A warm front moving through the region, aided by disturbances in the jet stream and a tropical air mass in place, lead to several rounds of showers and thunderstorms which trained across the state.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS PHI wrote it up.
A warm front moving through the region, aided by disturbances in the jet stream and a tropical air mass in place, lead to several rounds of showers and thunderstorms which trained across the state.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Aug 12, 9:04 AM EST, 56 minutes earlier.
Area Forecast Discussion National Weather Service Mount Holly NJ 1004 AM EDT Sat Aug 12 2017 .SYNOPSIS... A cold front will move across the east coast tonight. High pressure will briefly build across the area Sunday night into early next week. The front will stall to the south Monday into Tuesday as an area of low pressure develops along the boundary and moves eastward along the front. Another frontal boundary may affect the area Wednesday, before high pressure briefly builds across the area Wednesday night, then offshore Thursday. A frontal system could then affect the area late next week or early next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Showers will continue to pass across parts of northeastern Maryland, Delaware and southern New Jersey until early afternoon. The showers are expected to sink gradually to the south. Meanwhile low clouds will remain over eastern Pennsylvania, New Jersey and the upper Delmarva for the balance of the morning. The clouds are forecast to lift slowly. A cold front extended across the eastern Great Lakes and the Ohio River Valley this morning. The boundary will move eastward and it is expected to reach central Pennsylvania and western Virginia toward evening. A line of showers and thunderstorms is forecast to develop in advance of the front and it should arrive in Berks County, the Poconos and the Lehigh Valley late this afternoon. The thunderstorms there may bring strong wind gusts and hail along with frequent cloud to ground lightning and heavy rainfall. Depending upon how much clearing takes place this afternoon, conditions may be slow to destabilize over parts of southeastern Pennsylvania and New Jersey. As a result, the showers and thunderstorms may lose some of their strength as they move farther to the east late in the day. High temperatures are expected to favor the lower 80s. Once the marine layer erodes, the wind should settle into the south and southwest around 8 to 12 MPH. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... The low pressure system will be crossing thru New england tonight. A weak cold front attached to the low will cross our area from NW to Se overnight. Scattered showers and a few tstms will be ahead of the front this evening into early tonight, before pops decrease towards dawn. Low will drop into the upper 50s to low 60s across the nrn areas, and remain closer to 70 over Delmarva and metro Philadelphia. && .LONG TERM /SUNDAY THROUGH FRIDAY/... The cold front is forecast to push south of the area by Sunday morning, before a secondary front or surface trough may cross the area later on Sunday into Sunday night. Moisture and lift will weaken during the day, so it now looks like Sunday will be a dry day. The initial cold front is forecast to stall to our south through Monday and Tuesday. Weak high pressure is forecast to affect the area Sunday night into early next week. An area of low pressure is expected to develop along the front to the south and moves to our east Monday night through Tuesday. Also, a possible tropical low may lift northward over the Atlantic and combine with this low and move eastward along the front. Just like the last couple of days, the GFS remains farther south and east than the ECMWF with the low. There still remains the possibility some showers could move across portions of the area Monday through Tuesday, so we'll keep chance POPS in the forecast for now. Also on Tuesday, a weak surface trough may move across the area which may help create a few showers or thunderstorms as well. Another frontal boundary may move across the area Wednesday, Wednesday, before high pressure briefly builds across the area Wednesday night, then offshore Thursday. This frontal boundary and subsequent high pressure are forecast to contain dry weather. However, we move into the end of the week into the early part of the weekend, a warm front may lift across the area as high pressure builds offshore, followed by a cold front. The timing is uncertain as the GFS is slower than the ECMWF, but they both do indicate this system. So we'll have a chance of showers and thunderstorms from Thursday night through Friday night for now. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. A period of lower CIGS/VSBYS is across the terminals this morning, before conditions will improve during the late morning/early afternoon hours. More showers and tstms are expected this afternoon and into the evening as a cold front crosses the area. More MVFR/IFR will be possible at those times. Light variable winds early today will become SW at 5 to 10 kts this afternoon. VFR conditions expected later tonight behind the cold front. OUTLOOK... Sunday-Wednesday...Generally VFR conditions. Scattered showers and thunderstorms possible Monday-Tuesday which may temporarily reduce conditions. && .MARINE... Winds and seas will increase a bit this afternoon ahead of the low pressure system and front approaching from the Great Lakes. it doesn't appear that SCA conditions will be reached, so we will hold on the flag for now. A few gusts in the low 20s kts are possible and seas could reach 3-4 ft on the ocean, so near SCA conditions. Sct showers and tstms will bring some locally higher winds and seas this afternoon and in to the evening. Fair weather expected later tonight behind the cold front. OUTLOOK... Sunday-Wednesday...Sub Small Craft Advisory conditions expected through the entire period. RIP CURRENTS... The risk for the development of dangerous rip currents remains low for today. However, it may approach moderate along the New Jersey Shore late in the day as wind speeds increase from the south. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && Synopsis...Robertson Near Term...Iovino Short Term...O'Hara Long Term...Robertson Aviation...Robertson/O'Hara Marine...Robertson/O'Hara
