1 July 2009 Severe Weather Outbreak and Flash Flooding

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


The 1 July event was a continuation of the 30 June event that fit into the latest CSTAR research on upper lows

by Matt Scolara, most resembling a CSTAR Upper low Neutral Tilt Type A Event


This event was well-anticipated, with the Storm Prediction Center putting our region in the slight risk more than a day in advance. Operational guidance suggested that cooling aloft associated with the slow advance of a neutral tilt upper low, along with an upper impulse rotating around its periphery, would support severe weather in our region. However, the axis of best instability was further east than the day before (30 June) since the center of the upper low was further east, and was in fact weakening. The boundary layer and surface theta-e gradient were further east, as evidenced by the morning convection and heavy rain over eastern New England. The morning convection in eastern and southern New England was a significant issue for NWS BOX and NWS OKX, as was evident in the AFDs below. Still, areas of clearing in central NY and PA contributed to instability, and the western edge of the theta-e gradient was over eastern NY and western New England.


Upper air data, satellite imagery and surface data confirmed the existence of these features. Operational guidance also suggested a very diurnal nature to the convection. The convection would move east through the afternoon, then weaken as the convection moved into New England, where prior convection stabilized the atmosphere. Localized flash flooding was possible, even though precipitable water values were not anomalously high, but depended on whether convective lines formed and trained over locations. There was more low level southerly jet energy tracking into the region, with potential moisture advection and convergence that could support not only severe weather but flash flooding.


Storm Prediction Center Upper Air Analyses


500 hPa 300 hPa 850 hPa


Anomalies from 15Z 30 June SREF


Note the MSLP anomalies are 3-4 SD below normal, as are the 500 hPa heights. The 850 hPa V winds were 2-3 SD above normal and the PWAT was around normal.


MSLP 500 hPa 850 hPa PWAT 250 hPa


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



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.






Observed LAPS CAPE


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 1 July Soundings






18Z 1 July Soundings






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













Precipitation estimates vs. observed precipitation Did the radar bias cause over estimates of precipitation?



Precipitable Water values were not anomalous, however, with the relatively slow moving lines of thunderstorms, training over the same areas for 1-3 hours, flash flooding was reported in Montgomery County, NY and around Bennington, VT.


Warnings and Severe Weather Reports



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


NWS Binghamton, NY



NWS Albany, NY



NWS Taunton, MA



NWS Upton, NY



Flooding Photos from North Colonie, NY




Any questions or suggestions, please e-mail Neil.Stuart@noaa.gov