textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Flood Watch issued.

All groups have been updated.

KEY MESSAGES

1. Scattered showers and thunderstorms will continue into the early overnight period tonight.

2. A Flood Watch has been issued for Tuesday into Wednesday as an impactful system arrives across the region.

DISCUSSION

KEY MESSAGE 1... Scattered showers and thunderstorms will continue into the early overnight period tonight.

Scattered showers and thunderstorms have developed across the northern Middle Atlantic region this afternoon as increasing heat and moisture have arrived along with a few upper short waves. We are not expecting widespread severe weather, but with the possibility of strong downpours and some damaging winds could occur in a few spots, the Marginal risk for severe storms remains across our area for that reason.

The storms will be slow moving, so localized flooding is possible through the tonight period as well. A slight risk for excessive rainfall remains for Delaware tonight. The activity is expected to decrease after sunset.

KEY MESSAGE 2... A Flood Watch has been issued for Tuesday into Wednesday as an impactful system arrives across the region.

As the upper heights continue to drop and summertime warmth and humidity continue...Tuesday looks to feature the more widespread showers and thunderstorms. The H5 height falls and jet dynamics aloft will favor convective development nearly all day as surface low pressure develops just to our west. This will keep a steady stream of warm, moist air pumping into the area and keeping the environment conditionally unstable despite cloud cover. PWats will rise to near 2" by the end of the day. Some models suggest we could have a stalled or slow moving frontal boundary across the central or northern portion of the forecast area, which could act as a focusing mechanism for heavy rainfall. Heavy rain leading to flash flooding could end up being a bigger concern and greater impact than the severe thunderstorm threat.

The latest outlooks from WPC show most of our area in a SLIGHT risk for excessive rainfall, but northern NJ has a MODERATE risk for excessive. A flash flood watch has been issued for Tuesday and into Wednesday. As for severe weather, the southern half of the area including Delmarva, south NJ and metro Philadelphia have a SLIGHT risk for severe thunderstorms while areas to the north are in a MARGINAL risk. Damaging winds are the primary threat with thunderstorms on Tuesday.

The low pressure looks to be offshore to our east by Wednesday. There is some uncertainty with regards to how fast its effects diminish across the area. We'll continue with scattered showers and storms again by afternoon, at least across our NJ and PA zones, but the severe thunderstorm threat will be lower given lower instability. Flash flooding is possible Wednesday too.

AVIATION /18Z MONDAY THROUGH SATURDAY/

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

Tonight... Overall VFR, but scattered showers or tstms around with short periods of IFR if the rains/tstms arrive across a terminal. Low confid for placement/timing. Patchy fog possible late for areas that receive rains this evening. Light W/SW winds.

Tuesday through Tuesday Night...Periods of MVFR/IFR conditions likely with multiple rounds of showers and thunderstorms expected.

Outlook...

Wednesday through Wednesday Night...Restrictions possible with lingering showers and low clouds.

Thursday through Saturday...VFR. No significant weather expected.

MARINE

Sub-SCA conditions expected through tomorrow morning with southerly winds around 10-15 kt and seas 2 to 3 feet. Scattered showers and tstms into the early overnight period tonight.

Outlook...

Tuesday Afternoon through Tuesday Night...A Small Craft Advisory is in effect for all marine zones as south/southwest winds around 20-25 kt and seas of 3 to 5 feet are expected. Showers ans tstms expected.

Wednesday through Wednesday Night...SCA conditions possible (40-50%) especially on the northern waters as seas near 5 feet.

Thursday through Friday...No marine headlines expected.

Rip Currents...

For the rest of today, an 8 second period and breaking waves 2 feet or less along with shore parallel winds up to 10 MPH will result in a LOW risk for rip currents at all beaches.

For Tuesday, southerly flow strengthens with winds increasing to around 15-20 MPH with either a shore parallel or onshore flow component to a southerly wind. Multiple swell groups and increasing breaking waves to around 2 to 3 feet as well as the coming full moon will also add to the rip current threat. As a result, there is a MODERATE risk for rip currents at all beaches.

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

PHI WATCHES/WARNINGS/ADVISORIES

PA...Flood Watch from Tuesday morning through Wednesday afternoon for PAZ054-055-060>062-070-071-101>106. NJ...Flood Watch from Tuesday morning through Wednesday afternoon for NJZ001-007>010-012>020-026-027. DE...Flood Watch from Tuesday morning through Wednesday afternoon for DEZ001. MD...None. MARINE...Small Craft Advisory from noon to 8 PM EDT Tuesday for ANZ430- 431. Small Craft Advisory from noon Tuesday to 6 AM EDT Wednesday for ANZ450>455.