Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2017

Severe Thunderstorm Warning 164, NWS Philadelphia/Mount Holly

August 18, 2017Berks County, Chester County, Montgomery County, Pennsylvania; Cecil County, Maryland

NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Aug 18, 2017, 4:29 PM EDT for Berks County, Chester County, Montgomery County, Pennsylvania; Cecil County, Maryland. It was in force for 61 min. 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 18, 2017, 4:29 PM EDT (20:29 UTC)
Expired: Aug 18, 2017, 5:30 PM EDT
In force: 61 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Tornado: Possible
Hail: 1.0 in
Wind: 60.0 mph

Counties Cecil County, MD, Berks County, PA, Chester County, PA, Montgomery County, PA

The radar

The Dover AFB radar (KDOX), 132 km from the middle of the area, began a volume at 20:31 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, 5:25 PM EDT	TSTM WND DMG	Pikeland, PA	DOWNED TREE IN WIRES ON CLOVER MILL ROAD AND PIKELAND ROAD BETWEEN KIMBERTON ROAD AND CHURCH ROAD. ALL LANES ARE CLOSED. TIME ESTIMATED BY RADAR.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The watch it was issued in

The SPC watch in force over the same counties when this warning went out.

Issued	Product	Office	Lasted
Aug 18, 2:27 PM EDT	Severe Thunderstorm Watch	SPC	9 hr

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 8.5 hours before the alert went out and 163 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: 746 J/kg
Mixed-layer CIN: -72 J/kg
Mixed-layer LCL: 651 m above ground
0-6 km bulk shear: 26 kt
0-1 km storm-relative helicity: 12 m²/s²
0-3 km storm-relative helicity: 76 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.3

Open this sounding in Storm Lab

The text

As transmitted.

927 
WUUS51 KPHI 182029
SVRPHI
MDC015-PAC011-029-091-182130-
/O.NEW.KPHI.SV.W.0164.170818T2029Z-170818T2130Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Mount Holly NJ
429 PM EDT FRI AUG 18 2017

The National Weather Service in Mount Holly NJ has issued a

* Severe Thunderstorm Warning for...
  North central Cecil County in northeastern Maryland...
  Southeastern Berks County in eastern Pennsylvania...
  West central Montgomery County in southeastern Pennsylvania...
  Chester County in southeastern Pennsylvania...

* Until 530 PM EDT

* At 429 PM EDT, severe thunderstorms were located along a line
  extending from near Wyomissing to Holtwood, moving east at 20 mph.

  HAZARD...60 mph wind gusts and quarter size hail. 

  SOURCE...Radar indicated. 

  IMPACT...Minor damage to vehicles is possible. Expect damage to 
           trees and power lines. 

* Locations impacted include...
  Reading, Calvert, Pottstown, Phoenixville, Coatesville, Wyomissing,
  Downingtown, Birdsboro, Collegeville, Oxford, Royersford, Sinking
  Spring, Parkesburg, Trappe, West Grove, Rising Sun, Honey Brook,
  Schwenksville, Elverson and New Morgan.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

To report severe weather, contact your nearest law enforcement
agency. They will send your report to the National Weather Service
office in Mount Holly NJ.

Intense thunderstorm lines can produce brief tornadoes and widespread
significant wind damage. Although a tornado is not immediately
likely, it is best to move to an interior room on the lowest floor of
a building. These storms may cause serious injury and significant
property damage.

&&

LAT...LON 3974 7612 3973 7610 3974 7610 3976 7606
      3983 7604 3987 7599 3995 7600 4004 7593
      4011 7594 4014 7588 4027 7608 4036 7601
      4032 7535 3964 7592 3972 7618
TIME...MOT...LOC 2029Z 282DEG 16KT 4029 7597 3985 7633 

TORNADO...POSSIBLE
HAIL...1.00IN
WIND...60MPH
 
$$

SFJ

2 follow-up statements

031 
WWUS51 KPHI 182046
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
446 PM EDT FRI AUG 18 2017

MDC015-PAC011-029-091-182130-
/O.CON.KPHI.SV.W.0164.000000T0000Z-170818T2130Z/
Cecil MD-Berks PA-Montgomery PA-Chester PA-
446 PM EDT FRI AUG 18 2017

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 530 PM EDT
FOR NORTH CENTRAL CECIL...SOUTHEASTERN BERKS...WEST CENTRAL
MONTGOMERY AND CHESTER COUNTIES...

