Snow Across the Great Lakes, Central Appalachians, and Northeast; Unsettled Weather in the West

Light to moderate snow will continue into Saturday over the Great Lakes, Central Appalachians, and Northeast. This weekend into next week, a series of atmospheric rivers will bring gusty winds, periods of heavy rain, and mountain snow to northern California and the Pacific Northwest. Colder temperatures are in store for the weekend from the Great Lakes to East Coast. Read More >

Overview

Only a few days removed from Tropical Storm Isaias, another impactful weather event occurred over portions of the mid-Atlantic. A stalled frontal boundary waffled across the Delmarva region and southern New Jersey over the course of the day, with a couple weak waves of low pressure tracking along it. An environment of moderate instability and moderate wind shear developed along the front. In addition, the atmosphere was moisture-laden with dew points around 70F and high values of precipitable water. A cluster of severe thunderstorms developed along the front in southeast Pennsylvania during the late afternoon and moves east-southeast into portions of Delmarva and southern New Jersey through the evening. The worst of the impacts occurred in New Castle County, DE and Chester and Delaware Counties in PA. An EF1 tornado occurred in New Castle County, with several nearby areas of straight line wind damage. In addition, storms were slow moving and training over top of each other in the moist air mass. An area of 2 to 4 inches of rain occurred with localized totals over 6 inches. This led to significant flash flooding of both streets and streams. While not an especially classic high end severe weather environment, it is likely that complex storm-scale interactions and the close proximity of the frontal boundary caused a localized but significant enhancement of the severe weather and flash flooding threat in the areas discussed above. This case serves as a good example of how small scale features associated with severe convective weather can sometimes produce results different than what the synoptic environment would suggest.

KDOX radar reflectivity loop, at one half hour intervals from 5PM EDT to 9PM EDT, of the thunderstorms which produdced severe weather and flash flooding on 7 August 2020. The red dot north of Wilmington, DE denotes the approximate location of where an EF1 tornado occured.

Environment
Warnings
Storm Reports
LSR
Tornado and Wind Damage
Radar

Meteorological Environment/Setup

Synoptic Overview at 12z 7 Aug 2020 (courtesy of SPC)


Figure 1: 250-mb analysis	Figure 2: 300-mb analysis	Figure 3: 500-mb analysis


Figure 4: 700-mb analysis	Figure 5: 850-mb analysis	Figure 6: 925-mb analysis

Synoptic Overview at 00z 8 Aug 2020 (courtesy of SPC)


Figure 7: 250-mb analysis	Figure 8: 300-mb analysis	Figure 9: 500-mb analysis


Figure 10: 700-mb analysis	Figure 11: 850-mb analysis	Figure 12: 925-mb analysis

Surface Maps (courtesy of SPC)


Figure 13: 15z surface map	Figure 14: 18z surface map	Figure 15: 21z surface map


Figure 16: 00z surface map	Figure 17: 03z surface map	Figure 18: 06z surface map

Observed Soundings


Figure 22: 00z Wallops Island, VA sounding	Figure 23: 00z Sterling, VA sounding	Figure 24: 00z Islip, NY sounding

Preliminary Storm Reports


Figure 1: National Preliminary Reports 12z 7 Aug 2020 to 12z 8 Aug 2020	Figure 2: Zoomed Preliminary Reports for the same period.	Figure 3: Prelim Reports vs. 0600z SPC Convective Outlook

Watches, Warnings, and Advisories Issued

Click here for a county warning area based plot of local storm reports and warnings/advisories issued for the 7 Aug 2020 event.

Preliminary Local Storm Reports

NWUS51 KPHI 121446
LSRPHI

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1046 AM EDT WED AUG 12 2020

...STORM REPORTS FROM AUGUST 7...

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0502 PM     TSTM WND DMG     2 NNW SADSBURYVILLE     40.00N 75.91W
08/07/2020                   CHESTER            PA   DEPT OF HIGHWAYS 

            DOWN TREE IN WIRES ON OLD WILMINGTON ROAD 
            AND OAK STREET. TIME ESTIMATED FROM RADAR. 

0503 PM     TSTM WND DMG     MOUNT VERNON            39.81N 76.02W
08/07/2020                   CHESTER            PA   DEPT OF HIGHWAYS 

            DOWNED TREE INTO WIRES ON PA 472 NEAR 
            OXFORD. TIME ESTIMATED FROM RADAR. 

0505 PM     TSTM WND DMG     COCHRANVILLE            39.89N 75.92W
08/07/2020                   CHESTER            PA   911 CALL CENTER  

            TREE BLOWN DOWN BLOCKING SOUTHBOUND LANE AT 
            THE INTERSECTION OF LIMESTONE RD AND GAP 
            NEWPORT PIKE. TIME ESTIMATED FROM RADAR. 

