Ample low level moisture and instability provided the fuel for showers and thunderstorms in the afternoon and evening of the 27th. Some training of storms lead to high water on some streams and creeks in Elliotsville, Fayette county Pennsylvania.
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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 PBZ wrote it up.
Ample low level moisture and instability provided the fuel for showers and thunderstorms in the afternoon and evening of the 27th. Some training of storms lead to high water on some streams and creeks in Elliotsville, Fayette county Pennsylvania.
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 Pittsburgh, PA wrote its last area forecast discussion before the first event at Jul 27, 7:09 PM EST, 21 minutes earlier.
Area Forecast Discussion
National Weather Service Pittsburgh PA
809 PM EDT Thu Jul 27 2017
.SYNOPSIS...
Showers and thunderstorms will continue into Saturday. Heavy
rainfall is possible, especially southeast of Pittsburgh. Dry
and seasonable weather develops by Sunday.
&&
.NEAR TERM /THROUGH FRIDAY/...
A low-level axis of convergence is slowly sagging southward
through the area this evening. This is combining with a bit of
an increase in mid-level dry air concurrent with the
southeastward transitioning of a weak H5 trough. This is
combining to create an axis down with convection has developed
this evening from roughly New Philadelphia, Ohio, toward
Uniontown, PA. Activity has probably peaked given the time int
the diurnal and should slowly sag SE from here on out.
Unfortunately, due to the slow movement of the low-level
convergence zone, some areas may see fairly heavy rainfall from
this first, and much weaker, system this evening. Amounts on a
wide-scale basis shouldn't be particularly heavy, however some
of the areas that are receiving very heavy rainfall this evening
(especially Fayette County), may end up even more vulnerable
going into Friday.
All eyes are then turn toward the next system to affect the
area. A fairly potent mid-level low is quite evident on water
vapor imagery dropping into Minnesota at this time. Model
solutions drop this toward Ohio during the day on Friday with
impressive cooling at 500 mb noted on all solutions. What is
further impressive is the longevity with with a closed 500 mb
system is managing to survive deep into the mid-latitudes during
the peak of the summer. Further, MSLP anomalies from the NAEFS
indicate the deepest ever surface low reflection (for the date)
dropping toward and south of our area.
What this system is bringing with it will thus be impressive
instability via mid-level cooling, the formation of an very odd
warm season trowal that will develop as this system approaches
and crosses the Appalachians and moves from a positive to
neutral and eventually slightly negatively-tilted system.
Likewise, with the development of a trowal, easterly moisture
transport from the Atlantic develops in a quite notable way
going toward the weekend. This is evident via moisture transport
vectors in the 305-315K layer as well as via U-wind anomalies.
Thus, the stage is set for a first purely convective heavy rain
event that transitions into a much more large-scale forced rain
event that will start Friday but surely continue into the
weekend.
Flash flood watches were already issued by the previous shift.
Once the remainder of the 18z data and maybe the 21z SREF rolls
in, it may be necessary to already look at extending these into
Saturday. Fries
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
The upper low will continue to dig sewd on Fri and strengthen
through this timeframe while embarking on its slow trip across
wrn PA Friday night en route to the Delmarva. A surface low
will also strengthen off the Mid-Atlantic coast in response to
its approach. The departure of the low continues to trend
slower on the models as its strength increases and becomes
better resolved, with impacts continuing to linger into Sat at
least as vorticity maxima pivot around the parent low.
Strong 850-700 mb frontogenesis across southern PA may couple
with moist easterly flow to support heavy rain. Nearly-
saturated low levels and a deep warm-cloud layer also support
the heavy rain potential. Localized rain amounts in excess of
two inches are possible, which could promote flooding. A Flash
Flood Watch has been issued beginning early Fri morning and
continuing into early Sat morning.
High PoPs continue across the region through Fri evening as the
upper low crosses, with a slow taper toward the southeast
during the night. Little to no severe risk exists during this
period. The main concern likely will be heavy to excessive
rainfall, especially south and east of Pittsburgh.
In response to the slower model trends with the system's
departure, the decrease in PoPs was slowed through Sat evening,
with all precipitation exiting the area late Sat night.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
A strong upper ridge over the wrn CONUS will dominate the
weather pattern for the remainder of the forecast, spelling some
semblance of mean troughing along the east coast.
Great Lakes high pressure should provide mostly-dry but cooler
weather early next week. Heights begin to rise thereafter,
which will spell a warm-up toward climatological averages.
