weather.gov 
 
 
 
National Weather Service Burlington, VT Twitter Page National Weather Service Burlington, VT Facebook Page
Local forecast by
"City, St" or zip code
  
 Current Hazards
    
 Current Conditions
    
 Forecasts
    
 Model Data
    
 Climate
    
 Weather Safety
    
 Miscellaneous
    
 Contact Us
The July 21, 2010 Severe Weather Event across
Vermont and Northern New York


Part III: Radar Analysis
Radar Mosaic Overview
In this next section we will discuss in-depth radar signatures and provide analysis for several storms, which produced significant wind damage and large hail across the region. The areas we will investigate are the Bangor, New York supercell, which tracked into the Champlain Valley, and produced damage near Milton, Vermont, followed by the supercell near Brookfield, Vermont. We will first discuss the big picture northeast radar mosaic of the widespread areal coverage and intensity of the storms, followed by a detailed examination of the Bangor, New York, Milton and Brookfield, Vermont storms, with reflectivity and velocity cross-sections, vertical integrated liquid (VIL), and low level plain view velocity displays.
Click to enlarge
Figure 11 is a Northeast region composite reflectivity mosaic from 1736 UTC to 2356 UTC on 21 July 2010 with 5 minute lightning plot (white crosses indicate positive polarity cloud to ground lightning strikes and dashes suggest negative polarity flashes carrying negative current to the ground). This loop shows the widespread areal coverage and intensity of the storms, along with the tremendous lightning activity during this severe weather outbreak. In addition, the radar loop shows multiple long tracked supercell thunderstorms across the region, several of which affected the WFO BTV forecast area.


Bangor/Brushton, New York Storm
Click to enlarge
Figure 12 shows a close-up composite reflectivity mosaic loop from 1605 UTC to 2055 UTC on 21 July 2010 with 5 minute lightning plot across the WFO BTV CWA. This loop clearly shows several long-lived supercells (yellow arrows) across our forecast area. The first cell develops near Massena, New York around 1605 UTC and tracks east into Brushton/Bangor, New York around 1701 UTC, then weakens across northern Clinton County, before redeveloping across Grand Isle County, due to warm moist inflow from winds coming up the Champlain Valley. This storm continued to produce severe winds and hail in the Milton/Essex Vermont areas, before tracking toward Morrisville and into central New Hampshire by 2030 UTC. Before exiting Vermont, the storm produced 1.0" hail in Danville, Vermont at 2025 UTC. The next long-tracked supercell developed across the higher terrain of the northern Adirondack Mountains, near Mineville, New York, then tracked into central Addison County and produced 1.50" hail in Lincoln, Vermont around 1915 UTC, before producing large hail and damaging winds near Brookfield, Vermont at 2000 UTC.
Click to enlarge
Figure 13 shows a reflectivity cross-section loop near Bangor, New York from 1647 UTC to 1725 UTC on 21 July 2010, along with LAPS 0C and -20C isotherms (yellow). This reflectivity cross-section loop clearly shows a tall, well vertically developed thunderstorm, with a strong reflectivity core of greater than 60 dBZ above the -20C. This very strong core aloft suggested a vigorous storm updraft and as the reflectivity core descended toward the surface, due to the storm collapsing, strong damaging thunderstorm winds occurred near Brushton/Bangor, New York. The loop clearly shows the greater than 60 dBZ core (bright red/pink color) collapsing toward the surface as the supercell tracked across central Franklin County, New York.
Click to enlarge
Figure 14 shows the KCXX radar composite reflectivity cross-section near Bangor, New York at 1701 UTC on 21 July 2010, along with LAPS 0C and -20C isotherms (dotted yellow lines). This image clearly shows 65 dBZ (pink color) well above -20C isotherm, with 50 dBZ to 36,000 ft, and a storm top of over 45,000 feet. This large and strong reflectivity core above the 0C and -20C isotherms indicates the storm is capable of producing large hail and very strong winds, which was observed in the Bangor and Brushton, New York area. In addition, the bounded weak echo region (BWER) suggests the storm had a very strong updraft and was still in the developmental stage, with very good storm relative inflow of a warm/moist air mass. A BWER is a radar signature within a thunderstorm characterized by a local minimum in radar reflectivity at low levels, which extends upward into, and is surrounded by, higher reflectivities aloft. This feature is associated with a strong updraft and is almost always found in the inflow region of a thunderstorm. Finally, the weaker dBZ returns (light blue) located between 20,000 feet and 35,000 feet on the right side of the image is associated with the storm anvil.
Click to enlarge
Figure 15 is the KCXX radar velocity cross section near Bangor, New York at 1701 UTC on 21 July 2010. This velocity cross section shows a descending inbound 50 knots or greater (dark blue) wind maximum moving toward the surface, as the supercell collapses between 1656 UTC and 1706 UTC near Bangor, New York on 21 July 2010. This descending core of very strong winds produced numerous trees and powerlines down across central and western Franklin County, along with copious amounts of hail. The lack of warmer colors (yellow/oranges) suggests the storm had limited rotation or outbound winds, which resulted in straight-line winds and the damage falling in one direction from west-northwest to east-southeast across the region.


