-- Discussion containing changed information from previous version are highlighted. --
719
FXUS61 KPBZ 131428
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1028 AM EDT Thu Jun 13 2024

.SYNOPSIS...
-- Changed Discussion --
Day and warm conditions today will be followed by near average
temperatures tomorrow with a marginal chance of severe storms,
with the primary threat being wind around and south of
Pittsburgh. Next week, there is high confidence in a potentially
historic heat wave.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
KEY MESSAGES:

- Temperatures around 10 degrees above average.
- A low chance of showers north of I-80 after midnight.
-------------------------------------------------------------------

Surface high pressure is expected to drift off the eastern
seaboard today, and a low will pass well to the north through
Ontario and Quebec. This will strengthen the pressure gradient
today and incite light southwest flow as heights sit around
582dm. Only a few high clouds will traverse overhead; otherwise,
the area will remain mostly clear. This will encourage daytime
highs to top out around 10 degrees above average in the June
sun. Overnight, clouds will move in ahead of the surface trough,
and a light south- southeast flow will be maintained, keeping
lows around 10 degrees above normal as well.

Some ensembles do indicate that a pre-frontal trough brings
showers north of I-80 after midnight and before daybreak,
although this remains low probability. Even if showers do
materialize, they well be working with a couple hundred joules
of elevated CAPE, and flow around or less than 10kts up to
700mb with a shallow surface inversion. Thus, no severe threats
are anticipated.
-- End Changed Discussion --

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
-- Changed Discussion --
KEY MESSAGES:

- A cold front will bring a 1 out of 5 risk for severe weather
  Friday, primarily in the Pittsburgh area and south.
- Dry and near normal conditions prevail Saturday.
-------------------------------------------------------------------

Not much has changed for the daytime forecast update. The front
is still forecast to sag down across the area, bringing showers
and storms along with it. The front will enter the counties
north of I-80 in the morning hours, where even the
aforementioned maximum CAPE tops out around 500-700 J/kg. This
would limit the development of strong updrafts, and further
limit severe potential in the morning.

There is some uncertainty with tracking the timing of the front
progression across the Pittsburgh metro. NBM temperature spreads
in Pittsburgh at 2pm are as high as 8 degrees between the 25th
and 75th percentile, and 14 degrees between the 10th and 90th
percentile. This means that around half of the ensemble members
have the cold front clear Pittsburgh by 2pm, while the other
half have not.

In the more progressive scenario, instability generation would
be slower and confined to the areas south of the Pittsburgh
metro, where wind would be the primary threat with antecedent
mid-to-upper level dry air, 30-40kts of shear, and 500-1000 J/kg
CAPE this would bring a lower probability of severe weather
confined to a smaller area.

In the slower frontal progression scenario, the areas south of
the front would have a longer period to heat and generate
instability, with the high end CAPE being around 1000-1200 J/kg.
Combined with 30-40kts of shear, this would be more favorable
for wind and hail threats in the Pittsburgh metro and points
south. In addition, with around 1.4 modeled PWAT packed into the
low- to- mid levels and a slow- moving front, isolated flooding
could not be ruled out.

Behind the "cold" front, temperatures will drop to near normal
with clearing skies. This may allow for patchy valley fog
development Friday night. Into Saturday, mixing into drier air
will keep conditions comfortable and near normal. Saturday night
may very well be the last time we see lows in the 50s through
late June or even July.
-- End Changed Discussion --

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
KEY MESSAGES:

- High confidence in a dangerous heat wave setting up early next
  week with moderate to major heat impacts possible.
-------------------------------------------------------------------

Guidance has been consistent that a potentially-historic ridge will
continue to strengthen across much of the central and eastern CONUS
Sunday into at least early next week. WPC ensemble clusters are
highly consistent through Tuesday, indicating high confidence in the
temperature forecast. Near-record breaking heat will build in to
start off next week.

Sunday will bring minor to moderate heat risk across the area as
surface high pressure establishes off to our east. Significant
heat will be possible with this anomalously strong ridge,
especially Monday and beyond, when major heat risk is likely.
NBM probabilities for high temperatures reaching 95+ degrees
continue to go up, and are now widespread 50-70% across the
area, with pockets as high as 80%. These higher probabilities
are especially prevalent in lower elevation areas (e.g., river
valleys) and urban centers, which tend to be warmer than
surrounding areas. In addition, dewpoints are currently forecast
to remain in the mid 60s to lower 70s, which would result in
high enough humidity levels to support heat indices climbing to,
and potentially exceeding, 100 degrees. If dew points do hold
toward the lower end of that spectrum, we may be able to make a
run at 100 degree air temperatures Monday and beyond (last time
at PIT was 7/15/95); NBM probabilities for that threshold are
now up to 50% in spots. Only acting to exacerbate the prolonged
heat effects will be a 60-80% chance of low temperatures
greater than 70 degrees through the end of the week. Heat
impacts will need to be closely monitored and headlines may need
to be considered.

Three out of four clusters maintain a 594dm ridge through June
22nd with the one exception being a much lower probability
solution than the others. CPC suggests that excessive heat may
last through June 24th, indicating the potential for a long-
duration excessive heat threat. The last comparable, long-
duration heat event was from July 1994.

Impacts include heightened heat-related illnesses and potential
power grid issues with increased demand. It is strongly
encouraged to know where cooling shelters are located and stay
hydrated. There may be little relief at night. Gather food,
water and medication now. Make a list of friends and family to
check on and help them prepare. Strongly consider rescheduling
outdoor events. Prolonged exposure to excessive heat was the
primary cause of weather-related fatalities in 2023.
-- End Changed Discussion --

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
VFR conditions are forecast for today as high pressure slowly
works east of the region. Any patchy river valley fog, which is
currently not impacting TAF sites, will dissipate by 13Z. Only
high clouds are forecast through tonight, before an increase
towards sunrise as a cold front begins to approach.

Southwest wind around 10 knots is forecast for today once mixing
commences, with wind becoming light tonight.

.Outlook...
Restrictions in showers and thunderstorms return Friday with
a cold front. Largely VFR conditions are then forecast Saturday
through Monday.

&&

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

&&

$$

SYNOPSIS...Milcarek
NEAR TERM...Milcarek
SHORT TERM...Milcarek
LONG TERM...MLB/Milcarek
AVIATION...22/CL