Areal Flood Warning 6, NWS State College, PA

Area Forecast Discussion
National Weather Service State College PA
320 PM EDT Wed Sep 1 2021

.SYNOPSIS...
The post-tropical transition of Ida will bring extreme rainfall
amounts and considerable flooding and flash flooding impacts to
south central PA, the Lower Susquehanna Valley and the Western
Poconos late today and early tonight.

Rises to over flood stage will continue on the larger rivers
across southern PA into Thursday. Refreshingly cooler and drier
(lower humidity) air will follow through late week with fair
weather expected Thursday into the first part of the weekend.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
*High risk for excessive rainfall over south-central PA
*Enhanced risk of severe thunderstorms and a TOR Watch over far
 southeast PA through this evening.

Ida's remnant low center was located near Cumberland, Maryland
at 1830Z and will slide ENE late today.

Widespread moderate to heavy rain will add another 3-4 inches
and exacerbate flooding and flash flooding problems (to
potentially emergency conditions in some locations) near the
I-81 corridor from near Shippensburg, to Harrisburg and
Pottsville late today and this evening as the nose of a strong
40-50 kt southerly LLJ and elevated instability with 2+ inch
PWAT air results in Instantaneous Precip Rates equating to
1-1.5 inches per hour for the next several hours.

Across the NW half of the CWA the rain will gradually lighten
through dusk, then end during the mid to late evening hours,
with generally an inch or less of new rain anticipated after
19Z.

Tor Watch 483 is in effect across Adams, York, and
Lancaster counties through 02Z Thursday, while the Flash Flood
Watch for all but the NW mtns continues through 12Z Thursday
(but will likely be trimmed sooner over the NW part as the rain
tapers off early tonight).

The key for severe TSRA late this afternoon/early evening will
be how far north the warm front can orient itself, as this
boundary will serve as the northern demarcation of meaningful
tornado potential. It is not very often that a portion of our
CWA is included in a 10% tornado probability. Strong vertical
shear will be sufficient for fast- moving, low-topped supercells
with isolated, brief/weak tornadoes possible; the question will
be to the extent of heating/instability needed to support
robust updrafts. SPC kept the enhanced risk (level 3 out of 5)
virtually unchanged over the far lower Susquehanna Valley mainly
along and south of a line from Gettysburg to Lancaster.

Clearing skies approaching the PA/OH border will spread across
the Central and West by around midnight, then across the Susq
Valley and points east shortly before daybreak.

Considerable river flooding is forecast primarily on smaller
streams and creeks in south-central PA with several points
forecast to exceed minor/moderate flood levels. See the
hydrology section for more info and be sure to check the AHPS
page for the latest river forecasts.

MaxT will be -5 to -15F below climo today with 24hr deltas d/d
of the same magnitude.

Min temps at daybreak Thursday could dip into the upper 40s
across the NW, and settle to around 60F in the far SE.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
The departure of Ida's 1000 mb remnant sfc low off the New
England Coast will help to quickly amplify/deepen the SE
Canada/NE US upper trough. This will finally bring a welcome
push of cool and drier Canadian air across the Commonwealth for
at least Thursday and Friday. A refreshing, Autumn-like airmass
with dewpoints in the 40s (NW) and 50s elsewhere will overspread
the CWA on Thursday - aided by a moderately gusty NNW wind into
the 20s (mph).

High temps in the upper 60s (higher elevations across the
north) to low and mid 70s elsewhere will be 7-10 deg F below
normal in most locations. Similar departures are expected with
overnight lows Thursday night and Friday night.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As the Canadian surface high settles south to the Carolinas on
Saturday, dewpoints and temps could rebound slightly as a west
to southwest LLVL flow develops and milder air ridging aloft
pushes east-southeast from the Midwestern states and Upper Great
Lakes.

A cold front approaching from the Great Lakes and 1 or 2
distinct shortwaves dropping SE through a slightly amplifying
northern stream trough will bring a chance of showers back into
the forecast for Sunday or Monday, followed by mainly fair
weather again for Tuesday with just a slight chance of an
afternoon shower. Shower chances increase for Wednesday.

Temperatures next week will be seasonable, with highs in the 70s
and lows in the 50s.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
IFR to LIFR cigs and MVFR to IFR vsbys will persist across
Central and Eastern parts of the CWA through this evening,
before improvement gradually takes place to mainly VFR late
tonight and early Thursday.

LLWS will also be a hazard late Wed afternoon through the
evening across the Lower Susq Valley airfields, with NE flow up
to 45 kts in the lowest 2kft AGL.

Outlook...

Thu...VFR SE Valleys and areas of MVFR cigs central and NW
Mtns. Breezy with NW winds of 10-15 Kts and gusts of 20-25 kts.

Fri...Dry with VFR conditions.

Sat...Dry with VFR conditions.

Sun...Chance of PM showers.

&&

.HYDROLOGY...
Considerable riverine flooding is forecast across south central
PA. Several points are forecast to exceed minor/moderate flood
stages, with major levels certainly in-play given the extreme
6-9" rainfall forecast across the southern basins.

