textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

As of 8 PM, the Severe Thunderstorm Watch has been cancelled for all counties.

Updated Aviation Section for 00Z TAFs.

KEY MESSAGES

1. Hot and very humid conditions are expected to persist through Tuesday of next week. A Heat Advisory is in effect for portions of the area through Saturday.

2. There are daily chances for showers and thunderstorms through Saturday, as well as portions of next week. There is at least a marginal risk each day for localized heavy rainfall leading to flash flooding and locally damaging wind gusts with any stronger thunderstorms that develop.

DISCUSSION

KEY MESSAGE 1...Hot and very humid conditions are expected to persist through Tuesday of next week. A Heat Advisory is in effect for portions of the area through Saturday.

A relatively stagnant synoptic pattern is developing across our region. Quasi zonal mid and upper level flow will be in place through the middle of next week as Bermuda high pressure persists offshore. This will keep a steady stream of very warm and moist air in place across the region through the period.

A prolonged period of hot and, most notably, very humid conditions is expected to remain in place for the next several days. We look to have a weak cold frontal passage Sunday, ushering in slightly drier air. This will give some slight reprieve from the excessive humidity, though highs will still be in the upper 80s to low 90s. Moisture advection will return again by Monday though, and hot and very humid conditions are anticipated to return Monday through Tuesday. A somewhat stronger cold front looks to come through late Tuesday or Wednesday, which will help break the excessive heat and humidity some.

A Heat Advisory remains in effect for portions of eastern Pennsylvania, much of New Jersey except the far southern counties, as well as New Castle County, Delware.

KEY MESSAGE 2...There are daily chances for showers and thunderstorms through Saturday, as well as portions of next week. There is at least a marginal risk each day for localized heavy rainfall leading to flash flooding and locally damaging wind gusts with any stronger thunderstorms that develop.

The Severe Thunderstorm Watch has now been cancelled for all counties. With the loss of diurnal heating, storm intensity has waned. A few rain showers or thunderstorms are expected to continue through the rest of the evening, however no further severe weather or flash flooding is expected.

On Saturday, the extent of the convection remains more unclear. The current guidance shows isolated convection developing during the later afternoon into the evening hours. PWATs look slightly lower than today, and mean flow is a bit more westerly than southwesterly, but overall the thermodynamics appear similar. There will be less forcing, so the coverage is more isolated compared to today. We remain in a Marginal (level 1 out of 4) risk for excessive rainfall from WPC. In terms of the severe weather potential, SPC has added a Marginal (level 1 out of 5) risk for isolated severe thunderstorms for most of our area with the primary hazard being damaging wind gusts.

We look to have a weak cold frontal passage by Sunday, ushering in slightly drier air. This combined with subtle subsidence aloft will help briefly limit convection potential on Sunday. Moisture and forcing aloft will return by Monday as mean flow shifts more westerly and mid level flow increases. This should result in a greater severe thunderstorm threat compared to this week, and perhaps slightly lower flash flooding threat, but the details into the period early next week remain unclear. Long story short, Monday and Tuesday look to continue the hot and humid conditions and daily thunderstorm chances.

A somewhat stronger cold front looks to come through late Tuesday or Wednesday, which will help break the excessive heat and humidity some, but the pattern aloft may still support diurnally driven convection.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas.

Tonight...VFR expected at all terminals. Any shower or thunderstorm activity is expected to move offshore by 02Z. Some instances of patchy fog are possible, especially near KRDG/KABE mainly after 08Z. Southwest winds around 5 kt or less, becoming light and variable at times at some sites. Moderate confidence overall.

Saturday...VFR. Isolated to scattered thunderstorms in the afternoon may cause localized instances of sub-VFR conditions, however confidence in occurrence at this time is low. Southwest winds generally around 7-12 kt. Moderate confidence overall.

Outlook...

Saturday night...Mostly VFR except lower conditions possible with evening showers and thunderstorms.

Sunday-Sunday night...VFR conditions expected.

Monday-Tuesday...Mostly VFR except lower conditions possible with afternoon/evening showers and thunderstorms.

Wednesday...VFR.

MARINE

No prevailing marine hazards are expected through Saturday. Southwesterly winds around 10-20 kt with seas of 2-4 feet through Saturday.

Outlook...

Sunday through Wednesday...No prevailing marine hazards expected. Thunderstorms possible Saturday night and Tuesday night.

Rip Currents...

For Saturday...Southwesterly winds continue and should increase some to 10-20 mph. Breaking waves in the surf zone are forecast to increase some, especially for much of the Jersey Shore, at 2 to 4 feet. Given the increasing surf and southerly winds, went with a MODERATE risk for the development of dangerous rip currents for the Jersey Shore. Breaking waves should be a little lower still for the Delaware Beaches and coastal Monmouth County, therefore went with a LOW risk for the development of dangerous rip currents.

For Sunday...Similar conditions Sunday as Saturday. Southwesterly winds continue around 10-20 mph. Breaking waves in the surf zone are forecast to remain 2 to 4 feet. Given the increasing surf and southerly winds, went with a MODERATE risk for the development of dangerous rip currents for the Jersey Shore. Breaking waves should be a little lower still for the Delaware Beaches and coastal Monmouth County, therefore went with a LOW risk for the development of dangerous rip currents.

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

PHI WATCHES/WARNINGS/ADVISORIES

PA...Heat Advisory until 8 PM EDT Saturday for PAZ070-071-101>106. NJ...Heat Advisory until 8 PM EDT Saturday for NJZ008>010-012>015- 017>020-027. DE...Heat Advisory until 8 PM EDT Saturday for DEZ001. MD...None. MARINE...None.