16 July 2009 Severe Weather Outbreak

16 July 2009 Severe Weather Outbreak and Urban and Small Stream Flooding

(Click on any image to see loop or larger image)

A strong upper impulse and upper-level jet streak were tracking through the region, supporting a cold front that tracked through the region. An exceptional hail even occurred. One cluster of storms tracked through the Capital District of New York with hail in some cases >2”.

Storm Prediction Center Upper Air Analyses

Note the very little movement to the upper low north of the western Great Lakes. The upper level jet segment did not track very far east as well. There was a very distinct wind shift at 850 hPa, which likely provided some low level forcing to trigger and sustain convection.

500 hPa 12Z July 16 500 hPa 00Z July 17 300 hPa 12Z July 16 300 hPa 00Z July 17

850 hPa 12Z July 16 850 hPa 00Z 17 July

Satellite loops

Water Vapor – Note the upper low positioned north of the western Great Lakes that was not moving east very quickly. Also note the streaks in within the area of drying, representing the midlevel and upper level jet maxima. The streaks/discontinuities are labeled with white lines in the loop to the left. These streaks were some sort of density discontinuities above 600 hPa that may have contributed to enhanced midlevel forcing and enhanced upward motion. The loop to the right shows the evolution of the discontinuities and developing convection with better temporal resolution.

Visible loop – Note the cyclonic vorticity and broad band of convection

Visible loop 1 Visible loop 2 Visible loop 3 Visible loop 4

Data and Forecasts

Compare GFS and NAM CAPE forecasts. They both had similar predictions, with CAPEs above 1500 j/kg, largely supported by relatively high surface dew points. There was a surface wind shift boundary that tracked through the region, providing low-level convergence. Note the rapid increase in CAPE into the afternoon, and the rapid decrease toward and through the evening. The convection lingered in southern NY and western CT into the evening, where the maximum CAPE remained.

GFS40 CAPE NAM12 CAPE Observed LAPS CAPE MSAS surface DP and winds loop

Radar Loops

KENX Loop from 1600-1800 UTC of reflectivity and Severe Thunderstorm Warning Polygons

KENX Loop from 1800-2000 UTC of reflectivity and Severe Thunderstorm Warning Polygons

Individual plan view radar images and images from the Four-Dimensional Storm Investigator (FSI) between 1800-2000 UTC

KENX 1916UTC KTYX 1917 UTC

Notice the 70+ dBZ cores detected by both radars at the lowest elevation angle. Note the 3 body scattering pattern in the reflectivity (reflectivity extension from KTYX indicating very large hail.

KENX Loop from 2000-2200 UTC of reflectivity and Severe Thunderstorm Warning Polygons

Individual plan view radar images and images from the Four-Dimensional Storm Investigator (FSI) between 2000-2200 UTC

KENX 2003 UTC KENX FSI 2003 UTC KENX FSI 2008 UTC KENX FSI 2017 UTC

Note the 70+ dBZ core in the plan view. In FSI, note the unusually deep 60+ dBZ core, and well-defined high reflectivity core on the CAPPI (upper right) that is always set to the -20º C level. A 50+ dBZ core above the -20º C level can indicate the presence of hail. Quarter to ping pong ball sized hail was reported in this storm.

KENX FSI 2045UTC KENX FSI 2045 UTC KENX 2045 UTC KENX FSI 2053 UTC

As the storm tracked east, toward Rotterdam and Duanseburg, a strong wind core was detected at low levels, suggesting damaging winds were developing.

KENX FSI 2059UTC KENX FSI 2059 UTC KENX 2102 UTC KENX FSI 2103 UTC

Note the tilted deep high reflectivity core (2 vertical samples in two locations) and the peak reflectivities continued at 70+ dBZ as the storm tracked through the Schenectady/Rotterdam area to Altamont and Duanesburg. Large hail, in some cases golf ball to tennis ball sized hail and localized urban flooding occurred at this time.

KENX FSI 2113UTC KENX 2026 UTC KTYX 2134 UTC KENX 2035 UTC

The storm then tracked across the Guilderland and Albany areas with golf ball to tennis ball sized hail. Note the 70+ dBZ peak reflectivity signatures continued from KENX and KTYX, and the deep core of high reflectivity continued as well. Also note that the cone of silence was affecting the depiction of the deep high reflectivity core on KENX, resulting in a reduction of Vertically Integrated Liquid values (not shown).

KTYX 2147 UTC KENX FSI 2149UTC KENX 2158 UTC KENX 2216 UTC KENX FSI 2249 UTC

As the storm tracked out of the Albany area, it evolved into a bowing line, and the high reflectivity core diminished, as did reported hail sizes. There was very little damaging wind reported. The cone of silence continued to compromise radar analysis of the storms. The last upward pulsing of the storm occurred as it entered northern Columbia County, then new storms to the south and east strengthened.

KENX Loop from 2200-2400 UTC of reflectivity and Severe Thunderstorm Warning Polygons

Individual plan view radar images and images from the Four-Dimensional Storm Investigator (FSI) between 2000-2200 UTC

KENX FSI 2259UTC KENX 2259 UTC KENX FSI 2318 UTC KENX 2327 UTC

A storm in the northeast corner of Columbia County became dominant as it tracked toward the NY/MA/CT border. This storm developed structure similar to the previous storms with very large hail. Note the VIL increased above 70 g/kg (second panel from top on left side of image 4), which is quite rare.

KOKX FSI 2328UTC KENX FSI 2327 UTC KENX 2327 UTC KENX FSI 2349 UTC

The storm as detected from KOKX showed VILs above 70 g/kg, and some rotation developed, seen in the KENX Storm Relative Velocity. A new storm in Ulster County strengthened rapidly, evident in FSI.

KENX FSI 2328UTC KENX 2327 UTC KENX FSI 2327 UTC KENX 2349 UTC

As the storm tracked into and eventually through Litchfield County, CT. A broad line developed, with multiple high reflectivity cores, that affected different parts of Litchfield County, CT with hail up to the size of golf balls and some damaging wind through the rest of the evening.

KENX FSI 0050UTC KENX 0054 UTC KENX FSI 0132 UTC KENX 0131 UTC

These are the last images of the line of storms with multiple high reflectivity cores that tracked through Litchfield County, CT.

Precipitation estimates from KENX and Stage 3 from the River Forecast Center – Note the differences, with KENX overestimating likely due to hail contamination.

12Z 16 July Soundings

ALY BUF OKX

18Z 16 July Soundings

ALY

00Z 17 July Soundings

ALY BUF OKX

Storm Prediction Center Outlook

Storm Prediction Center Probabilistic Outlooks for tornadoes, hail and wind

Storm Prediction Center Mesoscale Discussions

Severe Thunderstorm Watch

Albany Area Forecast Discussions

Surrounding Area Forecast Discussions – NWS Burlington, VT, NWS Binghamton, NY, Taunton, MA and Upton, NY

BTV1 BTV2 BTV3

BGM1 BGM2 BGM3

BOX1 BOX2 BOX3

OKX1 OKX2 OKX3

Hail swaths determined by radar

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

NWS Binghamton, NY