Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2026

Severe Thunderstorm Warning 312, NWS Philadelphia/Mount Holly

August 20, 2026Chester County, Pennsylvania

NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Aug 20, 2026, 4:59 PM EDT for Chester County, Pennsylvania. It was in force for 46 min. 7 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 20, 2026, 4:59 PM EDT (20:59 UTC)
Expired: Aug 20, 2026, 5:45 PM EDT
In force: 46 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Tornado: Possible
Damage threat: Destructive
Hail: 0.75 in
Wind: 80.0 mph

County Chester County, PA

The radar

The Philadelphia radar (KDIX), 127 km from the middle of the area, began a volume at 21:02 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 20, 5:20 PM EDT	TSTM WND DMG	Honey Brook, PA	Trees down and blocking route 322.
Aug 20, 5:25 PM EDT	TSTM WND DMG	Downington, PA	Basketball hoop knocked over. Estimated max wind gusts up to 80 mph. Time estimated from radar.
Aug 20, 5:25 PM EDT	TSTM WND DMG	Glenmoore, PA	Trees and wires down across Creek Road with wires arcing. Time estimated from radar.
Aug 20, 5:33 PM EDT	TSTM WND DMG	East Brandywine Twp, PA	Report of power lines down in Guthriesville, East Brandywine Township. Time estimated from radar.
Aug 20, 5:38 PM EDT	TSTM WND DMG	East Nantmeal Twp, PA	Trees down.
Aug 20, 5:40 PM EDT	TSTM WND DMG	Downington, PA	Report and photos via social media of at least 2 trees down along East Pennsylvania Avenue in Downingtown. One felled tree appears to have crushed a shed. Time estimated from radar.
Aug 20, 5:40 PM EDT	TORNADO	East Caln Twp, PA	A brief tornado occurred in East Caln Township. The first damage was noted just south of the intersection of East Lancaster Avenue and Quarry Road, where several small tree branches were broken. A path of more broken tree branches, some with diameters up to 5

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

Did it verify

Verified. The Iowa Environmental Mesonet's Cow matched 6 storm reports to this severe thunderstorm warning; the first came 21 minutes after it went out.

Cow counts a report within 15 km of the polygon while the warning was in force: a tornado for a tornado warning; hail of 1 inch or more, a gust of 58 mph or more or wind damage for a severe thunderstorm warning; a flash flood report for a flash flood warning.

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 20, 2:31 PM EDT	Severe Thunderstorm Watch	SPC	7 hr
Aug 20, 2:58 PM EDT	Tornado Watch	SPC	7 hr

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 9.0 hours before the alert went out and 170 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: 97 J/kg
Mixed-layer CIN: -72 J/kg
Mixed-layer LCL: 1192 m above ground
0-6 km bulk shear: 47 kt
0-1 km storm-relative helicity: 115 m²/s²
0-3 km storm-relative helicity: 230 m²/s²
Significant tornado parameter: -0.0
Supercell composite: -0.0

Open this sounding in Storm Lab

The text

As transmitted.

479 
WUUS51 KPHI 202059
SVRPHI
PAC029-202145-
/O.NEW.KPHI.SV.W.0312.260820T2059Z-260820T2145Z/

BULLETIN - EAS ACTIVATION REQUESTED
Severe Thunderstorm Warning
National Weather Service Mount Holly NJ
Issued by National Weather Service New York NY
459 PM EDT Thu Aug 20 2026

The National Weather Service in Mount Holly NJ has issued a

* Severe Thunderstorm Warning for...
  Chester County in southeastern Pennsylvania...

* Until 545 PM EDT.

* At 458 PM EDT, a severe thunderstorm was located near Paradise, or
  9 miles east of Willow Street, moving east at 35 mph.

  THIS IS A DESTRUCTIVE STORM FOR CHESTER COUNTY.

  HAZARD...80 mph wind gusts.

  SOURCE...Trained weather spotters.

  IMPACT...Flying debris will be dangerous to those caught without 
           shelter. Mobile homes will be heavily damaged. Expect 
           considerable damage to roofs, windows, and vehicles. 
           Extensive tree damage and power outages are likely.

