Alert archive / Pennsylvania / Special Weather Statements in 2021

Special Weather Statement, NWS Philadelphia/Mount Holly

October 5, 2021Montgomery County, Pennsylvania

NWS Philadelphia/Mount Holly issued this special weather statement at Oct 5, 2021, 1:24 AM EDT for Montgomery County, Pennsylvania. It was in force for 36 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued
Oct 5, 2021, 1:24 AM EDT (05:24 UTC)
Expired
Oct 5, 2021, 2:00 AM EDT
In force
36 min
Issued by
NWS Philadelphia/Mount Holly
Hail
0.00 in
Wind
40

County Montgomery County, PA

The radar

The Philadelphia radar (KDIX), 83 km from the middle of the area, began a volume at 05:23 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 00:00Z, 5.4 hours before the alert went out and 216 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-pSkew-T log-p diagram, Washington/Dulle, VA at 00:00Z on 2021-10-05Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 1291 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Washington/Dulle, VA at 00:00Z on 2021-10-05The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 40 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
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
1291 J/kg
Mixed-layer CIN
-7 J/kg
Mixed-layer LCL
1228 m above ground
0-6 km bulk shear
25 kt
0-1 km storm-relative helicity
40 m²/s²
0-3 km storm-relative helicity
49 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.6

Open this sounding in Storm Lab

The text

As transmitted.

411 
WWUS81 KPHI 050524
SPSPHI

Special Weather Statement
National Weather Service Mount Holly NJ
124 AM EDT Tue Oct 5 2021
 
PAZ070-101>104-050600-
Eastern Montgomery PA-Western Montgomery PA-Delaware PA-
Western Chester PA-Eastern Chester PA-
124 AM EDT Tue Oct 5 2021

...A strong thunderstorm will impact portions of southwestern
Montgomery, northeastern Chester and northeastern Delaware Counties
through 200 AM EDT...

At 124 AM EDT, Doppler radar was tracking a strong thunderstorm over
Phoenixville, or 11 miles north of West Chester, moving east at 25
mph.

HAZARD...Wind gusts up to 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around 
         unsecured objects.

Locations impacted include...
Norristown, Phoenixville, Lansdale, West Norriton, East Norriton,
Conshohocken, Ambler, Collegeville, Royersford, Narberth, Trappe,
Pughtown, Bryn Mawr, Trout Lake, Radnor Township,
Lionville-Marchwood, Valley Forge, Plymouth Meeting, Paoli and
Chester Springs.

This includes the following highways...
 Pennsylvania Turnpike between mile markers 312 and 338.
 Northeast Extension between mile markers 21 and 29.
 Interstate 76 in Pennsylvania between mile markers 327 and 338.
 Interstate 476 in Pennsylvania between mile markers 11 and 19.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building. 

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4021 7567 4025 7519 4007 7519 4009 7522
      4006 7526 4001 7521 3999 7525 4003 7567
TIME...MOT...LOC 0524Z 270DEG 24KT 4013 7557 

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

$$

PO

The office that day

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

IssuedProductOfficeCountiesLasted
Oct 5, 12:49 AM EDTSpecial Weather StatementPHISalem26 min
Oct 5, 2:10 AM EDTAreal Flood AdvisoryPHIBurlington, Camden, Gloucester, Salem4 hr
Oct 5, 2:27 AM EDTFlash Flood WarningPHICamden, Gloucester3 hr
Oct 5, 2:51 AM EDTSpecial Weather StatementPHIAtlantic39 min
Oct 5, 3:20 AM EDTAreal Flood AdvisoryPHIAtlantic, Burlington, Ocean3 hr
Oct 5, 3:33 AM EDTSpecial Weather StatementPHIAtlantic57 min
Oct 5, 12:32 AM EDTSpecial Weather StatementPHIChester43 min

Nearby

Special Weather Statements in Pennsylvania, 2021Every 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; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.