10 June 2008 Severe Weather Outbreak

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Brief Description and Comments of the Event(s):

Rather prolonged yet significant event! Preceding the event was the unusual heat wave (4 days) with temperatures well into the 90s and dew points hovering around 70F. The morning of the 10th, dew points were above 70F and nothing less than pure sunshine. Upstream a cold front was progressing across the central Great Lakes with a lead wave/theta-e advection resulting in a band of thunderstorms across western NY. This prompted SPC to coordinate a watch that would cover large real estate for NY into western New England. The initial proposal was a Tornado Watch with BTV leading the way with emphasis toward the TOR when most of us just wanted a SVR. In the end, Tornado Watch was issued around 10 AM which continued through 6 PM. Best jet support was expected to remain across Lake Ontario and into portions of the Adirondacks. This is where the initial shot of convection and some severe weather occurred with an impressive bow echo tracking northward into the St. Lawrence Valley. After the passage of this complex of storms...most of the area "recovered" with impressive instability with CAPES climbing to at or above 4000 j/kg. We did 2 soundings, 15Z and 21Z which revealed a little cap remaining in place for most of the area. When the approach of the upstream front and upper trough, lapse rates increased and the convection organized from small clusters/bows into a more organized line (albiet broken) as it tracked across the CWA. With the extreme instability, updraft speed was impressive as were the reports of hail and wind. The Tornado Watch was replaced with a SVR Watch at 6pm. Most of the region was under a watch for at least 11 hours.

What was learned from this event:

·        Google Earth proved to be beneficial with lat/lon and retrieving obscure locations for reports.

·        Doing 2 special soundings proved to be quite nice for us, partners and SPC. Given the timing of convection, these 2 soundings were crucial and assisted SPC with watch decision.

·        SPC Coordination proved to be quite a challenge with one neighboring office, BTV. Initial collaboration was for SVR yet BTV was insistent as we only needed 2 reports of TOR to verify a rather large watch box. At the time of writing this, no TOR reports.

·        One impressive impact from this event was the community response. From the heat advisories to the convective watches, plans were altered/changed from surrounding schools and Emergency Management called for frequent updates.

Team Comments and Recommendations for Improvement:

·        We should look into adding additional phones to the operations area.

A look at some meteorology

A potentially significant severe weather outbreak was forecasted several days in advance, and not only by our office, but surrounding offices, and broadcast media were promoting that message days in advance as well.  Even though the system expected to produce the severe weather was originating from the Midwest, where many tornado outbreaks had occurred through the spring, the character of the system was expected to evolve as it approached our region.  The low-level air mass over the region was expected to be a bit dryer than in the Midwest, due to persistent upper ridging that was situated over eastern North America, and low-level jet energy, while forecasted to be relatively strong, was forecasted to be weaker than during many of the Midwest tornado outbreaks in past weeks.  In general, the mode of convection upstream in the Ohio Valley and Great Lakes would give clues to the mode of convection we could expect over our region.

On 9 June 2008, the day before our severe weather outbreak, the Ohio Valley and Great Lakes regions experienced widespread straight-line wind damage and large hail, with only one tornado reported in Ohio.  This was one significant clue that the threat for tornadoes in our region on 10 June was much less than the threat for wind damage and hail.  During the morning of 10 June 2008, area 12Z soundings offered additional insight into the severe weather potential for the day.

a.  b.

Figure 1.  10 June 2008 1200 UTC RAOBS for a) Albany, NY, and b) Buffalo, NY.  Note the shallow low-level directional cold advection in Albany, and the low-level warm advection at Buffalo.  The low-level winds were also stronger at Buffalo.  These conditions could be expected to translate east into the Albany area later in the day.

Based on figure 1, there was a cap noted around 700 Mb at KALB, but the cap showed evidence of disappearing at the KBUF sounding.  The wind shear at KBUF was largely unidirectional, but weak low-level cold advection was still occurring at KALB.  There was 2000-3100 J/Kg of CAPE seen in the soundings, but the shear was weak.  Based on this data, among all the other data available, and short term model guidance, a significant severe weather outbreak was expected during the afternoon and evening.  The 850 Mb theta-e contrast along the cold front was remarkable (Figure 2), and would produce strong forcing, supporting development of widespread convection that would likely become severe.  Both the NAM and GFS were predicting an 850 Mb theta-e gradient of around 30K (338-342K ahead of the front, to 308-312K behind the front).  This was well within the threshold (≥25K defined in a study of significant severe weather outbreaks that was presented at the 2004 Severe Storms Conference.

a. b.

