Areal Flood Warning 11, NWS Pittsburgh, PA

Area Forecast Discussion
National Weather Service Pittsburgh PA
207 AM EDT Mon Aug 30 2021

.SYNOPSIS...
Moisture on the van of the hurricane Ida remnant is expected to fuel
widespread and enhanced rainfall across the Upper Ohio Valley Region
on Tuesday night and Wednesday. In the meantime, warm and humid
weather continues with periodic scattered showers and storms.

&&

.NEAR TERM /THROUGH TONIGHT/...
Another warm and humid day is on deck for the Upper Ohio Valley and
Allegheny Mountains. Some shower activity may be ongoing around dawn
as overnight convection wanes, but may not diminish entirely given a
warm/moist airmass characterized by PWATs above the 90th percentile
and MLCAPE near 1000 J/kg. As a result, have kept low-end POPs
through the morning hours.

As the morning progresses, insolation will lead to another day with
temps in the 80s and dewpoints in the 70s. This heating will yield
MLCAPE increasing to around or possibly in excess of 2000 J/kg by
mid-afternoon. At the same time, a cold front dropping south from the
Great Lakes should advance to near the I-80 corridor. HREF members
focus convective activity farther south towards and south of I-70
today along a pre-frontal trough, likely the outflow boundary from
the overnight convection, coincident with the passage of a shortwave
trough. Given the orientation of the sfc trough to cloud-bearing wind
aloft, west-to-east training storms are definitely possible as the
system inches southward with system motion. Very high PWAT air / warm
cloud depths will lend itself to efficient rain processes, leading
to high rain rates. This could lead to instances of flash flooding
where convection segments train.

North of I-70, showers/storms should initiate near the cold front
boundary as well as it drops southward given the destabilized
airmass. However, HREF members and probs are indicating less coverage
with the sfc front during the day.

Previous Discussion concerning current overnight period...

1145 PM Update: Regional radars show a line of thunderstorms
extending along the Erie lakefront from the Buffalo area through
Cleveland and southwestward from there. Despite a nocturnally-cooled
sfc layer, mesoanalysis depicts MLCAPE upwards of 1000 J/kg between
the Pittsburgh Metro and the current placement of the line,
decreasing significantly east of I-79. The shortwave that helped
initiate and sustain the convection will dampen as it approaches the
Pittsburgh area that has/had been under the mid/upper- level ridge.
So current thinking is that the convective line will continue to
advance towards east-central Ohio, the northern WV Panhandle, and
western PA given modest instability and weak shear, but will lose
steam towards dawn as it advances close to the I-70 corridor and
Allegheny Mtns.

While severe weather is not expected, recent radar imagery of cells
ahead of the line have exhibited reasonably strong updrafts... thus
perhaps very small hail, brief heavy downpours, and some modestly
fast gusts may accompany the strongest of storms.

Otherwise, it'll be another warm night with temps struggling to drop
below 70. Any areas that manage to clear out for more than a couple
hours may see fog development in the typically-favored valley-type
locales.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY/...
By Tuesday morning, the aforementioned cold front will have
progressed to somewhere around the I-70 corridor. At this point, the
frontal boundary will become essentially stationary or at least very
slow-moving as we become sandwiched in a baroclinic zone between cool
northerlies from high pressure centered across Canada and warm,
tropical-like southerlies from the advancing remnants of tropical
disturbance Ida. 00z HRRR and NAM Nest both show scattered convection
initiating by the early-afternoon on Tuesday right along the sfc
front. The limiting factor to coverage and intensity of Tuesday's
storms will be the upper-level cloud cover from Ida. The less cloud
cover to begin the day, the greater we destabilizing and the
thunderstorm threat is in the afternoon... but if we remain clouded
in from the start, then thunderstorms will struggle with limited
CAPE. As far as temperature on Tuesday, look for a cooler day as
areas north of Pittsburgh will finally see some cold air advection...
while areas south of Pittsburgh will be underneath cloud cover
and/or rain.

Tuesday Night and Wednesday... here comes Ida.

