Numerous showers and thunderstorms developed south of a stalled frontal boundary that was draped from NW to SE across Pennsylvania. Several of these storms produced wind damage and/or large hail, primarily along and south of the Route 22 corridor.
Every event with a place to put it. 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.
Numerous showers and thunderstorms developed south of a stalled frontal boundary that was draped from NW to SE across Pennsylvania. Several of these storms produced wind damage and/or large hail, primarily along and south of the Route 22 corridor.
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 May 12, 2:22 PM EST, 8 minutes earlier.
Area Forecast Discussion National Weather Service State College PA 322 PM EDT Sat May 12 2018 .SYNOPSIS... A frontal boundary extending from Northwestern Pennsylvania to the Lower Susquehanna Valley at midday will wobble north and south over PA into next week. The front will keep the pattern unsettled with an almost- daily chance of rain. && .NEAR TERM /UNTIL 8 PM THIS EVENING/... Latest visible loop shows cu field rapidly expanding in depth and areal coverage across the SW third of the CWA where sfc based capes now exceed 1500 j/kg (INVOF and SE of a weak area of low pressure). Sat loop and meso obs also shows that the quasi-stnry front has sagged south to near I-80 in western and north central PA, and edged just slightly to the east over the Lower Susq Valley as of 19Z. Severe Thunderstorm Watch #84 recently issued through 03Z Sunday over our SW zones and potential exists for another watch (SVR or even Tornado) to be issued over the next few hours across the Lower Susq Valley where LLVL shear and helicity will be maximized along and just to the east of the shallow frontal boundary. The hodograph is highly curved/balloon invof of the sfc frontal boundary with storms likely to move about as they are now (across northern PA) from WNW to ESE at 40-50 MPH. This will generate high helicity/EHI (>1) from I-80 south in the late aftn/early evening. In fact, 0-1KM EHI values are as high as 3-4 m2/s2 along the RT 322 corridor SE of KUNV to KMDT, KLNS and KTHV. LCLs just to the south of the low track will by low - as a ribbon of <1500ft LCLs is progged from I-80 to the Turnpike. The shear is strong no matter what, so the CAPE is the wild-card. CAPE is in question as full solar heating is likely going to be realized just across the SW half of the CWA. Additional heating in the small warm sector over us will further boost MU CAPEs to >2000 j/kg across scent PA as the western llvl flow enhances downslope/adiabatic warming from near KJST and KAOO east to the Lower Susq Mainstem. 3 severe weather dangers are present today from these storms: Damaging wind, large hail and tornadoes. SPC mentions a possible evolution from large hail threat (and tornadoes) in the high shear and nearer to the warm front at first, then a turn to more of a linear/bow-echo mode as the storms sink southward into the high CAPE and slightly lower bulk shear. The set-up this evening also looks similar to the conditions favorable for tornadoes to be embedded in quasi- linear storms. Lastly, training west to east storm cells will bring an enhanced chance of locally heavy rain in excess of 2 inches in just an hour or so with flash flooding possible. Much of our southern CWA in within WPC's Slight risk for excessive rainfall late today and early tonight. So far the bulk of the heavy rain and likely some minor small stream/poor drainage flooding has occurred with a persistent area of showers and embedded TSRA over the northern tier of PA where 1-2 inches of rain has occurred since last night. Late afternoon temps will range from the chilly low to mid 50s across the north to the mid 80s over the tier of PA west of the Lower Susq Valley. && .SHORT TERM /8 PM THIS EVENING THROUGH SUNDAY NIGHT/... Storms should be pushing to the south of much of the area by 9 or 10 pm. While the rainfall may be heavy for brief times as these storms move through, they will be moving so quickly that the threat for (flash) flooding is low. However, the threat for flooding is being considered, as the almost daily showers and thunderstorms will continue into the next week since the flow aloft is expected to remain westerly. The soils will get very wet and the threat for flooding will likely increase through the next few days. Winds do go northerly tonight and try to dry us out. It could get foggy with some clearing