Bill Intensifies Slightly in Missouri (Fri 6/19); Recap of Bill’s Impacts in North Texas

I want to kick off this piece with a discussion of Tropical Depression Bill’s intensification over Missouri, hundreds of miles inland.

➡ Click here to skip to the North Texas impacts to see how much rain fell at DFW and what the peak winds were as Bill passed across the area.

At 4 p.m. CDT Friday, June 19, 2015, the center of Tropical Depression Bill was about 30 miles west of Cape Girardeau, Missouri. Amazingly, three days after making landfall and tracking hundreds of miles inland, Tropical Depression Bill maintains a well-defined circulation as it tracks over warm/saturated grounds resulting from very heavy rainfall in recent weeks. In a previous post, we discussed the brown ocean effect, and that seems to be helping to maintain Bill’s intensity as a tropical depression. Satellite and radar imagery as well as surface observations indicate that convective rainbands/thunderstorms have increased throughout the day to the southeast of its center of circulation. The central pressure has decreased 2 to 3 mb in the past 6 hours (between 10 am and 4 pm) and peak gusts in that area have increased to over 40 mph this afternoon.

7-Day Rainfall % of Normal (As of 12z Thursday 6/18, Before the Heavy Rain from Bill Arrived. Purple ~ 400% - 600% of Normal With Sharp Gradient on Southern Edge. Warm/Saturated Soil in this Area Led to Intensification on Friday 6/19/15

7-Day rain % of normal as of 12z Thu 6/18, before Bill’s heavy rain arrived. Purple ~ 400-600% of normal

Above is the 7-Day rainfall “% of Normal” (as of 12Z Thursday 6/18, before the heavy rain from Bill arrived). Purple represents approximateely 400% – 600% of normal (300% to 500% above normal).  Note the sharp gradient on southern edge.  Below is a snapshot of the radar image at 8 pm CDT on Friday, June 19, 2015, with the center of Tropical Depression Bill located near Paducah.  The image is suggestive of an eyewall in the convective bands around the center.  I believe that the warm/saturated soil in this area led to Bill’s intensification on Friday 6/19/15.  The combination of warm soil moisture and daytime heating created optimal conditions for latent heat fluxes into the atmosphere.

Radar image at 8 pm CDT on Friday, June 19, 2015 of Tropical Depression Bill, following a period of intensification.

Radar image at 8 pm CDT on Friday, June 19, 2015 of Tropical Depression Bill, following a period of intensification.


Recap of Tropical Storm Bill’s Impact Over North Texas

Through 4 am Friday (June 19), the top-3 rainfall amounts are:

  • 13.28 inches near El Campo, TX
  • 12.53 inches near Healdton, OK
  • 11.77 inches near Ganado, TX

Peak Winds in North Texas

On Wednesday, June 17, sustained winds of 25 to 35 mph, with gusts in excess of 50 mph, affected North Texas for a period of 6 to 8 hours.

  • DFW Airport reported a peak wind gust of 48 mph
  • Denton reported a peak wind gust of 51 mph
  • Dallas reported a peak wind gust of 46 mph
  • Krum reported a peak wind gust of 58 mph

Duration of Winds at DFW Airport and Denton.  Hours shown are consecutive. Periodic hours meeting these criteria weren’t counted.

Wind SpeedsDFW AirportDenton
Sustained 20+ MPH14 hours7 hours
Sustained 25+ MPH8 hours6 hours
Sustained 30+ MPH2 hours2 hours
Gusts 30+ MPH13 hours7 hours
Gusts 35+ MPH6 hours6 hours
Gusts 40+ MPH2 hours2 hours
Peak Wind Gusts in North Texas from Tropical Storm Bill on Wednesday, June 17, 2015

Peak Wind Gusts in North Texas from Tropical Storm Bill on Wednesday, June 17, 2015

Record Rainfall for DFW & Excessive Rainfall Around North Texas

Widespread 2 to 4 inches of rain fell across North Texas as Tropical Storm Bill moved northward across the area, with amounts of 5 to 10 inches west and northwest of the metroplex.

DFW Airport received 2.21 inches of rain on Wednesday, June 17

  • This broke the previous record for the date (previously 1.71″ in 1914)
  • Since records began in 1898, this was the 4th largest 1-day rainfall amount ever recorded after 15 (June 16 – June 30)
  • The 7th largest on any calendar day in the June 15 through July 31 period
  • The 8th largest for the full two months of June 15 through August 15
Total rainfall from Tropical Storm Bill in North Texas.

Total rainfall from Tropical Storm Bill in North Texas.

5-Day Satellite Loop of Bill’s Evolution, Non-Linear Motion, and Lifespan

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