Alert archive / Pennsylvania / Flash Flood Warnings in 2021
Flash Flood Warning 42, NWS Philadelphia/Mount Holly
NWS Philadelphia/Mount Holly issued this flash flood warning at Aug 18, 2021, 10:50 PM EDT for Bucks County, Chester County, Montgomery County, Pennsylvania. It was in force for 4 hr. 11 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 18, 2021, 10:50 PM EDT (02:50 UTC)
- Expired
- Aug 19, 2021, 3:00 AM EDT
- In force
- 4 hr
- Issued by
- NWS Philadelphia/Mount Holly
- Area
- Storm-based polygon
- Flood severity
- None
Counties Bucks County, PA, Chester County, PA, Montgomery County, PA
The radar
The Philadelphia radar (KDIX), 102 km from the middle of the area, began a volume at 02:49 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 18, 11:34 PM EDT | HEAVY RAIN 3.65 | Exton, PA | 3 INCHES HAS FALLEN SINCE 10 PM. |
| Aug 19, 12:06 AM EDT | FLASH FLOOD | 1 Sw Phoenixville, PA | TWO VEHICLES STRANDED IN FLOOD WATERS NEAR THE INTERSECTION OF MADISON AVE AND TYLER AVE. |
| Aug 19, 12:08 AM EDT | FLASH FLOOD | 2 Sw East Whiteland Twp, PA | WATER RESCUE IN THE AREA OF ROUTE 202 AT ROUTE 30 BYPASS. |
| Aug 19, 12:24 AM EDT | FLASH FLOOD | Exton, PA | DELAYED REPORT. SEVERAL VEHICLES STUCK ON LINCOLN HIGHWAY NEAR POTTSTOWN PIKE FROM WATER AND DEBRIS. TIME BASED ON DISPATCH REPORT. |
| Aug 19, 12:27 AM EDT | FLASH FLOOD | West Chester, PA | WATER RESCUE NEAR THE INTERSECTION OF MONTGOMERY AVE AND E GAY ST. |
| Aug 19, 12:55 AM EDT | FLASH FLOOD | 1 Sw East Whiteland Twp, PA | SEVERAL ROADS FLOODED IN THE AREA INCLUDING PLANEBROOK, VALLEY, BACTON HILL, AND ROUTE 401. |
| Aug 19, 1:00 AM EDT | FLASH FLOOD | 1 Ese West Whiteland Tw, PA | DELAYED REPORT. ROCKS AND DEBRIS COVERING COCKERHAM LANE FROM FLOODING. TIME BASED ON NEARBY REPORTS. |
| Aug 19, 1:14 AM EDT | FLASH FLOOD | Royersford, PA | WATER RESCUE ON 1ST AVE. |
| Aug 19, 1:30 AM EDT | FLASH FLOOD | 2 Sw East Whiteland Twp, PA | ROUTE 202 CLOSED IN THE AREA OF ROUTE 30. |
| Aug 19, 1:41 AM EDT | FLASH FLOOD | 3 Sse East Nantmeal Twp, PA | DELAYED REPORT. WATER RESCUE ON PENNSYLVANIA TURNPIKE NEAR LITTLE CONESTOGA ROAD. TIME BASED ON DISPATCH REPORT. |
| Aug 19, 2:05 AM EDT | FLASH FLOOD | West Chester, PA | DELAYED REPORT. WATER RESCUE NEAR THE INTERSECTION OF UNION STREET AND FRANKLIN STREET. TIME BASED ON DISPATCH REPORT. |
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 00:00Z, 2.8 hours before the alert went out and 216 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.
- Mixed-layer CAPE
- 1288 J/kg
- Mixed-layer CIN
- -8 J/kg
- Mixed-layer LCL
- 1100 m above ground
- 0-6 km bulk shear
- 30 kt
- 0-1 km storm-relative helicity
- 126 m²/s²
- 0-3 km storm-relative helicity
- 171 m²/s²
- Significant tornado parameter
- 0.6
- Supercell composite
- 5.9
The text
As transmitted.
