Alert archive / Pennsylvania / Flash Flood Warnings in 2018

Flash Flood Warning 58, NWS Philadelphia/Mount Holly

August 11, 2018Chester County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Aug 11, 2018, 1:40 PM EDT for Chester County, Pennsylvania. It was in force for 4 hr. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Aug 11, 2018, 1:40 PM EDT (17:40 UTC)
Expired: Aug 11, 2018, 5:45 PM EDT
In force: 4 hr
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

County Chester County, PA

The radar

The Philadelphia radar (KDIX), 114 km from the middle of the area, began a volume at 17:42 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.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 5.7 hours before the alert went out and 185 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: 963 J/kg
Mixed-layer CIN: -38 J/kg
Mixed-layer LCL: 1021 m above ground
0-6 km bulk shear: 23 kt
0-1 km storm-relative helicity: 59 m²/s²
0-3 km storm-relative helicity: 57 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 1.6

Open this sounding in Storm Lab

The text

As transmitted.

493 
WGUS51 KPHI 111740
FFWPHI
PAC029-112145-
/O.NEW.KPHI.FF.W.0058.180811T1740Z-180811T2145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Mount Holly NJ
140 PM EDT SAT AUG 11 2018

The National Weather Service in Mount Holly NJ has issued a

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

* Until 545 PM EDT.

* At 139 PM EDT, Doppler radar indicated thunderstorms producing 
  heavy rain across central Chester County where between 2 and 3 
  inches has already fallen since this morning. Flash Flooding is 
  expected in this area.

* Some locations that could experience flooding include...
  Coatesville, Downingtown, Parkesburg, Lionville,
  Lionville-Marchwood, Chester Springs, Glenmoore, South Coatesville,
  Modena, Thorndale and Exton.

LAT...LON 4012 7557 3988 7575 3991 7595 4007 7589

$$

jjm

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 11, 2:25 AM EDT	Special Weather Statement	PHI	Berks	65 min
Aug 11, 3:24 AM EDT	Flash Flood Watch	PHI	Berks, Bucks, Carbon, Chester, Delaware, Lehigh and 4 more	20 hr
Aug 11, 3:26 AM EDT	Special Weather Statement	PHI	Berks	64 min
Aug 11, 4:17 AM EDT	Areal Flood Advisory	PHI	Berks	4 hr
Aug 11, 4:26 AM EDT	Coastal Flood Advisory	PHI	Bucks, Delaware, Philadelphia	24 hr
Aug 11, 5:19 AM EDT	Flash Flood Warning	PHI	Berks	3 hr
Aug 11, 5:27 AM EDT	Areal Flood Advisory	PHI	Northampton	4 hr
Aug 11, 6:06 AM EDT	Areal Flood Advisory	PHI	Bucks, Northampton	6 hr
Aug 11, 6:31 AM EDT	Areal Flood Advisory	PHI	Bucks	7 hr
Aug 11, 12:16 PM EDT	Special Weather Statement	PHI	Chester	29 min
Aug 11, 12:48 PM EDT	Areal Flood Advisory	PHI	Chester	3 hr
Aug 11, 1:20 PM EDT	Areal Flood Advisory	PHI	Chester, Montgomery	3 hr
Aug 11, 1:33 PM EDT	Flash Flood Warning	PHI	Chester, Montgomery	4 hr
Aug 11, 1:48 PM EDT	Flash Flood Warning	PHI	Delaware, Philadelphia	4 hr
Aug 11, 1:51 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Chester, Delaware, Montgomery, Philadelphia	39 min
Aug 11, 2:00 PM EDT	Flash Flood Warning	PHI	Bucks, Lehigh, Northampton	9 hr
Aug 11, 2:14 PM EDT	Flash Flood Warning	PHI	Bucks	3 hr
Aug 11, 2:26 PM EDT	Special Weather Statement	PHI	Bucks, Philadelphia	34 min
Aug 11, 2:42 PM EDT	Special Weather Statement	PHI	Bucks	33 min
Aug 11, 3:06 PM EDT	Flash Flood Warning	PHI	Northampton	4 hr
Aug 11, 3:50 PM EDT	Areal Flood Advisory	PHI	Berks, Montgomery	115 min
Aug 11, 4:19 PM EDT	Areal Flood Advisory	PHI	Chester	3 hr
Aug 11, 4:19 PM EDT	Severe Thunderstorm Warning	PHI	Chester	29 min
Aug 11, 4:47 PM EDT	Special Weather Statement	PHI	Montgomery	28 min
Aug 11, 4:52 PM EDT	Areal Flood Advisory	PHI	Carbon, Lehigh	2 hr
Aug 11, 5:36 PM EDT	Areal Flood Warning	PHI	Bucks	4 hr
Aug 11, 5:58 PM EDT	Areal Flood Advisory	PHI	Chester, Delaware, Montgomery, Philadelphia	5 hr
Aug 11, 6:13 PM EDT	Special Weather Statement	PHI	Chester	32 min

Nearby

Flash Flood Warnings in Pennsylvania, 2018 Every flash flood warning in 2018

Sources

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