* Locations impacted include...
  West Chester, Coatesville, Downingtown, Kennett Square, Parkesburg,
  Honey Brook, Elverson, Homeville, Cochranville, Glenmoore, Chester
  Springs, Pughtown, Lionville, Marshallton, and Lionville-Marchwood.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Tornado Watch remains in effect until 1000 PM EDT for southeastern
Pennsylvania.

Remain alert for a possible tornado! Tornadoes can develop quickly
from severe thunderstorms. If you spot a tornado go at once into the
basement or small central room in a sturdy structure.

For your protection move to an interior room on the lowest floor of a
building.

This is an EXTREMELY DANGEROUS SITUATION. This storm is producing 
widespread wind damage across Lancaster County, PA. SEEK SHELTER NOW 
inside a sturdy structure and stay away from windows!

A Tornado Watch remains in effect until 1000 PM EDT for southeastern
Pennsylvania.

&&

LAT...LON 3983 7602 3985 7602 3985 7601 3987 7600
      3987 7599 3993 7600 3993 7598 3995 7599
      4004 7594 4011 7594 4014 7587 4017 7582
      4019 7559 4002 7553 3984 7561 3982 7604
TIME...MOT...LOC 2058Z 264DEG 32KT 3995 7609 

TORNADO...POSSIBLE
THUNDERSTORM DAMAGE THREAT...DESTRUCTIVE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...OBSERVED
MAX WIND GUST...80 MPH

$$

DeSilva

2 follow-up statements

107 
WWUS51 KPHI 202114
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
Issued by National Weather Service New York NY
514 PM EDT Thu Aug 20 2026

PAC029-202145-
/O.CON.KPHI.SV.W.0312.000000T0000Z-260820T2145Z/
Chester PA-
514 PM EDT Thu Aug 20 2026

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 545 PM EDT
FOR CENTRAL CHESTER COUNTY...

At 513 PM EDT, a severe thunderstorm was located over Parkesburg, or
13 miles southeast of New Holland, moving east at 35 mph.

THIS IS A DESTRUCTIVE STORM FOR CHESTER COUNTY PA.

HAZARD...80 mph wind gusts.

SOURCE...Trained weather spotters.

IMPACT...Flying debris will be dangerous to those caught without 
         shelter. Mobile homes will be heavily damaged. Expect 
         considerable damage to roofs, windows, and vehicles. 
         Extensive tree damage and power outages are likely.

Locations impacted include...
West Chester, Coatesville, Downingtown, Kennett Square, Parkesburg,
Honey Brook, Homeville, Cochranville, Glenmoore, Chester Springs,
Lionville, Marshallton, Lionville-Marchwood, West Goshen, and Atglen.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Tornado Watch remains in effect until 1000 PM EDT for southeastern
Pennsylvania.

Remain alert for a possible tornado! Tornadoes can develop quickly
from severe thunderstorms. If you spot a tornado go at once into the
basement or small central room in a sturdy structure.

For your protection move to an interior room on the lowest floor of a
building.

This is an EXTREMELY DANGEROUS SITUATION. This storm is producing 
widespread wind damage across LANCASTER COUNTY PA. SEEK SHELTER NOW 
inside a sturdy structure and stay away from windows.

&&

LAT...LON 3983 7602 3985 7602 3985 7601 3987 7600
      3987 7599 3993 7600 3993 7598 3995 7599
      4004 7594 4011 7594 4010 7556 4002 7553
      3984 7561 3982 7604
TIME...MOT...LOC 2113Z 270DEG 32KT 3996 7592 

TORNADO...POSSIBLE
THUNDERSTORM DAMAGE THREAT...DESTRUCTIVE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...OBSERVED
MAX WIND GUST...80 MPH

$$

DeSilva

364 
WWUS51 KPHI 202142
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
Issued by National Weather Service New York NY
542 PM EDT Thu Aug 20 2026

PAC029-202151-
/O.EXP.KPHI.SV.W.0312.000000T0000Z-260820T2145Z/
Chester PA-
542 PM EDT Thu Aug 20 2026

...THE SEVERE THUNDERSTORM WARNING FOR CENTRAL CHESTER COUNTY WILL
EXPIRE AT 545 PM EDT...

The storm which prompted the warning has moved out of the area.
Therefore, the warning will be allowed to expire.