The weakening tropical system Ida will begin to move northward
across the TN Valley Tuesday night and accelerate in response to a
northern stream trough digging southeastward from the Midwest. Rain
from the northern side of Ida will overspread northern West Virginia
and SW PA (and perhaps barely into SE Ohio close to the Ohio River)
overnight and continue through much of Wednesday as Ida moves
northeastward through Appalachia. This will pose a significant flood
threat to locations south and east of Pittsburgh and anyone in that
area needs to remain weather aware for the next few days.

How much rain and where exactly? That's the biggest question. Recent
model guidance has trended slightly farther SE, painting the axis of
heaviest rainfall somewhere between SW PA and the higher terrain of
WV, with Morgantown being near the center axis in several models.
Across the heaviest rainband, look for amounts between 3 and 6 inches
with localized higher amounts. Farther north, amounts should drop
off precipitously w/ areas north of Pittsburgh likely receiving less
than an inch. Where does this put the immediate Pittsburgh metro? In
an area of high uncertainty. Model guidance ranges from roughly just
1 inch upwards to about 5 inches for Allegheny County and
surrounding area, all dependent on the exact track of the system. We
should be able to hone in on these details by the evening suite of
model guidance.

Rain will come to an end by dusk or shortly thereafter on Wednesday
as the remnants of Ida depart eastward, with much cooler, drier air
filtering in behind the system.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Cooler and drier conditions are anticipated late week and into the
Labor Day Weekend with building high pressure.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
A broken line of shra and tsra will continue to advance east to west as
a trough advances off the Great Lakes. Periods of MVFR to IFR within
convection are likely. Showers and storms should wrap up after 12Z.
However, restrictions may prevail under a warm, moist atmosphere into
the late morning; expected MVFR fog and MVFR to IFR stratus deck.

Convection is likely again later today along an encroaching frontal
boundary.

.Outlook...
Rain chances and widespread restrictions are likely late Tuesday
into Wednesday with the remnants of Ida.

VFR and dry weather is expected after the remnants exit Thursday.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.

&&

Hazardous Weather Outlook
National Weather Service Pittsburgh PA
338 AM EDT Sun Aug 29 2021

OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>023-029-
031-073>076-WVZ001>004-012-021-509>514-300745-
Tuscarawas-Carroll-Columbiana-Coshocton-Harrison-Jefferson OH-
Muskingum-Guernsey-Belmont-Noble-Monroe-Mercer-Venango-Forest-
Lawrence-Butler-Clarion-Jefferson PA-Beaver-Allegheny-Armstrong-
Indiana-Washington-Greene-Westmoreland-
Higher Elevations of Westmoreland-Fayette-
Higher Elevations of Fayette-Hancock-Brooke-Ohio-Marshall-Wetzel-
Marion-Monongalia-
Ridges of Eastern Monongalia and Northwestern Preston-Preston-
Eastern Preston-Western Tucker-Eastern Tucker-
338 AM EDT Sun Aug 29 2021

This Hazardous Weather Outlook is for east central Ohio, western
Pennsylvania, and northern West Virginia.

.DAY ONE...Today and tonight.

Hazardous weather is not expected at this time.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

The potential for heavy rainfall and flooding will increase Tuesday
and Wednesday as the remnants of tropical system Ida move into the
Ohio Valley.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to Standard Operating Procedures.

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

Special Weather Statement
National Weather Service Pittsburgh PA
1127 PM EDT Sun Aug 29 2021

OHZ057-058-300400-
Guernsey OH-Muskingum OH-
1127 PM EDT Sun Aug 29 2021

...A STRONG THUNDERSTORM WILL IMPACT WEST CENTRAL GUERNSEY AND
NORTHEASTERN MUSKINGUM COUNTIES THROUGH MIDNIGHT EDT...

At 1127 PM EDT, Doppler radar was tracking a strong thunderstorm 8
miles northwest of New Concord, or 11 miles northeast of Zanesville,
moving east at 20 mph.

HAZARD...Wind gusts up to 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Otsego and Boden.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4002 8191 4013 8192 4015 8165 4001 8163
TIME...MOT...LOC 0327Z 269DEG 18KT 4008 8186

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH