-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 242325
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
725 PM EDT Wed Apr 24 2024

.SYNOPSIS...
Colder air filters in tonight with decreasing cloud cover.
Temperatures rebound tomorrow with marginal wire weather. The
weekend remains warm with intermittent precipitation chances.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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KEY MESSAGES:

- Freeze warning and frost advisories are in effect north and
  west of the Pittsburgh metro beginning at midnight.

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Ongoing cold advection in northwest flow will reinforce
saturation and cloud coverage in the low-levels through the
early overnight hours before drier air advects in from the north
and low level flow veers more northwesterly cutting off the
lake source.

Right now, there is high confidence in a freeze (80% to 100%),
potentially even hard freeze (60% to 80%), north of I-80 where
clearing is expected early tonight and radiational cooling will
develop. Elsewhere, the degree of cooling will depend on
clearing which remains the forecast challenge for tonight.

The freeze warning was hoisted for where probabilities
of subfreezing temperature are greater than 50%. For the areas
in the warning south of I-80, clearing is not guaranteed with
large spread between the low and high end of cloud cover in the
latest hi res ensemble guidance. Thus, there is a failure mode
for the warning. On the contrary, clearing may go as far as
covering areas in the frost advisory, where freezing
temperatures are also not out of the realm of possibility. Thus,
there is generally high uncertainty in temperatures in-between
I-80 and the advisory area; a sharp temperature gradient may
orient along the cloud extent maxima. Elsewhere, clearing is
not favored with probability for less than 50% cloud cover
generally sitting below 50%, thus frost formation and
significant cooling are also not favored.
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&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
KEY MESSAGES:

- Dry conditions with a warming trend are expected through
  Friday; showers return Friday night.

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Thursday will bring mundane weather. In the morning and early
afternoon, mixing will act to gradually erode the lingering
stratocumulus deck. This will lend to a rebound in temperature
under clear skies and high pressure.

The NBM clear sky under-mixing bias was accounted for in the
forecast as daytime highs were adjusted upward a couple of
degrees and daytime dews minimize at the NBM 10th percentile.
This has dropped relative humidities into the upper 20s and
lower 30s. Dead and fine fuel moistures may dip below 10% during
the day, although winds will remain calm to light. This will
lead to another day of marginal fire weather, with conditions
most favorable in northwestern Pennsylvania.

A temperature and dewpoint push is expected through Friday as
the high moves east and a southerly component to the flow
reestablishes. Low-QPF rain showers are possible Friday night
and early Saturday morning as a warm front approaches from the
south.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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KEY MESSAGES:

- Much warmer through the weekend
- Highest chance for showers on Saturday, and again Monday
  through Tuesday
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Model ensembles indicate the initial shortwave and warm
front supported rain will continue to cross the region on
Saturday. The front is expected to lift north of the region
Saturday night, as a strong ridge builds across the SE CONUS to
the Upper Ohio Valley region.

Mainly dry weather is expected Saturday night and Sunday with
the ridge axis across the area. There could be enough diurnally
driven instability to result in an isolated afternoon
thunderstorm Sunday, though most of the day should be dry, with
temperatures in the upper 70s to the mid 80s. 1000-500mb height
approach 583 dam Sunday into Monday, with 850 mb temperatures
peaking around 14 deg C.

Model ensembles indicate the ridge should slowly shift eastward
to the East Coast late Monday and Monday night, as the next
shortwave trough and surface cold front approach from the
Midwest. Scattered showers and thunderstorms are possible Monday
with building diurnal instability in moist SW flow ahead of the
trough. More numerous showers and possible thunderstorms are
expected Tuesday as the trough/cold front cross the region.
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&&

.AVIATION /23Z WEDNESDAY THROUGH MONDAY/...
Some isolated showers will continue to move across the northern
forecast area this afternoon and into the early evening likely.
Variable ceilings will continue through the afternoon given the
mix of VFR and MVFR/IFR conditions in place. The cold front has
effectively moved through the area with winds shifted around to
the northwest in most instances. The daytime heating in the
south is creating a gradient and showing at the terminals as sky
conditions show breaks in the cloud cover in the south.

MVFR cigs looks to remain through the evening and overnight
hours with improvement possible toward 12Z tomorrow morning.
Its not out of the question to still get some breaks at times in
the cloud cover through the TAF period as well.

.Outlook...
VFR conditions are expected Thursday and Friday.

The probability of showers and isolated thunderstorms increases
Saturday. This will come with additional restrictions likely.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Freeze Warning from midnight tonight to 10 AM EDT Thursday for
     PAZ007>009-013>016-022-077.
     Frost Advisory from midnight tonight to 10 AM EDT Thursday for
     PAZ020-078.
OH...Freeze Warning from midnight tonight to 10 AM EDT Thursday for
     OHZ039>041-048.
     Frost Advisory from midnight tonight to 10 AM EDT Thursday for
     OHZ049-050-057-058.
WV...Frost Advisory from midnight tonight to 10 AM EDT Thursday for
     WVZ001.

&&

$$

SYNOPSIS...Milcarek
NEAR TERM...MLB/Milcarek
SHORT TERM...Milcarek
LONG TERM...WM
AVIATION...Shallenberger