textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated Rip Current Section.

KEY MESSAGES

1. Unsettled conditions are expected through Sunday as a front and several weak upper systems move through, bringing periodic showers and isolated thunder for the weekend.

2. Heat builds back into the region for the middle and end of next week. There is increasing confidence that high temperatures will be well in the 90s to around 100 degrees, with maximum heat index values exceeding 100 degrees for multiple days.

DISCUSSION

KEY MESSAGE 1... Unsettled conditions are expected through Sunday as a front and several weak upper systems move through, bringing periodic showers and isolated thunder for the weekend.

A slow-moving front will essentially become stalled across the mid-Atlantic today into tonight, especially as a weak low pressure tracks east from the OH Vly into the region by tonight. This will cause some subtle moisture resurgence back into Delmarva and southern parts of the local area, especially southern NJ, during the day today. With PWs around 1.75" in these areas by this afternoon amidst an uncapped environment, scattered showers and isolated thunderstorms will likely develop/blossom through peak diurnal heating. The severe potential with these slow-moving downpours remains very low, owing to poor low-level and midlevel lapse rates and very marginal instability. The best chance for thunder will be in Delmarva where instability will be greatest by late afternoon.

Coverage of activity will be largely diurnhally-driven, meaning there should be a gradual decrease past sunset late this evening into tonight. That being said, with very subtle forcing and a sufficently-saturated environment in the region, some isolated activity should continue through the overnight into Sunday morning, especially for Delmarva and southern NJ.

Moreover, the latest guidance has trended slightly slower with boundary clearing the region, with the potential now for lingering showers and perhaps a few rumbles of thunder as well into the daytime Sunday (once again favored across southern parts of the PHI CWA). The very subtle/slow southward progression of the front will finally make a more concerted effort further S by Sunday night as a weak surface low finally pulls to the E of the region. This will allow for low-level wind fields to become more decidedly northerly, allowing for slightly drier air to overspread the region into Monday. Drier conditions are expected for the start of the workweek.

KEY MESSAGE 2...Heat builds back into the region for the middle and end of next week. There is increasing confidence that high temperatures will be well in the 90s to around 100 degrees, with maximum heat index values exceeding 100 degrees for multiple days.

Strong mid-level ridging will develop over the Great Lakes and Ohio Valley early in the new week, then will build into the Northeast and Mid-Atlantic starting on Wednesday and continuing through the end of next week. Hot and humid conditions will return with high temperatures well into the 90s to around 100 degrees with and max heat index values over 100 degrees. This will likely persist for multiple days, including into the upcoming holiday weekend.

01Z/27 NBM probabilities indicate probabilities >90% of high temperatures exceeding 95 degrees on both Thursday and Friday, with greater than 80% probability of high temperatures near/exceeding 100 degrees from the Lehigh Valley north and across the Delaware Valley, including Philadelphia, southern New Jersey, and Delmarva both Thursday and Friday. Max heat index values could exceed 105 degrees, which would necessitate potential Extreme Heat Warnings for much of the local area for several days.

Tonight

Showers with ISO TS will become more isolated by the end of the period. With a gradual moistening of the profile, expect that MVFR ceilings to develop/overspread southern sites by the end of the period. Some IFR ceilings and prevailing MVFR visibilities are also possible toward 12z Sunday.

Outlook...

Sunday...VFR. Lingering MVFR/IFR conds in the morning, improving to VFR by midday. ISO to SCT SHRA or TSRA at KILG, KMIV, KACY, primarily during the afternoon/evening.

Sunday night...VFR. NSW.

Monday through Wednesday...VFR. NSW.

MARINE

A nearly stationary front will remain entrenched across the region through today, providing a focus for periods showers and tstms. Overall, winds and seas will remain sub-SCA through tonight. A few tstms are likely prior to 09z, with another period of possible showers/tstms this afternoon and evening, with chances in the high chance/low likely category.

Outlook...

Tonight through Sunday...Sub-SCA conditions. VSBY restrictions in showers, scattered thunderstorms, and mist tonight through Sunday morning.

Monday through Wednesday...Overall, sub-SCA conditions. Cannot rule out a brief period of southerly 25+ kt gusts late Tuesday afternoon north of Barnegat Light.

Rip Currents...

For today, breaking waves in the surf zone are forecast to be around 2 feet with around a 6 second period and south-southeast swell. Winds should be mainly southeast around 10 mph. Given these conditions, we'll continue with a LOW risk for the development of dangerous rip currents for both the Jersey Shore and Delaware Beaches.

For Sunday, winds shift to mainly northeasterly around 10 mph with continuing breaking waves in the surf zone around 2 feet with a 6 to 7 second period and southeast swell. We will continue with a LOW risk for the development of dangerous rip currents for both the Jersey Shore and Delaware Beaches.

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

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...None.