A Tornado Watch remains in effect until 1000 PM EDT for southeastern
Pennsylvania.

Remember, a Tornado Warning still remains in effect for Chester 
County until 6 PM!

LAT...LON 3983 7602 3985 7602 3985 7601 3987 7600
      3987 7599 3993 7600 3993 7598 3995 7599
      4004 7594 4011 7594 4010 7556 4002 7553
      3984 7561 3982 7604
TIME...MOT...LOC 2141Z 264DEG 32KT 3998 7561 

$$

DeSilva

What forecasters said that day

The local office's own words before this severe thunderstorm warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Philadelphia/Mount Holly wrote its last area forecast discussion before this severe thunderstorm warning went out at Aug 20, 4:23 PM EDT, 36 minutes earlier. Its key messages:

1. A cold front will cross the region this evening, resulting in widespread showers and thunderstorms. Flash flooding, damaging wind gusts and tornadoes are possible later today. 2. Conditions look to remain unsettled through the weekend, with daily chances of showers and storms each day. 3. Fair weather is expected to return for early next week.

Area forecast discussion, Aug 20, 4:23 PM EDT, 36 minutes before

Area Forecast Discussion
National Weather Service Mount Holly NJ
423 PM EDT Thu Aug 20 2026

.WHAT HAS CHANGED...
Severe thunderstorm and tornado watches now in effect for most
of the forecast area.

&&

.KEY MESSAGES...
1. A cold front will cross the region this evening, resulting
in widespread showers and thunderstorms. Flash flooding,
damaging wind gusts and tornadoes are possible later today.

2. Conditions look to remain unsettled through the
weekend, with daily chances of showers and storms each day.

3. Fair weather is expected to return for early next week.

&&

.DISCUSSION...
KEY MESSAGE 1...Broad troughing will be the main driving force
in the sensible weather into the early to middle part of next
week across much of the Eastern Seaboard. A shortwave will round
the base of the trough today into this evening providing some
mid level synoptic forcing. At the surface a warm front has
lifted north into the Philadelphia metro area with a cold front
approaching from the west.

The trend for increasing QPF and increasing severe weather
potential is being realized this afternoon. Severe thunderstorm,
tornado, and flood watches are in effect for most of the
forecast area.

Mesoanalysis fields this afternoon show moderate to strong
instability centered roughly around the Delmarva peninsula, but
extending north into southern NJ and southeast PA. Deep layer
shear of 40-60kt along with backed low level flow and strongly
curved hodographs will support a tornado risk, most notably from
the Philadelphia metro area and points south. Primary mode at
the moment is supercellular with all attendant risks, but more
multicell clusters may become the primary mode along the cold
front.

The other threat this evening is the potential for flash
flooding. Guidance shows very moisture rich airmass surging into
the region with PWAT values raching 2-2.5 inches. Warm cloud
depths suggest warm rain processes and high precipitation
efficiency into this evening and WPC has introduced a moderate
risk of execessive reainfall from Philadelphia north and east.

In general, expecting anywhere between 1 to 2 inches of rain to
fall, with localized higher amounts up to 3 to 5 inches.

The severe and flooding rain threat will diminish by the late
evening and overnight hours.

KEY MESSAGE 2...Conditions look to remain unsettled through the
weekend, with daily chances of showers and storms each day.

Mid to long range NWP and AI guidance suggests that the pattern
could become unsettled Friday night and into the weekend.
The cold front crossing the area tonight will stall in the
offshore waters. waves of low pressure will ride along the
stalled front resulting in unsettled weather through the
weekend. The main periods to watch are early Saturday through
Saturday evening, with periods of rain increasingly likely, and
again on Sunday. The severe threat appears low at this time but
there could be additional flooding concerns, although no day
has more than a Marginal (1/5) Risk for excessive rainfall.

Temperatures will be seasonable, but humidity will be
uncomfortable.

KEY MESSAGE 3...Fair weather is expected to return for early
next week.