0508 PM     TSTM WND DMG     1 NE LONDONDERRY TWP    39.87N 75.88W
08/07/2020                   CHESTER            PA   FIRE DEPT/RESCUE 

            SEVERAL TREES DOWN ALONG PORTIONS OF ROUTE 
            41. TIME ESTIMATED FROM RADAR. 

0512 PM     TSTM WND DMG     1 SSW EAST BRANDYWINE T 40.02N 75.77W
08/07/2020                   CHESTER            PA   UTILITY COMPANY  

            SEVERAL TREES AND POLES DOWN JUST NORTH OF 
            FISHERVILLE ROAD. TIME ESTIMATED FROM RADAR. 

0525 PM     TSTM WND GST     2 E LONDONDERRY TWP     39.86N 75.84W
08/07/2020  E52 MPH          CHESTER            PA   MESONET          

            52 MPH WIND GUST MEASURED AT WEST GROVE DEOS 
            (DSCR) MESONET. 

0527 PM     FLASH FLOOD      PARKESBURG              39.96N 75.92W
08/07/2020                   CHESTER            PA   LAW ENFORCEMENT  

            WATER RESCUE REPORTED AT MAPLE ST AND S 
            CULVERT ST IN PARKESBURG BOROUGH. TIME 
            ESTIMATED FROM DISPATCH. 

0538 PM     TSTM WND DMG     HOCKESSIN               39.79N 75.69W
08/07/2020                   NEW CASTLE         DE   BROADCAST MEDIA  

            SOME TREES DOWN IN HOCKESSIN. TIME ESTIMATED 
            FROM RADAR. 

0540 PM     TSTM WND DMG     1 SE WEST GOSHEN        39.96N 75.56W
08/07/2020                   CHESTER            PA   DEPT OF HIGHWAYS 

            DOWNED TREE IN WIRES ON WESTTOWN THORNTON 
            ROAD AND FIVE POINTS ROAD. TIME ESTIMATED 
            FROM RADAR. 

0540 PM     TORNADO          ASHLAND                 39.80N 75.66W
08/07/2020                   NEW CASTLE         DE   NWS STORM SURVEY 

            AN EF1 TORNADO WITH WINDS TO 105 MPH TOUCHED 
            DOWN IN ASHLAND AND TRACKED TO MONTCHANIN IN 
            NORTHERN DELAWARE. NUMEROUS TREES WERE 
            DOWNED, SNAPPED OR UPROOTED. A NOTED 
            CONVERGENT PATTERN IN THE DEBRIS WAS 
            OBSERVED IN THE TREE DAMAGE ACROSS THE 
            WILMINGTON COUNTRY CLUB. 

0541 PM     TSTM WND DMG     1 W GREENVILLE          39.78N 75.62W
08/07/2020                   NEW CASTLE         DE   NWS STORM SURVEY 

            SIGNIFICANT STRAIGHT-LINE WIND DAMAGE 
            OCCURRED DUE TO A SEVERE REAR-FLANK 
            DOWNDRAFT WITH WINDS UP TO 95 MPH. THIS 
            OCCURRED FROM GREENVILLE TO WILMINGTON IN 
            NORTHERN DELAWARE. QUITE A BIT OF TREE 
            DAMAGE OCCURRED INCLUDING A TREE SNAPPED AT 
            ITS BASE. THE SIGNIFICANT DAMAGE ENDED NEAR 
            THE DELAWARE ART MUSEUM IN THE KENTMERE 
            SECTION OF WILMINGTON. SPORADIC DAMAGE 
            CONTINUED EAST TOWARD THE INTERSECTION OF 
            I-95 AND CONCORD PIKE WHERE UTILITY 
            COMPANIES HAD TO REMOVE DEBRIS FROM THE 
            POWER LINES AND ADDITIONAL TREES WERE 
            KNOCKED DOWN IN HAYNES PARK. 

0545 PM     FLASH FLOOD      HOCKESSIN               39.79N 75.69W
08/07/2020                   NEW CASTLE         DE   BROADCAST MEDIA  

            SIGNIFICANT FLOODING ACROSS LANCASTER PIKE 
            IN HOCKESSIN WITH AT LEAST ONE CAR STUCK IN 
            THE FLOOD WATERS. 

0550 PM     TSTM WND DMG     2 SE EAST NANTMEAL TWP  40.11N 75.69W
08/07/2020                   CHESTER            PA   LAW ENFORCEMENT  

            TREE REPORTED DOWN AT BLACK HORSE RD IN WEST 
            VINCENT TOWNSHIP. TIME ESTIMATED FROM 
            DISPATCH. 

0550 PM     TSTM WND DMG     1 N MONTCHANIN          39.80N 75.59W
08/07/2020                   NEW CASTLE         DE   PUBLIC           

            TREES AND WIRES DOWN ALONG MONTCHANIN RD 
            NORTH OF WILMINTON. TIME ESTIMATED BY RADAR. 

0550 PM     TSTM WND DMG     WEST HAVEN              39.76N 75.59W
08/07/2020                   NEW CASTLE         DE   TRAINED SPOTTER  

            NUMEROUS TREES DOWN OR SNAPPED WITH SOME 
            ONTO HOMES. TIME ESTIMATED FROM RADAR. 

0550 PM     TSTM WND DMG     1 NE WOODDALE           39.78N 75.62W
08/07/2020                   NEW CASTLE         DE   PUBLIC           

            SEVERAL TREES DOWN ALONG CENTERVILLE ROAD IN 
            WESTERN GREENVILLE. TIME ESTIMATED FROM 
            RADAR AND NEARBY REPORTS. 

0550 PM     TSTM WND DMG     GREENVILLE              39.78N 75.60W
08/07/2020                   NEW CASTLE         DE   PUBLIC           

            TREES DOWN IN GREENVILLE. TIME ESTIMATED BY 
            RADAR. 

0552 PM     FLASH FLOOD      1 S KENNETT SQUARE      39.84N 75.71W
08/07/2020                   CHESTER            PA   LAW ENFORCEMENT  

            ONE VEHICLE STUCK IN RISING WATER AT SOUTH 
            ST. AND HARVEY CIRCLE IN KENNETT SQUARE. 
            TIME ESTIMATED FROM DISPATCH. 

0552 PM     TSTM WND DMG     GREENVILLE MANOR        39.78N 75.60W
08/07/2020                   NEW CASTLE         DE   PUBLIC           

            TREES AND POWER POLES DOWN IN GREENVILLE. 
            TIME ESTIMATED FROM RADAR. 

0555 PM     TSTM WND DMG     ROCK MANOR              39.77N 75.55W
08/07/2020                   NEW CASTLE         DE   BROADCAST MEDIA  

            LARGE TREE UPROOTED AND BLOCKING SCHOOL ROAD 
            IN ALAPOCAS. TIME ESTIMATED FROM RADAR. 

0555 PM     TSTM WND DMG     WILMINGTON              39.75N 75.55W
08/07/2020                   NEW CASTLE         DE   BROADCAST MEDIA  

            TREES DOWN OR SNAPPED ON NORTH MADISON 
            STREET BETWEEN WEST 9TH AND WEST 10TH 
            STREETS IN WILMINGTON. TIME ESTIMATED FROM 
            RADAR. 

0555 PM     TSTM WND DMG     PHILLIPS HEIGHTS        39.77N 75.51W
08/07/2020                   NEW CASTLE         DE   AMATEUR RADIO    

            TREE DOWN ONTO POWER LINES AT WILMINGTON 
            WASHINGTON STREET EXTENSION AND HANOVER ROAD 
            IN NORTH WILMINGTON. TIME ESTIMATED FROM 
            RADAR. 

0555 PM     TSTM WND GST     WINTERTHUR              39.80N 75.61W
08/07/2020  M54 MPH          NEW CASTLE         DE   MESONET          

            GREENVILLE DEOS (DGRN) MEASURED A 54 MPH 
            WIND GUST. 

0556 PM     FLOOD            2 S KENNETT SQUARE      39.81N 75.71W
08/07/2020                   CHESTER            PA   911 CALL CENTER  

            STREAM WAS REPORTED BLOCKED AND CREATING A 
            LAKE ON THE ROADWAY AT THE INTERSECTION OF 
            BUCKTOE RD. AND CHANDLER MILL RD. 

0557 PM     TSTM WND DMG     EDGEMOOR GARDENS        39.76N 75.50W
08/07/2020                   NEW CASTLE         DE   FIRE DEPT/RESCUE 

            TREE ONTO A HOUSE WITH PEOPLE TRAPPED IN 
            EDGEMOOR GARDENS. POWER LINES DOWN. TIME 
            ESTIMATED FROM RADAR. 

0558 PM     FLASH FLOOD      1 NE TOUGHKENAMON       39.84N 75.75W
08/07/2020                   CHESTER            PA   LAW ENFORCEMENT  

            ROADWAY FLOODED AT BANCROFT RD AND CRESTVIEW 
            DR IN NEW GARDEN TOWNSHIP. TIME ESTIMATED 
            FROM DISPATCH. 

0603 PM     FLASH FLOOD      1 ESE TRAINER           39.83N 75.39W
08/07/2020                   DELAWARE           PA   911 CALL CENTER  

            WATER RESCUE REPORTED. 

0603 PM     FLASH FLOOD      1 S KENNETT SQUARE      39.84N 75.71W
08/07/2020                   CHESTER            PA   911 CALL CENTER  

            WATER RESCUE AT THE INTERSECTION OF SOUTH 
            STREET AND HARVEY CIRCLE. 

0609 PM     TSTM WND DMG     WINTERTHUR              39.80N 75.61W
08/07/2020                   NEW CASTLE         DE   TRAINED SPOTTER  

            TREES AND WIRES DOWN AT KENNETT PIKE AND OLD 
            KENNETT ROAD. 

