Tropical Storm Isaias tracked from south to north across far eastern Pennsylvania during the morning and early afternoon of August 4, 2020. Heavy rain impacted the Susquehanna Valley, and there was one report of a tree down on a home in Lancaster County.
Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS CTP wrote it up.
Tropical Storm Isaias tracked from south to north across far eastern Pennsylvania during the morning and early afternoon of August 4, 2020. Heavy rain impacted the Susquehanna Valley, and there was one report of a tree down on a home in Lancaster County. Later that day, isolated storms developed ahead of an approaching cold front with one storm producing a report of a tree down in Blair County with a wind estimated at only 45-50 mph.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS State College, PA wrote its last area forecast discussion before the first event at Aug 4, 10:05 AM EST, 7 minutes earlier.
Area Forecast Discussion National Weather Service State College PA 1105 AM EDT Tue Aug 4 2020 .SYNOPSIS... A corridor of very heavy rainfall associated with tropical storm Isaias will continue to impact eastern Pennsylvania through this afternoon. Heavy rain will rapidly come to an end by this evening and conditions will dry out tonight into Wednesday. Scattered showers and thunderstorms return to the forecast by late in the week as temperatures and humidity trend higher into the weekend. && .NEAR TERM /UNTIL 8 PM THIS EVENING/... The center of Isaias was estimated to be over Dorchester County MD at 14Z, continuing to accelerate north-northeast ahead of a closed low over the northern Great Lakes. Isaias will advance rapidly north-northeast across the western Delmarva Peninsula through midday and along the PA/NJ line this afternoon. Heavy rainfall will continue along a trough ahead of Isaias currently over far eastern PA. Most radar derived estimated pcpn is underdone with ground truth obs reporting 2.5-4 inches in the last 6 hours. Radar and latest guidance trends indicate the greatest potential for flash flooding is quickly shifting to the north/east. The back edge of the rain shield is pulling out of the western edge of the FF watch and will look to cancel at least a portion of the watch with the early afternoon update. Tornado threat appears to be staying to the east of Lancaster Co and we do not anticipate a tornado risk for the remainder of the storm. Heavy rain and flooding remain the primary hazards. NHC derived sustained winds and gusts across the far southeast zones remain below wind advisory criteria from eastern Lancaster to Schuylkill County. The event should be over by 00Z with just lingering showers into early tonight. && .SHORT TERM /8 PM THIS EVENING THROUGH THURSDAY NIGHT/... A few lingering showers will occur tonight, mainly over the western mtns of the state. The lingering effects/runoff of the prior rainfall may be making flooding of larger streams and creek over the ern locations on Wed. However, much if not all of any flooding should be receding by Wed night. Large picture starts with a slight trough with axis over the OH Valley. The upper pattern should then turn more zonal for most of the period but with a couple of small amplitude waves rolling through. Dry high pressure at the sfc will provide a mainly dry weather Wed-Thu as it sits overhead or just to our north. A weak wave of low pressure riding along stalled front to our south will produce a small chc of showers over the srn tier on Thursday. However, it will be light stuff, and no worries for any renewed flooding. && .LONG TERM /FRIDAY THROUGH MONDAY/... GEFS plumes indicate the best chance of rain in the extended forecast will come Friday, when all guidance tracks a decent shortwave east from the Grt Lks. Current forecast calls for around a 50pct chance of PM showers/tstorms based on latest NBM/Superblend. The bulk of medium range guidance supports drier weather next weekend, as shortwave exits the state and surface high pressure builds in. Expect near seasonal temperatures Friday-Saturday, then a return to above normal readings appears likely toward the end of the long term, as surface high passes off the coast and return southwest flow ensues. Have also introduced an increased chance of diurnal convection by Monday, as higher pwats arrive on southwest flow. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... Conditions starting to come down at times across the central and western areas as light rain has started. Earlier discussion below. As of 6 AM, rain and lower clouds starting to work into western areas. Overall looking at wet day, with CIGS lowering some. The morning rain has developed ahead of approaching Isaias, with its impacts peaking during a several hour period midday today as center of storm slides up across Delmarva, near PHI and into NJ. Rain, locally quite heavy will impact eastern third of CWA with continuing restrictions. Central and western areas will see some improvement late morning with lighter, more scattered rain activity as one heads further westward. Mentioned gusty winds across the southeast airfields Tue, with winds diminishing by later in the afternoon. Outlook... Wed-Thu...Trending drier/VFR with just an isolated shower or t-storm possible. Fri-Sat...Local impacts from sct showers/tstms. && .CLIMATE... July 2020 was a remarkably warm and dry month in Central PA. *Average Temperature* -Warmest month on record at Harrisburg & State College (82.2F at MDT, breaking the old record of 81.8F set in July 1999; 77.0F at STC, breaking the old record of 76.5F set in 1955). -T-3rd warmest month at Williamsport (78.2F, tied with July 1921 and behind 1955 with 79.1F and 1901 with 78.9F) *Average Maximum Temperature* -3rd warmest month on record at Harrisburg (92.2F behind 1999 with 93.5F and 1966 with 93.2). -5th warmest month on record at Williamsport (90.0F; record of 93.0F set in 1955 with other warmer Julys in 1988, 1934, and 1921). *Average Minimum Temperature* -Warmest month on record at Harrisburg & State College (72.2F at MDT, shattering the old record of 70.7F last year; 67.5F at STC, breaking the old record of 66.6F set in 2012) -2nd warmest month on record at Williamsport (66.4F behind 1901 with 71.1F) *90 degree days* -2nd most on record at Williamsport with 19, behind 1955 with 25. -T-2nd most on record at Harrisburg with 22, behind 1966 with 23 and tied with 1999. *Precipitation* -Driest July since 2007 at Williamsport (1.86") -Driest July since 2002 at Harrisburg (1.35") -5th driest July at State College (1.38") && .CTP WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through this evening for PAZ036-056>059- 063>066. && SYNOPSIS...Steinbugl NEAR TERM...Steinbugl SHORT TERM...Lambert/Steinbugl LONG TERM...Fitzgerald AVIATION...Steinbugl CLIMATE...Banghoff
