7 July 2009 Severe Weather Outbreak

7 July 2009 Severe Weather Outbreak and Flash Flooding

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

This was another solid example of severe weather with a cutoff low northwest of NY and New England fitting into the CSTAR research. Despite Maglenta Index indicating a minor event (lack of 0-3 km SRH and miniscule EHI)...anomalous cold pool of -21C air at 500 hPa over KBUF and -16C over KALB at 12Z with SBCAPE values of 1000-1500 J/kg were sufficient for low end major event. Also, favorable jet dynamics (left front quad of mid-/upper- jet streak and upper-level divergence) were in play. Never disrespect the cold pool with sufficient instability, moisture and jet dynamics in place.

Meso-analysis was done using SPC analysis Web page which had a sector centered at PSB, the local WRF and LAPS output on AWIPS. The WRF identified that there would be two rounds of convection moving through the area. The first line was ahead of an approaching occluded front and 500 hPA short wave. This line organized in the late morning and moved into New England by 1pm. Both ahead and behind this line there was ample sunshine as the cloud area's were only 100-200km wide. This allowed destabilization on both sides. The WRF identified both the mode and organization of both bouts of convection. The initial line of showers was organized by the short wave, and intensified during the late morning and early afternoon as it moved into more unstable air. The second round of convection initially began in a cellular manner over much of the area, organized along the Lake Breeze line in Central New York, and along the occluded front. The convection then progressed east and intensified. For the most part this convection was multi cellular in nature. The LAPS CAPE and LI values, were also useful in identifying the areas where convection would grow most rapidly an hour or so in advance.

Cape during the event was mainly 500 to 1000 with some areas reaching 1500. SPC graphics depicted the increasing of low and mid level lapse rates over the area prior to the second round reaching 6.5-7.5C over wide areas. The other primary forcing mechanism was a 60kt 500hPa jet max which passed southeast of the region across Pennsylvania...but placed the region strongly in the left exit region. Shear was respectable...by mostly at the higher elevations. The 0-3km EHI values were less than 1.0, and mostly around 0.5

Storm Prediction Center Upper Air Analyses

500 hPa 12Z July 7 500 hPa 00Z July 8 300 hPa 12Z July 7 300 hPa 00Z July 8

Satellite loops

Water Vapor – Note the upper low tracking across the region, and an upper level impulse was rotating through the region.

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

Visible loop 1 Visible loop 2 Visible loop 3

Data and Forecasts

Compare GFS and NAM CAPE forecasts. Both the GFS and NAM showed the larger CAPE values in eastern NY, very diurnally driven. Note the rapid increase in CAPE into the afternoon, and the rapid decrease toward and through the evening. The GFS CAPE forecast also resolved the 2 areas of instability and convection, the first in the morning, and the second in the afternoon, with an axis of stability between the convective complexes.

GFS40 CAPE NAM12 CAPE Observed LAPS CAPE

HIRESWRF loop of Forecasted Radar Composite Reflectivity – Performed well compared to observed radar reflectivity loops, resolving the axis of stability between morning and afternoon convective complexes.

Radar Loops

KENX Loop from 1700-1900 UTC of reflectivity and Severe Thunderstorm Warning Polygons

KENX Loop from 1900-2100 UTC of reflectivity and Severe Thunderstorm Warning Polygons

KENX Loop from 2100-2200 UTC of reflectivity and Severe Thunderstorm Warning Polygons

KENX Loop from 2000-2200 UTC of reflectivity and Flash Flooding Warning Polygons

12Z 7 July Soundings

ALY BUF OKX

18Z 7 July Soundings

ALY

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

BOX1 BOX2

OKX1 OKX2 OKX3

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

NWS Binghamton, NY