0610 PM     FLASH FLOOD      ASTON TWP.              39.86N 75.43W
08/07/2020                   DELAWARE           PA   LAW ENFORCEMENT  

            WATER RESCUE AT WEIR RD AND PENNELL RD. TIME 
            ESTIMATED FROM DISPATCH. 

0610 PM     FLASH FLOOD      1 NW ASHLAND            39.81N 75.67W
08/07/2020                   NEW CASTLE         DE   TRAINED SPOTTER  

            A HOME IN YORKLYN WAS TAKING ON WATER. 

0611 PM     FLASH FLOOD      ASTON TWP.              39.86N 75.42W
08/07/2020                   DELAWARE           PA   LAW ENFORCEMENT  

            WATER RESCUE REPORTED ON RAYMOND AVENUE IN 
            ASHTON TOWNSHIP. 

0612 PM     FLASH FLOOD      GREEN RIDGE             39.87N 75.41W
08/07/2020                   DELAWARE           PA   LAW ENFORCEMENT  

            ROAD CLOSURE AT E DUTTON MILL RD AND CHESTER 
            CREEK RD. TIME ESTIMATED FROM DISPATCH. 

0615 PM     FLASH FLOOD      UPPER CHICHESTER TWP    39.86N 75.46W
08/07/2020                   DELAWARE           PA   PUBLIC           

            PICTURE SHOWS DEEP WATER CLOSING A ROAD IN 
            UPPER CHICHESTER TOWNSHIP. TIME ESTIMATED 
            FROM RADAR AND NEARBY REPORTS. 

0615 PM     TSTM WND DMG     MEDIA                   39.92N 75.39W
08/07/2020                   DELAWARE           PA   TRAINED SPOTTER  

            SEVERAL TREES DOWN ACROSS THE SOUTHERN 
            PORTION OF DELAWARE COUNTY. TIME ESTIMATED 
            FROM RADAR. 

0615 PM     FLASH FLOOD      2 N AVONDALE            39.85N 75.79W
08/07/2020                   CHESTER            PA   911 CALL CENTER  

            WATER RESCUE AT THE INTERSECTION OF MCCUE 
            ROAD AND WOODVIEW ROAD. 

0616 PM     FLASH FLOOD      1 WNW SPRINGFIELD TWP   39.94N 75.35W
08/07/2020                   DELAWARE           PA   LAW ENFORCEMENT  

            CORRECTS PREVIOUS FLASH FLOOD REPORT FROM 1 
            WNW SPRINGFIELD TWP. WATER RESCUE REPORTED 
            ON OLD MARPLE RD MARPLE TOWNSHIP. TIME 
            ESTIMATED FROM DISPATCH. 

0617 PM     FLASH FLOOD      ASTON TWP.              39.87N 75.43W
08/07/2020                   DELAWARE           PA   LAW ENFORCEMENT  

            WATER RESCUE REPORTED AT CONCORD RD IN 
            ASHTON TOWNSHIP. 

0621 PM     FLASH FLOOD      3 S KENNETT SQUARE      39.80N 75.71W
08/07/2020                   CHESTER            PA   LAW ENFORCEMENT  

            CREEK FLOODING AT KAOLIN RD AND CALDWELL LN. 
            ROAD CLOSED. TIMES ESTIMATED FROM DISPATCH. 

0625 PM     FLASH FLOOD      1 ESE LANDENBERG        39.77N 75.74W
08/07/2020                   CHESTER            PA   LAW ENFORCEMENT  

            CORRECTS PREVIOUS FLASH FLOOD REPORT FROM 1 
            ESE LANDENBERG. BROAD RUN RD AT NEWARK RD 
            ROAD CLOSED DUE TO HIGH WATER. TIME 
            ESTIMATED FROM DISPATCH. 

0626 PM     FLASH FLOOD      1 ENE CONCORDVILLE      39.89N 75.51W
08/07/2020                   DELAWARE           PA   LAW ENFORCEMENT  

            WATER RESCUE AT BALTIMORE PIKE AND CHEYNEY 
            RD. TIME ESTIMATED FROM DISPATCH. 

0630 PM     FLASH FLOOD      1 SSW KENNETT SQUARE    39.83N 75.72W
08/07/2020                   CHESTER            PA   LAW ENFORCEMENT  

            WATER RESCUE AT W HILLENDALE RD AND CHANDLER 
            MILL RD. TIME BASED OFF OF DISPATCH. 

