Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2021

Severe Thunderstorm Warning 253, NWS State College, PA

August 18, 2021York County, Pennsylvania

NWS State College, PA issued this severe thunderstorm warning at Aug 18, 2021, 9:12 PM EDT for York County, Pennsylvania. It was in force for 33 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: Aug 18, 2021, 9:12 PM EDT (01:12 UTC)
Expired: Aug 18, 2021, 9:45 PM EDT
In force: 33 min
Issued by: NWS State College, PA
Area: Storm-based polygon
Tornado: Possible
Hail: 0.75 in
Wind: 60.0 mph

County York County, PA

The radar

The Sterling radar (KLWX), 127 km from the middle of the area, began a volume at 01:13 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 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, 11:37 AM EDT	Tornado Watch	SPC	11 hr

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 00:00Z, 1.2 hours before the alert went out and 124 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: 1288 J/kg
Mixed-layer CIN: -8 J/kg
Mixed-layer LCL: 1100 m above ground
0-6 km bulk shear: 30 kt
0-1 km storm-relative helicity: 126 m²/s²
0-3 km storm-relative helicity: 171 m²/s²
Significant tornado parameter: 0.6
Supercell composite: 5.9

Open this sounding in Storm Lab

The text

As transmitted.

203 
WUUS51 KCTP 190112
SVRCTP
PAC133-190145-
/O.NEW.KCTP.SV.W.0253.210819T0112Z-210819T0145Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service State College PA
912 PM EDT Wed Aug 18 2021

The National Weather Service in State College PA has issued a

* Severe Thunderstorm Warning for...
  Southeastern York County in south central Pennsylvania...

* Until 945 PM EDT.

* At 912 PM EDT, a severe thunderstorm was located near Shrewsbury,
  moving northeast at 40 mph.

  HAZARD...60 mph wind gusts.

  SOURCE...Radar indicated.

  IMPACT...Expect damage to roofs, siding, and trees.

* This severe thunderstorm will be near...
  Cross Roads around 920 PM EDT.
  Brogue around 930 PM EDT.
  Shenks Ferry, Sunnyburn and Safe Harbor around 940 PM EDT.

Other locations impacted by this severe thunderstorm include
Winterstown, Fawn Grove, Felton, Airville, Susquehanna Trails and
Peach Bottom.

This includes Interstate 83 from mile markers 0 to 6.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Tornado Watch remains in effect until 1100 PM EDT for south central
Pennsylvania.

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

A Tornado Watch remains in effect until 1100 PM EDT for south central
Pennsylvania.

&&

LAT...LON 3975 7680 3993 7644 3991 7639 3987 7638
      3985 7635 3983 7635 3977 7627 3975 7626
      3972 7636 3972 7678
TIME...MOT...LOC 0112Z 236DEG 34KT 3972 7666 

TORNADO...POSSIBLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH

$$

Jurewicz

The office that day

Everything else NWS State College, PA issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 18, 8:08 PM EDT	Severe Thunderstorm Warning	CTP	Lancaster, Lebanon	37 min
Aug 18, 8:27 PM EDT	Areal Flood Advisory	CTP	Lancaster, Lebanon	3 hr
Aug 18, 8:45 PM EDT	Special Weather Statement	CTP	Lancaster	45 min
Aug 18, 8:48 PM EDT	Areal Flood Advisory	CTP	Tioga	76 min
Aug 18, 9:11 PM EDT	Flash Flood Warning Considerable damage threat	CTP	Lancaster	108 min
Aug 18, 9:21 PM EDT	Severe Thunderstorm Warning	CTP	Lancaster	39 min
Aug 18, 10:28 PM EDT	Severe Thunderstorm Warning	CTP	Lancaster	47 min
Aug 18, 10:34 PM EDT	Areal Flood Warning	CTP	Lancaster, York	11 min
Aug 18, 10:48 PM EDT	Areal Flood Warning	CTP	Lancaster, York	2 hr
Aug 18, 10:53 PM EDT	Areal Flood Advisory	CTP	Lancaster, York	3 hr
Aug 18, 10:59 PM EDT	Areal Flood Warning	CTP	Lancaster	2 hr

Nearby

Severe Thunderstorm Warnings in Pennsylvania, 2021 Every severe thunderstorm warning 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.