Weak high pressure looks to bring quieter and drier weather in
the early part of the week, with more unsettled conditions
expected later in the week with seasonable temperatures.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Widespread showers and thunderstorms are likely at all
locations this afternoon and evening. Any storms will be
capable of producing very heavy rainfall and LIFR conditions.
Winds will vary depending on location, with northern terminals
experiencing northeast winds 5 to 10 kt where southern
terminals will encounter southeasterly winds around 10 kt. Winds
will be gusty and erratic near any storm. Bulk of the shower and
storm activity ending around 01-02z. Moderate confidence
overall, but low confidence on exact timing details.

Tonight...Sub-VFR conditions probable at times with showers and
thunderstorms continuing into the evening hours. Fog and/or low
stratus possible at night after the precipitation moves out.
Conditions should lift back to VFR near or not long after
daybreak. North/northeast winds around 5 to 10 kt. Moderate
confidence.

Outlook...

Friday through Friday night...Primarily VFR.

Saturday through Sunday...Periods of VFR and sub-VFR at times.
Restrictions expected with daily chances for showers and
thunderstorms.

Monday...VFR. No significant weather expected.

&&

.MARINE...
A cold front will move through tonight, with winds becoming
more north/northeasterly around 10-15 kt. Seas of 2 to 3 feet.
Showers and thunderstorms expected on the waters this evening
into tonight.

Outlook...

Friday through Monday...No marine headlines expected. Showers
and thunderstorms possible during the day Friday through
Sunday.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch until 2 AM EDT Friday for PAZ054-055-060>062-070-
     071-101>106.
NJ...Flood Watch until 2 AM EDT Friday for NJZ001-007>010-012>022-
     025>027.
DE...Flood Watch until 2 AM EDT Friday for DEZ001.
MD...None.
MARINE...None.

&&

DISCUSSION...Manning
AVIATION...Manning
MARINE...Manning

Hazardous weather outlook, Aug 20, 5:12 AM EDT, 11 hours 47 minutes before

Hazardous Weather Outlook
National Weather Service Mount Holly NJ
512 AM EDT Thu Aug 20 2026

MDZ012-015-019-020-210915-
Kent MD-Queen Annes-Talbot-Caroline-
512 AM EDT Thu Aug 20 2026

This Hazardous Weather Outlook is for northeast Maryland.

.DAY ONE...Today and tonight.

Numerous thunderstorms are expected between about 2 PM and 8 PM. These
storms may contain damaging wind gusts and potentially a couple of
tornadoes over the Eastern Shore. Storms will be capable of producing
heavy rainfall, with rainfall rates of 2 to 4" per hour possible.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

Hoeflich

In the hours before

Local storm report, Aug 20, 4:38 PM EDT, 21 minutes before

Preliminary Local Storm Report
National Weather Service Mount Holly NJ
438 PM EDT Thu Aug 20 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0400 PM     Rain             2 SW Stow Creek Twp     39.44N 75.38W
08/20/2026  M3.03 Inch       Cumberland         NJ   Mesonet

            NJNET Greenwich station reported 3.03 inches
            of rainfall in two hours.

&&

MJL

Local storm report, Aug 20, 4:47 PM EDT, 12 minutes before

Preliminary Local Storm Report
National Weather Service Mount Holly NJ
447 PM EDT Thu Aug 20 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0400 PM     Rain             2 S Smyrna Landing      39.28N 75.58W
08/20/2026  M1.92 Inch       Kent               DE   Mesonet

            DEOS Smyrna recorded 1.92 inches of rain
            over 3 hours from 1-4pm.

&&

MJL

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 20, 4:50 PM EDT	Severe Thunderstorm Warning Considerable damage threat	PHI	Berks, Chester	40 min
Aug 20, 5:22 PM EDT	Tornado Warning	PHI	Chester, Delaware	38 min
Aug 20, 5:27 PM EDT	Severe Thunderstorm Warning Considerable damage threat	PHI	Berks, Bucks, Chester, Delaware, Montgomery, Philadelphia	48 min
Aug 20, 5:39 PM EDT	Flash Flood Warning	PHI	Chester, Delaware, Montgomery, Philadelphia	4 hr
Aug 20, 6:13 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Delaware, Montgomery, Philadelphia	47 min
Aug 20, 6:26 PM EDT	Flash Flood Warning	PHI	Bucks, Montgomery, Philadelphia	4 hr

Nearby

Severe Thunderstorm Warnings in Pennsylvania, 2026 Every severe thunderstorm warning in 2026

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.