0640 PM     HEAVY RAIN       ASTON TWP.              39.87N 75.43W
08/07/2020  M3.51 INCH       DELAWARE           PA   PUBLIC           

            3.51 INCHES OF RAIN IN 50 MINUTES ENDING AT 
            6:40 PM. 

0640 PM     FLASH FLOOD      1 SSW BOOTHWYN          39.82N 75.45W
08/07/2020                   DELAWARE           PA   PUBLIC           

            PICTURE ON SOCIAL MEDIA SHOWS FLOODING AT A 
            LOCAL BUSINESS NEAR THE WEST BRANCH NAAMAN 
            CREEK. TIME ESTIMATED FROM RADAR AND NEARBY 
            REPORTS. 

0650 PM     TSTM WND DMG     YARDLEY                 40.24N 74.84W
08/07/2020                   BUCKS              PA   911 CALL CENTER  

            SEVERAL TREES AND WIRES REPORTED DOWN IN THE 
            AREA OF YARDLEY AND WOODSIDE. TIME ESTIMATED 
            FROM RADAR. 

0650 PM     TSTM WND DMG     WOODSTOWN               39.66N 75.33W
08/07/2020                   SALEM              NJ   PUBLIC           

            SOME TREES DOWN IN THE WOODSTOWN AREA. TIME 
            ESTIMATED FROM RADAR. 

0655 PM     FLOOD            2 E PILESGROVE TWP      39.67N 75.36W
08/07/2020                   SALEM              NJ   TRAINED SPOTTER  

            FLOODING ON KINGS HIGHWAY. 

0700 PM     FLASH FLOOD      MIDDLETOWN TWP.         39.92N 75.42W
08/07/2020                   DELAWARE           PA   TRAINED SPOTTER  

            ROUTE 1 CLOSED IN SEVERAL LOCATIONS DUE TO 
            FLOODING. 

0700 PM     TSTM WND DMG     2 SW GLENDORA           39.82N 75.09W
08/07/2020                   GLOUCESTER         NJ   DEPT OF HIGHWAYS 

            DOWNED TREE, POLE AND WIRES ON NJ 41 BOTH 
            DIRECTIONS NORTH OF GOOD INTENT ROAD IN 
            DEPTFORD TOWNSHIP. ALL LANES CLOSED. TIME 
            ESTIMATED FROM RADAR. 

0700 PM     FLASH FLOOD      LOGAN TWP.              39.80N 75.35W
08/07/2020                   GLOUCESTER         NJ   PUBLIC           

            CARS STUCK IN FLOODED WATER, KNEE HIGH DEEP 
            WATER IN SOME AREAS. TIME ESTIMATED RADAR. 

0705 PM     TSTM WND GST     2 NNE SEABROOK FARMS    39.53N 75.20W
08/07/2020  M89 MPH          CUMBERLAND         NJ   MESONET          

            RUTGERS AGRICULTURAL RESEARCH AND EXTENSION 
            CENTER AT UPPER DEERFIELD, NJ. 

0715 PM     FLASH FLOOD      WOOLWICH TWP            39.76N 75.31W
08/07/2020                   GLOUCESTER         NJ   TRAINED SPOTTER  

            WIDESPREAD FLASH FLOODING OF ROADS AND 
            PROPERTIES REPORTED IN SWEDESBORO. 

0717 PM     TSTM WND GST     4 NNW SEABROOK FARMS    39.55N 75.24W
08/07/2020  M69 MPH          CUMBERLAND         NJ   TRAINED SPOTTER  

            69 MPH THUNDERSTORM WIND GUST MEASURED ON 
            ROUTE 77 AT MILE MARKER 9. 

0720 PM     FLASH FLOOD      3 N PILESGROVE TWP      39.71N 75.38W
08/07/2020                   SALEM              NJ   DEPT OF HIGHWAYS 

            FLOODING ACROSS THE NEW JERSEY TURNPIKE BOTH 
            DIRECTIONS BETWEEN THE DELAWARE MEMORIAL 
            BRIDGE AND US 322. ALL LANES ARE BLOCKED. 

0721 PM     TSTM WND DMG     STILL POND              39.33N 76.04W
08/07/2020                   KENT               MD   DEPT OF HIGHWAYS 

            DELAYED REPORT. WIND-BLOWN DEBRIS CLOSED 
            STATE HIGHWAY 292 NEAR STATE HIGHWAY 566. 
            TIME ESTIMATED FROM RADAR. 

0728 PM     TSTM WND DMG     3 SSE KENTON            39.19N 75.65W
08/07/2020                   KENT               DE   UTILITY COMPANY  

            DELAYED REPORT. DOWNED TREE AND WIRES NEAR 
            SHAWS CORNER ROAD SOUTHEAST OF KENTON. TIME 
            ESTIMATED FROM RADAR. 

0728 PM     TSTM WND DMG     2 SE WOODLAND BEACH     39.31N 75.44W
08/07/2020                   KENT               DE   UTILITY COMPANY  

            DELAYED REPORT. DOWNED TREE AND WIRES NEAR 
            WOODLAND BEACH. TIME ESTIMATED FROM RADAR. 