At 446 PM EDT, severe thunderstorms were located along a line
extending from near Birdsboro to near Wakefield, moving east at 20
mph.

HAZARD...70 mph wind gusts and nickel size hail. 

SOURCE...Radar indicated. 

IMPACT...Expect considerable tree damage. Damage is likely to mobile 
         homes, roofs, and outbuildings. 

Locations impacted include...
Reading, Calvert, Pottstown, Phoenixville, Coatesville, Downingtown,
Birdsboro, Collegeville, Oxford, Royersford, Parkesburg, Trappe, West
Grove, Rising Sun, Honey Brook, Schwenksville, Elverson, New Morgan,
Glen Roy and Blake.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

To report severe weather contact your nearest law enforcement agency.
They will send your report to the National Weather Service office in
Mount Holly NJ.

Intense thunderstorm lines can produce brief tornadoes and widespread
significant wind damage. Although a tornado is not immediately
likely, it is best to move to an interior room on the lowest floor of
a building. These storms may cause serious injury and significant
property damage.

&&

LAT...LON 3974 7612 3973 7610 3974 7610 3976 7606
      3983 7604 3987 7599 3995 7600 4004 7593
      4011 7594 4014 7588 4022 7600 4035 7590
      4032 7535 3964 7592 3972 7618
TIME...MOT...LOC 2046Z 283DEG 19KT 4027 7586 3983 7622 

TORNADO...POSSIBLE
HAIL...0.88IN
WIND...70MPH
 
$$

SFJ

689 
WWUS51 KPHI 182113
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
513 PM EDT FRI AUG 18 2017

PAC011-182122-
/O.CAN.KPHI.SV.W.0164.000000T0000Z-170818T2130Z/
Berks PA-
513 PM EDT FRI AUG 18 2017

...THE SEVERE THUNDERSTORM WARNING FOR SOUTHEASTERN BERKS COUNTY IS
CANCELLED...

The storms which prompted the warning have moved out of the county. 
Therefore, the severe thunderstorm warning has been cancelled. 
However, a flash flood warning remains in effect for portions of the 
county.

A severe thunderstorm watch remains in effect until 900 PM EDT for
northeastern Maryland...and eastern and southeastern Pennsylvania.

LAT...LON 3973 7610 3974 7609 3976 7606 3983 7604
      3987 7599 3995 7600 4004 7593 4011 7594
      4023 7571 4034 7562 4032 7535 3964 7592
      3972 7617
TIME...MOT...LOC 2112Z 282DEG 16KT 4025 7572 3981 7608 

$$

MDC015-PAC029-091-182130-
/O.CON.KPHI.SV.W.0164.000000T0000Z-170818T2130Z/
Cecil MD-Montgomery PA-Chester PA-
513 PM EDT FRI AUG 18 2017

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 530 PM EDT
FOR NORTH CENTRAL CECIL...WEST CENTRAL MONTGOMERY AND CHESTER
COUNTIES...

At 512 PM EDT, severe thunderstorms were located along a line
extending from near Cedarville to near Mount Vernon, moving east at
20 mph.

HAZARD...60 mph wind gusts and nickel size hail. 

SOURCE...Radar indicated. 

IMPACT...Expect damage to trees and power lines. 

Locations impacted include...
Calvert, Pottstown, Phoenixville, Coatesville, Downingtown,
Collegeville, Oxford, Royersford, Parkesburg, Trappe, West Grove,
Rising Sun, Honey Brook, Schwenksville, Elverson, Glen Roy, Blake,
Pughtown, Mount Vernon and Marshallton.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

To report severe weather contact your nearest law enforcement agency.
They will send your report to the National Weather Service office in
Mount Holly NJ.

