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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 212243
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
643 PM EDT Sun Apr 21 2024

.SYNOPSIS...
-- Changed Discussion --
Frost/Freeze headlines are in effect early Monday morning for
the potential for sub-freezing temperatures. The next chance of
precipitation will be Tuesday night into Wednesday with a
passing cold front.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL MIDNIGHT TONIGHT/...
KEY MESSAGES:

- Below average temperature and clouds are expected through a
  large portion of the day.

- No Hazardous weather.

------------------------------------------------------------------

Temperatures will continue to trend below average through the
afternoon/evening time period under cold, northwest flow.
Currently, there is an elongated upper-level trough situated
over eastern Canada.

Based on Hi-Res model guidance and the PIT 12Z model sounding,
850mb temps will likely range from -6C to -4C throughout the day
and prompt very little mixing of warm air. Radiational heating
will be a limiting factor as well with lingering clouds through
at least 5pm. Therefore, will continue to keep MaxT temps 15
degrees below the climatological norm (near 50F) for a majority
of the region. The probability of 50F or higher will remain
focused south of I-70.

Probability of cloud coverage will decrease after 7pm tonight
from north to south with advancing dry air upstream. Temperatures
will quickly drop into the mid-30s just before midnight and
frost formation will begin.

&&

.SHORT TERM /MIDNIGHT TONIGHT THROUGH MONDAY NIGHT/...
KEY MESSAGES:

- Frost/Freeze headlines are in effect across the region between
  1am to 9am; sensitive plants will likely experience damage if
  not protected.
- Below average high temperatures will continue Monday afternoon
  as cold air lingers across the region.
- Frost/Freeze potential will remain low Monday night into
  early Tuesday with warm, moist advection.
----------------------------------------------------------------

A Frost Advisory and Freeze Warning are in effect from 1am to
9am Monday due to lingering cold air from an exiting trough to
the north, clearing sky, and light winds. Probability of <=32F
is above 80% for areas north of Pittsburgh and within the
ridges; hence the Freeze Warning. Elsewhere, a Frost Advisory
has been issued for temperatures ranging between 35F to 32F.

Temperatures will recover to near 60F during the day with
building high pressure and abundant sunshine, but will still be
several degrees below normal.

With warm, moist advection late Monday night, the probability
of frost/freeze products being issued is low. Temperatures will
actually be near the climatological norm across the region into
early Tuesday morning with cloud coverage building.

&&

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

- The potential for Frost/Freeze headlines remains low through
  Wednesday.
- The next low pressure system and associated precipitation
  chances is likely for late Tuesday into Wednesday.
- Frost/Freeze potential returns Wednesday into Thursday with a
  passing trough over the Great Lakes.
- There is a potential for strong thunderstorms Sunday into
  Monday.
-------------------------------------------------------------------

A flux in low-lvl moisture and southwest flow under a ridge will
decrease the potential of frost/freeze headlines through at
least Wednesday.

Near to above average temperatures are anticipated Tuesday
afternoon ahead of an approaching cold front and its associated
trough.

Probability of measured precipitation increases from
west to east after 18Z Tuesday. Prior to the onset of
measurable precipitation, expect gusty conditions with diurnal
mixing of linger dry air and 850mb winds ranging from 25kt to
35kts from the southwest.

The axis of heavier rainfall is expected to be in the vicinity
of I-80 with the passing cold front, associated with stronger
forcing and perhaps lake enhancement on the backside of the
front. For rainfall amounts through Wednesday, the latest run of
the NBM suggest areas south of Pittsburgh could range from 0.20
inches to 0.40 inches; areas near I-80 could range from 0.45 to
0.75 inches. Along with rain, shallow instability (35J/kg to
150J/kg) may prompt some thunderstorms along the cold front
between 4am to 11am Wednesday morning.

With clearing clouds late Wednesday, cold advection, and
moisture at the surface from recent precipitation, the
potential for frost/freeze conditions increases again early
Thursday morning. At the moment, confidence is medium that
Freeze Warning will be needed north of Pittsburgh and within the
ridges. However, the Warning may need to be issued as far south
as I-70 if the upper-lvl trough digs further south.

Cold air will likely exit the region Friday as a ridge axis
builds over the Great Lakes in response to a developing low
pressure system off the Rockies.

Shower and thunderstorms chances increase late Friday as this
noted disturbance advances into the northern Great Lakes.
Organized convection, at the moment, appear promising in areas
to our west (Indiana/western Ohio) than over our region due to
weak destabilization. However, if high pressure weakens over
the East Coast, allowing the advancement of low-lvl moisture
under strong bulk shear, there`s a chance of severe storms
Sunday and/or Monday.
-- End Changed Discussion --


&&

.AVIATION /22Z SUNDAY THROUGH FRIDAY/...
Mid-level moisture ahead of an approaching 500mb trough
continues to support VFR cumulus/stratocumulus across the
region. Continued diurnal heating will help the cloud deck to
become more cellular with time, with additional sunny breaks.
Increasing dry advection and subsidence, already evident
upstream in Michigan and northwest Ohio, will erode the cloud
cover during the late afternoon and evening period. Surface
ridging keeps conditions mostly clear tonight.

Afternoon northwest wind gusts between 15 and 20 knots will
continue given deep mixing, with wind decoupling and becoming
light and variable overall after sunset.

After sunrise, more VFR cumulus are expected to pop up by
midday, with a northwest wind of 10 knots or less.

.Outlook...
The approach and passage of a low pressure system late Tuesday
into Wednesday will be the next period with restriction
potential along with widespread rain. There is high confidence
in high pressure supporting VFR conditions to end the work week.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Frost Advisory from 1 AM to 9 AM EDT Monday for PAZ020-021-029-
     031-073-075.
     Freeze Warning from 1 AM to 9 AM EDT Monday for PAZ007>009-
     013>016-022-074-076>078.
OH...Frost Advisory from 1 AM to 9 AM EDT Monday for OHZ039>041-
     048>050-057>059-068-069.
WV...Frost Advisory from 1 AM to 9 AM EDT Monday for WVZ001>004-012-
     021-509.
     Freeze Warning from 1 AM to 9 AM EDT Monday for WVZ510>512.

&&

$$

SYNOPSIS...Hefferan
NEAR TERM...Hefferan
SHORT TERM...Hefferan
LONG TERM...Hefferan
AVIATION...CL