0744 PM     TSTM WND DMG     TEMPLEVILLE             39.14N 75.77W
08/07/2020                   QUEEN ANNES       MD   DEPT OF HIGHWAYS 

            DELAYED REPORT. WIND-BLOWN DEBRIS CLOSED 
            STATE HIGHWAY 302 NEAR BEAR POND ROAD. TIME 
            ESTIMATED FROM RADAR. 

0745 PM     TSTM WND DMG     1 NW MINOTOLA           39.53N 74.96W
08/07/2020                   ATLANTIC           NJ   PUBLIC           

            TELEPHONE PONES SNAPPED IN HALF WITH WIRES 
            DOWN ON BREWSTER AND FOREST GROVE ROADS. 
            TIME ESTIMATED BY RADAR. 

0745 PM     FLASH FLOOD      SUDLERSVILLE            39.19N 75.86W
08/07/2020                   QUEEN ANNES       MD   DEPT OF HIGHWAYS 

            MD 313 CLOSED AT CHARLES STREET DUE TO HIGH 
            WATER. 

0800 PM     FLOOD            NEWFIELD                39.55N 75.02W
08/07/2020                   GLOUCESTER         NJ   PUBLIC           

            SOCIAL MEDIA VIDEO SHOWS SEVERE BACKYARD 
            FLOODING. TIME ESTIMATED FROM RADAR. 

0828 PM     FLASH FLOOD      1 NW BUENA              39.53N 74.95W
08/07/2020                   ATLANTIC           NJ   DEPT OF HIGHWAYS 

            DELAYED REPORT. FLASH FLOODING CLOSED U.S. 
            HIGHWAY 40 BETWEEN MALAGA ROAD AND EAST 
            SUMMER ROAD IN BUENA. TIME BASED ON DISPATCH 
            REPORT. 

0835 PM     FLASH FLOOD      1 NW VINELAND           39.50N 75.04W
08/07/2020                   CUMBERLAND         NJ   DEPT OF HIGHWAYS 

            DELAYED REPORT. FLASH FLOODING CLOSED STATE 
            HIGHWAY 47 IN AREA OF OAK ROAD IN VINELAND. 
            TIME BASED ON DISPATCH REPORT. 

0846 PM     FLASH FLOOD      2 SW MILLINGTON         39.24N 75.87W
08/07/2020                   QUEEN ANNES       MD   DEPT OF HIGHWAYS 

            DELAYED REPORT. FLASH FLOODING CLOSED STATE 
            HIGHWAY 313 NEAR STATE HIGHWAY 544. TIME 
            BASED ON DISPATCH REPORT. 

0850 PM     TSTM WND DMG     1 ENE SEAVILLE          39.22N 74.68W
08/07/2020                   CAPE MAY           NJ   TRAINED SPOTTER  

            CORRECTS PREVIOUS TSTM WND DMG REPORT FROM 1 
            ENE SEAVILLE. TREE DOWN ON GARDEN STATE 
            PARKWAY NEAR MILE MARKER 21.9. TIME 
            ESTIMATED BY RADAR. 

0850 PM     HEAVY RAIN       VILLAS                  39.03N 74.94W
08/07/2020  M1.00 INCH       CAPE MAY           NJ   TRAINED SPOTTER  

            1 INCH OF RAIN IN JUST 10 MINUTES IN THE 
            VILLAS MIAMI BEACH SECTION. 

0850 PM     HEAVY RAIN       DENNISVILLE             39.20N 74.82W
08/07/2020  M1.10 INCH       CAPE MAY           NJ   TRAINED SPOTTER  

            1.10 INCHES OF RAIN IN JUST 9 MINUTES. 

0854 PM     MARINE TSTM WIND LUDLAM BAY              39.18N 74.70W
08/07/2020  E47 MPH          ANZ453             NJ   PUBLIC           

            41 KNOTS AT LUDLAM BAY. 

0907 PM     FLASH FLOOD      SUDLERSVILLE            39.19N 75.86W
08/07/2020                   QUEEN ANNES       MD   DEPT OF HIGHWAYS 

            DELAYED REPORT. FLASH FLOODING CLOSED STATE 
            HIGHWAY 300 AT STATE HIGHWAY 837. TIME BASED 
            ON DISPATCH REPORT. 

0938 PM     FLASH FLOOD      1 N NORTH WILDWOOD      39.01N 74.80W
08/07/2020                   CAPE MAY           NJ   DEPT OF HIGHWAYS 

            DELAYED REPORT. FLASH FLOODING CLOSED STATE 
            HIGHWAY 147 NEAR MARYLAND AVENUE IN NORTH 
            WILDWOOD. TIME BASED ON DISPATCH REPORT. 

0940 PM     FLASH FLOOD      2 NW CARDIFF            39.43N 74.61W
08/07/2020                   ATLANTIC           NJ   DEPT OF HIGHWAYS 

            DELAYED REPORT. FLASH FLOODING CLOSED U.S. 
            HIGHWAY 40 NEAR ENGLISH CREEK AVENUE. TIME 
            BASED ON DISPATCH REPORT. 

