall rate of 1.5" in 15-30 minutes was recorded. This was a precursor of what was to come later in the late afternoon, as this initial multicellular cluster moved into southern VT (Figs. 8a and 8b). More multi-cells and some isolated discrete supercells would impact parts of the region later.

One impressive thunderstorm formed in Otsego county and moved eastward in Schoharie and western Albany county. The velocity values increased to 55+ kts 800-1000 ft AGL near the KENX radar site (Figs. 9a and b). Also, an impressive elevated reflectivity core formed with the 50 dBZ ref echo height exceeding the -20C level by about 5 kft (not shown). Neighboring radars showed gridded VIL values of 50-55 kg/m2 and a high confidence warning was issued. 1" hail stones were reported in New Scotland and on the south side of Albany. Also extensive downburst damage (Fig. 10a) occurred in western Albany County (near Knox). The radar showed a downburst type signature (Fig. 10b). This cell was on the leading edge of a line that formed and appeared form into a clear meso-vortex as it moved across southern VT (Figs. 11 a and b)

The radar had some excellent downburst signatures with this event. The discrete supercell that may have evolved into a meso-vortex did impressive damage in Albany County eastward into parts of Rensselaer. There were several reports of straight-line or microburst damage. The AWIPS plane-view products and FSI were helpful diagnosing the microbursts. Water vapor, infrared and visible satellite loops below show the evolution of the event (Figs. 12-14).  Also, a reflectivity radar loop of the entire event shows the various modes of severe convection (Fig. 15). Finally, a graphic of the hail and wind reports from SPC for that day (Fig. 16).

 

 

Figure 1a)  1300 UTC 9 JUL 2014 SPC Day 1 Outlook. Most of the Northeast was in a See Text. Figure 1 b) 1630 UTC 9 JUL 2014 SPC Day Outlook had most

of the ALY forecast area upgraded to a SLIGHT Risk.  

 

Figure 2:  The 1630 UTC 9 JUL 2014 Day 1 Text is shown.  The increased threat of severe convection is described across NY and New England.

Figure 3: Mesoscale Convective Discussion issued at 1253 PM EDT                                            Figure 4: Severe Thunderstorm Watch #407 Issued at 415 PM

Figure 5a): 1200 UTC 9 JUL 2014 KPIT sounding                                                                                                   Figure 5b): 1200 UTC 9 JUL 2014 KALB sounding

     

Figure 6a): 2000 UTC SPC RAP 0-6 km Effect Bulk Shear Vectors (kts)                                                                                        Figure 6b): 2000 UTC SPC RAP SBCAPE (J/kg) and SBCIN (J/kg)

Figure 7a): 1959 UTC KENX Base Reflectivity (dBZ) and Severe Polygon overlayed                              Figure 7b): 1959 UTC KENX Velocity (kts) and Severe polygon overlayed

       

F Figure 8a): 2030 UTC KENX Base Reflectivity (dBZ) and Severe Polygons overlayed                          Figure 8b): 2030 UTC KENX Velocity (kts) and Severe polygons overlayed

      

Figure 9a): 2204 UTC KENX Base Reflectivity (dBZ) and Severe Polygons overlayed                            Figure 9b): 2204 UTC KENX Velocity (kts) and Severe polygons overlayed

    

Figure 10a): 2209 UTC KENX Base Reflectivity (dBZ) (bow echo NE of RDA)                                       Figure 10b): 2209 UTC KENX Velocity (kts) with downburst signature near RDA

      

Figure 11a): 2350 UTC KENX Base Reflectivity (dBZ) (Meso-vortex over southern VT)                           Figure 11b): 2350 UTC KENX Velocity (kts) with Meso-vortex over southern VT

        

Figure 12: 1430 UTC - 2300 UTC 9 JUL 2014 Water Vapor loop with NAM MSLP and fronts overlayed     Figure 13: 1515 UTC - 2315 UTC 9 JUL 2014 IR satellite loop

       

Figure 14: 1515 UTC - 2315 UTC 9 JUL 2014 Visible Satellite loop                                                                Figure 15: 1910 UTC - 2357 UTC 9 JUL 2014 KENX Base Reflectivity (dBZ) loop with LTG overlayed

Figure 16: SPC storm reports from 9 JUL 2014.