NWS Doppler Radar Dual Pol

Erin Strengthens to a Hurricane; Heavy Rainfall Possible in Puerto Rico and the Virgin Islands, the Upper Midwest, South Texas

Hurricane Erin may bring isolated flash and urban flooding, landslides or mudslides, and possible tropical storm conditions to Puerto Rico and the U.S. Virgin Islands this weekend. Scattered thunderstorms and heavy rainfall may bring areas of flooding this weekend over the Upper Midwest. A tropical disturbance will bring locally heavy rain and mainly urban flash flooding to far southern Texas. Read More >

NWS Doppler Radar (WSR-88D) Example Products

Conventional Doppler radar sends out a horizontal energy pulse providing a one dimensional view of precipitation. Dual pol radar sends both horizontal and vertical pulses, providing a two dimensional view. Thus, it provides much better information about the size, shape, and estimated amount of precipitation, distinguishing between rain, snow, and hail. Basic dual pol products include correlation coefficient (CC), differential reflectivity (ZDR), and specific differential phase (KDP). More information is available on our Dual Pol webpage.

Above, two clusters of thunderstorms had high base reflectivity values between 50 and 60 dBZ (upper left). Meanwhile, CC data (upper right) showed high values above 0.96 (dark red/purple) in the same area as the high reflectivity values. High CC indicates similarly-shaped precipitation vs. a mix of types (i.e., hail-rain mix). ZDR (lower right) depicted values of 3.0-5.0 in the same location, suggesting large hamburger bun-shaped rain drops. KDP (lower left), often used to assess heavy rain using dual pol data, showed values of 2.0-5.0 suggesting a large concentration of rain and large drops. The combination of CC, ZDR, and KDP all supported the occurrence of very heavy rainfall with large drops in the storms, and little or no hail. Reflectivity alone cannot be used to specifically identify the exact nature of precipitation type and size in a storm.

Erin Strengthens to a Hurricane; Heavy Rainfall Possible in Puerto Rico and the Virgin Islands, the Upper Midwest, South Texas

NWS Doppler Radar Dual Pol - Heavy Rain

NWS Doppler Radar (WSR-88D) Example Products