July 3rd, 2014 – Widespread Severe Thunderstorms

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Operational guidance showed a relatively strong consensus for the potential for a severe weather outbreak this day as early as Tuesday July 1 but it was decided that guidance was too aggressive with the forecasted instability and forcing and the front would be further west than the guidance suggested. So, only the heavy rain threat was highlighted in the forecasts and statements for eastern areas of the CWA for the July 3 time frame.

 

Figure 1a: Categorical Day 2 Outlook Issued by SPC on July 2nd at 0600Z for July 3rd.  Notice only a “SEE TEXT” area is depicted over the mid-Atlantic and Northeast, which downplayed the severe threat.

Figure 1b: Categorical Day 2 Outlook issued by SPC on July 2nd at 1730Z for July 3rd.  A “SLIGHT RISK” area was added across much of the region with this update.

 

Figure 2: The Categorical Day 1 Outlook issued by SPC On July 3rd during the early morning hours (0500z). 

After much coordination and collaboration, a Flash Flood Watch was issued on the very early morning hours of July 3rd. The reasoning behind this was most of our County Warning Area received 1-3 inches on the July 2 event. Most model data indicated another 1-2 inches of rain could fall in the same area due to training thunderstorms. Neighboring NWS offices also issued a Flash Flood Watch. 

By the morning hours on July 3, the cold front had progressed little and remained back across western NY. Because the cold front had barely moved, the air mass remained relatively unchanged from the day before. However, with abundant low-level moisture in place, there was patchy to widespread fog/low stratus across much of the forecast area helping to delay daytime heating. Because of this, convection was expected to occur slightly later in the day (mid-afternoon) instead of late morning. The 12z KALB sounding not quite as unstable as the morning before, with midlevel lapse rates down to 6.0°C/km. However, once the fog/low stratus burned off, there was the ability to easily reach CAPE values of 2000 J/kg again by the afternoon hours if temperatures could reach back into the mid-80s with dew points still hovering around 70°. The big difference this time was stronger forcing across the region, with the cold front expected to move through during later in the day and into the first part of the night.

A special sounding was done at 17z. By the early afternoon hours, CAPE values had increased to 1500-2500 J/kg. With the shear values so high, the forecast discussion targeted an enhanced severe threat (especially for wind).  Forecasts also mentioned that discrete supercells would initially be the convective mode, but quickly transition to linear as the shear vectors were oriented parallel to the cold front, especially considering the large amounts of unidirectional shear available in the mid layers.

 

Figure 3: The Special 17Z KALY Sounding.  Notice the available Most Unstable CAPE was 1519 J/kg.  Also, notable was the 41 kts of shear in the SFC- 6km layer.  The SFC-1 km shear was only 3 kts, which would downplay the threat for tornadic storms. Most of the shear was located within the 3-6 km layer.  The mid-level lapse rates were around 6°C/km.  While this is sufficient for severe weather, it certainly isn’t anything overly impressive.

A Severe Thunderstorm Watch was issued for the entire region by the Storm Prediction Center that lasted much of the afternoon and early evening. Initially, discrete cells, some supercells, formed in central New York.

Figure 4: The Severe Thunderstorm Watch box area and initial radar at the time of watch issuance.

These storms over central NY began to strengthen, showing some mid-level rotation.  Some of the storms began to approach the western Mohawk Valley for the mid-afternoon hours.  NWS BGM had issued several severe t-storm warnings for the storms.  With persistent mid-level rotation, a tornado warning was issued for far southern Herkimer County as this storm approached and showed a low-level hook echo (Figure 5).  While some low-level rotation was present, it wasn’t gate-to-gate, but this storm was also rather far from the KENX radar, so it was difficult to definitely say what was going on the lowest levels.  When the tornado warning was about to expire, another tornado warning was issued for the same storm as it continued through the Mohawk Valley. Again, there wasn’t a clear tornado on radar imagery, but enough rotation and hook echo were present to warrant the tornado warning (see Figure 6 for SRM imagery).  The office received an unconfirmed report of a “tornado on the ground” by a member of the public, but it turned out they were just reporting gusty winds to us and knowing a tornado warning was in effect.

 

Figure 5: Two-hour loop of KENX Reflectivity (Z) at 0.5° from 1935Z to 2133Z.  Warning polygons are also overlaid. Notice the apparent hook echo on the reflectivity imagery as the supercell approaching southern Herkimer County. 