Intense thunderstorm lines can produce brief tornadoes and widespread
significant wind damage. Although a tornado is not immediately
likely, it is best to move to an interior room on the lowest floor of
a building. These storms may cause serious injury and significant
property damage.

&&

LAT...LON 3973 7610 3974 7609 3976 7606 3983 7604
      3987 7599 3995 7600 4004 7593 4011 7594
      4023 7571 4034 7562 4032 7535 3964 7592
      3972 7617
TIME...MOT...LOC 2112Z 282DEG 16KT 4025 7572 3981 7608 

TORNADO...POSSIBLE
HAIL...0.88IN
WIND...60MPH
 
$$

SFJ

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 18, 3:39 AM EDT	Flash Flood Watch	PHI	Berks, Bucks, Chester, Delaware, Lehigh, Montgomery and 2 more	18 hr
Aug 18, 4:48 AM EDT	Areal Flood Advisory	PHI	Berks, Lehigh, Northampton	4 hr
Aug 18, 2:10 PM EDT	Areal Flood Advisory	PHI	Berks, Carbon, Lehigh	4 hr
Aug 18, 2:21 PM EDT	Special Weather Statement	PHI	Berks	24 min
Aug 18, 2:33 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Lehigh	42 min
Aug 18, 3:14 PM EDT	Special Weather Statement	PHI	Berks, Lehigh	31 min
Aug 18, 3:15 PM EDT	Areal Flood Advisory	PHI	Berks	4 hr
Aug 18, 3:19 PM EDT	Special Weather Statement	PHI	Northampton	26 min
Aug 18, 3:37 PM EDT	Special Weather Statement	PHI	Carbon	38 min
Aug 18, 3:43 PM EDT	Special Weather Statement	PHI	Berks	32 min
Aug 18, 3:45 PM EDT	Areal Flood Advisory	PHI	Carbon, Lehigh, Monroe, Northampton	4 hr
Aug 18, 3:46 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Lehigh, Montgomery, Northampton	44 min
Aug 18, 4:02 PM EDT	Flash Flood Warning	PHI	Berks	4 hr
Aug 18, 4:24 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Bucks, Montgomery	51 min
Aug 18, 4:57 PM EDT	Areal Flood Advisory	PHI	Bucks, Chester, Montgomery	3 hr
Aug 18, 5:03 PM EDT	Severe Thunderstorm Warning	PHI	Chester	42 min
Aug 18, 5:11 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Chester, Delaware, Montgomery, Philadelphia	49 min
Aug 18, 5:20 PM EDT	Areal Flood Advisory	PHI	Bucks, Delaware, Montgomery, Philadelphia	3 hr
Aug 18, 5:39 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware, Philadelphia	66 min
Aug 18, 5:54 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Montgomery, Philadelphia	66 min
Aug 18, 6:38 PM EDT	Special Weather Statement	PHI	Delaware, Philadelphia	37 min
Aug 18, 6:10 PM EDT	Severe Thunderstorm Warning	PHI	Caroline, Kent, Queen Anne's, Talbot	65 min
Aug 18, 6:12 PM EDT	Areal Flood Advisory	PHI	Cecil, Kent, Queen Anne's	3 hr
Aug 18, 7:07 PM EDT	Severe Thunderstorm Warning	PHI	Caroline, Kent, Queen Anne's, Talbot	53 min
Aug 18, 7:33 PM EDT	Areal Flood Advisory	PHI	Caroline, Talbot	3 hr
Aug 18, 7:53 PM EDT	Severe Thunderstorm Warning	PHI	Caroline, Kent, Queen Anne's, Talbot	48 min

Nearby

Severe Thunderstorm Warnings in Pennsylvania, 2017 Severe Thunderstorm Warnings in Maryland, 2017 Every severe thunderstorm warning in 2017

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.