Alert archive / Pennsylvania / Areal Flood Warnings in 2018

Areal Flood Warning 49, NWS Philadelphia/Mount Holly

August 4, 2018Chester County, Montgomery County, Pennsylvania

NWS Philadelphia/Mount Holly issued this areal flood warning at Aug 4, 2018, 8:48 AM EDT for Chester County, Montgomery 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 4, 2018, 8:48 AM EDT (12:48 UTC)
Expired: Aug 4, 2018, 12:45 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), 110 km from the middle of the area, began a volume at 12:50 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, 0.8 hours before the alert went out and 207 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: 148 J/kg
Mixed-layer CIN: -42 J/kg
Mixed-layer LCL: 598 m above ground
0-6 km bulk shear: 24 kt
0-1 km storm-relative helicity: -48 m²/s²
0-3 km storm-relative helicity: 5 m²/s²
Significant tornado parameter: 0.0
Supercell composite: -0.1

Open this sounding in Storm Lab

The text

As transmitted.

140 
WGUS41 KPHI 041248
FLWPHI

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Flood Warning
National Weather Service Mount Holly NJ
848 AM EDT SAT AUG 4 2018

PAC029-091-041645-
/O.NEW.KPHI.FA.W.0049.180804T1248Z-180804T1645Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Montgomery PA-Chester PA-
848 AM EDT SAT AUG 4 2018

The National Weather Service in Mount Holly NJ has issued a

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

* Until 1245 PM EDT.

* At 844 AM EDT, rainfall was tapering off across the area. However, 
  up to two to three inches of rain fell across the area earlier 
  this morning and is leading to local creeks and streams rising, 
  including French Creek near Phoenixville and the Perkiomen Creek. 
  Residual flooding will continue for the next few hours.

* Some locations that could experience flooding include...
  Pottstown, Phoenixville, Collegeville, Royersford, Trappe, East
  Greenville, Schwenksville, Elverson, Green Lane, Pughtown, Spring
  Mount, Valley Forge, Chester Springs, Geryville, Gilbertsville,
  Cedarville, Stowe, Boyertown, Pennsburg and Spring City.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

In hilly terrain there are hundreds of low water crossings which are
potentially dangerous in heavy rain. Do not attempt to cross flooded
roads. Find an alternate route.

Please report flooding to your local law enforcement agency when you
can do so safely.

A Flood Warning means that flooding is imminent or occurring. All
interested parties should take necessary precautions immediately.

&&

LAT...LON 4017 7582 4025 7569 4045 7553 4035 7537
      4006 7548 4015 7584

$$

Robertson

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 3, 8:35 PM EDT	Areal Flood Advisory	PHI	Carbon	4 hr
Aug 3, 9:03 PM EDT	Flash Flood Warning	PHI	Berks	8 hr
Aug 3, 9:10 PM EDT	Areal Flood Advisory	PHI	Monroe, Northampton	4 hr
Aug 3, 10:07 PM EDT	Special Weather Statement	PHI	Lehigh, Northampton	53 min
Aug 3, 10:23 PM EDT	Flash Flood Warning	PHI	Lehigh, Northampton	4 hr
Aug 3, 11:24 PM EDT	Areal Flood Advisory	PHI	Berks, Lehigh	6 hr
Aug 4, 12:24 AM EDT	Areal Flood Advisory	PHI	Carbon	4 hr
Aug 4, 1:08 AM EDT	Areal Flood Advisory	PHI	Monroe	4 hr
Aug 4, 1:15 AM EDT	Special Weather Statement	PHI	Berks	30 min
Aug 4, 1:47 AM EDT	Special Weather Statement	PHI	Berks, Lehigh	43 min
Aug 4, 1:59 AM EDT	Areal Flood Advisory	PHI	Chester	4 hr
Aug 4, 2:22 AM EDT	Areal Flood Warning	PHI	Lehigh, Northampton	21 hr
Aug 4, 2:27 AM EDT	Special Weather Statement	PHI	Lehigh, Northampton	63 min
Aug 4, 4:54 AM EDT	Areal Flood Warning	PHI	Berks	7 hr
Aug 4, 5:09 AM EDT	Areal Flood Advisory	PHI	Monroe	2 hr
Aug 4, 5:45 AM EDT	Areal Flood Advisory	PHI	Bucks, Chester, Montgomery	7 hr
Aug 4, 6:45 AM EDT	River Flood Warning	PHI	Chester	4 hr
Aug 4, 6:55 AM EDT	Areal Flood Advisory	PHI	Bucks, Montgomery	4 hr
Aug 4, 9:20 AM EDT	River Flood Warning	PHI	Montgomery	3 hr
Aug 4, 11:55 AM EDT	River Flood Warning	PHI	Chester, Montgomery, Philadelphia	12 hr
Aug 4, 4:41 PM EDT	Severe Thunderstorm Warning	PHI	Northampton	34 min

Nearby

Areal Flood Warnings in Pennsylvania, 2018 Every areal 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.