Alert archive / Pennsylvania / Flash Flood Warnings in 2020

Flash Flood Warning 46, NWS Philadelphia/Mount Holly

August 7, 2020Chester County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Aug 7, 2020, 4:32 PM EDT for Chester County, Pennsylvania. It was in force for 3 hr. 4 reports came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: Aug 7, 2020, 4:32 PM EDT (20:32 UTC)
Expired: Aug 7, 2020, 7:48 PM EDT
In force: 3 hr
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

County Chester County, PA

The radar

The Philadelphia radar (KDIX), 104 km from the middle of the area, began a volume at 20:32 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

What was reported inside it

Time	Report	Where	Remark
Aug 7, 5:27 PM EDT	FLASH FLOOD	Parkesburg, PA	WATER RESCUE REPORTED AT MAPLE ST AND S CULVERT ST IN PARKESBURG BOROUGH. TIME ESTIMATED FROM DISPATCH.
Aug 7, 6:45 PM EDT	HEAVY RAIN 2.8	Atglen, PA	MESONET STATION DW6440 ATGLEN.
Aug 7, 6:47 PM EDT	HEAVY RAIN 3.21	1 Sse Birmingham Twp, PA	MESONET STATION CW4403 CHADDS FORD.
Aug 7, 6:48 PM EDT	HEAVY RAIN 3.11	1 Ne West Goshen, PA	MESONET STATION FW4629 WEST CHESTER.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 8.5 hours before the alert went out and 197 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 301 J/kg
Mixed-layer CIN: -67 J/kg
Mixed-layer LCL: 665 m above ground
0-6 km bulk shear: 22 kt
0-1 km storm-relative helicity: -37 m²/s²
0-3 km storm-relative helicity: 18 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

473 
WGUS51 KPHI 072032
FFWPHI
PAC029-080230-
/O.NEW.KPHI.FF.W.0046.200807T2032Z-200808T0230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Mount Holly NJ
432 PM EDT Fri Aug 7 2020

The National Weather Service in Mount Holly NJ has issued a

* Flash Flood Warning for...
  Chester County in southeastern Pennsylvania...

* Until 1030 PM EDT.

* At 430 PM EDT, Doppler radar indicated that showers and 
  thunderstorms producing heavy rain were moving into Chester County 
  from the west. Flash flooding may begin shortly.

  HAZARD...Flash flooding caused by showers and thunderstorms.

  SOURCE...Radar indicated.

  IMPACT...Flooding of small creeks and streams, urban areas, 
           highways, streets and underpasses as well as other 
           poor drainage and low lying areas.

* Some locations that could experience flooding include...
  West Chester, Phoenixville, Coatesville, Westtown, Downingtown,
  Parkesburg, Honey Brook, Elverson, Pughtown, Marshallton,
  Lionville-Marchwood, Valley Forge, Glenmoore, Paoli, Chester
  Springs, Lionville, Cedarville, Radnor Township, West Goshen and
  Spring City.

Additional rainfall amounts of 1 to 3 inches are possible in the 
warned area.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Protecting yourself from immediate threats to life and safety shall
take priority.  Whenever possible, as long as it does not cause
greater harm, all COVID-19 protective action guidance should be
followed.

Excessive runoff from heavy rainfall will cause flooding of small
creeks and streams, urban areas, highways, streets, and underpasses
as well as other poor drainage areas and low lying spots.

&&

LAT...LON 4004 7593 4011 7594 4024 7570 4022 7561
      4024 7560 4015 7553 4016 7550 4014 7551
      4013 7546 4009 7545 4007 7536 4004 7541
      4000 7545 3998 7544 3995 7551 3988 7558
      3990 7600 3995 7600

FLASH FLOOD...RADAR INDICATED

$$

Iovino

1 follow-up statement

423 
WGUS71 KPHI 072348
FFSPHI

Flash Flood Statement
National Weather Service Mount Holly NJ
748 PM EDT Fri Aug 7 2020

PAC029-072357-
/O.CAN.KPHI.FF.W.0046.000000T0000Z-200808T0230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Chester PA-
748 PM EDT Fri Aug 7 2020

...THE FLASH FLOOD WARNING FOR NORTHERN AND CENTRAL 
CHESTER COUNTY IS CANCELLED...

The heavy rain has ended. Flooding is no longer expected to pose a 
threat in northern and central Chester County. Please continue to 
heed any remaining road closures.

LAT...LON 4004 7593 4011 7594 4024 7570 4022 7561
      4024 7560 4015 7553 4016 7550 4014 7551
      4013 7546 4009 7545 4007 7536 4004 7541
      4000 7545 3998 7544 3995 7551 3988 7558
      3990 7600 3995 7600

$$

Iovino

The office that day

Everything else NWS Philadelphia/Mount Holly issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 7, 6:49 AM EDT	Areal Flood Advisory	PHI	Berks	4 hr
Aug 7, 9:22 AM EDT	Areal Flood Advisory	PHI	Bucks	3 hr
Aug 7, 10:34 AM EDT	Severe Thunderstorm Warning	PHI	Carbon, Lehigh	56 min
Aug 7, 11:28 AM EDT	Special Weather Statement	PHI	Carbon, Lehigh	47 min
Aug 7, 2:34 PM EDT	Areal Flood Advisory	PHI	Berks	4 hr
Aug 7, 3:46 PM EDT	Areal Flood Advisory	PHI	Carbon, Lehigh, Northampton	4 hr
Aug 7, 4:10 PM EDT	Flash Flood Warning	PHI	Berks	2 hr
Aug 7, 4:20 PM EDT	Areal Flood Advisory	PHI	Chester, Montgomery	4 hr
Aug 7, 4:47 PM EDT	Special Weather Statement	PHI	Chester	28 min
Aug 7, 5:00 PM EDT	Severe Thunderstorm Warning	PHI	Chester	60 min
Aug 7, 5:03 PM EDT	Flash Flood Warning	PHI	Chester, Delaware	5 hr
Aug 7, 5:15 PM EDT	Areal Flood Advisory	PHI	Bucks	3 hr
Aug 7, 5:25 PM EDT	Areal Flood Advisory	PHI	Bucks, Montgomery, Philadelphia	3 hr
Aug 7, 5:38 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware, Montgomery, Philadelphia	52 min
Aug 7, 5:43 PM EDT	Flash Flood Warning	PHI	Montgomery, Philadelphia	4 hr
Aug 7, 5:49 PM EDT	Tornado Warning	PHI	Chester, Delaware	26 min
Aug 7, 5:57 PM EDT	Severe Thunderstorm Warning	PHI	Delaware, Philadelphia	48 min
Aug 7, 6:00 PM EDT	Tornado Warning	PHI	Delaware	30 min
Aug 7, 6:39 PM EDT	Severe Thunderstorm Warning	PHI	Bucks	27 min
Aug 7, 7:10 PM EDT	River Flood Warning	PHI	Delaware	7 hr
Aug 7, 7:17 PM EDT	Areal Flood Warning	PHI	Bucks, Montgomery	3 hr

Nearby

Flash Flood Warnings in Pennsylvania, 2020 Every flash flood warning in 2020

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.