0945 PM     FLASH FLOOD      ELKTON                  39.61N 75.82W
08/07/2020                   CECIL              MD   PUBLIC           

            WATER RESCUE ON DELAWARE AVE NEAR MEADOW 
            PARK. ROAD WAS CLOSED DUE TO FLOODING. TIME 
            ESTIMATED FROM RADAR. 

1003 PM     FLASH FLOOD      1 S POMONA              39.46N 74.54W
08/07/2020                   ATLANTIC           NJ   DEPT OF HIGHWAYS 

            DELAYED REPORT. FLASH FLOODING CLOSED U.S. 
            HIGHWAY 30 NEAR GARDEN STATE PARKWAY. TIME 
            BASED ON DISPATCH REPORT. 


&&

$$

CMS/MJG/LR/MPS/BAH/SFJ/DI

Public Information Statement - New Castle County Tornado

NOUS41 KPHI 101751
PNSPHI
DEZ001>004-MDZ008-012-015-019-020-NJZ001-007>010-012>024-026-027-
PAZ054-055-060>062-070-071-101>106-110600-

Public Information Statement
National Weather Service Mount Holly NJ
151 PM EDT Mon Aug 10 2020

...NWS DAMAGE SURVEY FOR 08/07/20 NEW CASTLE COUNTY DELAWARE TORNADO
AND STRAIGHT LINE WIND EVENT...

.New Castle County, Delaware Tornado...

Start Location...Ashland in New Castle County, Delaware
End Location...Montchanin in New Castle County, Delaware
Date...August 7, 2020
Estimated Time...5:40 PM EDT to 5:51 PM EDT
Maximum EF-Scale Rating...EF1
Estimated Maximum Wind Speed...105 mph
Maximum Path Width...450 yards
Path Length...3.8 miles
Beginning Lat/Lon...39.80/-75.66
Ending Lat/Lon...39.79/-75.58
* Fatalities...0
* Injuries...0

...Summary...
A tornado touched down around 5:40 PM on August 7th close to the 
Ashland Nature Center of the Delaware Nature Society or just east 
of the intersection of Brackenville Road and Barley Mill Road 
where some tree damage occurred. The tornado continued east 
southeast to the Swallow Hill area where there were multiple trees
down across Pyles Ford Road. Trees were snapped at the trunk, 
with one tree falling on the roof of a house. Pyles Ford Road was 
closed due to the amount of tree damage across the road. This wind
damage was estimated to be 105 mph, equivalent to an EF1 on the 
Enhanced Fujita Scale. 

The tornado continued in an easterly direction where substantial 
tree damage occurred just north of Valley Garden Park where over 
20 trees were uprooted or damaged. Campbell Road was also closed 
due to the multiple trees down. More damage occurred along Kennett
Pike between Kirk Road and the entrance of Wilmington Country 
Club where several trees were uprooted along with large tree limbs
knocked down. The tornado continued through the Wilmington 
Country Club where approximately 200 trees were damaged. A noted 
convergent pattern in the debris was observed in the tree damage 
across the Wilmington Country Club. The tornado then continued 
eastward before lifting prior to reaching Rockland, Delaware. No 
further damage was noted in the DuPont Country Club or on Concord 
Pike. 
 
Special thanks is extended to Mr. Lou Ruh, New Castle County 
Emergency Management, trained spotters, and the general public for
their extensive assistance with this survey.

.New Castle County, Delaware Straight-line Wind Event...

Location...Greenville and Wilmington in New Castle County Delaware
Date...August 7, 2020
Estimated Time...5:41 PM EDT to 5:59 PM EDT
Estimated Maximum Wind Speed...95 mph
Maximum Path Width...1800 yards
Path Length...4.51 miles
Beginning Lat/Lon...39.78/-75.62
Ending Lat/Lon...39.76/-75.54
* Fatalities...0
* Injuries...0

...Summary...
The straight-line wind damage, separate and south of the tornado 
track, was in a mostly divergent pattern and was associated with 
the storms severe rear-flank downdraft. The damage began just 
east of Hoopes Reservoir with around 4 trees down near the 
intersection Centreville Road and Barley Mill Road, and additional
tree damage on Hillside Road. Several trees were uprooted and 
fell on wires and poles within the Fairthone section. Additional 
trees were uprooted and damaged within the Greenville Manor 
section. Damage continued southeastward where several trees and 
large branches were knocked down on Buck Road and also in the 
Montchan section. Damage continued southward into the Henry Clay 
section where damage occurred near the Montchanin Road and Kennett
Pike intersection and continued southeast toward Rising Sun Lane.
Near Rising Sun Lane, in particular, a tree was snapped at the 
trunk with damage indicative of near 100 mph winds. Given the less
extensive amount of tree damage in this area compared to the 
Wilmington Country Club, have decided to rate the maximum value of
the estimated wind speed at 95 mph. The damage continued into 
Wilmington where trees were uprooted along West 19 Street and 
Tower Road, south of Rockford Park. Damage continued to the east 
side of Rockford Park where trees were knocked down on Rockford 
Road. The significant damage ended near the Delaware Art Museum in
the Kentmere section of Wilmington. Sporadic damage continued 
east towards the intersection of I-95 and Concord Pike where 
utility companies had to remove debris from the power lines and 
additional trees were knocked down in Haynes Park. 

