Moisture from Tropical Storm Henri brought rain and thunderstorms to the area. One storm became stationary over the New Holland area of Lancaster County, where up to 5 of rain fell in a short time, producing flash flooding.
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The episode as NWS CTP wrote it up.
Moisture from Tropical Storm Henri brought rain and thunderstorms to the area. One storm became stationary over the New Holland area of Lancaster County, where up to 5 of rain fell in a short time, producing flash flooding.
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 22, 1:31 PM EST, 42 minutes earlier.
Area Forecast Discussion National Weather Service State College PA 231 PM EDT Sun Aug 22 2021 .SYNOPSIS... A slow-moving, cut off upper level low is located just south of the area this afternoon while Tropical Storm Henri moves inland over southern New England. The will bring an easterly flow of moisture over the area this afternoon, leading to widespread showers. Some locations east of the Susquehanna Mainstem could see 24 to 36 hour rainfall totals of over 2 inches by late Monday morning. After another round of locally heavy showers and thunderstorms appears likely across the Susquehanna Valley and points east Monday afternoon and evening, before drier air pushes into the region. Summer heat will return by Tuesday lasting the rest of the week. && .NEAR TERM /THROUGH TONIGHT/... Upper level low over MD with TS Henri approaching SNE coast providing moist ENE flow to CWA. Showers across eastern portions of the area with a few pockets of heavy rain. Seeing some rainfall totals between 1-2+ inches, so no doubt there is some tropical moisture in this feed and will continue FFA across our eastern zones this afternoon. The most persistent and widespread rains associated with the western perimeter of Henri's deep tropical moisture will impact the eastern half of the CWA tonight and early Monday with moderate to localized heavy additional rainfall amounts - ranging anywhere from 0.25 to 1.5 inches. It's concerning to see at least a 3 to 4, 6-hour periods late today through Monday morning when the HREF's max QPF amounts to 2 to 3 inches across the Susq valley and points east. These not so subtle aspects of Hurricane Henri's western edge of its deep tropical moisture prompted us to issue a Flood Watch for 3 of our eastern CWA counties from 11 Z today through 12Z Monday. The western half of our CWA will see any isolated convection dying out this evening. && .SHORT TERM /MONDAY THROUGH WEDNESDAY/... With the upper level trough still over eastern PA and plenty of moisture, scattered afternoon and evening thunderstorms are expected again across the whole forecast area. High temps will be in the 80s and still humid with dew points in the lower 70s in many areas. Moisture from Henri will be moving out of the area Monday night into Tuesday morning, yielding rather a pleasant day for Tuesday. Heights will be building aloft so expecting a hot and humid mid week. Temperatures will reach the mid 80s to lower 90s under mostly sunny skies. Conditions will be muggy. Scattered afternoon thundershowers return for Wednesday. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... A cold front pushes southeast from Canada across PA Thursday and stalls to the south of PA Friday and Saturday. The high pressure center over Canada that helps drive the front through gradually shifts east to the coast by Sunday. Southwest flow on the backside of the high brings the front back north and northeast as a warmfront. Thursday will continue hot and muggy then some improvement Friday and Saturday behind the frond. Diurnal trends in POPs can be expected with scattered showers or thunderstorms each day with the fronts moving through. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... MVFR cigs and persistent showers are most likely across the eastern 1/3 of the airspace. Fog is probable again later tonight although could be tempered by rain showers and cloud cover. Outlook... Mon-Thu...Restrictions possible in scattered afternoon showers and isolated t-storms. && .CTP WATCHES/WARNINGS/ADVISORIES... Flood Watch through Monday morning for PAZ058-059-066. && SYNOPSIS...Ross NEAR TERM...Ross/Lambert SHORT TERM...Watson/Lambert LONG TERM...Watson/Gutierrez AVIATION...Ross
Hazardous Weather Outlook National Weather Service State College PA 513 AM EDT Sun Aug 22 2021 PAZ058-059-066-230915- Schuylkill-Lebanon-Lancaster- 513 AM EDT Sun Aug 22 2021 ...FLOOD WATCH IN EFFECT THROUGH MONDAY MORNING... 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. Flood Watch. .DAYS TWO THROUGH SEVEN...Monday through Saturday. Please listen to NOAA Weather Radio or go to weather.gov/StateCollege on the internet for more information about the following hazards. Flood Watch. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather. PAZ042-051>053-057-065-230915- Sullivan-Montour-Northumberland-Columbia-Dauphin-York- 513 AM EDT Sun Aug 22 2021 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...Today and tonight. Localized rainfall amounts of around one inch area possible within slow-moving rain bands. Minor ponding of water in poor drainage areas is possible. .DAYS TWO THROUGH SEVEN...Monday through Saturday. Localized rainfall amounts of around one inch area possible within slow-moving rain bands during the day Monday. Minor ponding of water in poor drainage areas is possible. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather. PAZ004>006-010>012-017>019-024>028-033>037-041-045-046-049-050-056- 063-064-230915- Warren-McKean-Potter-Elk-Cameron-Northern Clinton-Clearfield- Northern Centre-Southern Centre-Cambria-Blair-Huntingdon-Mifflin- Juniata-Somerset-Bedford-Fulton-Franklin-Tioga-Northern Lycoming- Southern Clinton-Southern Lycoming-Union-Snyder-Perry-Cumberland- Adams- 513 AM EDT Sun Aug 22 2021 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...Today and tonight. The probability for widespread hazardous weather is low. .DAYS TWO THROUGH SEVEN...Monday through Saturday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
The Philadelphia radar (KDIX), 142 km away, was scanning. The volume nearest the first event began at 19:13 UTC.
1 flash flood. Local standard time, as filed.
Small streams out of their banks and flooding local roads. Many roads closed and impassible. Flash flooding reported on Gristmill Road.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2021Every state in 2021This day in weather historyWarnings in Pennsylvania, August 2021
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: 968040.