Figure 2.  Equivalent potential temperature at 850 Mb from the 1200 UTC 10 June NAM80 for a) 1200 UTC 10 June, and b) 24 hour forecast valid 1200 UTC 11 June.  Note the forecast was for 850 Mb theta-e to fall >25K in 12 hours, the threshold for a significant severe weather outbreak.

The SPC put our forecast area in a Moderate Risk in the day 1 Convective  Outlook beginning at 2 AM EDT (Figure 3), and was slightly adjusted at 830 AM EDT (Figure 4).  A widespread straight-line wind damage event was being forecasted.  By 943 AM EDT, a mesoscale discussion was issued describing the near-term need for a potential weather watch (Figure 5), unspecified as to what type of watch.

 

Figure 3.  Day 1 convective outlook from SPC issued at 159 AM 10 June.  Note much of NY and PA is in moderate risk.

a)b)

Figure 4.  a)  Day 1 convective outlook from SPC issued at 834 AM 10 June and b) Area Forecast Discussion from NWS Albany, NY at 650 AM.  Note the moderate risk was expanded into western New England by SPC, and a significant severe weather outbreak was expected by NWS Albany with possible widespread wind damage and some tornado potential.

a)b)

Figure 5.  a)  SPC mesoscale discussion issued at 943 AM 10 June and b)  Area Forecast Discussion from NWS, Albany, NY at 815 AM still suggesting major severe potential with isolated tornado potential.  Note the SPC was focusing on the damaging winds and large hail, and lesser so on the tornado threat.  They intended to issue a watch before noon.

 

Figure 6.  a)  Areal outline of tornado watch with radar overlay and b) Area Forecast Discuaaion from NWS Albany, NY at 1016 AM.  Note the line of thunderstorms in western NY and the notification from NWS Albany of 2 special soundings that would be taken.

Shortly after 1400 UTC, a Tornado Watch was issued by SPC, despite a lack of tornado reports upstream, and a lack of low-level shear in the 1200 UTC soundings from KBUF and KALB.  The Tornado Watch (Figure 6) was issued for a large part of the northeastern U.S.  By 1500-1600 UTC new data was available from a KALB sounding (Figure 7a), which showed extreme instability, along with slowly increasing low-level shear.  There was very little convective inhibition, but the LCL was very high at nearly 7000 feet.  The Short Range Ensemble Forecasts for LCL showed the likelihood for high LCLs through the afternoon (Figures 7b-d). 

a.b.

c.d.

Figure 7.  a) KALB sounding from 1600 UTC 10 June and Short Range Ensemble Forecast (SREF) for Lifted Condensation Level (LCL) at b) 1800 UTC 10 June, c) 2100 UTC 10 June, and c) 0000 UTC 11 June.

a) b)

Figure 7.  Upper air soundings from a) KBUF at 1800 UTC 10 June, and b) KALB at 2100 UTC 10 June.  Note the directional cold advection and west wind direction at Buffalo, along with decreasing instability.  Also note that the shear and instability at Albany had increased, but the LCL was still relatively high, and an “Inverted V” sounding was observed, suggesting the potential for widespread damaging winds.

 

Figure 8.  Day 1 convective outlook from SPC issued at 1231 PM 10 June.  The moderate risk was whittled down from west to east with time as the cold front moved east.

a) b)

Figure 9.  Day 1 probabilistic forecasts from SPC for a) tornadoes, and b) straight-line wind damage.  Note the relatively low tornado probability compared to the straight line wind probability.  Yet, a tornado watch was issued during the late morning, which would be replaced by a severe thunderstorm watch during the afternoon.

a) b)

Figure 10.  a)  SPC mesoscale discussion issued at 349 PM 10 June and b)  Area Forecast Discussion from NWS Albany, NY at 248 PM.  Note the mesoscale discussion states that the severe weather threat for the tornado watch continues, but the emphasis is on damaging winds and hail.

 

a)b)

Figure 11.  a)  SPC mesoscale discussion issued at 650 PM 10 June and b)  Area Forecast Discussion from NWS, Albany, NY at 415 PM.  By this time a severe thunderstorm watch was in effect and many Severe Thunderstorm Warnings were being issued.

Figure 11.  Severe weather plot for 10 June.  Note the widespread wind damage and large hail reports, and no tornado reports.

Figure 12.  Radar reflectivity loop and polygon warnings on 10 June.

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

 

NWS Buffalo, NY

 

 

NWS Binghamton, NY

 

    

 

NWS Albany, NY

 

  

 

NWS Burlington, VT

 

  

 

NWS Upton, NY

 

  

 

NWS Taunton, MA