Alert archive / Pennsylvania / Areal Flood Advisories in 2021

Areal Flood Advisory 40, NWS Philadelphia/Mount Holly

July 1, 2021Chester County, Montgomery County, Pennsylvania

NWS Philadelphia/Mount Holly issued this areal flood advisory at Jul 1, 2021, 3:23 PM EDT for Chester County, Montgomery County, Pennsylvania. It was in force for 77 min.

The area

The outline as issued.

The facts

Issued: Jul 1, 2021, 3:23 PM EDT (19:23 UTC)
Expired: Jul 1, 2021, 4:40 PM EDT
In force: 77 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon

Counties Chester County, PA, Montgomery County, PA

The radar

The Philadelphia radar (KDIX), 107 km from the middle of the area, began a volume at 19:26 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 12:00Z, 7.4 hours before the alert went out and 189 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: 604 J/kg
Mixed-layer CIN: -48 J/kg
Mixed-layer LCL: 928 m above ground
0-6 km bulk shear: 32 kt
0-1 km storm-relative helicity: 61 m²/s²
0-3 km storm-relative helicity: 108 m²/s²
Significant tornado parameter: 0.2
Supercell composite: 1.2

Open this sounding in Storm Lab

The text

As transmitted.

111 
WGUS81 KPHI 011923
FLSPHI

Flood Advisory
National Weather Service Mount Holly NJ
323 PM EDT Thu Jul 1 2021

PAC029-091-012230-
/O.NEW.KPHI.FA.Y.0040.210701T1923Z-210701T2230Z/
/00000.N.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Chester PA-Montgomery PA-
323 PM EDT Thu Jul 1 2021

The National Weather Service in Mount Holly has issued a

* Flood Advisory for...
  Chester County in southeastern Pennsylvania...
  Montgomery County in southeastern Pennsylvania...

* Until 630 PM EDT.

* At 323 PM EDT, Doppler radar indicated that heavy rain due to 
  thunderstorms was approaching from the west. Minor flooding is 
  expected to begin shortly in the advisory area. Rainfall amounts 
  of 1 to 2 inches are possible in a short amount of time.

* Some locations that may experience flooding include...
  West Chester, Norristown, Pottstown, Phoenixville, Lansdale, West 
  Norriton, East Norriton, Coatesville, Westtown, Downingtown, 
  Souderton, and Kennett Square.

This includes the following highways...
	Pennsylvania Turnpike between mile markers 301 and 332.
	Interstate 76 in Pennsylvania between mile markers 327 and 330.
	Northeast Extension between mile markers 21 and 38.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Be aware of your surroundings and do not drive on flooded roads.

&&

LAT...LON 4024 7570 4045 7553 4022 7516 4006 7536
      4004 7541 4003 7540 3999 7545 3999 7544
      3994 7552 3992 7552 3987 7560 3984 7560
      3980 7570 3972 7577 3972 7614 3973 7609
      3987 7599 3995 7599 4004 7593 4011 7594

$$

Iovino

1 follow-up statement

547 
WGUS81 KPHI 012040
FLSPHI

Flood Advisory
National Weather Service Mount Holly NJ
440 PM EDT Thu Jul 1 2021

PAC029-091-012050-
/O.CAN.KPHI.FA.Y.0040.000000T0000Z-210701T2230Z/
/00000.N.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Chester PA-Montgomery PA-
440 PM EDT Thu Jul 1 2021

...FLOOD ADVISORY IS CANCELLED FOR CHESTER AND MONTGOMERY COUNTIES...

The heavy rain has ended. Flooding is no longer expected to pose a 
threat. Please continue to heed remaining road closures.

LAT...LON 4024 7570 4045 7553 4022 7516 4006 7536
      4004 7541 4003 7540 3999 7545 3999 7544
      3994 7552 3992 7552 3987 7560 3984 7560
      3980 7570 3972 7577 3972 7614 3973 7609
      3987 7599 3995 7599 4004 7593 4011 7594

$$

Iovino

The office that day

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

Issued	Product	Office	Counties	Lasted
Jun 30, 8:16 PM EDT	Special Weather Statement	PHI	Bucks, Montgomery	44 min
Jun 30, 8:37 PM EDT	Severe Thunderstorm Warning	PHI	Bucks	38 min
Jul 1, 2:51 PM EDT	Special Weather Statement	PHI	Chester, Montgomery	39 min
Jul 1, 3:13 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Bucks, Chester, Lehigh, Montgomery	47 min
Jul 1, 3:48 PM EDT	Areal Flood Advisory	PHI	Bucks, Delaware, Montgomery, Philadelphia	112 min
Jul 1, 3:50 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Chester, Delaware, Montgomery, Philadelphia	40 min
Jul 1, 4:27 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Delaware, Montgomery, Philadelphia	48 min
Jul 1, 4:59 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Philadelphia	46 min
Jul 1, 5:02 PM EDT	Tornado Warning	PHI	Bucks	28 min

Nearby

Areal Flood Advisories in Pennsylvania, 2021 Every areal flood advisory 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.