textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Flood Watch expanded to include the Lehigh Valley and Berks County.

A Severe Thunderstorm Watch has been issued for all of New Jersey and portions of Delaware and eastern Pennsylvania through 8 PM this evening.

The threat for flash flooding is ongoing and will continue through the afternoon with numerous reports of flooding across New Jersey and eastern Pennsylvania.

Updated the aviation section for the 06Z TAFs.

KEY MESSAGES

1. The threat of strong to severe thunderstorms and flash flooding will continue through this evening.

2. A cold front is expected to pass through the area on Friday.

DISCUSSION

KEY MESSAGE 1...The threat of strong to severe thunderstorms and flash flooding will continue through this evening.

Widespread showers and thunderstorms continue to impact much of New Jersey and portions of eastern Pennsylvania and Delaware this afternoon. The greatest threat from these storms will continue to be localized flash flooding, with many reports of road closures due to high water already. Some storms may also be strong to severe with large hail and damaging winds. A Severe Thunderstorm Watch remains in effect until 8 PM.

The latest hires guidance suggests that heaviest precipitation will be generally along the I-95 corridor and points northwest. Hires guidance has also pointed to areas along the I-78 corridor potentially seeing heavy rainfall amounts as well. Generally around 1-2 inches of rain with localized QPF values in excess of 3 inches. Widespread flash flooding still seems unlikely, but the localized threat remains elevated. The Flood Watch remains in effect for most of NJ and the I-95 corridor.

For severe hazards, latest CAMS and HREF guidance show SBCAPE values remaining around 1500-2500 J/kg with ensemble maximums in excess 3000 J/kg. Deep layer shear forecasts remain around 30kt with a strongly veering profile aloft. Boundary layer flow is not particularly strong but surface winds are more backed than previous forecasts so an isolated tornado is possible primarily along and west of I-95. That said, damaging wind gusts and hail will remain the greatest threat. Dominant mode should be multicell convection but a supercell can't be ruled out especially where cloud bearing shear is maximized. SPC has expanded the area of a slight risk (2 out of 5) to now include much of the area.

KEY MESSAGE 2...A cold front is expected to pass through the area on Friday.

The timing of this cold front will be critical in the risk for thunderstorm hazards. There are differences between models in both the timing, and if this will be a single cold front, or an initial cold front with a reinforcing shot of cold air advection coming in behind it. Saturday and Sunday appear to be dry across most of the area with the exception of southern areas Saturday where low probabilities of showers and storms will exist.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

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

Thursday...Periods of MVFR or lower due to scattered to numerous showers and thunderstorms. Continue to mention VCTS for the I-95 corridor with PROB30 or TEMPO groups for TSRA. Confidence has increased that there will be multiple rounds of storms with frequent lightning and low ceilings, which should begin to diminish at around 0Z.

Thursday night...VFR as showers and storms exit, but patchy fog and and low ceilings possible mainly across the I-95 corridor and RDG/ABE. Winds light and variable. Low confidence.

Outlook...

Friday...Periods of MVFR or lower are possible in showers and storms.

Saturday through Monday...Prevailing VFR conditions.

MARINE

No marine hazards expected. Southerly winds with gusts near 20 kt possible.

Outlook...

Thursday night and through Sunday...No marine hazards expected.

Rip Currents...

There is a MODERATE risk for the development of dangerous and life threatening rip currents at the Jersey Shore and a LOW risk at Delaware Beaches.

For Friday, winds in the morning are more westerly at 5 to 10 mph before becoming more southwesterly in the afternoon at 5 to 10 mph. An east-southeasterly swell remains with a period of 6-7 seconds with breaking waves around 2-3 feet. As a result, there is a MODERATE risk for the development of dangerous and life threatening rip currents at the Jersey Shore and a LOW risk at Delaware Beaches.

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

PHI WATCHES/WARNINGS/ADVISORIES

PA...Flood Watch through late tonight for PAZ060>062-070-071- 101>106. NJ...Flood Watch through late tonight for NJZ001-007>010-012>015- 017>020-022-025>027. DE...Flood Watch through late tonight for DEZ001. MD...None. MARINE...None.