Hazardous Weather Outlook National Weather Service Mount Holly NJ 914 AM EDT Sat Aug 12 2017 DEZ001>003-MDZ008-012-015-019-020-NJZ008>010-012-013-015>023-027- PAZ070-071-104-106-131315- New Castle-Kent-Inland Sussex-Cecil-Kent MD-Queen Annes-Talbot- Caroline-Morris-Hunterdon-Somerset-Middlesex-Western Monmouth-Mercer- Salem-Gloucester-Camden-Northwestern Burlington-Ocean-Cumberland- Atlantic-Cape May-Southeastern Burlington-Delaware-Philadelphia- Eastern Montgomery-Lower Bucks- 914 AM EDT Sat Aug 12 2017 This Hazardous Weather Outlook is for central Delaware, northern Delaware, southern Delaware, northeast Maryland, central New Jersey, northern New Jersey, northwest New Jersey, southern New Jersey and southeast Pennsylvania. .DAY ONE...Today and Tonight. The probability for widespread hazardous weather is low. .DAYS TWO THROUGH SEVEN...Sunday through Friday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. DEZ004-NJZ014-024>026-131315- Delaware Beaches-Eastern Monmouth-Atlantic Coastal Cape May- Coastal Atlantic-Coastal Ocean- 914 AM EDT Sat Aug 12 2017 This Hazardous Weather Outlook is for southern Delaware, central New Jersey and southern New Jersey. .DAY ONE...Today and Tonight. The probability for widespread hazardous weather is low. .DAYS TWO THROUGH SEVEN...Sunday through Friday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. ANZ430-431-450>455-131315- Delaware Bay waters north of East Point NJ to Slaughter Beach DE- Delaware Bay waters south of East Point NJ to Slaughter Beach DE- Coastal waters from Sandy Hook to Manasquan Inlet NJ out 20 nm- Coastal waters from Manasquan Inlet to Little Egg Inlet NJ out 20 nm- Coastal waters from Little Egg Inlet to Great Egg Inlet NJ out 20 nm- Coastal waters from Great Egg Inlet to Cape May NJ out 20 nm- Coastal waters from Cape May NJ to Cape Henlopen DE out 20 nm- Coastal waters from Cape Henlopen to Fenwick Island DE out 20 nm- 914 AM EDT Sat Aug 12 2017 This Hazardous Weather Outlook is for Atlantic coastal waters and Delaware Bay Waters. .DAY ONE...Today and Tonight. The probability for widespread hazardous weather is low. .DAYS TWO THROUGH SEVEN...Sunday through Friday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. NJZ001-007-PAZ054-055-060>062-101>103-105-131315- Sussex-Warren-Carbon-Monroe-Berks-Lehigh-Northampton-Western Chester- Eastern Chester-Western Montgomery-Upper Bucks- 914 AM EDT Sat Aug 12 2017 This Hazardous Weather Outlook is for northern New Jersey, east central Pennsylvania, northeast Pennsylvania and southeast Pennsylvania. .DAY ONE...Today and Tonight. Scattered thunderstorms are expected to move in from the west late this afternoon and this evening. A few of these storms could become severe and produce locally damaging winds. .DAYS TWO THROUGH SEVEN...Sunday through Friday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is possible late this afternoon and evening. JRK
Special Weather Statement
National Weather Service Mount Holly NJ
525 AM EDT SAT AUG 12 2017
DEZ003-004-121015-
Inland Sussex-Delaware Beaches-
525 AM EDT SAT AUG 12 2017
...A STRONG THUNDERSTORM WILL AFFECT SOUTHEASTERN SUSSEX COUNTY...
At 524 AM EDT, a strong thunderstorm was located over Selbyville, or
10 miles northwest of Ocean City, moving east at 25 mph.
Wind gusts up to 35 mph are possible with this storm.
Heavy rainfall is also occurring with this storm...and may cause
ponding on roadways and poor drainage areas. Do not drive your
vehicle through flooded roadways.
Occasional lightning is occurring with this storm. Lightning can
strike 10 miles away from a thunderstorm. Seek a safe shelter inside
a building or vehicle.
Locations impacted include...
Millsboro, Selbyville, Dagsboro, Millville, Long Neck, Ocean View,
Frankford and South Bethany.
LAT...LON 3856 7534 3863 7510 3862 7508 3864 7506
3862 7507 3861 7516 3859 7521 3857 7518
3859 7514 3858 7507 3860 7507 3860 7510
3861 7506 3860 7506 3845 7505 3845 7528
TIME...MOT...LOC 0924Z 248DEG 24KT 3848 7520
RobertsonPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1006 AM EDT SAT AUG 12 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1159 PM TSTM WND DMG 1 W TRAPPE 38.66N 76.08W
08/11/2017 TALBOT MD 911 CALL CENTER
A TREE WAS TAKEN DOWN BY THUNDERSTORM WINDS ONTO WIRES.
&&
EVENT NUMBER PHI1701465
GAINESThe national radar mosaic for the moment the first event began.
3 flood. Local standard time, as filed.
A pond and stream overflowed which flooded a large portion of a yard.
High water reported covering portions of Bethany Beach.
Several roads closed such as Clark Avenue, Polk Avenue, and Kings Highway due to flooding.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Delaware in 2017Every state in 2017This day in weather historyWarnings in Delaware, August 2017
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 706855, 706856, 706857.