Harrington, Delaware 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

712
FXUS61 KPHI 200828
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
428 AM EDT Thu Aug 20 2026

.WHAT HAS CHANGED...
Morris County, NJ was added to the Flash Flood Watch.

The tornado risk has increased, mainly for SE PA, central and
southern NJ, and northern Delmarva.

Increasing confidence in the flash flooding potential for
today, mainly for New Jersey, southeastern PA, and northern
Delaware.

&&

.KEY MESSAGES...
1. A strong cold front is expected to cross through the region
today, resulting in widespread showers and thunderstorms. Flash
flooding, damaging wind gusts and a few tornadoes are possible
later today.

2. Conditions look to remain unsettled through the
weekend, with daily chances of showers and storms each day.

3. Fair weather is expected to return for early next week.

&&

.DISCUSSION...
KEY MESSAGE 1...A strong cold front is expected to cross
through the region today, resulting in widespread showers and
thunderstorms. Flash flooding, damaging wind gusts and a few
tornadoes are possible later
today.

To the south of a closed upper low over eastern Canada, broad
troughing will be in place across much of the Northeast and Mid-
Atlantic. An embedded mid-level shortwave will pass through the
base of the trough today. At the surface, a warm front will
move into portions of the area tonight as a cold front will
begin to approach the area on Thursday.

With guidance coming into better agreement with the timing and
placement of frontal boundaries in our area, there has been an
uptick in confidence in what the evolution of what should
transpire later today. Multiple rounds of widespread showers
and storms are expected. With the cold front approaching from
the west, and a warm front expected to set-up across the
southern half of the area across the Delmarva and into southern
New Jersey, we will have to watch these areas for severe weather
this afternoon and evening.

Bulk shear values up to 30-40 kt support organized clusters
where locally damaging wind gusts are possible. Some of the 00z
CAMs have been suggesting some isolated discrete supercells
developing out ahead of the main batch of convection. Thinking
the models may have a good idea of how things will evolve today,
with scattered showers and thunderstorms starting out as
individual discrete cells in the early afternoon with a more
linear, multi-cell clusters taking over and pushing through by
the mid-afternoon and into the early evening.

With the warm front draped over portions of the area,
there will be a localized corridor of a tornado threat,
especially where any storm is able to latch onto the boundary.
SPC has introduced a 5% tornado risk over SE PA, northern
Delaware, and the southern half of New Jersey. Locally backed
flow at the surface near/south of the warm front will enhance
low-level shear. In addition to increased low-level shear, we
will have a very moist airmass overhead and low LCLs - factors
favorable for tornadogenesis. Some question remains in how far
north the warm sector gets, which will have implications for
where the largest tornado threat is. For now though, the
forecast currently has the area south of the PA Turnpike and
I-195 as the main area to watch. This does include the Philly
metro area. Cannot rule out isolated large hail as well as
temperatures aloft are rather cool for this time of year. Cloud
cover should increase at the morning goes on, which could be a
limiting factor in terms of instability buildup. The Slight
(2/5) Risk remains for most of the area.

The other, and possibly more concerning threat may be the risk
and potential for flash flooding across portions of the area.
Most guidance continues to depict a very moisture rich airmass
surging northward today where PWAT values are expected to top
out around 2.2-2.6 inches. Model forecast soundings also show
tall, skinny CAPE profiles and a relatively deep warm cloud
layer. The one saving grace is that the overall shear vectors
indicate that storms should be `relatively` quick moving.
However, any given storm will be capable of producing highly
efficient rain rates, at times around 2 to 4 inches per hour.
With this being said, WPC has maintained a SLIGHT risk (Level
2/4) for excessive rainfall today over most of the area. There
was talk of adding a Moderate Risk around the Philly metro, but
have held off for now. Added Morris County, NJ to the Flood
Watch since there was a slight trend north with the highest QPF.
Otherwise, no changes. The Flash Flood Watch remains in place
for most of New Jersey, southeastern PA, and northern Delaware.

In general, expecting anywhere between 1 to 2 inches of rain to
fall, with localized higher amounts up to 3 to 5 inches.
Guidance has remained relatively consistent all throughout
today. We will have efficient rainfall producers where some
areas could see multiple rounds, which is not a good
combination. This event will also be during the evening commute,
with travel disruptions likely. Have multiple ways to receive
warnings.

