Northwest Connecticut Snowburst of 19 February 2009 Gary P. Ellrod * NOAA/NESDIS (Retired), Certified Consulting Meteorologist, Granby, CT 5. RADIOSONDE PROFILES Radiosonde profiles for Albany, and Upton, NY at 00Z and 12Z 20 Feb 2009 are shown. Cloud top temperatures were -10 to -20 C, ideal for heavy snow. (Source: University of Wyoming). DESCRIPTION OF THE EVENT On the evening of 19 February 2009, a localized heavy snow event of up to 8 inches occurred in northwestern Connecticut. The heaviest snow was reported in a relatively narrow band from Washington to just west of Waterbury between approximately 6 PM to 10 PM EST. Newspaper accounts described snowfall rates of 4 inches or more per hour at times in some spots. 3. RADAR TIME SEQUENCE OF THE EVENT Snow squalls preceding the trough (panels a, b) were cellular with reflectivity of 35+ dBz, as seen by National Weather Service WSR-88D radar in Upton, Long Island, NY. Following the trough, a well defined, moderate-to-heavy snow band became quasi-stationary from northwest to southeast (c, d, e), and dissipated by 0329 UTC (f) (Source: NOAA/NWS via NCAR/RAL web site). a b c d e f 5:20 EST 5:55 EST 7:22 EST 8:20 EST 9:18 EST 10:22 EST 2. SURFACE AND UPPER AIR CONDITIONS The primary surface low center had moved off to the NE by 7 PM EST (0000 UTC, 20 Feb 09). The heavy snow was triggered by a well-defined mid-level trough at 500-700 mb, along with strong cold air advection (850 mb) and strong winds that extended down to the surface (Source: NOAA SPC / HPC). 300 mb 500 mb 700 mb 850 mb Surface 6. WRF MODEL FORECASTS Short range (9-12hr) forecasts from the 20km resolution Weather Research and Forecast (WRF) model accurately predicted the 700mb trough (left), and captured the character of the snow shower activity (right) (Source: UCAR) dBZ 4. GOES INFRARED SATELLITE IMAGES The GOES-12 Infrared sequence shows colder (whiter) clouds in advance of the mid-level trough and vorticity center in eastern NY and New England, although the low level snow band was not clearly defined. (Source: NOAA/NESDIS via NCAR/RAL web site) 7. SUMMARY The 19 February 2009 “snowburst” in northwest CT was a rare, mesoscale event triggered by a strong mid-level trough, followed by a surge of cold air, leading to a quasi-stationary snow band that lasted 2-3 hrs. The formation of the snow band was favored by a deep, unstable boundary layer. Cloud top temperatures were favorable for heavy snow (<-10C). This poster, as well as animated radar and satellite images are available at the following URL: http://members.cox.net/gellrod/CTsnowburst/ * Authors’ Email Address: Gary.Ellrod@gmail.com Web site: http://members.cox.net/gellrod/weather/