689
WGUS51 KPHI 190250
FFWPHI
PAC017-029-091-190700-
/O.NEW.KPHI.FF.W.0042.210819T0250Z-210819T0700Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Mount Holly NJ
1050 PM EDT Wed Aug 18 2021
The National Weather Service in Mount Holly has issued a
* Flash Flood Warning for...
West Central Bucks County in southeastern Pennsylvania...
Northeastern Chester County in southeastern Pennsylvania...
Northwestern Montgomery County in southeastern Pennsylvania...
* Until 300 AM EDT.
* At 1050 PM EDT, Doppler radar and automated rain gauges indicated
thunderstorms producing heavy rain across the warned area. Between
1.5 and 2.5 inches of rain have fallen. Additional rainfall
amounts of 1 to 1.5 inches are possible in the warned area. Flash
flooding is ongoing or expected to begin shortly.
HAZARD...Flash flooding caused by thunderstorms.
SOURCE...Radar and automated gauges.
IMPACT...Flooding of small creeks and streams, urban areas,
highways, streets, and underpasses as well as other
drainage and low lying areas.
* Some locations that will experience flash flooding include...
West Chester, Pottstown, Phoenixville, Perkasie, Downingtown,
Souderton, Collegeville, Royersford, Trappe, East Greenville,
Schwenksville, and Green Lane.
This includes the following highways...
Pennsylvania Turnpike between mile markers 309 and 321.
Northeast Extension between mile markers 30 and 42.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Turn around...don't drown when encountering flooded roads. Most
flood deaths occur in vehicles.
Be especially cautious at night when it is harder to recognize the
dangers of flooding.
&&
LAT...LON 4002 7577 4044 7552 4043 7550 4042 7548
4043 7547 4037 7524 3995 7560
FLASH FLOOD...RADAR AND GAUGE INDICATED
$$
JEO2 follow-up statements
003
WGUS71 KPHI 190517
FFSPHI
Flash Flood Statement
National Weather Service Mount Holly NJ
117 AM EDT Thu Aug 19 2021
PAC017-029-091-190700-
/O.CON.KPHI.FF.W.0042.000000T0000Z-210819T0700Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Bucks PA-Chester PA-Montgomery PA-
117 AM EDT Thu Aug 19 2021
...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 3 AM EDT EARLY THIS
MORNING FOR WEST CENTRAL BUCKS, NORTHEASTERN CHESTER, AND
NORTHWESTERN MONTGOMERY COUNTIES...
At 117 AM EDT, emergency management reported thunderstorms producing
heavy rain across the warned area. Between 3 and 5 inches of rain
have fallen. Several road closures and water rescues have been
reported in portions of Chester County. Flash flooding is already
occurring. The heavy rain has ended, but the flash flood threat will
continue due to the amount of rain that fell and continued runoff.
HAZARD...Flash flooding caused by thunderstorms.
SOURCE...Emergency management reported.
IMPACT...Flooding of small creeks and streams, urban areas,
highways, streets, and underpasses as well as other
drainage and low lying areas.
Some locations that will experience flash flooding include...
West Chester, Pottstown, Phoenixville, Perkasie, Downingtown,
Souderton, Collegeville, Royersford, Trappe, East Greenville,
Schwenksville, and Green Lane.
This includes the following highways...
Pennsylvania Turnpike between mile markers 309 and 321.
Northeast Extension between mile markers 30 and 42.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Turn around...don't drown when encountering flooded roads. Most
flood deaths occur in vehicles.
&&
LAT...LON 4002 7577 4044 7552 4043 7550 4042 7548
4043 7547 4037 7524 3995 7560
FLASH FLOOD...OBSERVED
$$
JEO528
WGUS71 KPHI 190657
FFSPHI
Flash Flood Statement
National Weather Service Mount Holly NJ
257 AM EDT Thu Aug 19 2021
PAC017-029-091-190707-
/O.EXP.KPHI.FF.W.0042.000000T0000Z-210819T0700Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Bucks PA-Chester PA-Montgomery PA-
257 AM EDT Thu Aug 19 2021
...FLASH FLOOD WARNING WILL EXPIRE AT 3 AM EDT EARLY THIS MORNING
FOR WEST CENTRAL BUCKS, NORTHEASTERN CHESTER, AND NORTHWESTERN
MONTGOMERY COUNTIES...
