Central Atlantic Storm Investigators

Central

Current Weather At CASI HQ:
Click Here For More Info

Atlantic

Storm

I n v e s t i g a t o r s

Backdoor Coldfront / Severe Thunderstorms
Eastern US 6/10/99

A strong backdoor coldfront came through the Mid-Atlantic US on June 10 1999, killing the recent heat wave and aiding in unusual westerly movement of storms and orographic lifting which was accompanied by slow moving severe thunderstorms. These combined to give very heavy rainfall over very localized areas, with up to 6.6" total and up to 4.3" per hour according to NEXRAD estimated precipitation. The storms were so stationary it was hard to tell them from anomalous propogation without using a satellite to confirm! Illustrations follow:

NWS Forecast Discussions from PA even early in the day call the orographic storms and slow-moving storms.
Most Of Nation Under Widespread Thunderstorms 6/10 : Loop | Summary
Temperature Plot At 20Z 6/10/99 (4pm) show 90's in SW PA, 60's in Central PA (CASI HQ)
Temperature Band Mapvia Penn State US Weather Stats Page shows temperature range in PA.
Temperature Graph From CASI HQ Weather Station shows the difference in temperatures after the front came through and the low clouds settled in.
Radar Loop shows westward moving storms in Western NC.
Base Reflectivity Radarfrom KCCX shows 67dbZ with the storm in NW PA at 4:46pm.
Local NEXRAD Loopfrom 3:41 - 4:22pm from KBUF, Buffalo NY, Shows the storm in NW PA not moving at all! Same story from KPIT Pittsburgh loop from 3:29 to 4:16pm which shows the NW PA storm form and become stationary, and also shows the storm in WV not moving.KUNV loop from 4:46 to 5:27pm shows the storm in NW PA finally sloshing to the NE.
It all started by me looking at a Regional NEXRAD Loop from 1:45-2:30pm which showed a storm in WV that was completely stationary.
Regional NEXRAD Loop from 3:40 - 4:20pm shows stationary behaviour of storms in PA and WV. An hour later the Regional NEXRAD Loop from 5-5:30pm shows the storms still stationary over nearly the same area!
NEXRAD Estimated 1-HR Precip Animation from KPIT shows a maximum 1-hour precipitation of 4.3"!
NEXRAD Estimated Storm Total Precip from KPIT at 4:36pm shows over 6" already from the NW PA storm, with a similar situation under the storm in WV. KCLE Storm Total Precip at 4:39pm insists 6.5". Later KCCX (State College / Central PA) shows a storm total of 6.6" of rain from the NW PA storm at 7:21pm.
NEXRAD Base Velocity from 4:29pm at KCCX shows velocity of Zero for much of the NW PA storm. Such high dbZ readings coupled with no movement flagged this type of data as anomalous propogation (false data) in my mind, until I could confirm via satellite imagery!
1KM Visible Satellite at 4:33pm Shows perfect storm over NW PA (check out the anvil & shadow!! Then at 5:46pm and 7:20pm see the storm begin to spread out, dissipate, and spread the anvil over Central PA.