&&

.CLIMATE...
Here are some rainfall records that are in jeopardy:

Maximum 1-Day Total Precipitation at Harrisburg:
1. 9.13 1972-06-22
2. 7.71 2011-09-07
3. 5.81 1972-06-21
4. 5.72 2013-10-11
5. 4.71 2017-07-23

Rainfall records for 09/01:
3.60/1952 Harrisburg
2.06/1952, 2003 Williamsport
1.15/1952 Altoona
(From remnants of Hurricane Able in 1952)

Rainfall records for 09/02:
2.69/2006 Harrisburg
3.87/2006 Williamsport
2.35/2006 Altoona
(From remnants of TS Ernesto in 2006)

Harrisburg wettest 2-day total September 1-2:
4.00 in 1952

Harrisburg wettest 2-day total August 31-September 2:
4.36 in 1952

Prelim rankings for August and Summer 2021 (JJA):
Harrisburg: 2nd warmest August; 4th warmest summer
Williamsport: 3rd warmest August; 9th warmest summer

Harrisburg average temperature (JJA)
1. 2020 77.9F
2. 1966 77.6F
3. 2016 77.3F
4. 2021 77.1F
5. 2010 76.9F

Harrisburg average minimum temperature (JJA)
1. 2020 68.2F
2. 2021 68.1F
3. 2016 67.9F
4. 2010 67.6F
5. 2005 67.3F

Harrisburg average maximum temperature (JJA)
1.  1966      90.2F
2.  1999      87.7F
3.  2020/1991 87.6F
5.  1943      86.8F
6.  2016      86.7F
7.  1988/1944 86.5F
9.  2002      86.2F
10. 2021      86.1F

Harrisburg average temperature (Aug)
1. 2016 79.1F
2. 2021 78.3F

Williamsport average temperature (JJA)
1.  2020/2016 74.4F
3.  1949/1901 74.3F
5.  1900      74.2F
6.  1995/1955 74.0F
8.  2005      73.9F
9.  2021      73.7F
10. 1991      73.6F

Williamsport average minimum temperature (JJA)
1. 1901      66.2F
2. 1899      64.0F
3. 2005/2021 63.1F
5. 2016      62.8F

Williamsport average temperature (Aug)
1. 2016 76.1F
2. 1995 75.9F
3. 2021 75.6F

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Thursday morning for PAZ012-017>019-
024>028-033>036-041-042-045-046-049>053-056>059-063>066.

&&

SYNOPSIS...Lambert/Steinbugl
NEAR TERM...Lambert/Steinbugl
SHORT TERM...Lambert/Steinbugl
LONG TERM...Colbert/Gutierrez
AVIATION...Lambert
HYDROLOGY...Lambert
CLIMATE...Lambert

Hazardous Weather Outlook
National Weather Service State College PA
103 PM EDT Wed Sep 1 2021

PAZ012-017>019-024>028-033>036-041-042-045-046-049>053-056>059-063-
021715-
Northern Clinton-Clearfield-Northern Centre-Southern Centre-Cambria-
Blair-Huntingdon-Mifflin-Juniata-Somerset-Bedford-Fulton-Franklin-
Northern Lycoming-Sullivan-Southern Clinton-Southern Lycoming-Union-
Snyder-Montour-Northumberland-Columbia-Perry-Dauphin-Schuylkill-
Lebanon-Cumberland-
103 PM EDT Wed Sep 1 2021

...FLASH FLOOD WATCH IN EFFECT THROUGH THURSDAY MORNING...

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.

   Flash Flood Watch.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

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.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report significant hazardous weather.

PAZ004>006-010-011-037-021715-
Warren-McKean-Potter-Elk-Cameron-Tioga-
103 PM EDT Wed Sep 1 2021

This Hazardous Weather Outlook is for central Pennsylvania.

.DAY ONE...This afternoon and tonight.

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

PAZ064>066-021715-
Adams-York-Lancaster-
103 PM EDT Wed Sep 1 2021

...FLASH FLOOD WATCH IN EFFECT THROUGH THURSDAY MORNING...
...TORNADO WATCH 483 IN EFFECT UNTIL 10 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.

   Tornado Watch.
   Flash Flood Watch.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

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.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report significant hazardous weather.

Lambert

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE STATE COLLEGE PA
255 PM EDT WED SEP 1 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0100 PM     FLASH FLOOD      1 SE BEDFORD            40.01N 78.50W
09/01/2021                   BEDFORD            PA   PUBLIC

            FLOODING REPORTED ACROSS ROADWAYS.

&&

REG

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE STATE COLLEGE PA
309 PM EDT WED SEP 1 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0308 PM     FLASH FLOOD      LINNTOWN                40.96N 76.90W
09/01/2021                   UNION              PA   EMERGENCY MNGR

            1 FT OF WATER ACROSS THE ROAD. MULTIPLE
            OTHER CREEKS NEAR BANK HEIGHT.

&&

REG

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE STATE COLLEGE PA
318 PM EDT WED SEP 1 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0315 PM     FLASH FLOOD      2 SW LITITZ             40.13N 76.33W
09/01/2021                   LANCASTER          PA   FIRE DEPT/RESCUE

            WATER RESCUE.

&&

REG