Alert archive / Pennsylvania / Flash Flood Warnings in 2018

Flash Flood Warning 57, NWS Philadelphia/Mount Holly

August 11, 2018Chester County, Montgomery County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Aug 11, 2018, 1:33 PM EDT for Chester County, Montgomery County, Pennsylvania. It was in force for 4 hr. 1 report 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 11, 2018, 1:33 PM EDT (17:33 UTC)
Expired: Aug 11, 2018, 5:30 PM EDT
In force: 4 hr
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

Counties Chester County, PA, Montgomery County, PA

The radar

The Philadelphia radar (KDIX), 83 km from the middle of the area, began a volume at 17:37 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 11, 2:03 PM EDT	FLASH FLOOD	Washington Park, PA	WATER RESUCE ON CROSSFIELD ROAD.

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, 5.6 hours before the alert went out and 213 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.

013 
WGUS51 KPHI 111733
FFWPHI
PAC029-091-112130-
/O.NEW.KPHI.FF.W.0057.180811T1733Z-180811T2130Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

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

The National Weather Service in Mount Holly NJ has issued a

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

* Until 530 PM EDT.

* At 130 PM EDT, Doppler radar indicated thunderstorms producing 
  heavy rain across northeastern Chester County...moving into 
  central Montgomery County. Soils in these areas are already wet 
  from previous rain. Flash flooding is expected in the areas of 
  heaviest rain.

* Some locations that could experience flooding include...
  West Chester, Norristown, Phoenixville, Lansdale, West Norriton, 
  East Norriton, Westtown, Conshohocken, Hatboro, Souderton, Ambler, 
  Collegeville, Jenkintown, Trappe, Hatfield, Abington, 
  Schwenksville, Bryn Athyn and Marshallton.

Additional rainfall amounts of 1 to 2 inches are possible in the 
warned area.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4036 7540 4015 7503 4007 7519 4009 7522
      4005 7526 4004 7524 4001 7530 4006 7536
      4005 7540 4003 7540 4000 7545 3998 7544
      3993 7554 3984 7562 3991 7573

$$

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, 1:40 PM EDT	Flash Flood Warning	PHI	Chester	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; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.