Alert archive / Pennsylvania / Special Weather Statements in 2021

Special Weather Statement, NWS Philadelphia/Mount Holly

September 28, 2021Montgomery County, Pennsylvania

NWS Philadelphia/Mount Holly issued this special weather statement at Sep 28, 2021, 9:23 AM EDT for Montgomery County, Pennsylvania. It was in force for 37 min. 2 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: Sep 28, 2021, 9:23 AM EDT (13:23 UTC)
Expired: Sep 28, 2021, 10:00 AM EDT
In force: 37 min
Issued by: NWS Philadelphia/Mount Holly
Hail: 0.50 in
Wind: 40

County Montgomery County, PA

The radar

The Philadelphia radar (KDIX), 94 km from the middle of the area, began a volume at 13:24 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
Sep 28, 9:35 AM EDT	HAIL 0.25	Collegeville, PA
Sep 28, 9:45 AM EDT	HAIL 0.25	1 Sse Kulpsville, PA

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, 1.4 hours before the alert went out and 222 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: 35 J/kg
Mixed-layer CIN: -322 J/kg
Mixed-layer LCL: 1669 m above ground
0-6 km bulk shear: 37 kt
0-1 km storm-relative helicity: 38 m²/s²
0-3 km storm-relative helicity: 138 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.1

Open this sounding in Storm Lab

The text

As transmitted.

210 
WWUS81 KPHI 281323
SPSPHI

Special Weather Statement
National Weather Service Mount Holly NJ
923 AM EDT Tue Sep 28 2021
 
PAZ101-103>106-281400-
Lower Bucks PA-Upper Bucks PA-Eastern Montgomery PA-
Western Montgomery PA-Western Chester PA-
923 AM EDT Tue Sep 28 2021

...A strong thunderstorm will impact portions of central Montgomery,
west central Bucks and northeastern Chester Counties through 1000 AM
EDT...

At 923 AM EDT, Doppler radar was tracking a strong thunderstorm over
Royersford, or 15 miles north of West Chester, moving northeast at 35
mph.

HAZARD...Wind gusts up to 40 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around 
         unsecured objects. Minor damage to outdoor objects is 
         possible.

Locations impacted include...
Norristown, Pottstown, Phoenixville, Lansdale, West Norriton, East
Norriton, Quakertown, Perkasie, Souderton, Ambler, Collegeville,
Royersford, Chalfont, Trappe, Hatfield, Schwenksville, Ivyland, Green
Lane, Fricks and Spring Mount.

This includes the following highways...
 Pennsylvania Turnpike between mile markers 315 and 320.
 Northeast Extension between mile markers 23 and 42.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building. 

&&

LAT...LON 4049 7534 4021 7507 4005 7560 4005 7561
      4022 7567
TIME...MOT...LOC 1323Z 244DEG 32KT 4018 7554 

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH

$$

MPS

The office that day

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

Issued	Product	Office	Counties	Lasted
Sep 28, 8:26 AM EDT	Areal Flood Advisory	PHI	Warren	2 hr
Sep 28, 7:14 PM EDT	Special Weather Statement	PHI	Gloucester	46 min
Sep 28, 7:29 PM EDT	Severe Thunderstorm Warning	PHI	Gloucester, Salem	31 min
Sep 28, 9:47 AM EDT	Special Weather Statement	PHI	Bucks, Montgomery	28 min
Sep 28, 6:15 PM EDT	Special Weather Statement	PHI	Chester	45 min

Nearby

Special Weather Statements in Pennsylvania, 2021 Every special weather statement in 2021

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.