possible after all the rain. On the negative side for fog will be the dry air which will move down briefly tonight and early Sun and the flow above the inversion which will stay out of the west and moist. Will just mention patchy fog for the northern half of the area for now since any clearing is in question. Mins will be in the m40s N and near 60 S. Sunday seems like another wet day with occasional showers. Instability is not really in the cards with lots of cloud cover and a diurnal range of only 10-15F in the north and perhaps less than 5F in the south. The NAM is wetter than the GFS and it even has some hint of convection in the PM. Will keep POPs higher than chance, but the scattered coverage at any one time will eventually add up to a likely-catg POP for the whole day. Maxes will be well below normal. The front is far enough to the south that the northern tier could remain dry Sun and Sunday night. Not enough of a flooding threat yet to do more than mention here in the discussion. Some minor problems may crop up in the usual/flashier points and small streams. But, everything is growing and can help soak up the rain and slow down the runoff. && .LONG TERM /MONDAY THROUGH SATURDAY/... The pattern remains quite unsettled through next week as the frontal zone meanders over the Mid Atlantic region. Increasing moisture/dewpoints and above average PW all suggest a daily risk for showers and thunderstorms. Areas of locally heavy rainfall are possible, with the potential for multiple rounds of convection. The specific areas most likely to receive heavy rains will likely be somewhat difficult to pin down until the short term when models begin to resolve mesoscale/convective processes. An upper low developing across the northeastern Gulf of Mexico will supply additional moisture which is projected to advect northward toward the Mid Atlantic by Wednesday. This may set up a potentially more organized moderate to heavy rainfall scenario later next week as the deep moisture plume interacts with the nearly stationary west-east frontal zone. After a cool day on Sunday (Mother's Day), expect temperatures to be above seasonal climate averages next week with a muggy summertime/humid feel given dewpoints in the 60s. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... Regional radar at 1600Z shows numerous showers and embedded thunderstorms across the northern tier counties of PA in association with the approach of a few mid/upper level disturbances riding over the steeper, stationary frontal boundary located in that region. Elongated sfc low pressure (1014 mb) just west of KPBZ will track east over SCENT PA this afternoon and help to enhance llvl convergence and helicity over SPC's Enhanced SVR threat region near and just to the west of the Lower Susq Valley after 19Z. Widespread VFR will occur for the next several hours acrs the SW half of PA, while low stratus cigs will stay intact across areas along and to the east of the Susq Mainstem. Included a trend toward lower conditions across much of the region later this afternoon, with potential strong wind gusts AOA 35kts from the west mentioned in all but the KBFD and KIPT TAFs anywhere from 19 Sat-00Z Sunday. Expect the northern tier of the state to experience frequent showers with low MVFR/high IFR cigs. Across the central and southern portion of the state, the main focus will be on the possibility for a round of strong late afternoon/early evening thunderstorms. Showers will diminish tonight, as the low pressure system tracks east of the area. However, residual low level moisture ascending the mountains will likely result in IFR cigs in the vicinity of KBFD and possibly KJST, while MVFR cigs are likely elsewhere. Outlook... Sun...Rain/low cigs possible. Mon...AM rain/low cigs possible. PM thunderstorm impacts possible southern Pa. Tue-Wed...AM fog possible. Scattered PM thunderstorm impacts possible. && .HYDROLOGY... Rain today does not look to be excessive in most places today, but FFG lower than it was yesterday due to the rainfall we had overnight. The mainl location to watch will be the northern tier of PA. The threat for flooding may increase slightly each day over the next 5 to 7 days with plenty of moisture available in this pattern. The near-tropical system over the eastern GOMEX could feed tropical and/or Atlantic moisture in mid to late week. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Dangelo LONG TERM...Steinbugl AVIATION...Lambert HYDROLOGY...