Milton/Essex, Vermont Storm
In this section we will investigate the same supercell that affected the Brushton and Bangor, New York area, but now is located near Milton/Essex, Vermont. This supercell tracked across northern New York and weakened slightly across the higher terrain near Lyon Mountain, New York, before increasing in areal coverage and intensity over the Champlain Valley, due to warm/moist air advecting into the storm system. This cell produced damaging thunderstorm winds and some hail across the Milton/Essex, Vermont area on 21 July 2010. We will review a reflectivity cross-section, vertically integrated liquid (VIL) product, and a 0.5° KCXX velocity display to identify areas of the strongest inbound winds.
Click to enlarge
Figure 16 shows the KTYX radar composite reflectivity near Milton, Vermont at 1850 UTC on 21 July 2010 with LAPS -20C isotherm (yellow dotted line) and 0C isotherm (green dotted line). This image shows a very tall storm top with greater than 35 dBZ (yellow color) over 45,000 feet, along with a 50 dBZ (red color) core to 36, 000 feet, and a 65 dBZ (pink color) reflectivity core to 20, 000 feet, which indicates a very similar storm structure to the Brushton/Bangor Storm. These potent reflectivity cores aloft, suggests the potential for hail and damaging winds, which did occur in the Milton to Essex to Jericho, Vermont areas on 21 July 2010. We use the KTYX radar in Montague, New York to investigate storms near the radar located in Colchester, VT, due to the cone of silence, which limits the radar data aloft. However, due to the distance the KTYX radar is from the thunderstorm (>100nm), reflectivity and other radar data is not available below 10,000 feet. Therefore during warning operations, NWS meteorologists at WFO BTV use a combination of both KTYX and KCXX radars to investigate all layers of thunderstorms for potential impacts.
Click to enlarge
Figure 17 shows the KTYX Vertical Integrated Liquid (VIL) at 1854 UTC on 21 July 2010. VIL is an estimate of the total mass of precipitation in the clouds. The measurement is obtained by observing the reflectivity of the air as obtained by radar. This measurement is usually used in determining the size of hail, the potential amount of rain under a thunderstorm, and the potential downdraft strength when combined with the height of the echo tops. When VIL values quickly fall, it may mean that a downburst is imminent, resulting in the weakening of the storm's updraft and the storms inability to hold the copious amounts of moisture/hail within the storm's structure and a greater potential for the storm to produce damaging winds. Figure 17 shows VIL (pink color) values between 60 and 65 kg/m2 near Milton, Vermont. This indicates a very well developed updraft, capable of producing large hail and damaging winds, especially when the storm collapses and weakens, which occurred between Colchester and Jericho, Vermont on 21 July 2010.
Click to enlarge
Figure 18 shows KCXX 0.5° velocity near Milton, VT on 21 July 2010 at 1851 UTC. The light to dark grayish blue color in the image shows inbound winds of 60 to 70 knots coming toward the radar located in Colchester, Vermont. These very strong thunderstorm winds were located between 300 and 400 feet above the ground and produced numerous trees and powerlines down from Colchester to Milton to Essex to Jericho, Vermont on 21 July 2010. The KCXX radar had excellent velocity quality for this storm at 1854 UTC, because the storm was moving directly down the radial, toward the radar tower, located in Colchester, Vermont. It's very rare to see such a widespread area of greater than 50 knot winds at such low levels, across our region. Also, note very limited outbound winds (yellow/red colors), indicating the storm had very limited rotation.