Flood waters have receded. The heavy rain has ended. Flooding is no
longer expected to pose a threat. Please continue to heed remaining
road closures.
LAT...LON 4002 7577 4044 7552 4043 7550 4042 7548
4043 7547 4037 7524 3995 7560
$$
JEOThe office that day
Everything else NWS Philadelphia/Mount Holly issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 18, 8:53 PM EDT | Areal Flood Advisory | PHI | Berks | 3 hr |
| Aug 18, 9:10 PM EDT | Areal Flood Advisory | PHI | Lehigh, Monroe, Northampton | 3 hr |
| Aug 18, 9:30 PM EDT | Flash Flood Warning | PHI | Berks | 2 hr |
| Aug 18, 9:35 PM EDT | Areal Flood Advisory | PHI | Berks, Lehigh | 3 hr |
| Aug 18, 9:45 PM EDT | Areal Flood Advisory | PHI | Berks | 3 hr |
| Aug 18, 9:47 PM EDT | Special Weather Statement | PHI | Berks | 58 min |
| Aug 18, 10:16 PM EDT | Flash Flood Warning | PHI | Berks, Lehigh | 3 hr |
| Aug 18, 10:44 PM EDT | Flash Flood Warning | PHI | Lehigh, Monroe, Northampton | 4 hr |
| Aug 18, 11:19 PM EDT | Areal Flood Advisory | PHI | Bucks, Lehigh, Northampton | 3 hr |
| Aug 18, 11:19 PM EDT | Special Weather Statement | PHI | Bucks, Chester, Montgomery | 41 min |
| Aug 18, 11:47 PM EDT | Flash Flood Warning | PHI | Chester | 2 hr |
| Aug 19, 12:04 AM EDT | Special Weather Statement | PHI | Bucks, Delaware, Montgomery | 71 min |
| Aug 19, 12:26 AM EDT | Tornado Warning | PHI | Bucks, Montgomery | 34 min |
| Aug 19, 12:31 AM EDT | Flash Flood Warning | PHI | Bucks, Chester, Delaware, Montgomery | 4 hr |
| Aug 19, 12:44 AM EDT | River Flood Warning | PHI | Chester | 5 hr |
| Aug 19, 12:47 AM EDT | Tornado Warning | PHI | Chester, Delaware, Montgomery, Philadelphia | 28 min |
| Aug 19, 12:48 AM EDT | Tornado Warning | PHI | Bucks | 27 min |
| Aug 19, 1:14 AM EDT | Special Weather Statement | PHI | Bucks, Delaware, Philadelphia | 91 min |
| Aug 19, 1:30 AM EDT | Flash Flood Warning | PHI | Bucks, Delaware, Montgomery, Philadelphia | 4 hr |
| Aug 19, 2:05 AM EDT | Areal Flood Advisory | PHI | Bucks | 3 hr |
| Aug 19, 2:13 AM EDT | Flash Flood Warning | PHI | Bucks, Philadelphia | 4 hr |
| Aug 19, 4:33 AM EDT | Areal Flood Warning | PHI | Chester, Delaware | 4 hr |
| Aug 19, 6:09 AM EDT | Areal Flood Warning | PHI | Bucks, Philadelphia | 3 hr |
| Aug 19, 8:50 AM EDT | Areal Flood Warning | PHI | Montgomery, Philadelphia | 3 hr |
| Aug 19, 10:40 AM EDT | Areal Flood Warning | PHI | Delaware | 3 hr |
Nearby
Flash Flood Warnings in Pennsylvania, 2021Every flash flood warning in 2021
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.