The severe and flooding rain threat should diminish overnight
into Friday morning.


KEY MESSAGE 2...Conditions look to remain unsettled through the
weekend, with daily chances of showers and storms each day.

Mid to long range NWP and AI guidance suggests that the pattern
could become unsettled Friday night and into the weekend.
The cold front will move offshore tonight but stall just
offshore. Multiple waves of low pressure will ride along the
stalled front, resulting in unsettled weather through the
weekend. The main periods to watch are early Saturday through
Saturday evening, with periods of rain increasingly likely,
especially along/east of the I-95 corridor. Another round of
rain is expected on Sunday as well. The severe threat looks low
but there could be further flooding concerns, although no day
has more than a Marginal (1/5) Risk for excessive rainfall.
The areas to watch for flooding may depend on where most of the
rain falls today.

In terms of temps, highs and lows will both be quite seasonable
for late August, but humidity levels may be uncomfortable at
times.


KEY MESSAGE 3...Fair weather is expected to return for early
next week.

High pressure looks to bring fair and tranquil weather to start
next week. The pattern potentially becomes more active again
towards the middle to end of next week. Seasonable temperatures
are expected.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Rest of Tonight (through 12z)...VFR. Light and variable to calm
winds though a west/southwest direction could be favored at
times. High confidence. High confidence.

Today...VFR in the morning with restrictions likely developing
in the afternoon (primarily after 18Z), as widespread showers
and thunderstorms are likely at all terminals. Any storms will
be capable of producing very heavy rainfall and LIFR conditions.
Winds will vary depending on location, with northern terminals
experiencing east- northeast winds around 5 kt where southern
terminals will encounter southeasterly winds around 5-10 kt.
Winds may locally become gusty and erratic near any storm.
Showers and storms ending by 01Z. Moderate confidence overall,
but low confidence on exact timing details.

Thursday Night...Sub-VFR conditions probable at times with
showers and thunderstorms continuing into the evening hours,
before diminishing overnight. Fog and/or low stratus possible at
night once precipitation moves out. Conditions should lift back
to VFR near or not long after daybreak. North/northeast winds
around 5 to 10 kt. Low confidence.

Outlook...

Friday through Friday night...Primarily VFR, though cannot rule
out isolated showers/thunderstorms for southern terminals which
could result in some restrictions.

Saturday through Sunday...Periods of VFR and sub-VFR at times.
Restrictions expected with daily chances for showers and
thunderstorms.

Monday...VFR. No significant weather expected.

&&

.MARINE...
No marine headlines expected through tonight. Winds increase to
around 10-15 kt out of the south/southwest for today. A cold
front will move through tonight, with winds becoming more
north/northeasterly around 10-15 kt. Seas of 2 to 3 feet.
Showers and thunderstorms expected on the waters this evening
into tonight.

Outlook...

Friday through Monday...No marine headlines expected. Showers
and thunderstorms possible, mainly during the day Friday through
Sunday.

Rip Currents...

For today, south to southeast winds increasing to near 10 mph.
Breaking waves will average around 1 to 2 feet. There will
continue to be a southeasterly swell with a 6 to 8 second
period. The result of these conditions is a LOW risk for the
development of dangerous and life threatening rip currents for
the Jersey Shore and Delaware Beaches.

For Friday, winds turn more onshore but will be light - around
10 MPH or less. Breaking waves will average around 1 to 2 feet.
There will continue to be a southeasterly swell with a 6 to 9
second period. The result of these conditions is a LOW risk for
the development of dangerous and life threatening rip currents
for the Jersey Shore and Delaware Beaches.

For specific beach forecasts, visit weather.gov/beach/phi

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch from noon EDT today through late tonight for
     PAZ070-071-101>106.
NJ...Flood Watch from noon EDT today through late tonight for
     NJZ008>010-012>022-025>027.
DE...Flood Watch from noon EDT today through late tonight for
     DEZ001.
MD...None.
MARINE...None.

&&

$$

DISCUSSION...DeSilva/Hoeflich/Staarmann
AVIATION...DeSilva/Hoeflich/Staarmann
MARINE...DeSilva/Hoeflich/Staarmann