Brookfield/Chelsea, VT Storm
In this section we will investigate the supercell which developed across the higher terrain of the northern Adirondack Mountains, near Mineville, New York, then tracked into central Addison County and produced 1.50" hail in Lincoln, Vermont around 1915 UTC, before producing large hail and damaging winds near Brookfield, Vermont at 2000 UTC. We will review a reflectivity cross section near Brookfield, Vermont, along with the KCXX 1.3° velocity display to highlight the damaging winds.
Click to enlarge
Figure 19 shows the KCXX radar composite reflectivity cross section near Brookfield, Vermont at 1953 UTC on 21 July 2010 with LAPS -20C and 0C Isotherm (yellow dotted lines). Once again the image shows a very tall storm top with greater than 35 dBZ (yellow color) over 45,000 feet, along with a 50 dBZ (red color) core to 36, 000 feet, and a 65 dBZ (pink color) reflectivity core to 20, 000 feet, which indicates a very similar storm structure to the Brushton/Bangor and Essex/Milton storms. This deep reflectivity core and storm structure indicates the potential for damaging winds and large hail, which occurred with 2.0" hail and numerous trees and powerlines down near Brookfield, Vermont. Also, like the other storms, this cell had a well defined storm anvil (light green color on right side of image), suggesting good outflow aloft.
Click to enlarge
Figure 20 shows the KCXX radar 1.3° velocity near Brookfield, VT on 21 July 2010 at 2002 UTC. This image suggests the storm had some weak broad rotation, with inbound winds (light green) of 20 to 30 knots and outbound winds (yellow to orange colors) of 40 to 50 knots. However, given that the rotation occurred over a diameter greater than 10 nm (nautical miles), the height of the rotation was high above the ground, and no strong gate to gate couplet was present, no tornado occurred with this supercell (as was verified by the NWS storm survey team). Nevertheless a strong descending rear flank downdraft did produce numerous downed trees and powerlines near Brookfield, Vermont associated with winds between 80 and 90 mph. The radar has difficulties with beam blockage due to the Green Mountains, especially in the low elevation scans (0.5°, 0.9°, 1.3°), which results in reflectivity and velocity data being underestimated by the radar and very poor radar data quality.


<<< Back to Part II Continue to Part IV >>>
Figure 14: KCXX Radar Composite Reflectivity Cross Section near Bangor, New York at 1701 UTC on 21 July 2010, along with LAPS 0C and -20C Isotherms (dotted yellow lines)
Figure 15: KCXX Velocity Cross Section near Bangor, New York at 1701 UTC on 21 July 2010
Figure 16: KTYX Radar Composite Reflectivity near Milton, Vermont at 1850 UTC on 21 July 2010 with LAPS -20C isotherm (yellow dotted line) and 0C isotherm (green dotted line)
Figure 17: KTYX Vertical Integrated Liquid (VIL) at 1854 UTC on 21 July 2010
Figure 18: KCXX 0.5° Velocity near Milton, VT on 21 July 2010 at 1851 UTC
Figure 19: KCXX Radar Composite Reflectivity Cross Section near Brookfield, Vermont at 1953 UTC on 21 July 2010 with LAPS -20C and 0C Isotherm (yellow dotted lines)
Figure 20: KCXX 1.3° Velocity near Brookfield, VT on 21 July 2010 at 2002 UTC


National Weather Service
Burlington
1200 Airport Drive
S. Burlington VT 05403
(802)862-2475

Webmaster: Webmaster
Page last modified: August 7, 2010
About Us
Disclaimer
Credits
Career Opportunities
Glossary
Privacy Policy