A frontal boundary will sag into the region mid-week, although
there remains uncertainty in the timing of its arrival and exact
placement. Given the presence of this feature and a moistening
boundary layer, low PoPs were included in the forecast to keep
the forecast during these periods closer to climatological
average.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Conditions should remain VFR at terminals until after midnight,
when MVFR ceilings should expand from south to north. Scattered
showers this evening should diminish after midnight, then also
expand from south to north around sunrise and into the afternoon
hours. Overall coverage of thunderstorms is expected to be
limited enough to not mention in TAFs at this time. Local IFR
conditions will be especially possible Friday afternoon at
locations south and east of Pittsburgh, either through ceilings
or more likely through visibilities in heavier rain showers.
.OUTLOOK...
Restrictions will continue through Sat with slow-moving low
pressure.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...Flash Flood Watch from 6 AM EDT Friday through late Friday
night for MDZ001.
OH...None.
PA...Flash Flood Watch from 6 AM EDT Friday through late Friday
night for PAZ014>016-020>023-029-031-073>076.
WV...Flash Flood Watch from 6 AM EDT Friday through late Friday
night for WVZ001>004-012-021-509>514.
&&Hazardous Weather Outlook...UPDATED National Weather Service Pittsburgh PA 228 PM EDT Thu Jul 27 2017 MDZ001-PAZ021-029-031-073>076-WVZ002>004-012-021-509>514-281830- Garrett-Allegheny-Washington-Greene-Westmoreland-Westmoreland Ridges- Fayette-Fayette Ridges-Brooke-Ohio-Marshall-Wetzel-Marion-Monongalia- Ridges of Eastern Monongalia and Northwestern Preston-Preston- Eastern Preston-Western Tucker-Eastern Tucker- 228 PM EDT Thu Jul 27 2017 ...FLASH FLOOD WATCH IN EFFECT FROM FRIDAY MORNING THROUGH LATE FRIDAY NIGHT... This Hazardous Weather Outlook is for western Maryland, southwest Pennsylvania, northern West Virginia and northern panhandle of West Virginia. .DAY ONE...This Afternoon and Tonight. Isolated severe thunderstorms capable of damaging wind gusts and locally-heavy rain are possible this afternoon and evening. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Flash Flood Watch. Heavy rain is possible Friday and Friday night, with localized storm total rainfall over two inches. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. OHZ039>041-048>050-057>059-068-069-281830- Tuscarawas-Carroll-Columbiana-Coshocton-Harrison-Jefferson-Muskingum- Guernsey-Belmont-Noble-Monroe- 228 PM EDT Thu Jul 27 2017 This Hazardous Weather Outlook is for east central Ohio. .DAY ONE...This Afternoon and Tonight. Isolated severe thunderstorms capable of damaging wind gusts and locally-heavy rain are possible this afternoon and evening. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Localized heavy rainfall Friday and Friday night could lead to sporadic flooding. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. PAZ020-WVZ001-281830- Beaver-Hancock- 228 PM EDT Thu Jul 27 2017 ...FLASH FLOOD WATCH IN EFFECT FROM FRIDAY MORNING THROUGH LATE FRIDAY NIGHT... This Hazardous Weather Outlook is for western Pennsylvania and northern West Virginia. .DAY ONE...This Afternoon and Tonight. Isolated severe thunderstorms capable of damaging wind gusts and locally-heavy rain are possible this afternoon and evening. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Flash Flood Watch. Heavy rain is possible Friday and Friday night, with localized storm total rainfall over two inches. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. PAZ014>016-022-023-281830- Butler-Clarion-Jefferson-Armstrong-Indiana- 228 PM EDT Thu Jul 27 2017 ...FLASH FLOOD WATCH IN EFFECT FROM FRIDAY MORNING THROUGH LATE FRIDAY NIGHT... This Hazardous Weather Outlook is for west central Pennsylvania. .DAY ONE...This Afternoon and Tonight. Isolated severe thunderstorms capable of damaging wind gusts and locally-heavy rain are possible this afternoon and evening. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Flash Flood Watch. Heavy rain is possible Friday and Friday night, with localized storm total rainfall up to two inches. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. PAZ007>009-013-281830- Mercer-Venango-Forest-Lawrence- 228 PM EDT Thu Jul 27 2017 This Hazardous Weather Outlook is for northwest Pennsylvania and western Pennsylvania. .DAY ONE...This Afternoon and Tonight. Hazardous weather is not expected at this time. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Localized heavy rainfall Friday and Friday night could lead to sporadic flooding. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. Kramar
The national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Member of the public reported high water running from Bog Sandy Creek across Quebec Road and Wharton Furnace Road.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2017Every state in 2017This day in weather historyWarnings in Pennsylvania, July 2017
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: 716997.