 

Figure 6: Two-hour loop of Storm-relative motion (SRM) at the 0.5° slice from the KENX radar from 1935Z through 2133Z. Warning polygons are overlaid. Note while some low level rotation is visible over southern Herkimer County & western Montgomery County, it never appears to be tight or gate-to-gate rotation. Much of the strong winds are located in the inbound (green) direction, suggesting straight-line winds as opposed to tornadic activity.

A tornado survey was completed the next day across southern Herkimer and Montgomery Counties.  There was not a tornado with this storm, but a series of microbursts occurred with the supercell as it moved northeastward.  Hardest hit areas were West Winfield & Jordanville in southern Herkimer County and Minden in western Montgomery County.  Much of the damage was to trees and maximum winds were estimated at 100 MPH.  Figure 7 is a map of the straight line wind damage track, which occurred over a stretch of about 30 miles.  This thunderstorm continued to produce sporadic severe damage across Fulton and Saratoga Counties, although by that point, the rotation had waned enough to not warrant a tornado warning.  However, severe thunderstorm warnings continued for this storm as it continued to track northeast. 

Figure 7: Damage path of Straight-Line Wind Damage from 3 July 2014 as determined by NWS Albany Storm Survey.

Meanwhile, another storm developed in the Glens Falls area around 2100Z and quickly strengthened and became severe. This storm produced significant damage in northern Washington County, especially the Fort Ann, Kingsbury and Hampton Areas between 2130Z and 2215Z.  Severe thunderstorm weren’t only limited to northern areas, either.  As storms moved from the Catskills towards the mid-Hudson Valley, they quickly strengthened.  SPC analysis showed the highest CAPE values were located in the mid-Hudson Valley, with values greater than 2500 J/kg.  This allowed any storm to intensify as it reached into this air mass.

Figure 8: Surface-Based CAPE from SPC at 21Z on 3 July 2014.  CAPE values were maximized in the Hudson Valley, with values greater than 2500 J/kg for areas south of Albany.

As storms entered the Hudson Valley, they quickly became severe, and several additional severe thunderstorm warnings were issued. 

Figure 9: Reflectivity (Z) Loop from KENX from 2135Z through 2220Z.  Notice storms intensifying as the exit the Catskills and reach the Hudson Valley, requiring severe thunderstorm warnings.  As with the northern storms, many of the supercells had a hook-look to them at the lowest levels with some broad rotation.  However, the rotation was not strong or tight enough to warrant the need of a tornado warning.  Also, notice how storms north of the Capital Region, began organizing into a squall line. 

Figure 10: Reflectivity (Z) Loop from KENX from 2223Z through 2358Z.  The storms over all of eastern NY continued to organize into a squall line, with even some Line Echo Wave Pattern (LEWP) characteristics as well.  The bowing segments continued to produce both wind damage and some hail as the line moved into western New England.

During this particular event, descending KDP columns were extremely helpful in detecting thunderstorms capable of producing severe hail. It was found to look for high values of KDP in the column located near the top (3 deg/km). This often indicates strong melting in the updraft core, which can enhance evaporative cooling effects in the downdraft for wet microbursts. These may not always be noticeable though as KDP is dependent on the moisture profile. However, in environments such as the one for July 3rd with high PWAT values and efficient warm rain processes, these radar signatures can occur more often.

 

Figure 11: The 0500Z Day 1 Outlook overlaid with severe reports of wind/hail.  The Day 1 Outlook verified quite nicely over eastern New York and western New England.  The majority of the activity occurred north/west of the Capital Region or south/east with few reports from severe thunderstorms from immediately within the Albany-Troy-Schenectady area.

 

Figure 12: Loop of Surface Maps during July 3rd into July 4th.  One of the biggest items of discussion was the role of TC Arthur.  There was some concern that indirect moisture from Arthur could be pulled into the region, causing a Predecessor Rain Event (PRE) to occur.  This was a reason why flash flooding was initially more of a concern than the severe threat.  While PWAT values were above normal (1.4 – 1.8 inches during the event), the true tropical air never really made it into our region.  The primary forcing was due to the surface cold front, and it turned out that the severe threat was much more significant than flash flooding.  No flash flooding was reported on July 3rd, although ponding of water did occur in low lying and urban areas due to the quick bursts of heavy rainfall from thunderstorms.