August 11th recap - convection

Yesterday's convective activity remained the scattered type usual for a summer afternoon in the Northeast U.S. In our experiment setting, the New York and D.C. area terminals were the region of concern for potential CAWS issuance. Shown below, the WRF simulated satellite imagery showed scattered convection beginning at ~2000 UTC.

20150811 1800 UTC simulated IR forecast. The red lines indicate the line along which weak convection was expected to occur at 1800 UTC (western line) and 2200 UTC (eastern most line) given the simulated imagery and other parameters looked at by participants.

To further determine the location and timing of this convection, the NearCast Model was examined.

20150811 1700 UTC NearCast Theta-E Difference

Note the area of blues along the Appalachians, indicating weak instability at 1700 UTC. This weak instability supported the forecast of scattered convection. Recall the simulated IR estimated 1900 UTC, but given the noted habit of the WRF to be slightly late in initiating convection, participants estimated that 1800 UTC would be more accurate.

An experimental CAWS, shown below, was issued for the area, indicating the time of impact of this convection at 1700 UTC over eastern PA, and 1900 UTC over the New York and D.C. terminals.

Experimental CAWS issued at 1518 UTC on August 11th

Below is 1-minute SRSOR imagery and PGLM lightning data; a still at 1817 UTC and a loop from 1915 - 2045 UTC.

20150811 1817 UTC Visible, PGLM lightning, and ASDI Flight tracks

20150811 1915 - 2049 UTC SRSOR 1-minute imagery, PGLM lightning strikes over D.C., and ASDI flight tracks

To the north of the forecasted line, convection initiated slightly faster than anticipated, while south was fairly accurate. The CAWS forecast for impact directly over the terminals around 1900 UTC was accurate, as shown by the animation and lightning data. Note the flight tracks around New York and D.C. shift as the convection moved in.