Tornado and Hail in Pennsylvania, May 6, 2025

Area Forecast Discussion
National Weather Service Mount Holly NJ
924 AM EDT Tue May 6 2025

.SYNOPSIS...
An upper level low will slowly move northeastward and cross the
Northeast and Mid-Atlantic regions by tonight, then it will
lift out during Wednesday. A cold front will cross our area
Wednesday night and Thursday morning. Another upper level low
develops across the Northeast and Mid-Atlantic regions Thursday
night and Friday with weak low pressure nearby, then it shifts
northeast on Saturday. A cold front may then move through during
Sunday with high pressure arriving for Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 920 AM, a wealth of low clouds continues across the
region although satellite trends are showing these clouds
especially across the southern areas are less smooth as heating
from above starts to lift them. Main broken band of showers
(some thunder offshore) continues to shift across our far
northern areas with little to no activity in its wake. Adjusted
the PoPs down quite a bit for most of the area this morning
given more of a lull anticipated. Still some fog around but this
will improve as well.

Otherwise, a persistent upper low across Ohio will continue its
slow northeast trek into western PA later this afternoon and up
into north PA by evening. Several shortwaves associated with
the low will cross the area today. Additional showers will be
across the area today with some thunderstorms. The thunderstorms
will be more common this afternoon as cloud breaks occur
allowing for more heating. There is an area of stronger south to
southwesterly shear ahead of the closed low and this will
spread into mostly eastern PA to northern NJ this afternoon.
Given the shear magnitude and enough instability, thunderstorms
could potentially become more organized for a time. The latest
Day 1 Outlook from SPC has a Slight Risk (level 2 of 5) across
most of eastern PA and northern NJ with a Marginal Risk (level 1
of 5) a bit farther south and east. Locally damaging winds and
hail are the main threats, especially where lapse rates are able
to steepen more. The PWAT values across the area are
climatologically high for early May, so a locally heavy rain
threat exists today.

It will remain a bit humid today but temperatures will be near
average. Temperatures will depend on the amount and timing of
the breaks in the overcast which develop this afternoon. Southeast
winds 10 to 15 mph will turn more southwest then west by
evening.

For tonight, the upper low will move from northern Pennsylvania to
New York State. Several more shortwaves will rotate around the low
bringing more chances for showers and a few thunderstorms to
the area this evening and again overnight. While some stronger
thunderstorms are possible to start the evening, the
instability decreases overnight with just showers. Lows tonight
will be in the 50s with some upper 40s for the far NW areas.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
The stubborn closed low will slide to the northeast on
Wednesday as it opens up again to merge with the polar jet. A few
possible showers may linger as the system departs in the
afternoon before departing at night. Highs will be in the low to
mid 70s again with nighttime lows in the low to mid 50s.

As we go through Thursday, quickly on the heels of the
departing and weakening closed low, another upper-level trough
starts to arrive during Thursday. This feature is also forecast
to close off as it arrives more into the Mid-Atlantic region and
Northeast Thursday night. Showers and a few thunderstorms will
develop through the afternoon and into the nighttime hours,
although the coverage is less certain especially whether or not
a more organized area of rain starts to organize. High
temperatures are forecast to top out into the low to mid 70s
across much of the area, although cooler right along the coast
and across the higher elevations. Nighttime lows will be in the
upper 40s to low 50s.

The closed low will settle across the Mid Atlantic on Friday,
supporting the development of low pressure along or just off the
New Jersey coast. Showers will continue to develop through the
day with a few embedded thunderstorms as well. Some guidance
suggesting a period of rain could be possible, though there
remains a bit of model spread regarding the coverage and
intensity of rainfall for Friday. Abundant cloud cover and rain-
cooled air should help keep temperatures at bay with highs
expected to only be in the 60s. As the low departs at night,
precip will taper off with overnight lows in the 40s.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
For Saturday and Sunday...The closed low is forecast to weaken as it
lifts out of the region during Saturday, however some lingering
troughing aloft may remain across our area. Drier conditions are
forecast and with heights rising some in the wake of the closed low,
temperatures will start to moderate. An upper-level trough then
sliding across much of eastern Canada will arrive across the
Northeast Sunday and this will toss a cold front across our area
during Sunday. As of now, the moisture looks to be limited and the
forcing is weak therefore any shower chances look to be on the low
side with the front.

For Monday...Some mid level ridging should arrive from the west and
this will allow surface high pressure to build over our region. This
will result in warmer temperatures, although with lighter flow there
could be a sea breeze in the afternoon. The surface high may start
to shift offshore Monday night with return flow already starting,
and some guidance has a disturbance off the Southeast U.S. coast.
Will have to see if this system occurs and if any moisture from it
starts to advect northward into parts of our area at night.

&&

.AVIATION /13Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...IFR ceilings lift to MVFR by later this morning and
especially this afternoon, with a trend more to VFR during this
afternoon. Some showers and thunderstorms, especially this
afternoon (included a VCSH and VCTS for now). Some locally
strong wind gusts possible with a few of the thunderstorms this
afternoon, especially near and north/west of KPHL. Southeast
winds 8-12 knots with some local gusts up to 20 knots possible,
becoming southwest this afternoon. Low confidence on coverage
and timing of thunderstorms.

Tonight...Some showers and thunderstorms around, especially in
the evening, and conditions improve overall. Southwest to west
winds near 5 knots. Moderate confidence overall.

Outlook...

Wednesday...Times of sub-VFR conditions with some departing showers,
mainly north.

Thursday and Friday...Sub-VFR conditions may develop with
showers. A few thunderstorms possible.

Saturday...VFR.

&&

.MARINE...
As of 920 AM, allowed much of the Dense Fog Advisory to expire
as visibilities continued to improve. Kept the advisory going
though until Noon for the two northern New Jersey zones as fog
remains on some of the beach cams. It doesn't appear that
conditions will reach SCA either today or tonight.

Outlook...

Wednesday and Thursday...The conditions are anticipated to be below
Small Craft Advisory criteria.

Friday and Saturday...Small Craft Advisory conditions possible,
mostly on the ocean zones, due mainly to seas increasing for a time
to around 5 feet.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Dense Fog Advisory until noon EDT today for ANZ450-451.

&&

SYNOPSIS...Gorse/MJL
NEAR TERM...Gorse/OHara
SHORT TERM...MJL
LONG TERM...Gorse/MJL
AVIATION...Gorse/MJL/OHara
MARINE...Gorse/MJL/OHara