Alert archive / Pennsylvania / Flash Flood Warnings in 2020

Flash Flood Warning 57, NWS Philadelphia/Mount Holly

August 12, 2020Chester County, Pennsylvania; Cecil County, Maryland

NWS Philadelphia/Mount Holly issued this flash flood warning at Aug 12, 2020, 3:36 PM EDT for Chester County, Pennsylvania; Cecil County, Maryland. It was in force for 108 min. 2 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 12, 2020, 3:36 PM EDT (19:36 UTC)
Expired: Aug 12, 2020, 5:24 PM EDT
In force: 108 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

Counties Cecil County, MD, Chester County, PA

The radar

The Dover AFB radar (KDOX), 116 km from the middle of the area, began a volume at 19:36 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 12, 3:45 PM EDT	FLASH FLOOD	1 Wsw Lincoln Universit, PA	OBSERVER REPORTS ROADS IMPASSABLE DUE TO FLASH FLOODING. TIME ESTIMATED FROM RADAR.
Aug 12, 5:25 PM EDT	HEAVY RAIN 2.06	1 Wsw Lincoln Universit, PA

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, 7.6 hours before the alert went out and 148 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: 127 J/kg
Mixed-layer CIN: -149 J/kg
Mixed-layer LCL: 1202 m above ground
0-6 km bulk shear: 15 kt
0-1 km storm-relative helicity: 0 m²/s²
0-3 km storm-relative helicity: 48 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

712 
WGUS51 KPHI 121936
FFWPHI
MDC015-PAC029-122230-
/O.NEW.KPHI.FF.W.0057.200812T1936Z-200812T2230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Mount Holly NJ
336 PM EDT Wed Aug 12 2020

The National Weather Service in Mount Holly NJ has issued a

* Flash Flood Warning for...
  Northeastern Cecil County in northeastern Maryland...
  Southwestern Chester County in southeastern Pennsylvania...

* Until 630 PM EDT.

* At 335 PM EDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Over 2 inches of rain has been 
  reported, and additional rain is expected. Flash flooding is 
  expected to begin shortly.

  HAZARD...Flash flooding caused by thunderstorms.

  SOURCE...Radar indicated.

  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 could experience flooding include...
  Calvert, Oxford, Rising Sun, Glen Roy, Zion, Blake, Lombard,
  Woodlawn, Andora, West Nottingham, Pleasant Hill, Mount Vernon,
  Kemblesville, Fair Hill, Farmington, Appleton, Richardsmere and Bay
  View.

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.

Turn around...don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.

&&

LAT...LON 3974 7612 3973 7610 3974 7610 3976 7606
      3981 7603 3983 7604 3982 7603 3984 7602
      3990 7587 3969 7579 3961 7609 3972 7614

FLASH FLOOD...RADAR INDICATED
EXPECTED RAINFALL...1-2 INCHES IN 1 HOUR

$$

JJM

1 follow-up statement

385 
WGUS71 KPHI 122124
FFSPHI

Flash Flood Statement
National Weather Service Mount Holly NJ
524 PM EDT Wed Aug 12 2020

MDC015-PAC029-122133-
/O.CAN.KPHI.FF.W.0057.000000T0000Z-200812T2230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Cecil MD-Chester PA-
524 PM EDT Wed Aug 12 2020

...THE FLASH FLOOD WARNING FOR NORTHEASTERN CECIL AND SOUTHWESTERN
CHESTER COUNTIES IS CANCELLED... 

Heavy rain has moved out of the area. Flooding no longer poses a 
significant threat in the area. Please continue to heed any 
remaining road closures.

LAT...LON 3974 7612 3973 7610 3974 7610 3976 7606
      3981 7603 3983 7604 3982 7603 3984 7602
      3990 7587 3969 7579 3961 7609 3972 7614

$$

JJM

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 12, 11:48 AM EDT	Special Weather Statement	PHI	Philadelphia	27 min
Aug 12, 12:43 PM EDT	Areal Flood Advisory	PHI	Bucks, Chester, Delaware, Montgomery, Philadelphia	3 hr
Aug 12, 1:12 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware, Montgomery, Philadelphia	48 min
Aug 12, 1:47 PM EDT	Flash Flood Warning	PHI	Chester, Delaware	2 hr
Aug 12, 1:54 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware, Montgomery, Philadelphia	51 min
Aug 12, 2:04 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Montgomery, Philadelphia	21 min
Aug 12, 2:40 PM EDT	Flash Flood Warning	PHI	Chester, Delaware, Montgomery, Philadelphia	3 hr
Aug 12, 2:44 PM EDT	Severe Thunderstorm Warning	PHI	Delaware, Philadelphia	46 min
Aug 12, 3:20 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware	29 min
Aug 12, 5:04 PM EDT	Areal Flood Advisory	PHI	Lehigh, Northampton	56 min
Aug 12, 5:09 PM EDT	Areal Flood Warning	PHI	Berks	51 min
Aug 12, 12:55 PM EDT	Areal Flood Advisory	PHI	Cecil, Kent	3 hr
Aug 12, 3:06 PM EDT	Areal Flood Advisory	PHI	Caroline, Queen Anne's	3 hr
Aug 12, 3:46 PM EDT	Flash Flood Warning	PHI	Caroline	3 hr
Aug 12, 4:02 PM EDT	Special Weather Statement	PHI	Caroline	28 min
Aug 12, 4:11 PM EDT	Areal Flood Warning	PHI	Caroline, Talbot	3 hr
Aug 12, 4:43 PM EDT	Areal Flood Advisory	PHI	Cecil, Kent	54 min

Nearby

Flash Flood Warnings in Pennsylvania, 2020 Flash Flood Warnings in Maryland, 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.