Special thanks is extended to New Castle County Emergency 
Management, Mr. Lou Ruh, trained spotters and the general public 
for their extensive assistance with this survey.

EF Scale: The Enhanced Fujita Scale classifies tornadoes into the
following categories:

EF0...Weak......65 to 85 mph
EF1...Weak......86 to 110 mph
EF2...Strong....111 to 135 mph
EF3...Strong....136 to 165 mph
EF4...Violent...166 to 200 mph
EF5...Violent...>200 mph

* The information in this statement is preliminary and subject to
change pending final review of the events and publication in NWS
Storm Data.

$$

Robertson/Haines/Miketta/Johnson/Gorse

Radar Interrogation

Notable Radar Imagery (GR2Analyst)


Figure 1: KDOX radar reflectivity factor (left) and storm relative velocity (SRM, right) for the 0.5 degree elevation angle valid at 2141 UTC 7 August 2020. This was near the time of the New Castle County tornado touchdown. Rotation is clearly present, but the storm was not exhibiting an especially classic tornadic couplet signature. The core of this storm was quite intense, as evidenced by the sizable area of >60 dBz echoes near the New Castle, DE and Chester, PA county borders. No severe hail was reported, but some suspended hailstones were likely present aloft.	Figure 2: KDOX radar reflectivity factor (top left), storm relative velocity (SRM, top right), spectrum width (SW, bottom left) and correlation coefficient (CC, bottom right) for the 0.5 degree elevation angle valid at 2148 UTC 7 August 2020. The tornado was near its peak intensity at this point, with a better defined though still not particularly tight velocity couplet visible in the SRM data. The large area of elevated SW values also confirms a messy and turbulent storm structure with multiple areas of strong straight line winds in addition to the tornado. No tornado debris signature (TDS) is evident in the CC data, with lowered CC values northwest of the couplet likely associated with hail in the storm core.

Figure 3: KDOX radar reflectivity factor (left) and storm relative velocity (SRM, right) for the 0.5 degree elevation angle valid at 2153 UTC 7 August 2020. By this time, the tornado had lifted, and the rear flank downdraft (RFD) was surging ahead of the remnant circulation. This in turn posed a significant straight line wind threat, with damaging wind continuing to occur after the tornado lifted thanks to this strong RFD surge.	Figure 4: KDIX radar reflectivity factor (top left), storm relative velocity (SRM, top right), spectrum width (SW, bottom left) and correlation coefficient (CC, bottom right) for the 0.5 degree elevation angle valid at 2150 UTC 7 August 2020, towards the end of the tornado’s lifetime. The KDIX and KDOX radars were at similar distances away from this tornado, but with very different viewing angles. The KDIX radar shows a slightly better defined SRM couplet. However, the more notable difference is in the SW data, with a well-defined “bullseye” of higher spectrum width values, a signature sometimes associated with tornadoes. Once again, no TDS is seen in the CC data, which was quite messy and also appeared to be contaminated by partial or non-uniform beam filling north of the circulation in the “streak” of significantly reduced CC values.

Figure 5: KDIX radar reflectivity factor (left) and storm relative velocity (SRM, right) for the 0.5 degree elevation angle valid at 2155 UTC 7 August 2020, a few minutes after the tornado had lifted. The KDIX radar does a particularly good job showing the transition from a tornadic wind threat to a straight line wind threat, with both the reflectivity and velocity data giving a strong impression that the RFD had surged forward and was producing considerable amounts of wind damage after the tornado lifted. These complexities can make it quite difficult to differentiate the cause of damage during storm surveys for these type of storms.

Figure 6: In addition to severe weather, significant flash flooding occurred on August 7, with storms moving slowly and over top of one another in a moisture laden environment. The radar loop in the Overview section illustrates this, and this map shows observed rainfall values from the Advanced Hydrologic Prediction Service (AHPS) for the 24 hours ending the morning of August 8. A stripe of 2 to 4 inches of rain was recorded, with some locally higher amounts. This produced both roadway and stream flooding, with the Red Clay Creek at Wooddale, DE and the Chester Creek near Chester, PA both reaching major flood stage. There were several reports of road closures and water rescues from vehicles. Saturated ground from the very recent Tropical Storm Isaias exacerbated the flooding problems.

Radar