Hazardous Weather Outlook National Weather Service State College PA 250 PM EDT Sat May 12 2018 PAZ024>028-033>036-056-063-064-131900- Cambria-Blair-Huntingdon-Mifflin-Juniata-Somerset-Bedford-Fulton- Franklin-Perry-Cumberland-Adams- 250 PM EDT Sat May 12 2018 ...SEVERE THUNDERSTORM WATCH 84 IN EFFECT UNTIL 11 PM EDT THIS EVENING... This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...This Afternoon and Tonight. Please listen to NOAA Weather Radio or go to weather.gov/StateCollege on the internet for more information about the following hazards. Severe Thunderstorm Watch. .DAYS TWO THROUGH SEVEN...Sunday through Friday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. PAZ057-059-065-066-131900- Dauphin-Lebanon-York-Lancaster- 250 PM EDT Sat May 12 2018 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...This Afternoon and Tonight. Severe thunderstorms with damaging winds 70 mph or greater and large hail exceeding 1 inch in diameter are probable late this afternoon and evening. A few tornadoes are also possible. .DAYS TWO THROUGH SEVEN...Sunday through Friday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. PAZ017>019-049-050-052-058-131900- Clearfield-Northern Centre-Southern Centre-Union-Snyder- Northumberland-Schuylkill- 250 PM EDT Sat May 12 2018 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...This Afternoon and Tonight. Severe thunderstorms with damaging winds 60 mph or greater and large hail exceeding 1 inch in diameter are possible late this afternoon and early this evening. An isolated weak, short-lived tornado is also possible. .DAYS TWO THROUGH SEVEN...Sunday through Friday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. PAZ010>012-041-042-045-046-051-053-131900- Elk-Cameron-Northern Clinton-Northern Lycoming-Sullivan- Southern Clinton-Southern Lycoming-Montour-Columbia- 250 PM EDT Sat May 12 2018 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...This Afternoon and Tonight. Strong to severe thunderstorms with gusty winds and hail are possible this afternoon into early this evening. Additional rainfall of up to one inch is likely by 10 pm this evening. This will bring 24-hour storm total rainfall of 1 to 2 inches since last night, causing significant rises on, and possibly even some minor flooding of small streams and creeks across northern Pennsylvania. .DAYS TWO THROUGH SEVEN...Sunday through Friday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. PAZ004>006-037-131900- Warren-McKean-Potter-Tioga- 250 PM EDT Sat May 12 2018 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...This Afternoon and Tonight. Rain with occasional thunderstorms will occur into early this evening. Additional rainfall of up to one inch is likely by 7 pm this evening. This will bring 24-hour storm total rainfall of 1.5 to 2.5 inches since last night, causing significant rises on, and possibly even some minor flooding of small streams and creeks across northern Pennsylvania. .DAYS TWO THROUGH SEVEN...Sunday through Friday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1122 AM EDT SAT MAY 12 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0520 PM TSTM WND DMG AMITY HALL 40.45N 77.00W
05/10/2018 PERRY PA 911 CALL CENTER
TREES AND WIRES DOWN ON AMITY ROAD
&&
EVENT NUMBER CTP1801771
TYBURSKISpecial Weather Statement
National Weather Service State College PA
317 PM EDT SAT MAY 12 2018
PAZ024-025-033-034-122000-
Bedford PA-Somerset PA-Blair PA-Cambria PA-
317 PM EDT SAT MAY 12 2018
...STRONG THUNDERSTORMS WILL AFFECT PARTS OF BEDFORD...SOMERSET...
BLAIR...AND CAMBRIA COUNTIES UNTIL 400 PM EDT...
At 316 PM EDT, Doppler radar indicated strong thunderstorms
developing along a line extending from Loretto to near Ligonier.
Movement was east at 45 mph.
Pea size hail and wind gusts up to 55 mph are possible.
Locations impacted include...
Belmont, Johnstown, Westmont, Hollidaysburg, Nanty-Glo, Altoona,
Windber, Portage, Ebensburg, Salix-Beauty Line Park, Osterburg,
Central City, Roaring Spring, Scalp Level, Ski Gap, Loretto, Belsano,
Boswell, Queen and Paint.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
&&
LAT...LON 4036 7900 4049 7892 4060 7875 4058 7818
4056 7820 4053 7817 4057 7813 4049 7815
4050 7813 4047 7813 4023 7829 4005 7861
4015 7916
TIME...MOT...LOC 1916Z 274DEG 39KT 4052 7867 4029 7921
RXRThe State College radar (KCCX), 102 km away, was scanning. The volume nearest the first event began at 19:29 UTC.
9 thunderstorm wind. Local standard time, as filed.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires on Killian Street in Johnstown.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires near Coaldale.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires east of Johnstown.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires near Thomas Mill.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires west of Hillsboro.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires east of Gettysburg.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires along Craley Road near Windsor.
A severe thunderstorm producing winds estimated near 60 mph knocked down a tree and wires along Dairyland Road.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires west of Rawlinsville.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2018Every state in 2018This day in weather historyWarnings in Pennsylvania, May 2018
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: 745455, 745456, 745457, 745458, 745459, 745460, 745461, 745462, 745463.