Hazardous Weather Outlook National Weather Service State College PA 1038 AM EDT Tue Aug 4 2020 PAZ004>006-010>012-017>019-024>028-033>035-037-041-045-046-049-050- 051445- Warren-McKean-Potter-Elk-Cameron-Northern Clinton-Clearfield- Northern Centre-Southern Centre-Cambria-Blair-Huntingdon-Mifflin- Juniata-Somerset-Bedford-Fulton-Tioga-Northern Lycoming- Southern Clinton-Southern Lycoming-Union-Snyder- 1038 AM EDT Tue Aug 4 2020 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...Today and tonight. No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. PAZ036-056-057-063>065-051445- Franklin-Perry-Dauphin-Cumberland-Adams-York- 1038 AM EDT Tue Aug 4 2020 ...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING... This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...Today and tonight. Please listen to NOAA Weather Radio or go to weather.gov/StateCollege on the internet for more information about the following hazards. Flash Flood Watch. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather. PAZ042-051>053-051445- Sullivan-Montour-Northumberland-Columbia- 1038 AM EDT Tue Aug 4 2020 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...Today and tonight. Heavy rainfall and localized minor flooding are possible through this afternoon. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather. PAZ058-059-066-051445- Schuylkill-Lebanon-Lancaster- 1038 AM EDT Tue Aug 4 2020 ...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING... This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...Today and tonight. Please listen to NOAA Weather Radio or go to weather.gov/StateCollege on the internet for more information about the following hazards. Flash Flood Watch. Strong wind gusts between 35 and 45 mph are possible through early afternoon as tropical storm Isaias tracks from the Delmarva through far southeastern Pennsylvania and New Jersey. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather. MS
Special Weather Statement
National Weather Service State College PA
839 AM EDT Tue Aug 4 2020
PAZ066-041315-
Lancaster PA-
839 AM EDT Tue Aug 4 2020
...SPECIAL WEATHER STATEMENT FOR PARTS OF LANCASTER COUNTY UNTIL 915
AM EDT...
At 838 AM EDT, Doppler radar indicated a shower with strong
winds near Churchtown, moving northwest at 45 mph.
Wind gusts of up to 55 mph are possible.
Locations impacted include...
Ephrata, Lititz, New Holland, Akron, Leola, Denver, Reamstown,
Rothsville, Gap, Adamstown, Brickerville, Terre Hill, Churchtown,
Bareville, Leacock, Bowmansville, Reinholds, Intercourse,
Fivepointville and Schoeneck.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 4010 7594 4004 7594 4000 7596 3997 7604
4024 7642 4025 7631 4031 7617 4031 7614
4014 7587
TIME...MOT...LOC 1238Z 155DEG 41KT 4009 7599
ColbertSpecial Weather Statement
National Weather Service State College PA
955 AM EDT Tue Aug 4 2020
PAZ066-041500-
Lancaster PA-
955 AM EDT Tue Aug 4 2020
...SPECIAL WEATHER STATEMENT FOR PARTS OF LANCASTER COUNTY UNTIL 1100
AM EDT...
At 953 AM EDT, Doppler radar indicated torrential downpours and
strong gusty winds along a line extending from near Monroe Township
to near Wilmington to Rock Springs.
Movement was north at 40 mph.
Wind gusts of up to 55 mph and localized flooding are possible.
Locations impacted include...
Lancaster, Ephrata, Elizabethtown, Columbia, Lititz, Millersville,
Willow Street, Mount Joy, New Holland, Manheim, East Petersburg,
Akron, Leola, Paradise, Salunga-Landisville, Denver, Maytown,
Reamstown, Rothsville and Strasburg.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with these storms, and may
lead to areas of flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 3983 7635 3991 7639 3995 7648 4005 7653
4006 7666 4012 7672 4016 7670 4019 7661
4025 7631 4031 7616 4014 7587 4010 7594
4004 7594 3996 7599 3987 7599 3985 7602
3976 7606 3973 7610 3974 7611 3972 7622
TIME...MOT...LOC 1353Z 175DEG 35KT 3962 7497 3976 7554 3972 7616
ColbertThe national radar mosaic for the moment the first event began.
1 strong wind, 1 flash flood, 1 thunderstorm wind. Local standard time, as filed.
A strong wind gust associated with Tropical Storm Isaias that was estimated near 50 mph knocked down a tree onto a home in East Hempfield Township.
Flash flooding was reported across the area. A water rescue was performed at the 2400 block of Beaver Valley Pike in New Providence. Flooding blocked one lane of traffic on Route 283 near Route 30 eastbound. Flooding was reported 2 miles north of Ephrata. Flooding was reported on Route 897 in East Cocalico Township. In Lancaster flooding was reported along Steel Way and across Route 283 in Manheim Township.
A thunderstorm producing winds estimated near 45 mph knocked down a tree onto wires and a car at Route 22 and Drass Lane to the west of Williamsburg. A nearby ASOS at KAOO reported a gust to 45mph, and this was the estimate given to this report.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2020Every state in 2020This day in weather historyWarnings in Pennsylvania, August 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 911750, 918712, 911752.